Automotive Race car suspension Class

[Hillbillyd]

What affect will it have running 2" less scrub radius on the front left compared to the right front?
I have been researching this and my understanding left scrub wedges the right rear on turn in and tightens up the car.
I have seen a lot of cars running a 2" spacer on the right front and and 1" less off set on the left front rim to keep the track width with in the rules and when I've asked them about it they've said they've done it to gain more left side weight. I was seeing it as a scrub radius gain as many of these newer stock cars run very little scrub radius.

 

[Ranger Mike]

Read post 325 on page 13. Kingpin Inclination Angle (KIA) when installed is a compromise between scrub radius and weight jacking. The KAI and caster combine to weight jack the car in a turn. The amount of KIA will vary and you can change the KIA when you are building the race car. Caster can be dialed in at the track. In a left hand turn Positive caster will cause the left front corner to rise and add weight to that corner and the right rear corner. Adding positive caster to the left front will take out wedge or cross weight and loosen up the car. Most drivers run a split caster so the car will naturally turn left. Wheel spacers are a tuning trick I never much believed in as the car should have been built with maximum left side weight to be gin with. So if you build I right, you will have +1° left side caster and +3° right side caster (+4° caster for power steering) with the proper cross weight, left side weight camber build stagger etc.…
If the scrub radius is correct, the tire rotates left and right directly on it's contact area with the ground. It turns freely and doesn't fight the geometry of the steering or affect handling adversely.
If the scrub radius is not correct, the tire is being moved through an arc across the ground. It's harder to steer and very much fights the steering geometry.

Also, the greater the scrub radius, the more the bumps, pot holes and other pavement variations cause the wheel to be deflected from it’s desired path. The steering wheel will be rotated by the wheel deflection...kind of “the tail wagging the dog”...
Also tends to increase loading on suspension components and wheel bearings, especially the distribution of weight between the large inner bearing and the smaller outer bearing. All in all, no good comes from too much scrub radius

Keeping the center of the tire as close as possible to the center of the king pin/ball joint center line, the happier the suspension will be and we have the least amount of scrubbing.

Positive scrub radius (KPI line or SAI line hits the ground inside the center of the contact patch) imparts a toe out force on the tires. This is typical of RWD cars. Negative scrub radius (KPI/SAI line hits the ground outside of the center of the contact patch) imparts a toe in force on the tires. This is typical of FWD cars. The selection of tire diameter and rim offset can radically change scrub radius. Sometimes changing it from + to - or - to +. All cars I have worked on have a little bit of scrub radius designed in and it helps with road feel. The reason for 'toe out on turns' is because the inner front wheel turns a tighter radius than the outer front during cornering. Without it the inner wheel will be dragged slightly sideways. If you draw a perpendicular line from the center each wheel of a during a turn, the lines should intersect at a common point. This is the point about which the car is rotating during a turn. Because of slip angle, dynamically that point is slightly ahead of its theoretical location. Slip angle is how far you have to turn the wheels compared to how far you would have to theoretically turn them to make a corner. The heavier the car, the faster you are going and the tighter the corner, the greater the slip angle.

 

[Hillbillyd]

Excellent!
Thats it i didn't take into consideration the positive camber and my reduced KAI will reduce the left side scrub Radius
Starting to understand this Thanks again

 

[Ranger Mike]

Why are coil overs “ better” than the separate coil spring / damper arrangement. Well, a lot of times they may not be. But if we look into this question a little deeper, the real question is – What is the best set up for my class to WIN.
If your track rules permit, I would say coil overs are the best way to go if the budget permits. You cannot beat a refined concept and the evolution of coil overs has reached this point. Most high-end coil overs are lighter than the factory components they replace to reduce unsprung weight and further increase handling. They are easier to tune in and adjust.
Penske 3 way adjustable shock weight 8#

Coil over spring 4#
Stock coil rear spring 11#

Stock type tube shock mounted up side down – 1# sprung 3 # unsprung
Stock type rear spring / shock weight total – 15#

Coil over rear spring / shock weight total – 12 #
But now look at Unsprung weight – coil over sprung weight is 6# and stock type coil set up is 14# per side so we are talking about 12# unsprung with coil overs versus 28# unsprung with stock coils/shocks.
Now the real inside baseball stuff begins to make sense. ALL Coil springs will have side loading.
From http://www.pawangroup.co.in/archives/10531
Definition of Eccentric Load: When the load applied to a portion of the column (spring) is not symmetric with the central axis of the column (spring), the load applied is called eccentric load
see spring 1 pic belowExplanation: In above figure (Diagram 1) P is applied load, L is length of the object under load. Here load P is not symmetric with the central axis of the object.

