22 replies to this topic

[dcostello]

I have been wondering this for a while and have never had an adequate response.   With all other things being equal (except a properly valved shock) and a class that allows you to change tire pressure, spring rate, and/or sway bar which is it better to stiffen a rear end by.  I am looking at adjusting the rear of a front wheel drive car for looseness/rotation.   Keep in mind it is a relatively smooth racing surface.

 

What I have heard is that every lb. of air pressure is approximately 10 lbs. of spring rate.  Therefore, if I need to spring an 800 lb. corner of a car, with the desired balance/rotation, I could use say 30 lbs. of air pressure in the tire (30x10 lb. = 300 lbs.), a 300 lb. spring (rate), and a 1 inch thick sway bar to pull 200 lbs. of spring rate from the other side of the car.  Let’s say once we load and match the 800 lb. corner weight at that point the car starts to rotate.   With this premise, I could run 25 lbs. of air pressure (25x10 lb. = 250 lbs.), a 550 lb. spring, and no sway bar to get the same effect.  Or even 50 lbs. of air pressure in the tire (50x10 lb. = 500 lbs.), a 200 lb. spring, and a 1/2 inch thick sway bar to pull 100 lbs. of spring rate from the other side of the car.

 

Please keep in mind increasing tire pressure crowns a tire, increasing spring makes a tire skip over the road, and increasing sway bar makes your suspension less independent and/or more connected.

 

With all that said I have two main questions…

 

What should you increase or decrease and why (tire pressure, spring, or sway bar)?

 

On a short wheel base, solid rear axle, Honda CRX I am trying to reduce snap oversteer.  I am thinking to reduce tire pressure to maximize tire contact patch and compliance to ground. Then increase spring rate and get as much bind as possible out of the rear end suspension to maximize the articulation of the rear end with its pan hard bar geometry. 

 

Thoughts?

 

[cbstdscott]

"I am trying to reduce snap oversteer." You sure know how to bury the lede.

 

If this is your problem it is easy to fix. Snap oversteer in an understeering pig like our cars is caused by... driver error. Let me explain.

 

How do we get snap oversteer in these cars? Simple really. When you are in the turn, and you are going too fast, and you tap the brakes, you are shifting the weight of the car forward. The rear wheels, barely touching the ground in a car with 60% of its weight over the front wheels at rest and even less under braking, lose what ever contact they might have had with the road and the back end has nothing to keep from swinging around on you. Does this make sense? 

 

Weight shifting is an important concept. As you accelerate, the weight of the car shifts backwards. As you brake, the weight of the car shifts forward. The same thing happens when you brake in a turn. That light rear end has little to no traction and it will swing around.

 

The solution is to drive like a pro. Do your braking BEFORE the turn, in a straight line. This way you enter the corner (relatively) slowly,and you can get on the gas as you pass the corner's apex and exit fast.

 

In slow, out fast. In slow, out fast. In slow, out fast. That is your new cornering mantra.

 

Tire pressure: Pressure should be correct for the tire and by that, the tread should be flush to the ground. Not too high or too low. The exception to this rule is if you are autocrossing on street tires, then you can give them some more pressure so that you are not driving on your sidewalls. Sidewalls do not have good traction

 

The best way to control body roll, is with sway bars. If you are driving your car hard, you will want an external rear sway bar. The internal "sway bar" in the rear axle is better than nothing, but not by much.

 

Springs and shocks are there to keep your tires on the ground. Too much or too little compression and rebound will cause your tires to leave the road surface. With the EW engine 24mm torsion bars and 350 lbs. rear springs is a good combination, but you might want 27mm T bars and 500 lbs rear springs. It is up to you and your kidneys. Adjustable shocks are a must for racing to get your suspension tune right. I highly recommend Konis (discontinued but occasionally available used) or Teins available from https://www.heeltoeauto.com/

 

Rotation: There is a secret to getting these cars to rotate because they normally do not like to.

