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Anyone here experienced with FWD racecars?

Hey gang,

I'm looking for advice setting up a Front engine, FWD car. Specifically spring rates and dampers.

I confess that I am lost in the FWD world and am looking to get some baselines on setup. Any leads or contacts for someone that I can speak to would be very helpful.

Thanks,

Chris
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Old 01-16-2006, 11:15 AM
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Chris... The closest I've ever come to setting up a FWD car is setting up an AWD car. Still, you gave kind of a blanket statement, you can have a FWD car with a 70/30 weight distribution, or one with a 50/50 weight distribution, that would drastically alter spring/damper rates, and alignment issues. Any more specific info on the car? That would help with giving advice. Any setup you do is going to be very specific to the car and how it is behaving.
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Old 01-16-2006, 05:18 PM
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Thanks Andrew.

I'm definitely aware of that and will have more information on the car soon. I'm really looking for some basic information to get me started. I don't have time to spend 3-4 months reading as I normally would as I may have to turn a hot street car into a racecar in a matter of weeks.

So I'm gonna need the crash-course.
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Old 01-16-2006, 06:27 PM
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Well, keeping in mind that everything will be completely relative to the weight, balance, etc... of the car. The first part of the crash course is that you're going from a 911 that loves to oversteer, to a FWD car that's sole purpose in life is to understeer. I'm not even sure you can spin some FWD cars if you try. Lol, be prepared to trail brake like you've never trail broken before. You've really got to use the brakes to rotate the car and get it pointed where you want it to go.

As I said, I've never personally setup a FWD car. The little FWD setup experience I have is helping a friend with a Honda Civic ... the front spring rates tend to be almost double that of the rear... I believe he ran 10kg/mm front and 6kg/mm rear I couldn't tell you what the valving was on the shocks because he ordered them, but they were matched to the springs, and were recommended for the car. You end up needed a lot more negative camber up front, as well. On turn in, combined with some toe out, it helps offset the understeer, and provides you with more grip through the turn. We ended up taking the car out to a lapping day, and he'd come in tell me how it felt, and we'd make a change, and see what happened next. There was nothing drastic about the final setup except that he ended up running like 3.8 degrees of negative camber up front... lol, as long as you keep turning the tires like it. We still ran negative camber in the rear, but honestly the rear tires don't do much. I believe he ended up with 4mm toe out up front. 1 out in the rear. Of course a lot of that was his personal preference.

I am by no means and expert, that was just my experience with one FWD car. The internet is a pretty good source... there are some pretty good sites and forums to look at, although I will say, I learned with my WRX, that 911 guys tend to be a little more car savvy than others and you have to filter a little more information out. A lot of SCCA classes run FWD cars, some of those guys would probably be great to ask.
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Old 01-16-2006, 06:58 PM
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Hi Chris!

I'd have to agree with Andrew. I've had a bit of experience with them over the years in both rallying and circuit (road) racing. Although I'm sure some other guys out there could give you more specific information regarding the particular make and model, I'd say that generally, weight bias, overhang and suspension design play a huge part in determining the kind of set-up used.

I have found them far more driver sensitive to most other layouts and that often throws another spanner in the works... Two identical cars could perform quite differently in different drivers' hands. I know that can be said for anything, but the effect seems more pronounced with FWD's.

Whether the driver is going to left-foot brake, for example, will also affect the basic set-up.

It also depends what kind of racing the car is taking part in. If it will be racing in a mixed class against RWD's or AWD's, then you have to set it up to exploit the few advantages of FWD and minimize the many disadvantages to be able to keep good clean and consistently competitive lap times. But if it is going to take part in a FWD only category or a one-make series, then setting it up much more "twitchy" like an ice-racer, is better for doing battle in the pack.

Sorry, it's not really the answer you're looking for, but I hope it helps a little.

Cheers mate!

Chris

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Old 01-16-2006, 07:08 PM
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Whatcha lookin' into Chris? I'm interested to see what's brewin' over there at your place?
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Old 01-16-2006, 07:46 PM
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Can't say just yet Jay

...but PlanB is a gooood one.
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Old 01-16-2006, 09:05 PM
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Quote:
Originally posted by cstreit
So I'm gonna need the crash-course.
No pun intended, huh? The best performing FWD track cars I've seen are the Redline Acura Integras. I just googled them briefly and came up with nothing.

