Suspension Tuning For RoadRacing

[REH]

Anyone here want to share their experience?
As most of you already know I used to sell driving lessons, but I always liked to hear other opinions and experiences about suspension tuning.:breakdance:

[freeride]

i'm working on getting more experience with the suspension of my shopping cart...

found this interesting neg vs positive rake forum post.

Neg vs Pos (http://forums.evolutionm.net/showthread.php?t=271668)

[REH]

Shopping cart huh. Well I know one thing, the front wheels have ALOT of caster! The corner weights are usually off though. And sometimes they pull in one direction because one wheels has too much drag. One could make a killing fixing those problems. As a customer, I'd be happy.

[Act162this]

just curious - what kind of tuning experiences are you looking for/at?

camber/caster settings, spring rates, corner weights, f/r sway bar sizing, etc?

[REH]

Just for fun right now. I have my way of basic setup. Just wanna hear what other people's thought are.

[spider_monkey52]

Shopping cart huh. Well I know one thing, the front wheels have ALOT of caster! The corner weights are usually off though. And sometimes they pull in one direction because one wheels has too much drag. One could make a killing fixing those problems. As a customer, I'd be happy.
hmmmm... how about me and you create a business out of tuning shopping cart suspensions. we'd be busy all the time and make bank. how's about a 65/45 split since you came up with the idea. ^_^.

[freeride]

lol! you guys make me laugh...

i never considered the positive effects of neg rake on an evo. most peoples want to just drop their them for looks regardless of the fact that pos rake in these cars creates more understeer....

[REH]

You know what . . . I've thought about the shopping cart tuning business for awhile now. As a matter of fact, the shopping carts at Kapolei Safeway were so bad, that they went and bought new ones. they could've saved a bundle if there was a company that repaired them. Sam's Club right now would be a good target.

Why would you have negative rake? Over 100mph the car would catch air. Also, I don't see the value of having a 50/50 weight balance. F1 is about 10/90. I can lift the front of our Mirages off the ground. What is that 150lbs? The entire car weighs about 1,100lbs.

[corytomo]

You don't need a 50/50 balance, but having the turning wheels touching the ground on corner exit would help! F1 cars are an exception to the rule, they have hundreds of pounds of downforce on the front to keep front end traction. Most production cars have lift rather than downforce, so you do need a good weight balance.

I have this really awesome sheet somewhere that helps tune suspensions. Deals with caster, camber, toe, ride heights, damping, compression, spring rates, tire pressures, etc. I use it to tune for the low speed - quick transition stuff for autox. At superlap, I had to tune for more understeer since the sweeper was not a place I wanted to tail out at over 70mph.

[Act162this]

cool! you actually kept a log...

i used to keep a log of tire pressure, spring height (coil overs), damper settings, but i got lazy. didn't have the ability to change caster/camber angles easily, and the auto-x car was my dd, so didn't want to spend too much time messing with it.

eventually just left it on race settings when i got another dd.

found out that auto-x rate springs/settings/bars do not make for a happy roadrace car (or driver) - the chicane was fine, transitions were quick, but the sweeper was a bit of a white knuckle ride (of course, i wasn't used to going fast, so it may have been more that than anything else).

decided to stick to auto-x.

[zff]

Stock, early NSXs like mine ran a lot of toe-out up front and a lot of toe-in in back. Honda's engineering paid no attention to tire life when they tuned the NSX's suspension. Acura will actually tell you to expect a set of tires on your early NSX to last about 6000 miles.

Even worse, there's not a lot of camber adjustment. If you lower your car, you probably won't be able to keep the camber in spec -- and your tires wear out even quicker. According to what I've read online, some NSX owners just accept the fact they have to buy new tires every time they change their oil.

I like the way the NSX handles, but after having to buy two complete sets of tires the first year I had it, I got sick of it. I changed the front toe-out from 3.5mm to 0.1mm. I changed the rear toe-in from 6.6mm to 4mm (which is the spec for newer NSXs). I left all the other alignment adjustments the same. (My camber is 1° out-of-spec all around because the car is lowered.)

