Race car suspension Class

[loganc_racer]

Very interesting approach HowlerMonkey. So this method would be similar to NASCAR teams using their pulldown or 7 post rigs? (or whatever they call them)

 

[Ranger Mike]

great feed back guys...a happy new year to us all and let's get some checkers !

 

[zerohero]

I race winged pavement sprint cars... What's your take on weight? Our minimum is 1600lbs, I'm right at it... my stuff is full of titanium and lightweight stuff to make it. a lot of guys are overweight, in fact one of the fastest winged pavement cars out there is a hefty 1750. I've got a very strong engine package in my stuff and can afford to carry some weight. Would it be worth sacrificing to strap 100/150 lbs in a nerf bar or extreme left side to gain a big left side weight percentage?

 

[Ranger Mike]

Like all racers, I hate to add weight. I am not a sprint car guy having minimal exposure to this type race car.
Look at post #560 on page 28 thru post #564 on page 29. I had a lot of private messages on this one...”light is right”
We cover polar moment and Center of Gravity in these posts.

Are you at the limit of % left side weight now? are you at limit of rear % weight?
I assume you are ifin you are at minimum..this takes a lot of money to get to the minimum.
1. Easy thing to do if your are NOT at max left side weight is to strap on the lead and see.
If you are maxed out, as I suspect you are,think about this.
2. Lower the COG. One area I am not sure about if the fuel cell you now have. Is it one big honking bladder? You have sling weight on that monster. Can you engineer a different fuel storage system like two or three smaller bladders located at more advantageous location on left side...and lower than what you have?
3. What rear suspension are you running? Birdcage?
I assume you are push start with Mag and no battery or starter..right?
One thing I do know about outlaw sprints is the delicate front end components. I have watched these cars bend front ends when they run up on the berm but that is dirt and you are running paved tracks. There is an old saying in racing, “ you can't win Ifin you don’t finish” so I would look at my most frequent breakage part and engineer for durability.

The most dangerous place in racing is the hot pit for sprints. These cars come in hot ( 35 mph or more). These cars do not have battery , starter or clutch or transmissions to save weight. They have a dog clutch that is in or out. There is no in between like a standard clutch/transmission situation. You had better be SOBER and paying attention at the pits when the Sprint cars come to town. I always hated racing after they were on track qualifying. The sprint car is push started and this means the engine takes 3 laps to get up to temperature to make good horsepower. They are blowing oil past the piston rings until they make proper temperature and this is blowing out the headers onto the asphalt. As we all know asphalt if petroleum based as are the tires..What a mess.
If I owned a sprint car I would seriously think about adding clutch and starter and battery for two reasons.
Safety- I have seen race situations where the car spun out and stalled and the pack came howling down on it. The driver manager to bump the starter enough to move 6 inches that was just enough for the pack to slip thru..was hairy but...that’s racing. You are dead on the track in a push start car.
Horsepower- If your engine is started and idling before the rest of the field gets push started you will have rings upon to temp and make better HP than the field in the early laps.
just thinking out loud..

 

[zerohero]

Pretty much everyone runs some kind of engine heater as far as your temp question. We have no left side max rule, so that's what made me think about that. Yes we all run bird cage suspension, and as far as fuel tanks go mine is small, only 23 gallons. The small tank allows me to move the fuel more forward in the car, but the disadvantage is the fuel is higher...I'm probably going to get a huge 38 gallon tank so the fuel sits lower, but it will add a small about of rear weight...but me much much lower. I thought about making a custom fuel cell, but I know it'll be a $2500 waste because they will outlaw it right away. My car is a 4 link, some guys run a z-link also. My 4 link is SUPER short, the radius rods are only 24" long, most are about 48" long. I'm thinking about extending my 4 link to the firewall which will make the radius rods about 48". My car was fast, but very tight in the center all year... I think the short 4 link was a huge contributor to that, I'm not sure though.

 

[zerohero]

Silver Crown cars have clutches, but no on board starter system. There's zero chance I'd put a clutch and starter on a sprint car that's a ton of weight, I don't think anyone would... I can't even think of anyone that's ever done it.

 

[Ranger Mike]

I would then concentrate on the rear end. Look at the longer radius rods. Look at better control of rear steer. This should help on middle out tightness. I am not permitted to go into detail on this matter ( pledged to secrecy ) but look at the bird cage and rear steer and super trick stuff in this area to get major advantage.