 

But first a warning. I will get in trouble with the "smart guys" on this site for telling you the secret. They know that they are right and that I am  wrong about this. Fuck'em. They do not race, they have never tried my technique and they largely do not know what they are talking about. Again, fuck'em.

 

If you want these cars to rotate, take the internal rear sway bar out of the rear axle and throw it away. Leave the articulated right trailing arm free, do not bind it in any way. Use an external rear sway bar to control body roll.

 

With that mod, your car will find all sorts of new rotation that you could never have imagined before, In fact, I got a little too much rotation for my taste. I am able to control that oversteer with a stiffer setting for my front shocks.

 

I hope this helps. And come over to the "Official Red Pepper Racing"  forum on Facebook. 

 

Scott

[anjin]

To add to Scotts post, and yes it is a personal experience thing.

 

Tire pressure is important in getting the correct tire temperature. You need hot tyres for grip.  Too cold and there is no grip.  I have run tyres as low as 18 psi in the rear to heat them up in the rain.  I'm not game to go lower, and wish I could.  In terms of your desire for rotation, it is controlable rotation you are after.  You need to start with grip in order to have control.

 

Your sway bar/spring combination needs to keep the tyre surface flat.  Again, to  maximise and control grip.

 

Like Scott, I can dial in understeer or oversteer.  I have hit a balance point - in my case 31 mm torsion bar and civic 4 wd front sway bar, and 600 lb springs and 14mm DC2 interga standard sway bar and no internal bar and no locked swing arm. And camber adjustment front and rear (but the camber is dialled in to maximise grip, which is measured by equalising  tyre temperature over the tyre.)   By altering the damper rates at the front and rear I can have the rear move out or in through corners by differences in the natural slip of the front and rear tyres over the road surface.  Note that - natural slip as the tyre surface interacts with the road, not artifical slip. The tyres will slip at about 5-7% and still maintain excellent grip.

 

You want more than natural slip then you are wanting tyre breakaway. You may be a good enough driver to be able to control that in a fwd car.  I'm not that good.

 

Last point.  I used to have snap oversteer. That was caused by the rear sway bar bushes binding, allowing the sway bar to store compression until it overcame the friction at which point it released suddenly.   Look up 'Porsche tuning day excitement' on you-tube.  Thats me airborne and backwards into a corner. Not fun.  I grease those bushes now.

 

Hope this helps

[niccer]

Great discussion, guys.  I remember reading one like this on HT yeaarrrsss ago and pretty much forgot all the little nuances but retained the meat of the subject.  I have little real world experience, with only a handful of track events under my belt, but I'll chime in.

 

Are you autox'ing or racing on a track?  Sounds like autox since you're trying to engineer/math the shit out of this problem!     

 

What tires are you running?  Could be a really sticky tire that's not giving you good enough warning when its about to let go?

 

Do you have any in-car video showing the snap-overstreer?

 

What's your current setup?

 

 

Sway bar endlink binding is apparently a pretty common issue and should be considered before you go diving into completely changing your setup.  From what I recall, there wasn't a complete pecking order of importance between the three individual parts, but a symbiosis.  Sway bars and springs are cheap and easy enough to swap out to where you can buy two or three sizes/spring rates to test with.  I'd love to hear the results.

[niccer]

To add to Scotts post, and yes it is a personal experience thing.

 

Tire pressure is important in getting the correct tire temperature. You need hot tyres for grip.  Too cold and there is no grip.  I have run tyres as low as 18 psi in the rear to heat them up in the rain.  I'm not game to go lower, and wish I could.  In terms of your desire for rotation, it is controlable rotation you are after.  You need to start with grip in order to have control.

 

Your sway bar/spring combination needs to keep the tyre surface flat.  Again, to  maximise and control grip.