The NSX used to have this uncannily razor sharp turn in. I used to like dodging potholes just to feel how connected the front of the car was to the steering wheel. After taking all the toe out, it still handles great, but that amazingly super-sharp turn in is gone. Still, I've been on the same set of tires for the last 2 years now, so I don't mind one bit.

[Ronin]

I run factory settings for toe, camber & caster.

Tires:
- sizes: Usually narrower in the front (205/45/17 or 215/45/17) for that quick turn in response. Lately I've been leaning more towards 225s tires for the front tho. The turn in is slower and so is the feedback I receive from the front during a slide. It Gives me a bigger margin for error in case I'm too slow to counter steer. I don't really care what I have in the rear.
- pressure: For daily driving I usually run it close to max. For drifting, I usually run it a little low in the front and the rear.

suspension:
Dampening set to full soft up front and half-way in the rear (compression & rebound aren't individually adjustable on my coilovers).
I have a fair amount of pre-load on my springs. Makes the ride really bouncy for daily driving, but works pretty well when the car is sliding.
This achieves what I wanted in the sense that I can shift the weight of my car fairly easily. I got enough suspension travel to dip the front when I brake or squat when I gas.

I bought this book to help me out when I got interested in tuning my suspension. Its fairly old but the basic principles are the same (somewhat). It also comes with a tuning sheet that you can photocopy over and over as you change settings around.

http://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468/ref=sr_1_1?ie=UTF8&s=books&qid=1202435821&sr=8-1

[MasterFunk]

I like everything tight up front, and soft in the rear end. I run higher tire pressures up front, stiffer shocks, front sway on full tight. Gives nice crisp turn-in. As much negative camber as I can get. I'd love to run some toe out, but for a street-driven car it just isn't practical.
I like the rear-end soft to keep it planted in the corners, and only oversteers when I give it enough throttle to do that. I also like the rear-end to be as light as possible, with a near-empty tank of gas. It makes it easier to swing the rear-end around, and easier to catch.

Unfortunately, I can only adjust most of that kinda stuff on my miata, but not on the 2002. The 2002's front toe can be adjusted, and thats it. No adjustable strut/shock options, and I don't have adjustable sways.
I really need some more negative camber. I'm gonna try to put in some fixed camber plates soon, but that'll only get me 0.5 degrees. In order to get more, you gotta go with full coilovers, adjustable camber plates, and bend the strut housing out a little bit. I can't afford that stuff right now, so I'll just deal with having no camber.

Yes, I run mostly autocross, but have spent time on HRP and Mid-Ohio. Wish I could do some wheel-to-wheel, but not enough money or time.

[corytomo]

Roadracing has a huge difference on car set up. For autox, the miata likes these settings:

1/8 total toe out front
0 total toe rear
2.5 degrees neg camber front
2 - 3 degrees neg camber rear
caster is unchanged
stock front sway
removed rear sway
max rebound/compression on tein flexes (single adjustable) front
3/4 rebound/compression on tein flexes (single adjustable) rear
225/50/15 V710's with 30psi front
225/50/15 V710's with 26psi rear

for roadracing:

1/8 total toe out front
1/16 total toe in rear
2.5 degrees neg camber front
3 degrees neg camber rear
caster is unchanged
stock front sway
stock rear sway
3/4 rebound/compression on tein flexes (single adjustable) front
1/2 rebound/compression on tein flexes (single adjustable) rear
225/50/15 V710's with 32psi front
225/50/15 V710's with 28psi rear

The compression/rebound settings for road racing are a guess because I only had stock suspension when HRP was open. Wish I could try it now with real suspension, better tires, and more power.

[REH]

Wow, that's some really good input. You guys are right on. I don't think that there is any one formula for suspension tuning. If you think about it, the chassis flex, weight distribution and roll center is going to make you go back to the drawing board.

