solo-x

Ponder this for a moment.

In 08, I ran a setup on the ITR with 1000lb front springs, 900lb rear springs. This works out to a slightly rear stiff spring bias. At the Toledo Pro that year, the car pulled 1.2-1.22g's of lateral acceleration. This year, I went 200lbs stiffer with the front springs, and WAY softer with the rear springs. Like, 550lbs/in soft. This year at Toledo, the car pulled 1.3-1.35g's worth of lateral acceleration.

Yes, there were some other minor changes in there, but nothing of the magnitude approaching the spring change. The front alignment was unchanged, and the rear alignment was changed to have less static camber and less toe out.

Fun to see those numbers after everyone tells me "you need more rear tire, you're throwing away grip!", or "you need more rear camber, you're throwing away grip!" or "you need stiffer rear springs, you're throwing away front grip!". At 1.35g's, I've got all of 230lbs on the inside front tire and the inside rear tire, whilst down on the ground, has barely enough load to keep the tire rolling when I'm off the brakes.

Do I think I've found all the grip I can find? Nah, I've got a half dozen ideas for next year to target the transient phases (slaloms, early corner entry, and early corner exit) and maybe even find a bit more peak lateral acceleration. There is some indication that the front tires may still benefit from additional static camber or increased roll stiffness or both. I need to start getting rid of bind and stiction now too, as well as increase bushing stiffness (still running OEM 100k mile rubber in most locations, fresh OEM in a few spots) which may help reduce my static front camber requirement. It's probably also about time to go back and start looking into damper tuning to see if I've got any time hiding there.

Do remember that my car runs 275 hoosiers up front, with 205 hoosiers out back, 15x10.5 front wheels, 15x6 rear. It is setup for Solo D Street Prepared class and competes well against the BMW's in the class. This year saw a win for me at the Peru Tour and Toledo Pro, with a 3rd at the Blytheville Pro. Due to a loss in the family shortly before nationals I was not able to compete in this years Solo Nationals.

Egezzy

iTrader: (2)

this is awesome.

i have thought about pming you and seeing your reasoning for "front bias" but didnt know how you would react. i am the conventional "rear bias" guy so there is no reason for me to open my mouth...my thoughts and beliefs are followed by many and done by many.

ps. you were at peru nat stop?? SOB i thought about going up there but it was raining on saturday so i decided not to go on sat and then on sunday i had plans that i dont remember what for. sooooo sheet!!!

anyways i am ready to see what people have to add/say/belief.

90_EX_Civic

it's funny when some of the hs guys ask me about my setup and i tell them that im running full stiff (spss3 koni) all around and a big bar up front. they all look at me with a ? they always ask me were i got my setup from, and every time i say " dont' know the guys name, but he's on honda tech." some of the guys ask me is it Chen? i just shrug and say not sure.

i could never get the setup right. actually more like my driving skill was lacking. but i do have to say thanks for all the advice. will have to pm you again soon and ask you about a different setup i had in mind doing for next year.

string

Is that sustained 1.35g (i.e. circles) or transient? I'm also interested in how you came about the 230lb of load remaining on the inner tyre.

Wai

Looks like you're happy with that setup. I also wonder if you remember back in 2002 I brought up the "weird" setup from Japan that won the 2001 national gymkhana championship? I posted that the EK9 (CTR) was running front 20K rear 6K on KYB race shocks. And everyone thought I was out of my mind....

descartesfool

So are all four tires on the ground? I always figured you could get more grip from 4 tires than from 3. Bikes corner on 2, rear biased FWD cars on 3, and the rest of the world on 4. Go figure. What about rotation?

solo-x

Sustained 1.3's. The DL1 is really good at filtering out spikes. If you remove that filtering, the spikes are really high.

The car rotates beautifully, and the amount of rotation can easily be dialed in with small rear tire pressure changes. All 4 tires are down, but that inside rear tire isn't contributing to grip. If I accidentally drag the brake, it lightly smokes all the way around the corner. Combined dive and roll will still lift the inside rear an inch or two as well.

