Learn Me: How to cure FC RX7 understeer

^oooooh clever...but does welding not affect the springyness of the sway bar metal?

I has a spare front AND rear. Maybe I will weld on some straight sections to both. Then I could test which one helps more! (Stiffer front or Stiffer rear)

Thanks for the idea!

Rob R.

I ran a massive bar on the front of my Miata. Haven't messed with sway bars yet on the RX7 because when you have 10" slicks you just grip everywhere...

wvumtnbkr wrote: I has a spare front AND rear. Maybe I will weld on some straight sections to both. Then I could test which one helps more! (Stiffer front or Stiffer rear) Thanks for the idea! Rob R.

Thats a great idea to go with.....let us know which works better.

gameboy, antiroll bars don't need to be "springy", their diameter traditionally affects how much they flex under load(granted there are other factors at play there like material, wall thickness, overall shape, etc)

Try and borrow or buy a pyrometer so you know what is going on. Also like what others have suggested, you dont want to try and make the rear oversteer to balance the car, you want to add grip to the front. You have a 50/50 balanced car on a square tire setup so your goal is to get max grip on both ends which should be doable. Focus on the front. the stiffened sway bar will probably help. another idea is move as much weight to the rear as you can. Maybe even some ballast might be needed. Id get rid of the tow in. It might be helping your turn in but it isn't doing any favors mid corner. You also will probably need moar camber on stock springs. This is where the pyrometer will help you find the right amount. If you cant fork out for a long acre then get one of the cheap inferred ones from HF. anything to tell you what the f is going on.

Good luck hope ive been of some help.

I found a big front bar to increase front end grip tremendously probably because the tire is more perpendicular to the road. Before installing the rear steer eliminator bushings on mine the rear end was very snappy to say the least making it very difficult to drive without a tank slapper ocurring.

What about spring rubbers?

Does anybody use them in road racing?

Can I just jam a bunch of them (2 or 3) between the front coils and increase my spring rate?

Thanks,

Rob R.

I don't see why not. The roundy round guys do that all the time. Use a zip ties to help them stay put.

In normal situations the FC doesn't suffer from too much understeer, it's fairly neutral. You could increase the front spring rate vs. the rears. You'll noticed that the more racy aftermarket spring options have high front spring rates vs. not too high rear spring rates. The rear springs are typical 2.5" springs, with the fronts you could look into making a creative DIY coilover kit (non-adjustable or adjustable).

How do you find the car for Lemons and Chumpcar? I figured the FC would be a pretty good solution as it's extremely tough in racing conditions.

wvumtnbkr wrote: What about spring rubbers? Does anybody use them in road racing? Can I just jam a bunch of them (2 or 3) between the front coils and increase my spring rate? Thanks, Rob R.

Yup.

However, modifying the front bar will increase the front roll stiffness WAY more than spring rubbers will. Maybe do both? Also, modifying the spring rate usually will reduce how well your shocks match the springs, where the swaybar does not - so I wouldn't go too crazy.

Strategically cutting the springs could lower the car a bit and increase your rate as well. Draining and refilling the shocks with ATF or fork oil can increase your damping too.

In reply to Snrub:

We finished 6th in its debut race at Monticello this past weekend (out of 120).

It runs well. it was reliable. It wasn't the fastest or the slowest in a straight line. The lap times suffered due to the understeer. Probably losing 2+ seconds a lap compared to the 1st gen RX7 we run in the Denver races (that car is NOT pushy!).

I am going to weld some additional steel to my spare swaybar AND buy some spring rubbers. I have some cheap coilover springs for this car. I just think they are a bit cheaty. I woudl rather weld / cobble a cheaper solution.

It sounds like swaybar is the ticket. I may also try to sneak a little more camber into the front end. Actually, as I am writing this, I may not need to with the bigger front bar.

Thanks for all the help!

Rob R.

A pipe on two bearings and arms going down to the control arms makes for a pretty beefy sway bar.

Soften the front. Reduce neg. camber on the rear. Try 0 toe on front, small toe out on rear. Just some things to try. Experiment with tire pressures also.

I was thinking of drilling new mounting holes for the swaybar.

What says the collective? Can I just drill a new hole in the swaybar roughly 1" inch from the current hole and effectively make a stiffer front swaybar? (shorter moment arm)

I am also planning on adding a small amount of front camber (up to 3.5* per side) and increasing the spring rate front and rear by cutting some coils and adding spring rubbers.

Thanks,

Rob R.

wvumtnbkr wrote: Thanks guys! No idea on Tire temps. I would like to not stiffen the front. The rear steer could definitly be an issue. I have the eliminator bushings. I will do that as well. Thanks!