Effect of Eccentric Load on Spring: Spring is an elastic body which when subjected under any type of load starts to deform. If the applied load is in allowable physical tolerances the spring gets back to the initial position due to its elasticity.

It is very important that the applied load is not just in the given physical tolerances but, is also applied properly. If a spring is applied be load P of which the axis is not symmetric with the central axis there is a chance of spring buckling, which can lead to spring breakage.
see spring # 2 pic belowWhen eccentric load acts on the spring the stresses on spring coil increases and load parameter also varies. Due to eccentric loading the stresses on the farthest side (ref. Diagram 2) increases i.e. side A. The stresses on the nearest side of eccentric load decreases due to extra compression. The effect of eccentricity on spring varies considerably with the shape of end coil and also the number of coils in the spring. Stress increase due to eccentric loading varies directly with the distance between central axis and load axis (e).

In plain hillbilly tech – when you compress any coil spring you will have side loading. This side force loading is caused by the springs ends not being able to distribute the compression forces equally to the spring perches. This is magnified if you got the spring ending in a non parallel ground seat. You have at best about one half a coil displacing the load. For the typical grocery getter you would never care about spring eccentric loading.
see coil spring # 3 pic belowParallel ground coil springs used on coil overs are a lot better but inherent characteristic of a coil spring when mounted co-axially around the damper of a vehicle with fixed position spring perches is that it will generate a lateral load due to its not being able to distribute load forces evenly around the face of its end coils. This lateral loading manifests itself as a bending load in such coil over applications, and results in greatly increased frictional forces within the damper. The answer is the hydraulic device supplied by Hyperco. Their ultra high quality spring rate and load test scale, which charts axial load as well as longitudinal load found with some configurations, 98% of the lateral forces were eliminated. You can run softer spring set up since a portion of the old spring rate was going to side loading and not compression. You get better shock life and better tire grip than the other guy running coil overs. You add ½ pound to sprung rate with these coil perches.

 

[Ranger Mike]

thank you all for the past ten years. been fun...hope next 10 are as fun!
rm

 

[LogicIndustries]

I'm working on a design for a pavement modified, more or less an IMCA style car, but not running under that sanction. Track used to be NASCAR but has since gone outlaw, rules remain more or less the same though.

I've been doing my front end geometry calculations and layouts by hand in AutoCAD, but that is time consuming and tedious, so I was thinking of buying a geometry program (or two, if needs be), but I cannot find any real feedback from people I'd consider knowledgeable, so here I am.

The two I've looked at most heavily are the ones from Chassis R&D (which seems to have disappeared off the face of the Earth as a company, their website just goes to a generic Network Solutions Under Construction landing page) and Performance Trends Circle Track Analyzer. Price is about the same for either one, but I can't even figure out if the Chassis R&D stuff will run on a Win10 machine. Literally no one who sells the stuff lists the system requirements for it (not a good sign).

The only feature I like better from CR&D that the PT-CTA doesn't explicitly have is the balanced front/rear roll angle thing that Bolles is always on about, though maybe similar information can be teased out of CTA as well and it's just called something else. I've never used either one, so I'm just going by what their sales literature says.

Any advice you can render would be most helpful.

Thank you for your time.

 

[Ranger Mike]

All you need to do is look at page 1 written 10 years ago. it recommends performance trend software. I began using it in 1995. I have circle track analyzer and suspension analyzer. no endorsement just my opinion.
the suspension analyzer is way more detailed and takes a lot more time to get the measurements but will be better than the other when you are scratch building a front end. You want quick and dirty feed back on already existing front end go with circle track analyzer,

you can down load free version to test drive too

 

[LogicIndustries]

So, that was sort of like not reading the FAQ, wasn't it? Sorry about that.

Is the Full Vehicle version worth the price? It's nearly twice as much money as the standard version, and close to three times the price of the CTA.

My project is kind of half way between a scratch build and salvaging an existing system. My rule set dictates that I use the stock lower control arms, in the stock location, on the stock front stub, but everything else can be scratch built to suit, with a maximum track width of 80" outside side wall to outside sidewall (at spindle height). That stock lower arm thing is going to lead to a few funky compromises with the spindles and scrub radius in order to maximize the track width, but shouldn't cause too many problems otherwise.

Steering wise, I have to use the stock style of steering box (but NOT the actual stock box, just one that will bolt up in the same place) in the stock location with the stock idler arm, but then everything else can be scratch built there too.

I like the rule set. It leaves me plenty of room to play without turning the class into Late Models that are missing the front fenders. The stock stub and the 8" tires keep the Modifieds a handful to drive without the speeds getting way out of hand.

Thanks again for the advice, I appreciate it.