I usually start with a common base line setting: a bit of positive rake, even corner weights then 1~1/2 deg of negative camber up front, 3/4~1/4 degree out back. 4 degrees of caster in the front and 0 for the rear. Front toe depends on where your steering rack is located. If it's in front of the front axis then go toe out, opposite for the reverse. I don't usually add too much toe unless i have a problem chassis. Do all this with the sway bars disconnected. And, in this order: camber, caster, toe. Then go back and check and adjust. I'm a firm believer in stiff sway bars and springs. Shocks are adjusted to spring rate. you can mess with the set up by adjusting rebound. A handy tool is a pyromater. Measure tire temp inner, center and outer. Adjust your camber accordingly. Remember: more camber means less braking.

Now this is just the tip of the iceberg. Test driving and understanding what's going on with the car is priceless. Clock yourself on lap time not driver comfort. Some of the fastest cars I've driven were unbareable to drive.

[MasterFunk]

I think it depends a lot on personal driving style and preferences. I've shared cars with other (maybe better) drivers, and what works for them, feels like crap to me and is horribly slow. Maybe thats just my lack of ability speaking, though.

[REH]

Well, that's what I'm talkin about. Only the clock will tell. Granted, the car has to match the driver, but, the old saying goes: "a good driver can drive anything fast". That sums it up as far as car and driver goes. The machine hasn't surpassed the human . . . yet.

[MasterFunk]

Only the clock will tell.

In my case, the clock said I was far slower with it set up to someone else's preference. But thats because I was plowing horribly bad in the corners. I think other drivers often prefer to have the car to have more of an understeer tendency at the limits, but I hate trying to control understeer. I really prefer oversteer.
On a road course though, I probably wouldn't notice the understeer as much. It's just the really tight corners on an autocross course when the front end just starts plowing really bad on me.

[REH]

I duuno what's worse; understeer or oversteer? Understeer, you're just waiting there (as the clock ticks) for the corner to straighten out. Oversteer, your trying to keep control of the car (while the clock is still ticking). If those were my only choices, I would choose understeer. Because it makes you work harder to turn the car with inertia verses the steering wheel. In the process you're moving forward. Bottom line is, understeer makes you drive the car harder and faster while you're trying to turn the car.

[Act162this]

that's a good question - may depend on personal preference. i have heard that manufacturers dial in a certain degree of understeer because it's safer for the average joe driver than a tail-happy car. if you go into a corner too hot, the car will just scrub off speed until the tires recover and you can turn again (or hit something, that will also stop you).

OTOH, i've heard driver's say that "looser is faster", so they prefer a tail-happy car that they can step out at will to tighten up the turn or square off a corner. i'm guessing you scrub off and lose less speed in an oversteering state, because you can sort of slide the car through the corner, keeping rpm, wheel speed, and momentum up, instead of losing all three while plowing the front.

i've found that understeer really kills speed in an auto-x in an underpowered car (this is just me, and i'm not the best driver by a long shot), so i planned and mix-and-matched my suspension to try to dial in a certain degree of neutral to oversteer conditions. allows me to keep my entry and corner speeds up, since stepping on the gas generally doesn't do much more than make noise.

[corytomo]

Oversteer is definitely faster in autox, the whole skill of it is getting just enough oversteer to keep up momentum without getting too large an angle or spinning. It's always my problem to stay at the limit. If I can pull off riding the edge like that, I'm top 4 overall. Usually I mess up and end up being 8th or 9th... and 3rd in my class. I purposely set my car up to be very very loose, I really enjoy being able to swing the back around at anytime, especially when I'm too close to a cone and know the rear will hit - just let the tail slide a bit and it's clear!

[REH]

i have heard that manufacturers dial in a certain degree of understeer because it's safer for the average joe driver than a tail-happy car. if you go into a corner too hot, the car will just scrub off speed until the tires recover and you can turn again (or hit something, that will also stop you).

Cars nowadays are engineered much better. The handling is more neutral then before. This probably explains a stock STi can turn 39's at Super Laps.