 

Like Scott, I can dial in understeer or oversteer.  I have hit a balance point - in my case 31 mm torsion bar and civic 4 wd front sway bar, and 600 lb springs and 14mm DC2 interga standard sway bar and no internal bar and no locked swing arm. And camber adjustment front and rear (but the camber is dialled in to maximise grip, which is measured by equalising  tyre temperature over the tyre.)   By altering the damper rates at the front and rear I can have the rear move out or in through corners by differences in the natural slip of the front and rear tyres over the road surface.  Note that - natural slip as the tyre surface interacts with the road, not artifical slip. The tyres will slip at about 5-7% and still maintain excellent grip.

 

You want more than natural slip then you are wanting tyre breakaway. You may be a good enough driver to be able to control that in a fwd car.  I'm not that good.

 

Last point.  I used to have snap oversteer. That was caused by the rear sway bar bushes binding, allowing the sway bar to store compression until it overcame the friction at which point it released suddenly.   Look up 'Porsche tuning day excitement' on you-tube.  Thats me airborne and backwards into a corner. Not fun.  I grease those bushes now.

 

Hope this helps

 

 

How do you like your stiff setup and what struts are you on?  I'm not 100% what mine is, but I think the torsion bars are at most 24mm w/ disconnected front sway bar.  Rears are probably 350lb springs with a ~1" (25mm) sway bar.  I've been on Tokico Illuminas and am now switching to Koni Yellows.  I left the car exactly as the previous owner, who raced it, had it setup since I'm a novice at suspension tuning.  The car feels very neutral and I can introduce over or understeer with gas pedal modulation.  I'm looking into the future and will be getting the Koni's rebuilt, which will probably include revalving.  The thing is, I don't know what spring rates I want to run.  I've had 27mm T bars in a car before and thought they felt pretty good, but never tracked it.  Are they equivalent to 350lb springs?  

 

Hope the OP doesn't mind my asking a question too, but figured since this site is so inactive we can share threads.   

[dcostello]

First off, thank you for your input.  To Scott, I do know my driving style is too aggressive and I need to smooth out my inputs but I believe there is more work to do on the rear end.  I had the opportunity to drive a few national champion cars last year and this year and what I noticed was their rear ends were a lot more predictable.  You could feel it get light, then slightly loose, then throw some more inputs and get complete rotation.   I believe this is from having a greater contact patch on the rear of the car.  I also noticed some blatant personal technique issues that I will be working on next year.  To anjin’s point I was already planning to pull the entire rear end apart and re lube everything as I am pretty sure I am binding.  I also have a new coilover setup I am working on to reduce tire pressure and make the whole rear end articulate better.  

 

My current setup is 500 + spring rate up front and near double that in the rear with both internal and external sway bars along with about a degree of camber.  All my koni’s just came back from Truechoice freshened/revalved for next year.  Good and bad they are going under the Christmas tree this year as I told my wife I spent enough money.     

 

To niccer, this is a dedicated FSP autocross car (trailer queen) that I took to nationals and placed 2nd this year (2016) and my daughter took her first national championship in FSPL.   It is a well prepped car that is for sale but I am going to run the hell out of it until it sells.    

[cbstdscott]

Anjin and I recommend throwing away the internal rear sway bar (torsion bar). Again, you will find a lot of new rotation once you do this.

 

End link binding? Maybe you guys have then cranked too tight. I have mine just to the point that the "jingling" in the hardware goes away. Over tightening the endlinks will preload your suspension and you get less bang for your buck.

 

Tires, tires, tires. Your contact with the road is four pieces of tire, about the size of your hand. Not really a lot of contact when you are looking for traction. Quality tires make all the difference. The very best "performance" street tires ain't shit when compared to real racing tires. For my usage and purposes, I am using Toyo R888 205/60/13 tires on 13x6 wheels.

 

Light wheels. This is often overlooked by "Form over Function" guys. I really do not care what my wheels look like, I just want the lightest wheels I can afford because lighter wheels help to keep the tires in contact with the road.

 

Stiffness- You can not build in too much chassis stiffness. Our cars are many things when they come from the factory, but stiff is not one of them. I have added front fender braces (homemade) and a front strut brace. In  back I have a B pillar and a C pillar brace plus rear strut brace. The rear strut brace does not add much, that is the stiffest part of the car, but the B and C pillar braces certainly stiffen the body.

