Automotive Race car suspension Class

[Ranger Mike]

Welcome Chris..we have these at the local tracks...nice clean racing...see post 293 on stinging the car..measuring toe is best deon with scribing a line on the tire but this takes two people t o scribe the line and hold " dumb end " of the tape measure...we use a toe gage..i will see if i can get photo of this on line..onme person can check the car and adjust...really close results..the Legends or Dwarf cars are real fun but rules say you can not do a lot to them..which does keep cost down...

 

[chriswh86]

interesting. here are a couple items I found at longacre

tire scribe
toe gauge that will measure to 1/32"

seems like a good setup.

Yah the dwarf cars are pretty cheap to run. We are just a local club so we designed our own rules there's a lot of grey areas etc but they also state if its not in the rules you can't do it so I am not to sure. But you can still design the setup however you want pretty much, which is quite nice.

I will look over the string line post. Thanks!

Chris,

 

[Ranger Mike]

Anti Squat and Anti Dive

Anti-dive and anti-squat ( I didn't explain calculations on post 314 so here it is)

Please read post 314 on page 20-

I had a question from Conrad on setting up his front suspension. Both Anti Dive and Anti-squat refer to the front diving under braking and the rear squatting under acceleration. They came about because passenger cars would require very stiff springs to counter act braking and acceleration forces and the difference in design is due to the different design goals between front and rear suspension, assuming symmetrical design between the left and right of the vehicle.

Percentage is the method of determining the anti-dive or anti-squat and this depends on whether the suspension linkages react to the torque of braking and accelerating. For example, with inboard brakes and half-shaft driven rear wheels, the suspension linkages do not, but with outboard brakes and a swing-axle driveline, they do.

To determine the percentage of front suspension braking anti-dive ( outboard brakes like GM metric chassis uses)

1. Determine the tangent of the angle between a line drawn, in side view, through the front tire patch and the front suspension instant center, and the horizontal.

2 Determine the percentage of braking effort at the front wheels.

3. Multiply the tangent by the front wheel braking effort percentage.

4. Divide by the ratio of the center of gravity height to the wheelbase.

A value of 50% would mean that half of the weight transfer to the front wheels, during braking, is being transmitted through the front suspension linkage and half is being transmitted through the front suspension springs. Passenger cars are as high as 30%, stock car racers run 5 to 7% if they even bother to figure it.

For inboard brakes, the same procedure is followed but using the wheel center instead of contact patch center.

Forward acceleration anti-squat is calculated in a similar manner and with the same relationship between percentage and weight transfer. BUT..you can have Anti-squat values of 100% and more (common in drag racing). all of the weight transfer is being carried through the suspension linkage but remember, this does not mean that the suspension is incapable of carrying additional loads (aerodynamic, cornering, etc.) while braking or during acceleration. 50% or less are more common in cars which have to undergo severe braking. Higher values of anti-squat commonly cause wheel hop during braking.

 

[chriswh86]

Off topic

we run a 235 60 13 tire in our dwarf car class, I've seen some people running 13x7 rims but most on 13x8 rims that stretch the tires out pretty good.

I am wondering if there would be much benefit to going to a 13x9 if that would pull the side walls a little straighter and maybe take away some tire roll...

Chris,

 

[Ranger Mike]

is wider tire better

like everything in racing , its all about compromise..we went thru this mind drill in FC ( Formula Continental) a few years back. In a class that races open wheel and limited horsepower the traction benefits of wider boots on all four corners may not be worth is. The key factor is engine output ( torque and HP). Open wheel cars get killed with big aero drag and tires account for at least 40% of total drag.
If.. and this is a big if the tire and wheel combination is the same as your current combination, and yoor wheels are under the car not hanging out in the air stream..Id run them. But if they are heavier than the current set up (come on...it takes more metal to make them... more metal = more weight). There's also more rolling mass. More rolling mass = slower rotation = slower speed. Figure about 2% more grip per inch tire width you add,,,but,,,parasitic drag is a BEAR...esp in open wheel limited hp racing.

see post below on General Physics forum,

How does traction compare to the width of a tire?