 

[Ranger Mike]

CTA is all you need..look at street stock and metric topics in the index..you can use stock impala lowers and swap out stock mustang and pinto spindles and mix a lot of stock stuff to get some good camber build..all stock appearing stuff...good luck

 

[LogicIndustries]

The stub I'm working on is a 68-72 Chevelle, so the big Impala lowers won't fit. Wouldn't gain me anything width wise anyway.

Building the spindles from scratch, that's not a big deal, I've done that before. Think I'm going to go with the big bearing GN hubs and bolt-on rotors. More rotor and bigger bearings at about half or less the weight of the stock big Impala hubs/rotors, plus that let's me use one hub both front and rear. May be awesome, may go terribly, we'll see how it turns out.

Appreciate the advice.

 

[Vintageracer13]

Hi All. I had a good season this year and learned a lot including the value of less crossweight in my setup. I was wondering if anyone has used the Computerized Chassis Setup Software from Steve Smith. I have a straight axle car and this one has capability to work with my setup

 

[John LNZ]

Hi Mike, I have been working with the Performance Trends programme to assist in re-design of front suspension on our dirt cars. I am particularly looking at my front roll-centre migration. We run a stacked right front spring and as such have 2.5 deg of roll. I seem to have quite a lot of rollcentre migration - up to 12 inches - say 10.5inches left of centre line to 2 inches right of centre line. We are trying to maximise our moment arm length as we run on flat slick tracks predominantly (1/4 mile). Is that much migration expected in your opinion?
Thanks John Lovelady

 

[Ranger Mike]

Racing and winning is about tires, Tires, TIRES..
It is all about the best tire contact patch. He who has it – wins.If you do not have access to the software programming to find your Roll Centers, I think the racer who can adjust track side and can drive the best will win the race. If you can measure the car and find the roll centers and the software can show the roll center migration in roll and dive, you have a significant advantage over the no software racers. The software will get you close to the dynamic measurements. It assumes things move dynamically in true arcs and straight up and down moves.BTW - Those non-believers of roll center logic are lost causes. You can not see gravity but drop that sledge hammer on your toe once. RC matter and understanding it is very important.
The ultimate is to have your car and best set up on a PULL DOWN RIG. This rig shows the effects of suspension components in a dynamic state. Basically the race car is mounted on the stands where the tires are at proper pressure and stagger. Hydraulics are attached to the chassis and the car is forcibly moved to a roll and dive position to replicate the cars cornering attitude under speed. Actual measurements show all the sins of track abuse, bent A-arms, worn bushings, bent tie rod arms. Control arms , bent rear ends, bent Ball joints you don’t know about until post season tear down etc.…
This is the true movement condition of your car in a turn. It is the closest to track side as you can replicate. We used to do this on a chassis puller used to straighten frames. Was a bunch of slotted rails placed in concrete and we would hook a come along or cable rachet tightener on the corner of the race car and read the camber gage as the car was pulled toward the right side down under load. Today’s pull down rigs have large displacement transducers that measure movement and the input goes to a slick computer program to show toe, camber, castor, roll steer. Pretty tech!
So if you can change out your suspension components, you want to get the best tire contact patch you can get in a dynamic state. Also rear roll steer will help on dirt. The roll center migration should orbit around 1 to 2 inch from static. The less migration the better but we are talking real world so do your best.

 

[John LNZ]

Thanks Mike - what are your thoughts on the moment arm theory which Bob Bolles talks about regularly. Whilst working on our roll centre migration we are also trying to keep our right front camber change to the minimum. We run about 3.5 deg negative with about 0.7 loss through 2.5 deg of roll and 1inch dive. I have noticed that the late models seem to run quite a bit more than that even when the right front is locked down. What do you feel is the right number of degrees to get the best contact patch? Is this something you would use the pull down rig to quantify? We have a datalogger in the car and we have used the corner entry measurements from the travel indicators to set the car on the workshop floor at its dynamic state by changing the coil over heights. This verifies our camber change but I have not plotted all my suspension points with the car at that state - perhaps that would be a good exercise? Thanks

 

[Ranger Mike]

Read post 1433 page 58. My opinion on moment arm theory.Why would you copy what an entire different class is doing with camber settings?

Would you replicate how the formula 1 cars are set up?

Money see monkey do racing is very expensive and provides much frustration as the money doing it does not understand what is done and why.The point about adding static camber is to lean the tire when going down the straight away knowing full well the tire is only making contact with the track half the time. This set up is compromise so when the car does go into the turn the cornering force jacks the suspension to straighten up the tire ( zero camber) for maximum contact when most needed.

You want ZERO CAMBER for maximum contact patch in the turn.The best tool you have is a tire pyrometer to take tire temperatures. And the track will change so you need to constantly monitor the temps and adjust accordingly.

So your current set up is neg. 3.5 ° camber going to 2.8° in dive. Why not make it go to ZERO if you can?