OTOH, i've heard driver's say that "looser is faster", so they prefer a tail-happy car that they can step out at will to tighten up the turn or square off a corner. i'm guessing you scrub off and lose less speed in an oversteering state, because you can sort of slide the car through the corner, keeping rpm, wheel speed, and momentum up, instead of losing all three while plowing the front.

Only in really tight corners, say an autoX setup. Anything over 45mph, an understeering car is faster given the US and OS is equal. Let's look at our Sweeper corner. In an US car I would charge up to the corner at full throttle even after the turn in, then feather the throttle to turn the car and then get back on to accelerate by the inner guardrail. An OS car, I would brush the brakes before turning in and then balance the car after the turn in and then accelerate. Which is faster? Once you give up your speed and momentum, you can never get it back now matter how soon you begin to accelerate for the exit. (Uh, oh, I'm giving driving lessons for free again).

i've found that understeer really kills speed in an auto-x in an underpowered car (this is just me, and i'm not the best driver by a long shot), so i planned and mix-and-matched my suspension to try to dial in a certain degree of neutral to oversteer conditions. allows me to keep my entry and corner speeds up, since stepping on the gas generally doesn't do much more than make noise.

That sound right except that US and lots of power don't go well together. Alot of times (because drivers know the importance of exit speed) the driver will indeuce US with too much power.

Here's a funny story: One day I had 2 different drivers schedule for testing (20 minute lapping session). I used the same car for both drivers (they were scheduled at different times and never saw each other). The first driver after practice said the car was an OS'ing car. The second driver said just the opposite. Well, guess what? The first driver was new and drove timidly, the second, a veteren, had a heavy right foot. Too much throttle=US. Not enough throttle=OS. Same is true for braking. I set all the car up to have a slight US condition. Usually, it's the driver that induces the conditions. Very rarely does a tube-frame purpose-built racecar have any gross US or OS unless something is broken, bent or misaligned. Because of this, I usually talk to the drivers about, you guessed it, their driving style. I could always adjust the car to the driver, BUT, in this case the car was set up to turn fast laps. Driver need to learn what that feels like and adjust their driving accordingly.

Now, back to the dynamics of all the working suspension parts and their significant roles in handling.

[corytomo]

You hit that right on the nose Tom. I have to set up my cars to be more US then OS in a road race condition, and Kermit is set up to be perfectly neutral. OS on a fast course like Button Willow is downright scary and dangerous, and I'd be scared to drive it at anything close to 10/10ths.

[Ronin]

REH? I'm assuming you're a racing instructor or something cuz you seem to know your stuff really well. Do you know of any books you would recommend purchasing to learn more about this? I'm looking for a more updated book with modern suspension reference.

[REH]

I learned from experience, trail and error. Also from some race mechanics. You'd be very surprised how little even people in the racing business know about suspension dynamics. Tha's probably why I haven't ran into any good books on the subject. There are some basic principles on it though.

Here's a quick question most people fail: If you disconnect the sway bar will the vehicle drop? Hint: the sway bar is a spring.

[Ronin]

I'm gonna say that No it won't drop the car.

The sway bar is a torsion bar. It connects to both of my lower control arms. I think that all it does is keep both wheels level as the car turns.

correct me if I'm wrong.

[REH]

Hey, I got an idea. I'll be willing to rent out my alignment pad for anyone wanting to tweak their suspension. I have toe gauges, camber gauge, even a bump steer gauge. I also have a corner weight gauge, but your car would have to weigh less than 2000lbs.

Of course since I'll be there, I'll help you with any info you need.