Mar17-12, 07:03 AM
Mender had some good insight

 

[Liju GKM]

sir, we are participating in mini baja. can you tell the steps of designing suspemsion in the correct order?

 

[Ranger Mike]

how high is the sky?

 

[chriswh86]

Interesting question I am having a hard time figuring out.

As I've seen, most circle track cars run some sort of offset on the rim backspacing to create more left side weight?

I recently got a newer used dwarf car which has set multiple track records, multiple points championships etc and it runs 13x8 aero rims @ all 4 corners with 1" backspacing.

I am having a hard time figuring out what the benefits of running this type of offset is at all 4 corners. there's a few other cars in the club running 1-2" backspacing at all 4 corners and they are fast as well.

Is it a way to better load the contact patches on acceleration? I just can't seem to get an answer i understand as to how this works.

Chris,

 

[mustngthundr]

Greetings! Just my general opinion on the wheel offset post above, iv seen a lot of circle track cars run both ways, equal offset side to side and different offsets to move the left side wheels further under the car. Iv talked to a few racers that feel it improves the left side weight with a higher offset wheel on the left. Maybe in static state on your scales it does, but in the dynamic state while your in mid corner it actually may be hurting you. Track width is one of the components that effect weight transfer. The other components are cornering force(Gs), weight, and center of gravity height. One of these components must change to effect weight transfer. In other words, there will be less weight transfer left to right if the track width is wider. Watch for wheel scrub when making your track width wider with wheel offset alone, however. Too much wheel scrub can be detrimental to handling as well, but in my opinion, that's why it's set up that way and that's at least part of the reason that the other fast cars are doing it too.

Mustngthundr

 

[Ranger Mike]

Wheel Back space

when you lay the wheel on the garage floor with valve stem up and measure distance from floor to the center section you measue the back space. The lower the number the further the tire is located from the car centerline. Too much offset really applies a big lever to the wheel bearings and on heavy cars you are asking for trouble. Some hot dogs in legend cars and dwarf cars run huge offsets ( real low numbers ) thinking the wide is right scenario works. I did some posts on the wide vs narrow thing on post 255 @ page 16, post 322@22 post 264@17. As limited as you are in this class, about ther only thing you can do is mess with wheel offset and chassis adjustments.
One way is to go W I D E... I helped a guy one season on a legend car and we opted to go left side ...low amount of back space on right side and high number on the left side..you are shifting the vehicle weight slightly to the left.
So the question is..go WIDE or max left side weight...??

Wider track offers less load transfer through the middle of the turns and therefore more retained left-side weight. If the wider track reduces the load transfer by more than the difference in left-side percentage, then it would be best to go with the wider track.

If the difference in left-side percent is more than the load transfer difference, then obviously you would go with the higher left-side percent.

If all were equal, I’d go with the wider track. With the low center of gravity of your Modified, there’s less load transfer than would be seen by a Late Model or stocker. But, why not try for both?This is where tune and test comes into play..these cars are so light that no way will you damage wheel bearings over one season running a 1 inch back space...I have no data on amount of left side wieght increase you can get since the racer who had the legend car did not own scales...if I had to guess...if you are already at 58% left side weight..if you can add 4 inch track width ..go for it..

 

[chriswh86]

Most guys in the dwarf class tend to run right at our max tire width, as measured from the outside of the left front to the outside of the right front, same on the rear...max 62"

Im currently running 1" backspacing at all 4 corners, so If i was to try a 4" on the left, id have a very short track width as I am close to 62" as is.

I like the 1" backspacing all around because it has obviously worked wounders in our class, I just had no clue how it worked.

But from what I have gathered from the last 2 posts, having 1" backspacing on the left side tires is probably saving a large transfer of weight from left to right at the center of the corner thus helping mid corner and exit?

Correct me if I am wrong. Cheers to all

 

[Fahlin Racing]

I see this thread has grown quite a bit, been pretty busy myself. I have to get some snacks and sit back and read again.