 

Weight reduction- My '87 Si came from the factory at about 2000 pounds, I have it below 1800 lbs with a full interior.

 

My front setup is 23mm torsion bars, Koni yellows, stock front sway bar, ~1 degree of negative camber and max caster.

My rear setup is no internal torsion bar, 3/4" rear sway bar and Koni yellows.

[dcostello]

Niccer, I am in Omaha, about 45 min from Lincoln NE., where we run on pretty smooth concrete therefore running stiff is not a problem.  For my front’s I have two sets of custom Koni yellows shortened, made double adjustable, and custom valved for the larger torsion bars.  For the rear’s I am running the standard Honda CRX 88-92 Koni yellow sports race gas shock that has been revalved to the higher rear spring rate.   To my understanding, you can (in some respects) balance a car at any spring rate and yours are fine based on a daily driver.  Don’t quote me on these numbers but if you use a stock torsion bar say 175 lbs. of spring rate you can get rotation with 275 lbs. of rear spring rate.  If you use an aftermarket torsion bar say 24mm at 210 lbs. of spring rate you can get rotation with 320 lbs. of rear spring rate.  If you use an aftermarket torsion bar say 27mm at 350 lbs. of spring rate you can get rotation with 450 lbs. of rear spring rate.  If you use an aftermarket torsion bar say 29mm at 430 lbs. of spring rate you can get rotation with 550 lbs. of rear spring rate.  Hoping you are getting the idea of “balance” here.

 

Please keep in mind that my rear spring rates are high because of my large front rates and the fact that I am autocrossing with a top speed of around 70 MPH (average of 45 MPH ish).  If I was on a road course I would be scared with how loose this thing would be at 100 MPH and would probably drop my rear rates down 200 lbs. a corner.

 

Lastly, I am running Hoosier A7’s 225/45/13.  Not the widest tire I can get but after long discussions about extra weight, extra track with for driving around cones, and extra track softening the torsion bars due to extra leverage I am currently sticking with the narrower tire.

 

Oh, and since reading the last post my car is currently 1,643 lbs wet as of a heartland park scale on April 30th of this year.

 

Hope this helps with some of the discussion.

[anjin]

Response to

How do you like your stiff setup and what struts are you on?  I'm not 100% what mine is, but I think the torsion bars are at most 24mm w/ disconnected front sway bar.  Rears are probably 350lb springs with a ~1" (25mm) sway bar.  I've been on Tokico Illuminas and am now switching to Koni Yellows.  I left the car exactly as the previous owner, who raced it, had it setup since I'm a novice at suspension tuning.  The car feels very neutral and I can introduce over or understeer with gas pedal modulation.  I'm looking into the future and will be getting the Koni's rebuilt, which will probably include revalving.  The thing is, I don't know what spring rates I want to run.  I've had 27mm T bars in a car before and thought they felt pretty good, but never tracked it.  Are they equivalent to 350lb springs?

 

The stiff set up came about because I wanted the front to roll and dip as little as possible.  Therefore 31mm torsions and the civic wagon sway bar.  I then inceased the back until I got balance. That meant 600 ib rear springs and surprisingly the stack integra 14 mm rear sway bar.  I did try 350 lb rear spring with a bigger rear bar, but decided I liked the springs to do most of the work and allow the sway bar to do the minor work. 

I daily drive it.  The seat allows me to do this - it has a spring style seat with padding, which does enough insulating to make the driving easy on the body.

 

I have run 24mm and 350 lb rears, and 27mm and 500 lb rears. I may move back to the 27 combination in time for a slightly more relaxed drive. Really its a choice and track matching exercise.

 

Re other parts of set up.  RPF1 15 x 7 rims.  Very light. Semi R compound, 205 15 50 or 225 15 50 The latter are slower because of the larger diameter. Yokohama A50 or Toyo 888.