With that said, I remember parts of a 1983 Car and Driver three-car comparison test, pitting the Camaro Z/28, Mustang GT and Dodge Daytona Turbo Z, which was FWD, against one another. As I recall, the testers concluded the way to drive a FWD car fast around corners was to turn in very late because of the plow. This is very true as it's quite easy to get an FWD car into understeer. As a starting point, I think the FWD car has to be quite light to mitigate understeer.

I canyon raced a Ford Fiesta with Sachs adjustable shocks and 13x6 BBS-type wheels with Phoenix Stalflex tires. This was almost twenty years ago. The car handled very well and shot off like a cannon when the Webers kicked in with the 410-lift rally cam hit stride. As I recall, oversized sway bars were used - at least twice the size of stock. The car was also lowered 2 inches below stock.

I would advise you to call some of the aftermarket tuners, but who's to say they track any of their products. Your best bet could be picking up Grassroots Motorsports, and check out the FWD-race cars in the magazine. Then call the team that supports these cars, and see if they might advise you.

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Old 01-16-2006, 09:24 PM
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You're fishing in the wrong pond. You might want to try the SCCA IT or Production forums. Lawrence Loshak posts alot on the Prod forum, and has very good technical posts- he ran an E-prod Honda Prelude and should have won the runoffs.
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I know that some of the FWD autoXers (Honda CRX) use significantly higher spring rates in the rear of the car than in the front. This is to get the car to rotate, as most FWDs understeer terminally.

Chris, didn't you run a CRX about eighteen months ago in a major enduro? If so, you might talk to the folks you ran with to find out about their setup. IIRC, it was a 1st-gen with torsion bars in the rear and springs up front, so the direct comparisons may be a little difficult, but...

I searched around for the CRX prep articles I've seen, but didn't run across any. Sorry.

I think I'd follow Garth's advice, myself, and see what the IT and Prod folks have to say.

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Old 01-17-2006, 09:14 AM
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Thanks guys,

Yeah I did run the CRX. This thing had like 800# springs in the back to get it to rotate. So much spring that the rear acted more like a trailer than anything else, haha!

That being said I'm wondering what the corner-weight to spring ratio is. I got some good contacts fromt he techs at H&R so I'm going to try these guys first. Failing that I'll start soliciting feedback from teh FWD guys I know. Problem is that local competitors don't always want to share as much.
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Old 01-17-2006, 09:51 AM
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Quote:
I'm not even sure you can spin some FWD cars if you try.
My co-driver would beg to differ:
http://www.shedracing.net/NASA_thill_oct05/ron_spin2.wmv

For what it's worth, in my Rabbit GTI we run Ground Control coilovers, 550 lb in front and 450 in the back, with Bilstein Sport shocks. The spring rate is much higher than Bilstein reccomends, but it is a spec shock, so that is what we run. The car is around 2100 lbs race weight. The ride height is set in the front so the lower control arms are close to paralell with the ground (McPherson struts, too low is bad) and the back is as low as we can get it.

We run as much negative camber as we can in front, which isn't much, with 1/16-1/8 toe out on Toyo RA1s. In back we have about 1.5 deg negative camber, with about 1/16 toe out.

We run non-adjustable sway bars front (25mm) and back (28mm). Of the guys we race with, one runs without a front bar, and has welded angle iron to his rear sway bar to stiffen it (some IT VWs run 2 swaybars in back). We tried running without a front bar, and hated it. It pushed really bad.

We run the rear tire pressures very high (~52 PSI hot), to try and reduce the rear grip and get the car to turn.

We must be doing something right, in the hands of my co-driver the car set a class track record at Thunderhill back in October.

Try perusing the Improved Touring forums for the car you are thinking about, you may find some info.

http://itforum.improvedtouring.com

Good luck,

Tom
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Chris; I ran a FWD ITB cars for a number of years. I'm no expert but I learned a few things.

Basic Principle: Get the back end to turn (just enough), and the front end to grip.

1) Toss the front roll bar away. If you need more front roll stiffness, stiffen the springs. You want to avoid unweighting the inside front tire at all costs. Both because it will spin (assuming that you're not running a LSD -- which is something that you'll need), and because you'll need as much traction as possible at the heavy end of the car. In a 911 it doesn't matter if the inside front lifts, in a FWD car it's guaranteed lap time death! Be careful not to overspring the front since this will just make it push more and lose grip on rough surfaces.

2) Whatever you have for front spring rate -- you'll need a lot more in the back. You'll also want a big sway bar. I've seen some early Honda Civics actually rig up 2 bars in parallel. I don't think that you really can have too much rear roll stiffness. Rather you'll just start to get deminishing returns.