 

[Ranger Mike]

chris..yes i think you nailed it..the go W I D E crowd is dominating. I have not doen the math on the max left side weight thing but i suspect the % will not " out weigh" ( sorry, bad pun) the wide is right argument since what ever the left side weight is..will transfer regardless vs the wide is right theory of minimum transfer...
plus . correct me if i am wrong..you have prety hard Spec tires to begin with..not good for max Gs anyway

 

[Ranger Mike]

The following is index listing Post and page
Anti Squat 314@20
Bump Steer 13 @ 1
Caster 319@20
Eccentric 298@16
Four Link 132@9
Four Link Instant Center 301@19
Panhard Bar 246@16
Rear suspension motion rate 308@20
Rear Steer 116@8
Roll Center, front 251@16
Roll Center 229@15
Scrub Radius 325 @ 21
Shocks Penske shocks 217@14
Shocks Rubber Shock stops 220 @ 14
Spindle Angle 325 and 332 @ 21
Spring Rate Calculating spring rate 19@2
Spring Rate vs Wheel Rate 17@2
Stagger 36@3
Stringing the car ( measurements) 293@19
Third link Top Link 81@6
Third Link Mount 253@16
Third Link Spring Rate 261@17
Track Width 255@16, 322@21, 264@17
Upper Arm Angle 312@20

 

[chriswh86]

Ahh ok, Ranger - would you know of maybe a cardboard experiment i could do to understand the differents between high and low offsets and weight transfer. I realize I got the right idea of what the low offsets are doing and how they are dominating. But in my head i can't understand how it works :)

And we use american racer uhh Nedwarfs or something like that. The ratings on the tire are HORRIBLE...As for class rules...we can do ANYTHING we want basically. We have no left % max or anything like that. I am currently at left 52%, The car is extremely light weight, I am at 1220 race ready, 1200 is the minimum we need to be after a race...Sorry i don't have the best info yet, but there is at least 40pnds of lead by the left front tire...I always here. get to the max left weight %. Now with an open rule book on that and such a light car. I am guessing a lot of left weight won't be benefical? Id also like to get my weight back down to say 1210, enough weight left over for tire wear and gas at the end of the main. But i think the left weight is benefical in getting the front and back % close to each other, and sticking the left front

 

[Ranger Mike]

look at illustration on post 255 @ page 16...note the cornering Gs increase with 4 inch wider track..
thats a lot of weight but...if you need it to be legal...what size battery are you using?
are you running three link rear set up?
if it is wide open...i would be in hog heaven with all kinds of ...innovatative stuff...

 

[chriswh86]

Got to remember our track width, 62" max is a rule
Wheel base is 73" +/- 1/2" that's another rule


I am running a pretty small battery, a little red top, measures about 4" long, 5" in height and about 2-3" thick. Also I've see a SMALL battery on a bike that i don't think even weighs a pound. Mine is a few pnds.

its a 3 link rear setup. Long panhard, Long trailing arms, and a long 3rd link that is mounted on the rear end just above the RR trailing arm...

I need to find ways to loose more weight though :)

 

[chriswh86]

Something id love to see ranger, which may be a lot of work, is to list some good books folks can get.

ex.

Front Asphalt suspension designs by. blahblah

"Ranger Mike" -> i find this book good because it explains... and so on.

So maybe like a book title and what you feel its good for ect.

How do you feel about this? I used to have the circle track suspension book but its gone to some other racer probably

 

[chriswh86]

Hey all,

Something I've been thinking of lately. I've recently decided to move my car from the shop its normally at, to where i live. I've got a 7x16' enclosed trailer that will now be my tow trailer to the track as well as a bit of a shop when I am at home. A place to store my tools and so on.

Now i have a carport where I live but the cement is cracked in a few spots and its definantly not level.

I am woundering what options i have (im not made of money) for a rig/place etc to setup my car. I live 250km+ to each race track, so quick use of there flat pad won't work, nor do I have an area near where i live for it, so I am looking for what i can do at home in the carport for car setup.