 

[zerohero]

I would then concentrate on the rear end. Look at the longer radius rods. Look at better control of rear steer. This should help on middle out tightness. I am not permitted to go into detail on this matter ( pledged to secrecy ) but look at the bird cage and rear steer and super trick stuff in this area to get major advantage.

What are you in the CIA's race car suspension department lol

 

[Ranger Mike]

close..the Ranger part of Ranger Mike was from active duty military officer with neat things like airborne, ranger, s.f. qualifications...but that was years ago
Happy New Year to all racers..and race fans!

 

[jlambo04]

I race figure 8. so basically you can consider it a road race car. our minimum weight is 2600. I currently run a 3 link rear suspension set up were everyone else is running leaf springs. I'm trying to compete without doing the monkey see monkey do routine and learn more of the technical info about how to set up a road race car. any help would be appreciated. our current rules don't allow coil overs in the rear end but they are allowed in the front. we also can't use any rebuildable shocks. frame height is at least 4" only because the car will bottom out in certain areas of the track. i run a camaro front clip. the rest of the car is a tube chassis. I'm sure there is a lot of other info you would need to help me out and i will get it as needed. thanks again.

 

[MachineMasters]

Ranger Mike,

what are your thoughts on front suspensions setup for zero droop? Dirt late models are running zero left front suspension droop a lot lately and I'm wondering why they might be doing this. I've read that it may make corner entry "snappier".. I've also had personal experience with the car being very tight on entry with a LF limiter, I assume because weight was not able to transfer to the RR to free up entry.

Let me know what you're thinking. I don't think it's just done for aero purposes as I've found many Formula Ford guys are doing it, too.

Thanks,
MM

 

[Ranger Mike]

welcome Jlambo and Machmaster,
on figure 8...i never ran it. Road course racing a large passenger car..well some guidelines are set it up neutral relative to wheel weights. what's do you have now?
i would run coil overs on front simply for tune-ability.
on dirt car with limiter..i did this on the formula car and never liked it. you can do this on dirt a lot easier due to t he track surface but it will never beat a suspension in proper working order that is tuned in..you are just making a giant Go Kart out of a suspension with a damping mechanism and means to react to the cornering momentum
i would have replied earlier but been in caribbean in 90 degree weather not this 2 degree F temp...ouch

 

[Tyredone]

Hi Ranger Mike , What a great site with a wealth of information :) perhaps you could help? I'm resurrecting a mid seventies sedan witch was raced in the 90,s on asphalt . Was originally 6 cylinder , but have fitted v8 & 4 speed. Has a arm front suspension with steering box similar to 70,s Camaro . Have fitted lowered spindles , going to fit steering rack. With the rear was thinking independent for adjustment ? Has factory 6 cylinder 10 bolt Gm style differential . If you could help in front setup, rear design please or point me in the right direction that would be great. Tyredone

 

[Ranger Mike]

Welcome and thanks for the kind words...the best reference source for your project is two books..Paved track stock car technology and Street stock chassis technology both by steve smith
www.stevesmithautosports.com

buy them and read them..will save hours of trial and error
stay with 3 link rear suspension or keep the leaf springs if rules require it..

 

[Ranger Mike]

I was on another post on Mechanical Engineering talking about why stiffer springs are more responsive. First of all, Responsive is a pretty much arbitrary thing as you can not hang a number on it. Let us focus on a standard grocery getter commuter car with suspension designed for everyone from Grandmother to the hog dog teenager. When we drive into a left hand turn, forward momentum will cause the car to roll to the right as stationary asphalt causes the tire contact patch to push back on the momentum force. Since we have soft springs which compress under this load we have a steering feed backs that feels like mush.

The trick here is to think in 4-D. In a turn we are dealing with X,Y,Z movement and Time. Things are not 2-D as typically indicated in many discussions on this matter.
The front suspension on todays automobile have spindles that turns via the steering wheel ( thru linkage to the steering box or Rack and Pinion mechanism). These spindles are mounted in such a way that they have caster. Like a fork on a bicycle the top of the front wheel fork is slanted toward the rear and the bottom of the fork is slanted forward. Anyone who ever road e bike knows this arrangement cause self centering which adds to the stability of the steering. Same with the spindle on a race car. The spindle is slanted so the top is slightly behind the axel center line and the bottom is slightly forward of the axel center line. This Caster causes the race car to lift slightly when the steering is turned because the whole arc of rotation is tilted to begin with. Add to this dynamic , the fact that the spindle is made with an inclination angle between 5 and 10 degrees. When the spindle is turned the part that mounts the tire and wheel actually lifts the chassis. The combination of caster and Spindle inclination angle (SIA) can lift the right front of the race car and inch when turning the steering wheel.