Rear cage and forward side intrusion bars running from the roll bar to the foot of the A pillar, connecting to an outside bar along the sill from the base of the roll bar to the base of the A pillar.  Very good stiffness.

Built B18C, with over 190 whp at the wheels. Actually too much for daily use, but it is fun.

 

 

Dan.  Thats a very high rear spring rate.  I gold standard on crx's has been to set the rears 150 lb above the front. That could be what is giving you the snap oversteer with your driving style. Something to consider.  maybe see what a lower rear spring rate does as a trial.

 

Anyway, all part of the fun of driving these cars.

[dcostello]

I like the overall stiffness for my driving style and based on pictures and the scraping on the front splitter I am still getting a lot of body roll.  I am actually planning to go up on my rear spring rate with some ideas of putting more camber in the rear as well as some suspension mods to get the rear end to articulate better.

 

Just love trial and error, edjumacated guesses, and testing.

 

Ha

[rallyxcrx]

I was at an event talking to a national level driver about car set up, he was saying that you need ultimate handling at both ends of the car, I'd say he has never set up a front drive before. No matter what springs shocks or bars, I always end up with understeer. Super stiff rear springs might work, but this would be dangerous when you hit a bump in the road. In the end, I end up adding a little air to the rear, but remember, understeer at a autocross = you lose, and oversteer on the racetrack = you crash

[anjin]

I was at an event talking to a national level driver about car set up, he was saying that you need ultimate handling at both ends of the car, I'd say he has never set up a front drive before. No matter what springs shocks or bars, I always end up with understeer. Super stiff rear springs might work, but this would be dangerous when you hit a bump in the road. In the end, I end up adding a little air to the rear, but remember, understeer at a autocross = you lose, and oversteer on the racetrack = you crash

You should be able to get a neutral balance, unless your courses have a great variety of entrance speed and radius.  Just a suggestion, but have someone else with fwd experience drive your car. It's a good check on what you think you are experiencing. Well worth arranging.

[rallyxcrx]

Thanks! and so glad you're not a competitor here in California, Dave

[dcostello]

The only thing I will say is a little bit on opinion here...  It is my belief a person can only set up a car to be "perfectly" balanced at maximum adhesion for one corner, maybe type of corner, at one maximum speed in that corner.  With that said I do my best to set the car for the most similar corners at the most similar speeds on that days autocross course by fine tuning shocks and rear tire pressures for balance.  By the addition of aerodynamics last year and dialing in the car a little bit better with corner weighting, alignments, shock tuning, and most importantly upping my high speed car control skills I have been able to widen the window of one corner/one speed and get very close to winning Nationals in 2016.  

 

Lastly taking the last few postings to heart... this past year (2016) I had three National champions which, good and bad, they all beat me.  Bad, it sucks getting beaten in your own car.. Good, its not the car its me!  And their times would have won Nationals...

 

I have my plan for this years changes and then am waiting for the first test n tune to get this years changes dialed in.  

 

It has been a long journey to get to this level but I feel there is still a ton to learn.  Not sure if this helps but its just some ideas laid out on a post.

[cbstdscott]

"No matter what springs shocks or bars, I always end up with understeer."

 

Now that you have tried "everything" perhaps it is time to move on to the next phase.  

 

The rear axle design of these cars is unique, "Semi-independent."  Not fully independent, but not a solid axle either. Consider that the rear suspension was designed at the time that Honda and other FWD manufacturers were looking for solutions to FWD understeer. Various "rear wheel steer" designs came out in the 80's, most notably from Renault and Honda.

 

I know that the "smart" guys will shout me down, but from my own first hand experience I know that it is possible to turn your 1st/3rd into a perfectly balanced machine with over or under steer available at your desire and controllable by your driving style. 

 

All you have to do is remove the rear axle torsion bar and all restrictions on movement in the right rear trailing arm's articulation. In my case, I found that my car went from understeer to oversteer with this change. I added front end stiffness to my car to remove the oversteer and now it is dead neutral.

 

You are welcome.