I had thought of scale pad levelers which i could do and it sounds like it would work out with a scale system, but now I am a bit lost at how i could get proper frame height measurements, that's most of my concern.

Also, I am looking for ideas on how I can create a flat pad system or something for where I can put the car (no scales) and check the car settings/frame heights etc etc

I have a dwarf car, 1220pnds 73" wheel base, 62" track width, 113" long (bumper to bumper)

Thanks all, I can't wait to here what ideas are out there

Chris,

 

[Ranger Mike]

I think a scale platform ( 4 roll off ramps..maybe connected??) is what you need. Easy to make with plywood or OSB. You can make roll off ramps and use these to check set up chassis height. I have a set and i spray paint each roll off ramp and the scale pad location after i made a shim plate of proper thickness to " level" that pad at that location relative to the other three. The platform is cheap, easy to make, light weight and easy to transport ...some times ..wood isa good..

 

[chriswh86]

interesting...mike, any photos of your ramp setup?

update -> I just had a brain far Mike. If I got scale pad leveler setup with built in roll off areas for each 4 wheels. I could just set my car on the scales and do what i need to do, then using the roll of part, i can put my tape measure on the roll off section and up to my frame rail and measure there...thats the only measurement id need to take really?

If i wanted shock heights etc i could attach a piece of metal to the roll off section that extends across to the next pad or something and measure to that piece of metal

this system would probably work good eh, i was thinking of a full pad leveler/roll off/roll off ramp setup, but i believe a scale pad leveler setup x4 with little roll off sections on the back of each scale pad area would work perfectly

such as> http://www.intercomp-racing.com/Products/25_SCALE_PAD_LEVELER_WROLL-OFF_PAD_822.cfm

or at least, if i can build my own and build the platform to extend toward the inside more on each tire, ill be able to measure to the frame rail

 

[Ranger Mike]

Roll off ramps easy to make
you need these to adjust the chassis...jounce the shock springs when both ARBs are disconnected
then roll it back on the scales after everything settles

 

[chriswh86]

interesting mike...and you adjust yours via shim plates under the wood?


New Question: I've used stagger tapes (only a couple times) and I've used a knock off longacre stagger gauge and i haven't really been happy with the stagger gauge setup, i find it to flex/sqwish a bit and i can be off on stagger by a 1/4" or so.

Im woundering if I should go back to the tape measure style of measuring or is there a better system I can use. I am looking for speed and consistancy

Cheers
Chris,

 

[Ranger Mike]

Tire stagger

You will get better results with the tape measure method. Use a stagger tape that is about 1/4 wide. I have both..but being on road course...not much point to doing this.
For round track stagger is everything. We used to run nitrogrn and bleeders in the wheels.
One tip...go to a horse tac shop and buy a curry comb..it is great tool to remove gravel from the slicks so you can get good measurments..

 

[chriswh86]

Interesting, good idea on the comb! we have treaded tires, so it will be crutial with the tape to get it in the middle of the tire each time for repeatable results...

Is there any good 1/4" wide tapes for stagger that have a good end on it for the tire etc or are they mostly all the same


Another question, My new car has aluminum lug nuts on course 5/8" studs, what's the best way/amount to torque them...Also, I may go with aluminum jam nuts as well, best just to snug them up on the radius rods and add a little extra quarter turn?

 

[Ranger Mike]

I think all the stagger tapes have long hook at the end..hoosier , longacre,,etc,,
use a torque wrench on the wheels...i like the kind that clicks when you reach proper setting..dont forget to back it off after use .
you do not need jam nuts on the lugs...on the suspension components of course...use jam nuts

 

[Ranger Mike]

Heat cycle machine

If you have that restrictive a sanctioning organization..you may want to look into building your self a trie heat cycle machine.