You want ZERO CAMBER for maximum contact patch in the turn.

 

[Vintageracer13]

That is the tough part with a straight axle. The camber you have doesn't change. I have been experimenting with different angle kingpin snouts at different tracks and checking tire temps

 

[Blue Foxy]

Hello Mike,

What an interesting thread.
As an engineer working in motorsport in France. Most of the people in EU did not carry so much about roll center migration.

Many author suppose in their calculation, roll axis is constant during chassis roll, which is no often the case, thus their calculation might be wrong.

My though are, if the roll center is the instant point toward the chassis roll in dynamic, it make sense to making it not moving regarding center of gravity, in order to get the driver having a constant feeling.

On your experience on the track, what create on a car a side ways movement of roll center?

On the other hand, design a suspension with upper and lower wishbone, with a minimum movement of the roll center in heigh and laterally, is solving a three bars compatibility problem, this can be done graphically (15mn work on my side, if the wishbone length are not crazy short).

From my experience, roll center not far from the ground, give minimum track variation under bump and rebound, because IC is near to the ground.

Jacking, I would say, let's consider suspension is mechanical system, which spring are the only element which can be deformed under load. If you calculate the vertical and lateral effort on each tire (inner and outer) due to weight transfer and grip tire, and then calculate effort on all suspension element (wishbones, springs) on each side , it shows that too low or too high roll center generate asymetric deflection on springs, thus moving the COG in height during roll.

English is not my native tongue, so I beg your pardon if I make mystake while writing.

 

[Ranger Mike]

Unless the race car is works built from the ground up, you will have roll center migration. You should try to have it orbit within 1 to 2 inch of the static location. The less movement the better but it will move. The suspension links will make this so because of the original design ( usually passenger car engineering). You should read posts regarding location ( see index ). Weigh Jacking is a result of roll center location and tire contact patch. See Jacking effect in index. Tires defelct as well as the springs and you should understand this. There is no such thing as weigh transfer. How the tires and suspension handle momentum should be understood.

You have good language skills and welcome to the forum.

 

[Blue Foxy]

May be, I did well explain what I meant.

Since a suspension is a mechanical system, Newton physics rule are right. That 's why I prefer calculate the force on the tires due to vertical and lateral acceleration, then calculated all the force in upper and lower wishbone and on spring (inner and outer wheel). Since I have the effort on spring and know their rate, I know their deflection font static position, I redrawn the suspension with those deflection and itirate the calculation.
Then I have a whole picture of the suspension in roll, movement of RC, movement of COG, roll angle, etc.
It gives also me a clear wiew of jacking effect.

It is the solution I use, and I made my own software on CAD.

I prefer to use this method, because less approximation that moment calculation.

Regarding roll center migration, It exists a construction methods that allow to minimize his displacement. it is the same construction problem as having no bumpsteer ot having no CVD plunge. If you have a example to submit, I will be happy to show the method.

 

[Ranger Mike]

that may work good for left and right turn racing but not for left turn only round track racing in USA.

 

[Blue Foxy]

What may work? Roll center construction method?

 

[OCR]

What. . .??

There is no such thing as weight transfer.

Well. . .!

...but drop that sledge hammer on your toe once.

It sure as hell feels like there is. . . . .Lol. . . . .

OK, carry on. . ✔

.

 

[Blue Foxy]

that may work good for left and right turn racing but not for left turn only round track racing in USA.

Strange answer, a straight line is a straight line, and a corner is a corner, whatever the country.
Physics laws are the same (Newtons laws) whatever you are place on earth.

I do not really understand what you mean? Can you clarify?

 

[Ranger Mike]

you did not understand because you obviously did not read the forum posts. page 28 post # 691. it is all there and all you need do is read. A corner is a corner but how you traverse it properly is the difference in left turn only racing and road course racing. And you are missing one huge factor not eve naddressed in the software..any guess as to what that may be??

 

[Blue Foxy]

you did not understand because you obviously did not read the forum posts. it is all there and all you need do is read. A corner is a corner but how you traverse it properly is the difference in left turn only racing and road course racing. Unless you understand this all the software in the world will not get you a win.

Honestly, do you think your reply is clever.
For your knowledge, I have an mechanical engineering degree, I have been working for 20 years in motorsport, I have been chief designer in company which produce single seaters (wich have produce more win than you expect).
I do not say I understand everything, I try to be open mind in a technical discussion on this thread.
The post is 59 pages, I tried to read most of them.

I open the discussion on roll center location, and I say it exist a geometric construction that allows to minimize his dispacement, you reply : Unless the race car is works built from the ground up, you will have roll center migration, you even not ask me: ok I m curious show me. I show a example of what is possible with this geometric constrcution (+-100mm suspension travel , 0.34 mm moving in height), that's just a example of what is possible. I do not say it is perfect, but it took 15 mn to achieve this.

