Ideas for suspension

[cyberguy]

I have a MY2010 D4D Yaris and recently after upgrading the ECU (115HP and 250 nm) I changed my rims to Japanracing Jr3 15x7 40ET with Toyo R1R (195/50/15) in order to get some more traction. The result was great, I have much better grip but I have a new problem. In fast long turns the car raises the inner back wheel (with stock rim/tire dimension I had no such problems in the same roads) and the Traction control is using the breaks to lower the speed.

I suppose that the problem appeared because R1R has really hard sides and the height is lowered to 50 from stock 60, so the tire does not absorb anything, resulting in all force stressing the front outer suspension.

What I am thinking as a solution
1)change the rear sway bar to a thinner one.
2)KYB AGX Suspension with eibach springs
3)Bilstein coilovers with custom springs

Has anyone experienced a problem similar to mine? If yes how did you solve it. Also if anyone else has something else to suggest, I would appreciate it.

[xnamerxx]

FWD cars do that. Changing the suspension to stop it will only make the car handle worse. Since that tire is unloaded its really not contributing much to grip anyway.

[Bluevitz-rs]

you'll want a STIFFER rear sway bar. The traction control is kicking in because you're understeering.

The computer is seeing more steering input than yaw rotation.

[cyberguy]

Originally Posted by xnamerxx

FWD cars do that. Changing the suspension to stop it will only make the car handle worse. Since that tire is unloaded its really not contributing much to grip anyway.

Because the side walls of the tire are harder than normal tires, it provides a better feeling but not less grip. Basically R1R are excellent in handling. Is that what you meant by "unloaded"?

[cyberguy]

Originally Posted by Bluevitz-rs

you'll want a STIFFER rear sway bar. The traction control is kicking in because you're understeering.

The computer is seeing more steering input than yaw rotation.

I had a friend follow me and he saw the back inner wheel beeing raised for the whole turn in towards the apex. The two back wheels have a difference in rotation and thats why the Traction control is beeing activated.

I have no understeer at all (unless you mean someting else by yaw rotation).

Also about the sway bar, if I use a stiffer one (more mm width) it will raise faster the inner wheel, I believe I need a thinner one.

Please elaborate

[Bluevitz-rs]

Your issue is not with traction control, it's with stability control.

What suspension mods have you done so far? Because if you haven't changed anything but the wheels and tires, your car will understeer (the front of the car is sliding in a turn before the rear). The rear is lifting because front outside tire has much more grip and much more weight is being transferred to it. Once you pass the limit of grip, the front will start to slide because the one rear tire on the ground has less load than the front but the same about of grip from the tire. Adding a rear sway bar will increase the load on that tire and increase the available grip to the front tire.

This is a common problem on FWD cars.

[xnamerxx]

Originally Posted by cyberguy

Because the side walls of the tire are harder than normal tires, it provides a better feeling but not less grip. Basically R1R are excellent in handling. Is that what you meant by "unloaded"?

It has nothing to do with the tires per se, basically FWD cars have a stiffer rear frequency than front. So whats happening, when you go into a corner, the outside front takes the load\(some people find it easier to use the term weight) and the outside rear loses its load\weight. Well enough load is transferred quickly enough and for enough of the front suspensions travel, you'll end up picking up a rear tire. So the more "grip" you give the car the more it'll pickup a rear tire, since the outside rear tire isn't really doing anything it generally doesn't hurt much.

The other issue that "could" be at play, is stability control is apply brakes to the rear of the car which will also cause a rear tire to lift. Rear suspension generally has quite a bit of anti-lift built into it, so when torque is applied to the suspension(hitting the brakes) the rear of the car will want to squat down. A easy way to test this is to put the ebrake on and gently try to move forward, you'll feel the rear squat down.

I don't fight rear tire lift on my road race car, its generally just something you have to deal with on FWD cars.

[dragoonmc]

I'd upgrade the front sway at to a bigger one which should help keep the front of the car flatter and might level out the rear. Otherwise figure out how to turn off stability control

[cyberguy]

Originally Posted by dragoonmc

I'd upgrade the front sway at to a bigger one which should help keep the front of the car flatter and might level out the rear. Otherwise figure out how to turn off stability control

the front sway bar is a great idea. I know how to turn off TCS, unfortunately you need to do this each time you turn on the ignition and there is no button to manually enable/disable it.