 

[chriswh86]

ahh yes, i forgot to mention, i ment using aluminum jam nuts for the suspenion arms, I was woundering how to tight they should be, before they break


im not sure I completely follow your reply on building a head cycle machine. I would however LOVE to build a tire shaving machine, get rid of half or more of that tread and see how the tires perform. I am still looking to see if anyone around here still shaves tires to see if that will be easier than building one

 

[MikeGaynor]

Mike (and the rest of you) thanks for giving me a couple of days of reading to go through this whole topic. It's tricky for me to pull out the information I want though as I'm not a) american, b) driving a live axle, c) using double wishbone front end, or d) racing round an oval... But still, lots of valuable information.

Now, I'm not sure if this is going to make me seem like an arsehole but I'm actually into drifting... As in, sliding a car around the track like Formula D. I don't wear flat peak baseball caps and I do have a huge interest in car setup but I think most people who like drifting don't really know what they are talking about when it comes to the physics of suspension. I plan on competing again in the UK so am building a BMW e10 2002.

My main objective in my latest "from scratch" build is to design a good suspension setup to provide LOTS of rear end traction (forward acceleration from the tyres, despite them spinning), whilst giving a savage self-centering effect on the steering. So from most of the discussions here my main interests are:

Roll centres front/rear to give control and balance during transitions (from a left to right slide)
anti/pro-squat in the rear to encourage as much traction as possible
ackerman/KPI/caster in the front to give a sharp steering response

So aside from my life story, and maybe encouraging some open conversations and thoughts about my points above, my main gripe is the effects of squat in the rear.

My car uses a BMW e36 rear end, which has a trailing arm, with two diagonal/forward pointing (from the hub into the subframe) arms one above the other. The trailing arm controls the fore/aft forces from the wheel, the upper and lower track control arms control the side to side forces from the wheel, as well as controlling camber gain. Together they all form a complex sort of semi-trailing-arm suspension system where the wheel ultimately cambers and toes all over the place under compression and extension depending on the lengths of the arms.

I want to know whether I should be looking to use anti-squat to push the wheel into the ground by mechanical leverage of the suspension arms (the wheel trying to ride under the CoG), or whether to use pro-squat (or less anti-squat) to allow the CoG to shift backwards over the rear wheels and use the springs to push the wheels down into the ground.

Quoting something Ranger Mike said earlier in the thread, regarding the effects of lateral forces acting on the tires, it was made clear that roll is good as it uses the springs to push the outer tire into the ground, rather than using a higher roll centre to reduce the amount of roll and convert it into lateral shear force on the tire through the suspension arms. Does this translate into longitudinal forces and the CoG on the lines drawn to calculate anti-squat?

 

[Ranger Mike]

welcome and thanks...pls clear up one thing..when drifting..you want the car to respond instantly to your desire to spin the tires..right?
and all efforts are to achieve this? or is handling also in the equation?

 

[MikeGaynor]

Thanks for the reply Mike. I'll try and clarify on your questions.

The car should be responsive to direction changes, and should have the grip/drive to push itself out of corners, but the spinning of the wheels is going to happen any way - there's no need to try and artifically sharpen the response of the rear wheels breaking traction. Beleive it or not drift cars should be built to have as much rear end grip as possible, so to make it slide you have to be going faster and driving harder (which is in turn an advantage when competing). If your car is on a tight rope trying to spin the wheels at the slightest touch then you end up drifting a track much slower than the opponent.

Everybody has different ideas but in my opinion I just want a "solid" feeling car which has as much rear end acceleration traction as possible. Since the throttle is constantly being adjusted you have to allow for a predictable change from accel to deccel forces but ultimately you want the most traction for the acceleration, without it brake-hopping as a result (brakes and handbrake are used occasionally).

"handling" in the traditional sense isn't really applicable, but certain aspects of it need to be considered. Just try and think of it being a drag race, whilst sliding around corners. Maybe like dirt racing (where most of the focus is on the rear end) but on smooth tarmac rather than rough dirt.

I imagine in an ideal situation my inside front tire would be off the ground when mid-corner, assuming a drift angle of around 45deg to the track, giving full weight transfer to the rear end for forward acceleration.