Did you eliminate the rear steer? You didn't mention it in the update so I'm guessing you did.

wvumtnbkr wrote: I was thinking of drilling new mounting holes for the swaybar. What says the collective? Can I just drill a new hole in the swaybar roughly 1" inch from the current hole and effectively make a stiffer front swaybar? (shorter moment arm)

As long as you're drilling through a flat section, go for it, but make sure you won't be reducing leverage at the sway bar links, or the links will just rotate instead of transmitting force.

wvumtnbkr wrote: What says the collective? Can I just drill a new hole in the swaybar roughly 1" inch from the current hole and effectively make a stiffer front swaybar? (shorter moment arm)

Yeah, you can do that. Just remember, stiffness will vary linearly with the distance from the pivot with this change. Stiffness will vary with the diameter of the bar to the 4th power.

I.E. Adding material to the bar will make a whole lot more difference

ProDarwin wrote:

wvumtnbkr wrote: What says the collective? Can I just drill a new hole in the swaybar roughly 1" inch from the current hole and effectively make a stiffer front swaybar? (shorter moment arm)

Yeah, you can do that. Just remember, stiffness will vary linearly with the distance from the pivot with this change. Stiffness will vary with the diameter of the bar to the 4th power. I.E. Adding material to the bar will make a whole lot more difference

Right! Maybe a bit of both then!

Thanks guys!

Oh yeah, I did eliminate the DTSS (rear steer).

Rob R.

Id add the camber. From the sound of things you need to add grip to the front, so keep working on that.

I said it previously but get a pyrometer. That will help out tremendously in telling you what is going on up there!

I'm a bit late, but did you get it fixed? My first reaction is that most of this is useless until the bushings are correct. If your suspension is moving around, it's difficult to nail down a handling issue. Especially in a FC with it's rear end issues.

That said, I did race one for a while years ago. To start, it's an understeering car by nature. You literally had to "drag" it screaming and kicking around the track. In stock form, they're not a track car the way an E36 M3 is. But it can be made to work very well with a bit of work.

In ours, "fixing" it's rear steer solved a multitude of problems. The first step is to solve all the suspension movement. After that you can work with the all toe, camber, pressure, bars, springs solutions. I can't stress enough that even stock it had these, and with worn bushings, it makes very difficult to deal with.

Add camber in the front, reduce body roll, increase caster.

Found this.

"Roll couple distribution" Old Steve Smith book. Roll couple distribution is the controlling factor of understeer and oversteer. The roll couple is how much of the cornering force is handled by the front suspension and how much is handled by the rear suspension. the roll couple is controlled by spring rate. The stiffer end of the car will lose traction first so if a particular car's front suspension is stiffer than the rear suspension , the roll couple distribution will produce understeer because the front is handling more weight transfer."

Don't know if this will help at all.

One question that I didn't see asked - have you lowered the front suspension significantly? Since your got 205/50R15's I suspect you have. If so, realize the front suspension geometry will now experience in significant camber lose under bump. That's why you have to dial in so much static camber. Stiffening up the front and preventing roll will help mitigate this.

In my FC I get a bit of understeer in corner entry, but that just means I overcooked the turn-in and need to slow down a bit.

Good luck,

-bill

Stiffening the front , rather springs or rollbar Is going to increase the under steer.

The reason a bigger bar works on some cars is to overcome a suspension deficiency. sort of a crutch. Stock suspension cars tend to roll a lot and if they have struts there is no camber gain, causing the outside tire to lose traction. with the bigger bar, it reduces roll so that the R Comps will stand up straighter. This is when any increase in negative camber is not possible or allowed. Negative camber is a better way to go.

Okay time to update.

There were 2 main reasons for the understeer.

First, we had a blown drivers side front strut (on a track with mostly right hand turns). Bad

Second, we replaced a lot of bad bushings. This helped a ton!

Since this thread started, we have finished 1st, 3rd, 6th, 8th, and 15th in both Chump and Lemons races.

The car is not really lowered that much (maybe 1" over stock - front arms are still level). The rear springs are cut (1 coil) stock sprngs with a 200# front spring. The stock spring rates are 95# front 90# rear.

The balance is good, but still a little pushy for me. With the way the rules are, we can't afford to modify the swaybar (it would be a $50.00 value add). We CAN change spring rates. We may go to a 250# front spring (testing has been difficult to come by).

I did buy a pyrometer, but haven't had a chance to use it.

I plan to use the pyrometer to help set tire pressures, AND camber.

The problem with running MORE camber is that braking can be negatively affected. I would trade good braking for a little understeer all say long in an endurance car.

Rob R.