[corytomo]

They would be great! Sign me up, I need to redo my suspension after I get my new uber adjustable suspension.. hehe

[ikeyballz]

hm.; ok my question is totally untechnical and might be off topic..but..

my car has feathered edges on the front tires. they're stock 275mm tires and are less than one year old.. why is is all worn on the OUTSIDE edge? it was all straightened and everything and it turns decently, grabs hard in turns... (front tires suck tho) is it just cuz of the fatness? or is it something they aligned wrong? i cant rotate any tires eithier cuz my back tires are fatter and id rather have the good tires in the back also.

i was under my car the other day and saw some bolts that looked like they had been adjusted... for the first time in the cars life. (prolly when they 'aligned' the tires) should these not have been moved or is the outside edge feathering normal...

[Ronin]

Thats either alignment or the tire was not balanced right.

[corytomo]

Outside wear is usually a sign of toe-in or under inflated tires. Check pressure first, then go see whats up with your alignment.

I have massive outerwear, but that's because I race on mine.. hehe

[Ronin]

Hey, I got an idea. I'll be willing to rent out my alignment pad for anyone wanting to tweak their suspension. I have toe gauges, camber gauge, even a bump steer gauge. I also have a corner weight gauge, but your car would have to weigh less than 2000lbs.

Of course since I'll be there, I'll help you with any info you need.

Thats a tempting offer. I'll get back to you when I get the time to install all my links. I have tie rods, tension rods and rear upper control arms to install. I was going to get it all aligned once they're on the car. We'll see tho.

I might just get too lazy to do it myself and just pay to get it done.

[ikeyballz]

i always check my pressure :] specs call for 35, so i should be ok. all 4 are at 35 right now, and i only boost the rear tire pressures to 40 when i know im gonna be speeding a bit...

its gotta be balanced ok since i dont feel any weird vibrations through the steering wheel. maybe i'll take my car in to sears to re-check my alignment.. do you think it'll be a problem if they 'aligned' the tires for a diff size? or does size not matter for alignment (width)..since my car isnt really a factory option (the SS) most after market companies only offer specs/items for the Z28 model, and i have to go to the 1998 SS model which WAS offered by the factory...
hmm. ill go talk to sears :ack:

thanks doodes. =P

oh, and its like..cupping(?)..on the outside.. when i rub my hands one way on it, its smooth but then the other way it gets all pokey?! idk how to explain lol i'll go talk w. the sears-es :D

[REH]

Let's get a few of you guys to see what it takes. I'm thinking more performance orientated than street car set up. Obviously, you want to replace worn out parts before doing the tweeking alignment.

[corytomo]

Oh, cupping tires is also a sign of bad shocks or worn/loose suspension parts.

[REH]

I'm gonna say that No it won't drop the car.

The sway bar is a torsion bar. It connects to both of my lower control arms. I think that all it does is keep both wheels level as the car turns.

correct me if I'm wrong.

Right. Funny thing is, most mechanics I questioned thought the sway bars were part of holding the chassis up like a torsion bar.

[REH]

i always check my pressure :] specs call for 35, so i should be ok. all 4 are at 35 right now, and i only boost the rear tire pressures to 40 when i know im gonna be speeding a bit...

its gotta be balanced ok since i dont feel any weird vibrations through the steering wheel. maybe i'll take my car in to sears to re-check my alignment.. do you think it'll be a problem if they 'aligned' the tires for a diff size? or does size not matter for alignment (width)..since my car isnt really a factory option (the SS) most after market companies only offer specs/items for the Z28 model, and i have to go to the 1998 SS model which WAS offered by the factory...
hmm. ill go talk to sears :ack:

thanks doodes. =P

oh, and its like..cupping(?)..on the outside.. when i rub my hands one way on it, its smooth but then the other way it gets all pokey?! idk how to explain lol i'll go talk w. the sears-es :D

Really sounds to me like you have too much toe in. The naked eye can see a 1/16th difference. Go look carefully at the difference in toe. Can you adjust the camber? You wider tires than 275's in the rear?

[corytomo]

So how much would it be to redo my suspension with 1/8" total toe out front, max camber and max caster (that stock miatas can get), 1/16 toe in rear?
It's gonna be a few more months till I get my double adjustable coilovers and 275 tires, but I'll for sure need it!

[REH]

Going to PM.