Apologies for this whole thing sounding amatuerish compared to racing, but it is still very competitive as a motorsport and I think suspension design really hasn't been developed beyond off-the-shelf bolt on parts.

 

[MikeGaynor]

https://www.youtube.com/watch?v=qzChg2Wetrg
(I hope that link works)

Excuse the poor quality but this was me a few years ago in the grey e30, it shows so well that I am losing ground on the opponent cars in every battle. The idea is for the chase car to show that they can be inches away from the lead car, but with more angle and style and precision. If you are the chase car then having huge mechanical grip gives a huge advantage as you can close the gap between you and the car infront at will.

For those of you with minimal experience of the effects of grip on spinning wheels, the rules seem to work basically the same but the effects of tyre temperature and the lateral forces deforming the rear wheels are greatly reduced as the tyre is already spinning.

 

[Ranger Mike]

i am not too up on drifting...about the only thing i can say is set up the chassis to road course specs..as close to 50 - 50 as possible..avoid bump steer fnt and rear..min camber build as possible..aero up as much as possibnle..reduce weight to bare min..add tuneable 3 way shocks as minimum...go with aftermarket ARB...lighten up any rotating weight to bare minimum

 

[MikeGaynor]

Thanks Mike, that's the general idea for what I was going for anyway. Whilst not being an expert on drifting, hopefully you can help clarify my below thoughts re: squat. From reading elsewhere it seems that IRS is not as sensitive or effective with anti-squat but I still have to mount my trailing arms somewhere and still have free reign of the height of my rear roll centre so I want to put it all in the best place for traction. Thanks.

my main gripe is the effects of squat in the rear.

My car uses a BMW e36 rear end, which has a trailing arm, with two diagonal/forward pointing (from the hub into the subframe) arms one above the other. The trailing arm controls the fore/aft forces from the wheel, the upper and lower track control arms control the side to side forces from the wheel, as well as controlling camber gain. Together they all form a complex sort of semi-trailing-arm suspension system where the wheel ultimately cambers and toes all over the place under compression and extension depending on the lengths of the arms.

I want to know whether I should be looking to use anti-squat to push the wheel into the ground by mechanical leverage of the suspension arms (the wheel trying to ride under the CoG), or whether to use pro-squat (or less anti-squat) to allow the CoG to shift backwards over the rear wheels and use the springs to push the wheels down into the ground.

Quoting something Ranger Mike said earlier in the thread, regarding the effects of lateral forces acting on the tires, it was made clear that roll is good as it uses the springs to push the outer tire into the ground, rather than using a higher roll centre to reduce the amount of roll and convert it into lateral shear force on the tire through the suspension arms. Does this translate into longitudinal forces and the CoG on the lines drawn to calculate anti-squat?

 

[Ranger Mike]

i would concentrate on up grade to LSD..i assume you already have limited slip diff
go to strut tower braces if you do not have alrerady
coil overs
add driver seat
unless you really want to get serious and buy suspension software, don't monkey with any of the geometry...oh you could if you have lots of time to do trial and error but it is better to have a map when going into unknown territory..

 

[MikeGaynor]

I'm happy to buy suspension software but need to know what I should be aiming for with anti squat... The whole thing confuses me. On one hand I have the theory that more squat means more weight transfer and more of the springs pushing my wheels vertically down, on the other hand less squat means more of my suspension trying to push the wheels down and into the floor. Since I don't have a live axle I'm limited to more linear force vectors on the rear tires rather than torque twisting the arms, but I still need to know roughly what I'm aiming for.

Thanks for the general advice too but I'm a bit beyond the "drivers seat" and "tower brace" stage of modifications :) That's why I'm here! I'm literally offering subframes up to a hollowed out bare shell with no front chassis rails and no rear floor pan. Once I've sorted the basic geometry out I will then continue the build. Full roll cage with tower and subframe ties, welded diff, coilovers, spherical/rosejoints throughout the suspension, reduced weight to a bare minimum etc, but the backbone of the whole build pivots around (excuse the pun) my suspension geometry.