Wai, I do remember that.

The inside front load is determined with some math and a few educated guesses. weight * cg height * lateral acceleration / track gives you total lateral load transfer (TLLT). Since I know the inside rear has nothing on it, I subtract it's static load from the TLLT, the rest has to come off the inside front. With an optimistically low cg, my TLLT is over 1000lbs.

Oh yeah, still using the stock diff too. Had to learn a little trick to get the inside front to stay hooked up and not turn that tire into a cloud of smoke.

RR98ITR

If you didn't generate so many g's, you'd transfer less weight, and then you'd have better grip, and you could go even faster.

Scott, who is trying to picture how much I need to roll my front fenders to get clearance for 345/12.5-15's...

beanbag

Maybe you should datalog suspension travel instead of trying to guess math.

solo-x

NOW we're talking! Er, wait a second.....

solo-x

I didn't guess on the math, I guessed on the cg height. The formula is solid.

STN_Pat

Do you think this also translate to faster, bigger track type of event ? I could never get enough rotation out of a front biased set-up without running crazy amounts of rear toe out and removing the front swaybar.

Nice thread btw !

Egezzy

iTrader: (2)

also to be stated...do you just autox or do you hit up track days also??

slammed_93_hatch

Kensai(sp)/compass360 (team, manufactures, and drivers point leaders in Koni Challenge ST) run a "front stiff" setup.

At the same time other teams, in the past, ran the same cars with the VASTLY different setups and were just as fast if not faster.


Really it just depends on tons of factors.

It isn't as easy at nate, makes it sounds.

Most road race cars run fairly similar tires sizes front to rear, many are required to run a specific size, and or wheel width.

Even those of us who run smaller (width) rear tires aren't running something as crazy as nate is.

And it would kill your top end straight away speed.

So yep nate's setup works great for autoX, but if you put his car on a road course i'd bet some money that it would not do well.

Now that doesn't mean you can't get a front stiff setup car to work on a RR car, you can..

nscirocco

lat G is a function of corner radius and speed .. i don't know much about autocross, but if the track layout changes from year to year then your max Gs would vary even if you didn't change your setup. external factors like track grip, temps, etc etc all contribute as well.. also if your car leans over more than it did last year, then the angle of your datalogger in corners also changes the results.

a better test of max sustained Gs would be a skidpad and a stop watch.

anyways just trying to say that more than just your spring changes affect the datalog traces, interpreting data without stepping back can sometimes lead you in the wrong direction.

i've never autocrossed and my car would probably be slower than yours on a tight course, but i can do 1.3Gs on 205/15 R888 and my setup is the complete opposite .. so i guess the answer is .. well .. "it depends"

TunerN00b

Um, most RWD cars corner on 3 tires as well. They lift the inside front. To use language that is drivetrain agnostic, cars lift the inside undriven wheel during a corner as an artifact of that end having greater roll resistance (if it does).

For example:

solo-x

I've come to the conclusion that one can't compare numbers from one datalogger to another (unless we're talking same logger and both are mounted perfectly in their respective cars and both cars roll the same amount. incredibly rare and hard to do). Case in point, two of my friends have achieved lateral acceleration numbers according to their loggers that would put my car on it's roof. Both cars are on narrower, harder tires.

And don't worry, I'm acutely aware of what variables will impact data logger data. The DL1 does a great job compensating for roll and it helps that the logger has not been moved in the car. It lives were it has been mounted and is fairly square to the chassis and level.

The affect of the radius of the corner would only affect lateral acceleration if my speed did not change in response to the different corner radius. And as I already stated, environmental conditions were as close to exactly the same as ever could be possible. The surface at this site is also quite consistent, especially when you get 6+ shots at each course.