By feel, adding a stiffer Anti Roll Bar (ARB) or sway bar ,we keep the car from rolling over like a big old whale in the turn ( stiffer front springs will do the same). With less spring compression to deal with the forward momentum, the tires must take up more of the load being transferred. In most cases they do not and we have a classic under steer condition. Race car Pushes like a freight train. Stiffer springs make the car lift on that corner a lot quicker than the softer springs trying to cope with the load coming forward and then pushing up on that corner of the car due to Caster and KIA. So the steering on stiffer springs / ARB is more “ responsive”.

So what is the answer? Just like in life, balance is the key. A good spring package and sway bar set up and good shocks to time the compression and rebound is the ticket.

 

[maverick 5582]

Ranger Mike:
I have been reading the posts and downloading information for the last two weeks into a notebook full of notes. My background is in dirt modifieds, Late Model Sportsman, and Cup. My first introduction to suspension was when I worked building Cup cars back in the 70's using the Ford rear steering front clips and the first front steering Chevy clips. I built upper and lower control arms for them and truck trailing arms for the rear suspension. I have a small fab shop with TIG, MIG, lathe, vertical mill, and sheet metal equipment. Small, but it serves my purpose.

Last year I was approached by one of my buddies and asked to take a look at a 99 GRT late model chassis he had. He wanted me to take the old dirt late model body off and mount a 36 Chevy coach body on the chassis to run in a vintage dirt series. The project got delayed till this year because the dirt series pretty much folded. He now wants me to convert this round tube dirt chassis into a vintage asphalt modified. I told him that the chassis would have to be stiffened up and all the front end geometry gone thru and completely changed for asphalt. I suggested he buy an old Troyer asphalt chassis, but he insists on making the GRT chassis work. We are limited to 10" wheels and 3100 lbs. Everything else is pretty much left up to you. I am including a photo of what I want to end up with. I would like to get some input from everyone before I commit to this.

 

[Ranger Mike]

Welcome Maverick and thanks for the kind words. I would never recommend this change over to anyone who is just starting in the race community. Your background tells me you will be able to successfully rework the car to competitive specs. If the chassis is solid and the straight you can change over to a good offset front end and a good 3 link rear coil over set up. It will not be cheap and it will be labor intense. The 3100 # limit means a lot of lead ballast and i assume spec tires. What does rules say about engine height, offset, rear location, % left side and rear weight, wheel base? etc..
Before committing i would find out car weight as of today, % rear weight, % left side weight, is engine offset and by how much and how high is it mounted ? This will tell you how much work you need to put into moving the engine, reworking front end. As usual where are the Roll centers front and rear??

 

[maverick 5582]

Ranger Mike:
The car will be delivered to my shop this week end. I told my buddy the first thing I required was the Suspension Analyzer v2.4 Full Vehicle Version software for my laptop. I used the trial version sometime back and was impressed with the capabilities. If you are not familiar with the 99 GRT chassis it is a straight right rail chassis, first of the round tube chassis. Coil over suspension.

I will scale the car as it sits. I will have to put in a block, heads, headers, bellhousing, transmission, and driveshaft. I will have to use lead to make up for the weight of the crank, rods, pistons, water, fuel load, etc.

There are no rules on LS percentage, Rear Weight Percentage, etc. The tires are whatever you want to run as long as they mount on a 10" wide wheel. Wet sump pan required. Engine will be a small block Chevy. I am thinking about a 6 1/2" sump pan with 2" ground clearance so that will be as low as the engine can go. I am thinking that with the 3100 lbs., the LS percentage can be in the 58-60% range. Once I plot the suspension out we will have some figures to work with. The car has a 4 link with bird cages that I want to change to a 3 link with a spring loaded top link. I realize that there will have to be some creative thinking where to place all the lead required with a +250 lb. driver.