I can find out where my roll centres are easily, with suspesion software, and can plot how it will move to keep it as stable as possible, but I need to know where things should be for optimum traction beyond "keep the tires flat on the floor". The car is going to be around 900kg with driver so I need to make the most of what little weight there is into more forward traction.

Even if you ignore my drifting question, just treat my question like drag racing, and hopefully clarify the theory behind anti squat as not many people who know what they're talking about share their knowledge online! Just try searching for "e36 anti squat" and you get a few pages of BS on the entire internet.

 

[Ranger Mike]

if that is the case Mike..then why not set up as 4 link and tune from there?

 

[MikeGaynor]

Because I don't have access to any decent live axles or spares and I think it's a backwards step in terms of unsprung weight and traction over uneven surfaces.

 

[Ranger Mike]

HP required to overcome Aero drag

4 link is the hot set up on dirt...nuff said

 

[Ranger Mike]

I ran across this when doing Aero research. This was written by one savvy guy...

 

[b00sted]

Wow, there's a lot of good information here.

I ran across this forum while doing a Google search. I'm teaching myself SolidWorks and want to eventually design and build my own car...A tube-chassis design similar to a Locost/Lotus 7, but with round tube, a safer cage, and much nicer suspension.

Anyone here own this book? http://books.sae.org/book-r-146
It was recommended to me by another guy on a drag racing forum. After looking through the table of contents and reading a few of the reviews, it sounds like it will be a good thing to have on hand.

 

[Ranger Mike]

Welcome..if I had an extra $100 I would buy it

 

[rick7343]

Anyone got any theories on the front vs. rear roll center heights?

I've only found one article with much info... it stated that the front roll center should be 50-66% of the height of the rear or the car will understeer going into the corner and oversteer coming out...

That is exactly what my car is doing, and I've been trying softer and softer RR springs. It is getting better, but still not good... I have a The rear RC is pretty fixed since we have to run the stockish 4 link in the rear...

If the rear RC is around 22", then my front should be at least 11''... sounds crazy!

Opinions?

 

[Ranger Mike]

my opinion
stk clip heavy car with iron heads should have frt roll center 2.5 inch above ground.
ifin you are pushing goin int and loose coming out...frt springs way too soft...going into the turn.. the weight is coming forward and washing out rt ft tire grip...tire shear...and weight is staying there ...up front...so coming out the car is way too nose heavy and rear tires do not have enought weight to hook up the rear drive tires,,,results- they spin instead of driving off the turn..

 

[rick7343]

OK thanx...

But there is less than an inch front shock travel, and softening the outside rear spring is helping, which would seem that the front wants to roll more than the rear...(?)

 

[rick7343]

Interesting... I was down in the big city today talking to one of the leading race shops and they said the light hollow Hotchkiss bar can't be preloaded... they are not strong enough...hmmm...

I suspected the bar was twisted when I set the car up last weekend... (crap!) Maybe that's why adjustments didn't have mush affect...

We are stuck with stock mounted bars... Have to find a solid bar now I suppose...

Why can't things be simple anymore...?? lol

 

[chriswh86]

Rick - What springs are you running? Getting a large sprint split up front or in the rear could be crutching a bigger issue

"I suspected the bar was twisted when I set the car up last weekend... (crap!) Maybe that's why adjustments didn't have mush affect..."

Sounds like you are setting your car up with the sway bar attached? it shouldn't be while scaling and setting ride heights etc...

 

[rick7343]

Lf. 600. Rf. 650
Lr 200 Rr 175. (4 link)
Car has never felt hooked at all until I increased outside air pressures, always felt greasey lik it was always sliding...tires squealing , etc... just starting to make some progress.

The idea was to run softer front springs and bigger bar (1-3/8" 540lb) to be able to get the front CofG down in the corners, But the shock package was too stiff to let this happen...So I put the springs back in that the race shop that built the shocks advised (current)

Seems the presures the other cars are running are too soft for my car and the tires get greasy, but running too much seems to take a while for the tires to get hot enough to stick really good...