You are correct though, a better test would be on a skidpad, but with more then just a stopwatch. You'd want the logger there as well, and you'd want to log steering angle and throttle position to make sure all variables are controlled. I don't have the budget to rent a skidpad for a day and burn through 3-4 pairs of front tires during the testing. You're talking several thousand $$$ for the day. True, a lot will be learned from it, but for now I stick with what I can afford and make sure I don't blindly follow the data.

solo-x

Ah, but you posted a pic of a rear drive, rear engine car with poor mcstrut front suspension. e36 BMW's do the same thing quite extensively, even in DSP trim like my car. And they'll all tell you that as soon as that inside front tire comes off the ground, the cars pick up a push. Any car lifting a tire is compromising grip due to the dynamic cg height changes associated with lifting a tire. That said, I've got a picture of me driving a Reynard Formula Ford in CM trim lifting the inside front tire as well.... at considerably more lateral acceleration then 1.3g's.

solo-x

I haven't taken this car to a track day yet. After my national level autocross effort's budget and time commitments are taken into account, there isn't much left for track days where I might wad my car up at. That and the wife would murder me if I left her for more car stuff then I already do. That said, the car is setup too loose steady state for track work. I'd add more rear camber then I currently have to compensate. Beyond that, it would work quite well for track duty I think.

As far as Jimmy's comment that I make it seem simple, that is not the point. This is just hard, empirical data that illustrates how there is more then one way to skin the cat.

descartesfool

Modern Porsche race cars do not corner like that, nor does any other properly set up modern non FWD race car. Just watch a GT3 Cup race or GT2 cars in an ALMS race, with Corvettes, Porsches and Ferrari's: all four tires on the ground. And every modern race I have seen at Mosport with World Challenge touring cars has all fours on the ground at virtually every corner. you can always find some conditions of braking and turning or riding over curbs or on diving or off camber corners where they lift, but I have watched them many times from the rear in the high speed corners at Mosport and taken lots of pictures, and all I see is all four tires on the ground. Obviously not much load on the inside rear, but suspensions are set up stiff enough and with the balance setup to maximize grip, and that seems to include not lifting the inside rear.

I run a rear stiff setup on track because I like the way it rotates, and I'm too lazy to keep experimenting by taking off the coil-overs and swapping springs. I just want to drive the car. Going to Mont Tremblant tomorrow morning.

Egezzy

iTrader: (2)

i wouldnt go that far. look at nascar with the cot at say watkins glen. even the smaller nascar series like camping world west have guys lifting wheels at portland. alot of that has to do with some thinking of soft springs stiff bars in that form of racing.

solo-x

NASCAR is a poor example. The rules in that series result in them doing some pretty absurd things. Things like running really soft springs and lots of shock rebound to dynamically lower the car at speed to improve aero. They also don't get to use adjustable shocks, and are stuck using a really narrower and hard tire on a really heavy car with a live axle rear suspension.

RR98ITR

I don't think Nascar is a poor example at all. That shot was taken at a road course, and the car was setup for a road course - by people who aren't idiots. Yes, the tire sizes have something to do with the setup required - same as for any race car. Current F1 cars unload the inside front in the era of similarly sized front and rear.

Scott, who would say "Yes, there is a right answer"...which doesn't actually answer the question...

JW racing

Compare nascar to handling like a motorhome,with 850rwhp...you need to be soft in the rear to have traction at all under power,so they will always sacrifice for that and happen to lift a front wheel since they use such ridgid bars in the front to eliminate front roll.It's a weight and traction issue.A lighter Grand am GT car does not do this like those heavy cars.

A RWD needs some weight transfer for traction and will normally be slightly softer in the rear vs front,as we know FWD needs stiffer rear for the opposite effect.

To me the flatter the car, the the faster it is;however you need to achieve that by stiff rear or front is up to the chassis and tires.

solo-x

They aren't idiots, but the rules they have to play under are pretty archaic. F1 isn't a great example either, as getting a stable aero platform trumps all else. They do things like droop limit the front suspension and use unconventional suspension geometry all in an effort to keep the aero optimized.

There is a "right" answer, but it's far from something as simple as which end has the stiffest springs.