You wrote: Weigh Jacking is a result of roll center location and tire contact patch. This a big approximation, as often you can find on books.

The jacking is a result of distribution in load in the suspension compenent (upper lower wishbone and spring), on certain construction more load go threw upper and lower wishbone, and less to the spring. To be convince to this, you should calculate every load on suspension component, if you are able to.

I though this thread was a open mid discussion and knowledge exchange, as a forum should be.

 

[Ranger Mike]

I did not think it was clever as i revised it after reflection. this is not my forum and the administrators are the best you can find. And i can understand you not reading the entire long 59 pages of posts. I do get bothered when i have addressed this RC issue many times, page 10 post 229 pg 11 post 251, pg 28 post 691 pg 41 post 811 pg 44 post 879. Seems like i am whistleing in the wind sometimes.

 

[Hillbillyd]

Please bear with me as i try to explain my question reverse rotation of the drive shaft and using reverse rotation crown wheel and pinion to correct it so the car drives forward normally.
Now this is a purpose built race car to run a dirt oval with double A arm suspension and 3 link rear coil over suspension and i have researched this and read about Smokey reverse torque special https://macsmotorcitygarage.com/another-look-at-smokey-yunicks-reverse-torque-special/
What are your thoughts on the rear diff torque loading the right rear and unloading the left rear can this be over come by moving the 3rd link further to the left to load the left tire?
Have i just lifted the lid on the can of worms?

 

[Ranger Mike]

Hill
i love smokey yunick! he was the best! I am all for the rev rotation. Yes 3rd link offset can assist. I would have gone rev rotation if it were not so expensive. doomed by production design from get go i guess. i am for anything that adds down force to the lazy left side tires.

 

[Hillbillyd]

Hill
i love smokey yunick! he was the best! I am all for the rev rotation. Yes 3rd link offset can assist. I would have gone rev rotation if it were not so expensive. doomed by production design from get go i guess. i am for anything that adds down force to the lazy left side tires.

Thanks for the quick reply Ranger Mike could you please give a quick list of the advantages

 

[Ranger Mike]

Engine - driveline torque produces an equal and opposite reaction upon the chassis, lifting the left side of the body, pushing down on the right side, and redistributing the load to the outside of the corner in a left-hand turn. This is exactly what we want thru body roll. So if we reduce the body roll and can put the same amount of down force on the right front tire, we can keep the nose down and seal up the aero just like the big bar soft spring set up. But on the rear end, Torque reaction lifts the right end of the rear live axle and pushes down on the left, with the axle housing forming a sort of lever. On a typical car developing oh, 300 lb-ft of crankshaft torque, there might be 75-120 lbs. of force loading one end of the axle and unloading the other. For oval racing at least, this redistribution is in a nominally helpful direction—from the outside to the inside tire. And note that reversing the engine’s rotation does not cancel the reaction forces in any event. It simply reverses them. And in the case of the forces acting on the axle housing, it’s in the wrong direction for oval racing. So reverse rotation is a help to the front but bad for the rear end set up. Drivers who have raced the rev rotation set up also state it works great but you had to stay on the gas pedal in the turns or it wants to make right turns if you lift.

Engine specific changes are - is the fact that the coolant flow is reversed. The engine doesn't cool as efficiently with flow entering the top and exiting the bottom.

Some engines have the cranks knurled for that rotation only. Running them backwards they will leak oil at the front & rear seals. The wrist pin was slightly offset in the piston ( they do that to make sure there is no piston slap...), so you had to turn the pistons 180 deg in the bores.The engine needs a different cam, and the little driveshaft that goes between the oil pump and the distributor. ( the gear on it meshed with a gear on the cam ). Water pump & alt or generator need reverse rotation models from marine application that ran the right way ( alt might work either way, but the cooling fins next to the pulley will be pointed the wrong way.) Need starter that runs backwards too. Clutch and transmission should be ok but pinion gear has to go on right side in differential.


I don’t think it is worth the hassle and I look at track side repairs. You cannot win ifin you don’t finish and you are super screwed at the track when you have many special order items. You are at the track and suddenly a starter, water pump goes out on you. Reverse flow – neat trick but not worth it.

 

[Blue Foxy]

I did not think it was clever as i revised it after reflection. this is not my forum and the administrators are the best you can find. And i can understand you not reading the entire long 59 pages of posts. I do get bothered when i have addressed this RC issue many times, page 10 post 229 pg 11 post 251, pg 28 post 691 pg 41 post 811 pg 44 post 879. Seems like i am whistleing in the wind sometimes.

811 is page 33 not 41, and 879 is page 36 not 44, seems like you are whistleing in the page.