How is optimum tire pressure determined?

I called the manufacturer, they said to start at : rf 36,rr 34,lr 32, lf 30 and drop a couple psi if needed... most top racers in the class say no more than 28 hot in the outside and 16-18 hot on the inside... at 16 hot on the inside I can feel the lf tire fold over and hop coming out sometimes...

One of the fast cars that passed me the other night looked like he was sliding all over... not hooked either... had more power than me and got the job done though!
we have to run Towel City recap on 8" Hoosier casings... Also have to run a lot of extra stagger to make them work..

wonder if we all are missing something?

 

[Ranger Mike]

Rick, you are limited to running hard tires in this racing class. The lite spring big ARB idea is not working for this car on this track. Forget about getting Center of Gravity down in the corners...why would you want to do that? What is the purpose? CoG is a starting point but the Roll Center is where everything happens.

Hard tires require RT front weight in order to increase traction and properly turn the car in a corner. They require rear weight in order to hook up and driver off the turn. Springs control amount of weight transfer ,,, Shocks control rate of transfer. Tuning these two are key to making the car handle.

Tire temperatures are indication of how good the actions above are working. You should have no more than ten degree spread over the inside, center and outside tire temp readings.
Adjust tire pressure until you get the 10 degree spread.

I had a driver once who insisted on running 10 psi on Hoosiers when the Hoosier tech said 20 was minimum..car bottomed out..no wonder..but some people just will not listen and want to run the “ hot setup” without understanding what is really going on...

Go back to more conventional spring / ARB set up and work on the right front wheel geometry. Reduce bump steer, reduce camber build, add Ackermann. On rear , eliminate and roll under/over steer to avoid mixed signals...when you get the car to turn going in ..then work on hooking up the rear end...my opinion

 

[rick7343]

"Rick, you are limited to running hard tires in this racing class. The lite spring big ARB idea is not working for this car on this track. Forget about getting Center of Gravity down in the corners...why would you want to do that? What is the purpose? CoG is a starting point but the Roll Center is where everything happens.."

Tires are supposed to be 60 duro, they "ball up" like slicks a bit..

Center of gravity down... why are lower cars faster around the corners?

"Hard tires require RT front weight in order to increase traction and properly turn the car in a corner. They require rear weight in order to hook up and driver off the turn. Springs control amount of weight transfer ,,, Shocks control rate of transfer. Tuning these two are key to making the car handle."

How much weight is too much for the right front? I would like to use all the tires...

How much is too much rear weight..local guys are saying 50% rear is too much...

Other teams are saying their roll centers are way left to keep weight on the left front...Mine is almost in the canter @ 3.5"


"Tire temperatures are indication of how good the actions above are working. You should have no more than ten degree spread over the inside, center and outside tire temp readings.
Adjust tire pressure until you get the 10 degree spread."

I made a mistake by listening to others on camber (6 degrees) and tire pressure... less camber and more air works better so far... with 28lbs hot in the RF it just gets greasy... I will reset with temps... I had eliminated bump... not sure how to accurately measure ackerman... ?

"Go back to more conventional spring / ARB set up and work on the right front wheel geometry. Reduce bump steer, reduce camber build, add Ackermann. On rear , eliminate and roll under/over steer to avoid mixed signals...when you get the car to turn going in ..then work on hooking up the rear end...my opinion "

Bump is almost zero, camber build is less than a degree per inch...

Am going to fix the rear roll steer since the back of the car jumps over a bit when fuel is applied in the corner...

Last race ,it finally started feeling hooked up on the rear, so it's not really that far off... everyone says it looks good... it doesn't feel good yet, and not much feedback thru the steering wheel.. I changed gearing for last race and lost ground, so it looked worse than it was... new, modern custom cam on the way... engine is old and tired...

Thanx Mike!

I was really frustrated because chassis adjustments and changes weren't making any difference until I got some laps on the tires and finally added air..