3) Take a good look at your cage and how it attaches to the suspension system. Torsional stiffness is critical since you'll constantly be using the rear suspension roll stiffness to prop up the front end.

4) Lowering the car (without distorting the geometry) will make a big difference in so much as it reduces the weight transfer. Some guys just forget about any geometry issues and slam the car on the ground which lowers the front roll center significantly and increases the front end's tendency to roll. They make up for this by cranking in a lot of static camber and huge springs. The strategy is as spelled out in my signature.

5) Take a close look at your front geometry. Most FWD cars have MacPherson Strut front suspension which tends to lose camber in roll. Adding Caster can add a lot of this camber back. Within reason it doesn't hurt the steering effort much since the front wheels are pulling the car, so if this change results in any "steering trail" you'll wind up with the tire patch pushing the steering axis as opposed to RWD cars where the contact patch is dragging behind the steering axis (like a grocery cart). Keep in mind that you will lose some self-centering action by making this change.

6) A small amount of rear toe-out can often help the car to rotate. How much depends on the track and how high speed the corners are. If there are a lot of sweepers, then no toe-out may be better. For auto-x, more will most likely be better. By the same token, some guys run narrower tires on the back then on the front. As you mentioned, the rear tires aren't doing much anyhow. Making sure that you have maximum track width on the back end is also important.

7) Don't be shy about considering asymetrical set-ups. At LRP ( 5 out of 6 corners are to the right), I would generally take some load off of the left front by removing some shims. Basically this transfers load to the RF and LR tires. In 5 of 6 corners both of those tires were nowhere near as stressed as the outside front tire.

8) Finally don't forget the shocks. It's really important that you have your shocks valved to match your springs. Some objectives:
A) Dampen the stiff spring rates. FWD cars can get a really funny/scary oscellation that alternates from the front to the rear. It used to be a big problem when the BTCC started to use FWD cars until they got a handle on it. I occasionally ran into it with my Mazda 323 and the first few times you experience it, it can be plenty scary. It doesn't throw the car off the track or anything so all that you need to do is grit your teeth and drive through it. I never got around to spending the money on shocks to fix it in my case, but oscellation problems generally require a shock fix.
B) You don't want a lot of rebound dampening in the front, once again to keep both tires on the ground.

BTW, My inspiration for using the Mazda 323 was the old Amos Johnson Team Highball Racing IMSA Challenge cars. They seemed to always keep the Acura's honest back when they raced against each other. Unfortunately family expansions cut my development time short. Alas....
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Old 01-17-2006, 10:39 AM
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Thanks for the great information guys. That's really useful.

We'll be doing a 3-day setup session in April so that sort of thing will really help my tuning efforts while we're out there.

I've got a lot of reading to do clearly, but this gives me some grounding to understand it!
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Old 01-18-2006, 05:41 AM
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My advise is to take a spirited ride in the car before making adjustments to it first to see what the balance is. In my experience, my heavy hatchback (toyota matrix) suffers from a huge amount of push in stock form and unfortunately without LSD, wheelspin in tight to moderate sweeping corners. I have neutralized it a great deal with stiffer springs in the rear compared to the fronts. You have to attempt keeping both front wheels on the ground in order to power around a corner and stiffing the front did not help. Mind you, this is my daily driver too. So, with LSD on a road course might be different animal. Main thing is to experience the balance of the car and adjust accordingly. You can check here for some basic adjustment ideas... http://www.hadamotorsport.com/tech/vehicledynamics.htm
Old 01-18-2006, 11:57 AM
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ah...what is FWD?

Jim
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Old 01-18-2006, 03:20 PM
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ah...what is FWD?

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Quote:
Originally posted by addictionMS
ah...what is FWD?
Front Wheel Drive.

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Old 01-18-2006, 06:28 PM
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I used to race a Sentra SE-R in SCCA ITS. I also know someone who works for a Mazda World Challenge team.

To be able to advise you properly it would require knowing the specific car. Honduhs are going to tend to have different motion ratios from strut cars.

By and large what the pros are doing is running 600+ springs in the front and about 1.5-2x that in the rear (sometimes more). Speculation is that the ultra-high spring rates are to prevent camber change by severly limiting suspension movement.

You can certainly set up a FWD car to oversteer. In fact, with a FWD car, if you set it up for some oversteer, you just hammer the throttle as the rear starts to come around and it can be very well behaved.
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Old 01-18-2006, 06:47 PM
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Ask Ghettoracer.

Opps - wrong forums...

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