The thing about "vintage racing" is "don't stink up the show". You can ride up front as long as you don't leave everybody in the dust. The "vintage dirt series" was fine till someone brought in a Northeast Modified chassis with an old Ford coupe body on it and proceeded to lap the field. There was no weight rules in place till they discovered this car was 300 pounds lighter than everyone else. Then it was found that the car has a short Bert racing trans in it that did not comply with the rules so the car was banned till it was changed. There was no easy way to place a regular trans in that car, so it is just setting now. Most of the "vintage series" I am interested the cars have to have an external appearance of "vintage". The chassis is the end game for me.

This chassis will wind up being something like a Super Late Model chassis more so than a modified. The 36 Chevy coach body will drop right over the straight right rail chassis. Most of these cars running vintage modified are just plain straight right rail chassis for convenience sake. Look forward to getting to use the software program.

 

[Ranger Mike]

Glad its going well..i take off for Europe today but will have email..hopefully

 

[mikey531]

I am not sure if this the place to ask my question but, has anyone used any chassis setup software? I have looked at several, and what I want is software that I can input the tire temps and have it figure out what I should change for optimum tire temps. We run an asphalt modified and we do make changes based on tire temps but never enough information from limited practice so we are not sure if we are doing the right change. We don't have much practice before the heat race and then all different tires the next race so we get lost sometimes trying to get consistency. We are having fun enjoying what we do we just want to be a little more competitive.

Thanks
Mike

 

[Ranger Mike]

Mickey...welcome..good to know another racer..
i know of no software that does this though there probably is some where. The best reference i have used is book by Steve Smith called " Paved Track stock car technology" found at SteveSmithAutosports.com
the Chapter on Tires & Wheels covers Reading Tire Temperatures very well. You need a tire pyrometer that stores the Temps so you can average the three reading per tire. Next you need to compare the averages to find out what your set up is doing on each corner and make changes accordingly.

 

[mikey531]

I have a temp with storing and I use the" Paved Track stock car technology" book as my bible I was just looking for something quicker that I could input temps and spit out a solution. We have talked before and you were very helpful.

 

[Ranger Mike]

i realized that Mickey after i posted it...sorry about that...a lot of things rattling around the brain pan today getting ready for trip

 

[maverick 5582]

Ranger Mike: I have been taken suspension measurements on the chassis. I have made 4 jack stands with 1" jackscrews. The chassis is now at a height of 16" from the shop floor to the bottom of the frame rails. It has been leveled with a digital protractor. When I take my height measurements I subtract the 16" measurement for the worksheet. Now do you add the ride height measurement back to these measurements to get the correct height?
I am using a ride height of 3 3/8" from the floor to the bottom of the frame rail. I have two dummy shocks in place and used two 3" blocks between the lower control arms and the bottom of the frame rail to get the correct distance for the shocks.

How do you transfer the Performance Trends Suspension Analyzer info here?

 

[Ranger Mike]

now the fun part. i assume you have the chassis software of some type?
read Bench marking the car on post #285 page 15,

this is how to measure the pivot points etc..
also post 269 on page 14 on squaring the car, post 293 page 15, post 270 page 14, drawing the suspension components post 391 page 20

 

[maverick 5582]

I did all the squaring to begin with. I bought the Performance Trends Suspension Analyzer software. I made the measurements. I wrote down the results. I entered the information into the program. I used the file LH2003-HMS for a Left Hander Chassis and entered my info in place of their info. How do I post the file on here?

 

[Ranger Mike]

well now you are asking a computer question. if you can store the results as a Jpeg. store it on desk top on you computer. you can upload it. just click upload button below, browse your desk top and select the jpeg and upload it.
you may have to print it out and scan the print out as Jpeg and upload it.

 

[maverick 5582]

Here it is.

 

[maverick 5582]

The previous post had some incorrect data. Evidently it did not save my updates when I saved the file. This one should be correct.

 

[Ranger Mike]

camber initial setting should be close to +1.5 degree left ft. and –3 degrees right ft.
Flat to medium bank track chamber gain should be 1.25 to 1.75 degree negative per inch
and left side should gain .5 to .75 degree positive per inch rebound.
caster for manual steering +1.5 degree left , +3 degree right side
power steering +1.5 degree left side + 4 degree right side

toe out 1/16 “ to 1/8” toe
make sure to check bump steer and dial into less than .030” per inch
roll center is to far to right side. I like a low roll center but typical metric chassis is 3.25” above ground 4 inch offset to the right for dirt, 3 “ asphalt.
work on moving ball joint height to reduce the roll center offset. Also animate and see roll center migration over 3 inch chassis roll