I read all the post you mention, with attention, lot of approximation, I wil reply you via direct message.

 

[Hillbillyd]

Engine - driveline torque produces an equal and opposite reaction upon the chassis, lifting the left side of the body, pushing down on the right side, and redistributing the load to the outside of the corner in a left-hand turn. This is exactly what we want thru body roll. So if we reduce the body roll and can put the same amount of down force on the right front tire, we can keep the nose down and seal up the aero just like the big bar soft spring set up. But on the rear end, Torque reaction lifts the right end of the rear live axle and pushes down on the left, with the axle housing forming a sort of lever. On a typical car developing oh, 300 lb-ft of crankshaft torque, there might be 75-120 lbs. of force loading one end of the axle and unloading the other. For oval racing at least, this redistribution is in a nominally helpful direction—from the outside to the inside tire. And note that reversing the engine’s rotation does not cancel the reaction forces in any event. It simply reverses them. And in the case of the forces acting on the axle housing, it’s in the wrong direction for oval racing. So reverse rotation is a help to the front but bad for the rear end set up. Drivers who have raced the rev rotation set up also state it works great but you had to stay on the gas pedal in the turns or it wants to make right turns if you lift.

Engine specific changes are - is the fact that the coolant flow is reversed. The engine doesn't cool as efficiently with flow entering the top and exiting the bottom.

Some engines have the cranks knurled for that rotation only. Running them backwards they will leak oil at the front & rear seals. The wrist pin was slightly offset in the piston ( they do that to make sure there is no piston slap...), so you had to turn the pistons 180 deg in the bores.The engine needs a different cam, and the little driveshaft that goes between the oil pump and the distributor. ( the gear on it meshed with a gear on the cam ). Water pump & alt or generator need reverse rotation models from marine application that ran the right way ( alt might work either way, but the cooling fins next to the pulley will be pointed the wrong way.) Need starter that runs backwards too. Clutch and transmission should be ok but pinion gear has to go on right side in differential.I don’t think it is worth the hassle and I look at track side repairs. You cannot win ifin you don’t finish and you are super screwed at the track when you have many special order items. You are at the track and suddenly a starter, water pump goes out on you. Reverse flow – neat trick but not worth it.

Ok what would be the suspension advantage of it?
I’ve read and understand what you’re saying about the engine but if the race car was in your hands how would you design and set up the suspension ?
I have chosen Double A arm front 3 link rear because it’s a simple design
Actually our suspension rules are free! build what you can

 

[Ranger Mike]

like i said i do not think it is worth it. if you wish to go rev rotation, keep us updated. Your Double A arm front 3 link rear is a good foundation. now find a rev rotation rear end. the rest is simple.

 

[Hillbillyd]

like i said i do not think it is worth it. if you wish to go rev rotation, keep us updated. Your Double A arm front 3 link rear is a good foundation. now find a rev rotation rear end. the rest is simple.

Ranger mike I am not sure if you think I'm wasting your time here? I have already got the reverse rotation crown wheel and pinion rear done and also the reverse rotation of the drive shaft.
How would you set up the suspension if this race car was in your shop?
Im here asking for advice because lots of people can not answer my questions which is understandable as most people have never even heard of it let alone thought about building it.

Write who Arans thanks for business award speech

 

[Ranger Mike]

By no means do i think i am wasting time. this is a forum for racers. Any question is ok as long as it is in compliance with the administrators who are THE BEST. I am not doing this to sell software or books. Just passing on what limited knowledge i have as long as the person reads what i already wrote and does not ignore it and then continues to dog the issue.

Hill, you are most welcome to ask, no problem.

Once you have all the working pieces of rev rotation i would back off the front roll center off set since the engine torque will provide down load. All yo ucan do is use tire temperature to see how much down force you are getting and tune from that. Otgher than the Rc set it up as you have before. You need to get the car to handle going then work on center out.

 

[Surdge]

Good afternoon I finally finished my four link race car I drove it for the first time past weekend whent well just one question we drive on clay oval track as soon as I exit the corner and I climb on throttle the rear starts to jump up and down any ideas where I went wrong

 

[Ranger Mike]

I assume you are NOT running stock rubber bushings. What are tire temperatures. what are the 4 link angles set at? are you running rear steer? if so how much? You have the classic wheel hop on acceleration it sounds like!

 

[Surdge]

Thanks for quick reply no I'm not running rubber bushes I'm not sure of Tyre temperature will check next event running rear steer it turns about 10 degrees. If ur behind car looking forward on left side top link 18 degrees bottom 12 degrees right side 22 degrees bottom 6 degrees

 

[Ranger Mike]

rear is too rigid causing pogo effect of wheel biting then bouncing up and spinning and dropping down .
18 ° should be MAXIMUM on upper links...14° minimum and left side should be less than right side.
both bottom links should be 5 ° starting out.
ball park settings
left top 13° rt top 18° up hill left and rt bottom 5° down hill

 

[Hillbillyd]

By no means do i think i am wasting time. this is a forum for racers. Any question is ok as long as it is in compliance with the administrators who are THE BEST. I am not doing this to sell software or books. Just passing on what limited knowledge i have as long as the person reads what i already wrote and does not ignore it and then continues to dog the issue.