Originally Posted by xnamerxx

It has nothing to do with the tires per se, basically FWD cars have a stiffer rear frequency than front. So whats happening, when you go into a corner, the outside front takes the load\(some people find it easier to use the term weight) and the outside rear loses its load\weight. Well enough load is transferred quickly enough and for enough of the front suspensions travel, you'll end up picking up a rear tire. So the more "grip" you give the car the more it'll pickup a rear tire, since the outside rear tire isn't really doing anything it generally doesn't hurt much.

The other issue that "could" be at play, is stability control is apply brakes to the rear of the car which will also cause a rear tire to lift. Rear suspension generally has quite a bit of anti-lift built into it, so when torque is applied to the suspension(hitting the brakes) the rear of the car will want to squat down. A easy way to test this is to put the ebrake on and gently try to move forward, you'll feel the rear squat down.

I don't fight rear tire lift on my road race car, its generally just something you have to deal with on FWD cars.

You verify what I thought was the problem, it is not a tire problem but better traction amplified the problem with the rear axle. This is the first time I own a "fast" fwd car and I am used to my subaru Sti (track day car) which has a different philosophy.

So one solution, which dragoonmc suggested, is to upgrade the front sway bar. What do you think will happen if I buy a proper coilover (bilstein pss) or kyg agx with eibach springs?

I believe that the front outer suspension will have less compression than the stock one, so the rear will be lift less, so the inner rear wheel may not lift at all, so the traction control will not be activated.

Do you agree or not? please elaborate.

[froger]

How long have you had it on.?Some of the newer systems have a learning ability,so you might have to drive it for a little while before it becomes less
intrusive and learns how you drive.But it might just mean that you are pushing the car to the limit and it is detecting a bigger slip angle between your input and what the car is actually doing.(under steering)I would try a rear sway bar on the rear so the back loses traction first ,canceling the under steer.Right now it seems like your front tires are losing traction first causing a under steer issue , meaning you are turning the steering wheel more to compensate and make the car turn the direction you want to go.By adding just a front sway bar you just adding to this problem by making the front tires lose traction even faster .

[cyberguy]

Originally Posted by froger

How long have you had it on.?Some of the newer systems have a learning ability,so you might have to drive it for a little while before it becomes less
intrusive and learns how you drive.But it might just mean that you are pushing the car to the limit and it is detecting a bigger slip angle between your input and what the car is actually doing.(under steering)I would try a rear sway bar on the rear so the back loses traction first ,canceling the under steer.Right now it seems like your front tires are losing traction first causing a under steer issue , meaning you are turning the steering wheel more to compensate and make the car turn the direction you want to go.By adding just a front sway bar you just adding to this problem by making the front tires lose traction even faster .

Unfortunately the traction control does not have any learning capabilities. I have been racing for many years now and when I say that the car does not understeer I am certain 100%.

The problem exists because the inner rear wheel is raised from the ground and the traction control is activated due to the difference of rotation between the two rear wheels. I am certain of this, as I have even installed a gopro in order to verify it. Of course this does not happen in normal driving but not in extreme conditions too. If for example normal speed for a turn is 90km/h and extreme speed is 140km/h, the issue appears at 100-110km/h

[dragoonmc]

Getting overall stiffer suspension might also help. Generally lowering spring are stiffer to compensate for the less allowable travel. I am not sure the normal spring rate for coil overs on this car. But lowering would also give more potential droop for that inner rear wheel to move before loosing contact

[CoryM]

Why not disable the traction/stability control and see how the car handles? If it's well balanced and does what your want, you are done. The Yaris T/C was not designed with performance in mind so probably will always limit your driving. If you really need T/C, I'd upgrade to an aftermarket, performance oriented unit.

As far as rear wheels coming off the ground: It's normal

[xnamerxx]

The STI being based off FWD is known to do the same thing, I wouldn't worry about it. Disable the TC and see if the slowness is still a problem. I setup my racecar to lift a rear wheel so I can get better weight transfer to the rear on throttle.

[aspro]

I second the notion of disabling trac and stability control. You shouldn't be on the track with it on anyway. It will kill your lap times...

[cyberguy]

Originally Posted by aspro

I second the notion of disabling trac and stability control. You shouldn't be on the track with it on anyway. It will kill your lap times...

I will try to find if there is a specific fuse that controls the TCS and install a switch (my wife drives this car too, so I want it on for her protection) to turn it off.

I will also install a stiffer suspension in order to improve handling.

Any suggestions? I tried to find kyb agx but they dont seem to be available in europe for yaris. I could only find kyb ultra-sr. If I install a normal suspension I will buy eibach springs too.

Otherwise I will install a coilover.

Thank you all for your ideas and suggestions