Hill, you are most welcome to ask, no problem.

Once you have all the working pieces of rev rotation i would back off the front roll center off set since the engine torque will provide down load. All yo ucan do is use tire temperature to see how much down force you are getting and tune from that. Otgher than the Rc set it up as you have before. You need to get the car to handle going then work on center out.

Thanks for your reply one of my concerns is the lift of the left rear tyre under power.
Going off the Steve Smith book calculating the 3rd link mount location is based on your left side percentage weight to load the tyres evenly i.e. centre of the mass of the car, in my case I'm wondering if there is a calculation to determine where to mount my 3rd link for reverse torque?
So my understanding will be that i will be loading the right rear and left front under power?
How would this affect spring weights?

 

[Ranger Mike]

Use same mount location. it is for % left side weight. Your rear wheels will still be rotating forward regardless of the rotation of engine since your rear end has also been chage to right side pinion gear.

 

[Hillbillyd]

Use same mount location. it is for % left side weight. Your rear wheels will still be rotating forward regardless of the rotation of engine since your rear end has also been chage to right side pinion gear.

quote from Smokey
And note that reversing the engine’s rotation does not cancel the reaction forces in any event. It simply reverses them. And in the case of the forces acting on the axle housing, it’s in the wrong direction for oval racing.
So your not concerned about the torque is reverse and it will lift the left rear under power?

 

[Ranger Mike]

the torque is not reversed relative to tire rotation. This stays the same since you now have reverse rotation differential.
You have the engine torque now twisting to driver side ( vs traditional way of twisting to the right front) and the rear twist it going to the left rear vs traditional twist to the right rear.
This is what happens when you go rev rotation.

 

[Hillbillyd]

the torque is not reversed relative to tire rotation. This stays the same since you now have reverse rotation differential.
You have the engine torque now twisting to driver side ( vs traditional way of twisting to the right front) and the rear twist it going to the left rear vs traditional twist to the right rear.
This is what happens when you go rev rotation.

Ranger mike thank you for your patients I misunderstood what i was reading about lifting the rear under power
Quote from Smokey
The idea of reverse rotation is, when you accelerate hard the weight comes to the left front and left rear, and pulls weight off of the right front. This more evenly distributes weight across the chassis, increases your lateral traction on the front and back end. You go faster.”

 

[Hillbillyd]

quote from Smokey on a standard rotation torque
Torque reaction also lifts the right end of the rear live axle and pushes down on the left, with the axle housing forming a sort of lever. On a typical car developing oh, 300 lb-ft of crankshaft torque, there might be 75-120 lbs. of force loading one end of the axle and unloading the other. (Or, maybe why your vehicle’s right rear wheel spins helplessly when you’re stuck in the snow.) But for oval racing at least, this redistribution is in a nominally helpful direction—from the outside to the inside tire.
This i have seen at the drag strip many times of tuff street cars lifting the left front and burying the right rear up in the wheel well
So the way he explains it reversing the rotation of the drive shaft has the opposite effect on the rear axel lifting the left tire and planting the right tire.
Ranger Mike I'm happy to be proven wrong here as i will have learned something just getting under my car and rotating the pinion clockwise viewed from the rear it makes sense to me under load the right tire gets pushed down in the same direction of the rotation of the driveshaft.

 

[Ranger Mike]

rev rotation will lift right front tire and plant the left rear tire exactly opposite of current drag cars.

 

[Hillbillyd]

The last set of loads that the axle housing experiences comes from the reaction of the propshaft rotation against the wheels on the pavement through the axle gearing. As mentioned earlier, the propshaft is rotating in a counter-clockwise direction when viewed from the rear of the vehicle. This rotation and subsequent torque on the pin-ion is trying to rotate the axle housing. This rotation applies a downward force on the left wheel, and an upward force on the right wheel. So the load on the left wheel is increasing, and the load on the right wheel is decreasing. This is similar to the front-to-back weight transfer on the chassis during hard acceleration.

 

[Shorttracker93]

Hello Mike, I have read a large amount of your posts here and have a good understanding of most the suspension design concepts and roll centers for a asphalt oval car. Have you dealt with or seen the new " center pull" trailing arm setup everyone is going to on the rear 3 link? I kinda understand that it is accomplishing the same effect as a birdcage setup on a dirtcar but really don't understand what its doing geometry wise and what particular height adjustments change. The gentleman with Day motorsports that we spoke with at the Snowball Derby said that everyone's starting point is in the range of 6* up driver side and 12* up passenger side. i will attach a link for Port City Racecars design. It uses vertical screw adjusters but you will have to re adjust your square every time. Day motorsports carries a climber bracket that moves in an arc, I think it is produced by Wehers, I cannot find a link to it at the moment. I will be running the suspension on a Openwheel Modified and we are going to also install it on my fathers Outlaw latemodel.

Center pull kit Port city
https://www.portcityracecars.com/CENTER-PULL-REAR-SUSPENSION-KIT-1-3-4-ROUND-ADJUSTERS-DOUBLE-ADJUSTERS-FOR-J-HOOKS.htmlInstalled on chassis

https://gallery.mailchimp.com/3b755...ages/4261f5d6-3f5e-47e4-aae0-102ace3f8564.jpg

 

[Ranger Mike]

Couple of quick observations. This Center pull suspension with J bar links combines the best of 4 link and 3 link suspensions. The 4 link is the best set up for dirt as you need maximum traction tuning. This center pull set up eliminates the lower links of the 3 and 4 link suspension. Less weight hanging below the axel and less garbage to get snagged up on a bad track. Everything is above the rear axel tube out of harms way.

Look at the Instant center angle. I do not have the hard numbers but it sure looks like the intersection of the two J bars and the pull bar is way out in front of the axle. Like 10 foot in front of the car! We want the angles of the rear suspension linkage to form an Instant Center (IC) as far forward as possible. This longer lever cushions the acceleration when the tires hook up. This set up does not have a shock damper on the top link. Too short an IC distance means we have a lot of angle change on both sides and the car will be real darty when you nail it. Longer is better and gives the driver more control because you don't have a lot of angle change as the shorter IC has. The top link angle can be zero to 5 degrees down hill for traction.See attached forces on rear axle -
It is easier to pull a chain than push it. Race cars love forces that directly pull versus forcers that push and this set up is strictly a PULL. All links are pulling on the chassis. We have more initial static angle on the driver side of 6 ° and the right side angle of 12 ° . This means the car in chassis roll will grow more angle in chassis ROLL as the right side angle reduces as the right side springs compress. This is a feature that 3 link has but to a much lesser degree due to the limitations of the lower links. About the only thing you could to bias the rear wheel loading was to off set the top link mount. With the J bar design you can dial in rear wheel load directly to each wheel.

This is HUGE!
Question for you to ponder- What happens when the rear end is in Roll? What happens to wheel base on left and right side?

 

[Shorttracker93]

Couple of quick observations. This Center pull suspension with J bar links combines the best of 4 link and 3 link suspensions. The 4 link is the best set up for dirt as you need maximum traction tuning. This center pull set up eliminates the lower links of the 3 and 4 link suspension. Less weight hanging below the axel and less garbage to get snagged up on a bad track. Everything is above the rear axel tube out of harms way.

Look at the Instant center angle. I do not have the hard numbers but it sure looks like the intersection of the two J bars and the pull bar is way out in front of the axle. Like 10 foot in front of the car! We want the angles of the rear suspension linkage to form an Instant Center (IC) as far forward as possible. This longer lever cushions the acceleration when the tires hook up. This set up does not have a shock damper on the top link. Too short an IC distance means we have a lot of angle change on both sides and the car will be real darty when you nail it. Longer is better and gives the driver more control because you don't have a lot of angle change as the shorter IC has. The top link angle can be zero to 5 degrees down hill for traction.See attached forces on rear axle -
It is easier to pull a chain than push it. Race cars love forces that directly pull versus forcers that push and this set up is strictly a PULL. All links are pulling on the chassis. We have more initial static angle on the driver side of 6 ° and the right side angle of 12 ° . This means the car in chassis roll will grow more angle in chassis ROLL as the right side angle reduces as the right side springs compress. This is a feature that 3 link has but to a much lesser degree due to the limitations of the lower links. About the only thing you could to bias the rear wheel loading was to off set the top link mount. With the J bar design you can dial in rear wheel load directly to each wheel.

This is HUGE!
Question for you to ponder- What happens when the rear end is in Roll? What happens to wheel base on left and right side?

Just by watching the cars running it at the Derby that won and have it figured out already it was essentially moving like a dirt car, the left rear tire was traveling into the fender well, the rear of the car was rising and the left ear tire was just being pounded into the pavement. We all know modifieds with 8" tires are an animal at the end of the race but mot anymore with this setup. same thing with the super Late models. I will add they are running the rear calipers on the bottom of the axle tube also. Yet again this is things I've seen on dirt but am not familiar with dirt as we've always ran pavement.