Looking for advice: Snappy rear end

[Rta95]

Just did an autocross day yesterday after a year off almost. So definitely feel rusty and it might be a skill issue too, but any advice on getting the rear end to be less snappy? I did my runs in 3rd gear but it still felt like the rear end was kicking out aggressively at higher RPMs (I guess when boost hits, right?). Again, probably skill issue but I had an instructor drive my car (mainly because it's just fun having a proper pro ring your car out lol) and he had the same observation/feedback.

Right now, I just have f/r eibach sway bars, both at the middle setting and RT660s on my wheels, 295s at the rear.

I don't want to go crazy with suspension off the bat but rather build my way up and address the car to my driving. And one thing I still find myself struggling to do is reel in the rear end.

Anything I can do to help? Mods? Dial in alignment more? Driving advice is welcomed! Or whatever can be given without actually seeing me drive lol.

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[Subydude]

I'd take a look at the rear toe and see where it is. Given you have a 2022 in your sig for the car, the boost is pretty progressive, but in sport mode it will command a higher throttle opening for a lower pedal press (makes the car feel more sporty). So if you're noticing it's stepping out at higher RPM, it might be worth working on smoother pedal.

Although, I'd still say check rear toe first and give it a smidge of rear toe in to help calm it down. Like .1 degree per side or so. Then just work on getting seat time to dial in yourself.

One other note, RT660's like to heat cycle out over time. The new 660+ isn't a compound change, just a construction change so they will (likely) cycle out the same. Since the + is a new compound there isn't a lot of evidence if they will, but it's kind of expected. I only mention the 660's cycling out because if they've been on the car a while they might be contributing to the lack of grip.

In order to check, rear toe, get more seat time, then next year if you've still got the bug, get some fresher tires.

 

[Rta95]

I'd take a look at the rear toe and see where it is. Given you have a 2022 in your sig for the car, the boost is pretty progressive, but in sport mode it will command a higher throttle opening for a lower pedal press (makes the car feel more sporty). So if you're noticing it's stepping out at higher RPM, it might be worth working on smoother pedal.

Although, I'd still say check rear toe first and give it a smidge of rear toe in to help calm it down. Like .1 degree per side or so. Then just work on getting seat time to dial in yourself.

One other note, RT660's like to heat cycle out over time. The new 660+ isn't a compound change, just a construction change so they will (likely) cycle out the same. Since the + is a new compound there isn't a lot of evidence if they will, but it's kind of expected. I only mention the 660's cycling out because if they've been on the car a while they might be contributing to the lack of grip.

In order to check, rear toe, get more seat time, then next year if you've still got the bug, get some fresher tires.

Yeah rear toe is what I was thinking too! Can the rear toe be adjusted much with stock components or would I need further adjustable toe links?

But thanks for the advice on modulating the pedal. I think I can definitely work on that.

 

[razorlab]

What is your current alignment? As mentioned already, rear toe settings can make the difference between a car that wants to kill you or be nice and composed.

I run some pretty aggressive rear toe-in to tame the rear because of my power level and my driving style.

Yes, OEM toe adjustment should be fine unless the car is slammed or something.

 

[Subydude]

Yeah rear toe is what I was thinking too! Can the rear toe be adjusted much with stock components or would I need further adjustable toe links?

But thanks for the advice on modulating the pedal. I think I can definitely work on that.

I'm utter shit when it comes to adjusting multilink rear suspensions since everything seems to cross talk. I can say I recently had my Supra aligned and the adjustment range is pretty large in the back. Both camber and toe had plenty of room to move around so I don't think you'd need anything.

I have some camber plates up front, but simple drop springs otherwise so my front camber is maxed out at -3.4 and 0 toe. The rear is -2 degrees and .1 degree toe in. I could have gone up to around -2.5 rear camber and kept the toe the same.

If you have toe plates you can check what you're at now for a rough guess.

The pedal modulation thing won't be as much return for effort, but it's a good thing to think about over time as you get more seat time. The Supra makes pretty good linear power, but even the 2026 I have will rotate in lower gears if you give it too much throttle too quickly.

 

[Rta95]

What is your current alignment? As mentioned already, rear toe settings can make the difference between a car that wants to kill you or be nice and composed.

I run some pretty aggressive rear toe-in to tame the rear because of my power level and my driving style.

Yes, OEM toe adjustment should be fine unless the car is slammed or something.

This is what I had it adjusted to after putting in the sway bars.

 

[Subydude]

I'd get the rear toe moved to .1 ish in on each side for a total of .2. Small toe changes in the back make a big difference. Toe is also what can eat tires over time, so unless you're doing a lot of track or autox without much normal driving I generally don't suggest going too high.

Watch them do the adjustment if possible. The toe arm is easy to adjust since it's a cam bolt, but seeing how much it cross talks to camber might be useful.

 

[razorlab]

This is what I had it adjusted to after putting in the sway bars.

You basically have no toe-in in the rear so that is why it wants to kill you. On power, the oem bushings will basically flex enough to toe out the rear and you get drifito machine dynamics.

I run about 2.5mm toe-in in the rear. Not sure what that translates to degrees. I do my own alignments and use a mm ruler.

Even with that setting, I get even tire wear and I drive to/from events and on the street, but not a daily.

 

[Rta95]

You basically have no toe-in in the rear so that is why it wants to kill you. On power, the oem bushings will basically flex enough to toe out the rear and you get drifito machine dynamics.

I run about 2.5mm toe-in in the rear. Not sure what that translates to degrees. I do my own alignments and use a mm ruler.

Even with that setting, I get even tire wear and I drive to/from events and on the street, but not a daily.

Hopefully I'll get resourceful enough to do my own alignments lol. But I appreciate the advice. I don't really daily my car but I'll take it out any chance I can. So I guess same boat.

 

[Rta95]

I'd get the rear toe moved to .1 ish in on each side for a total of .2. Small toe changes in the back make a big difference. Toe is also what can eat tires over time, so unless you're doing a lot of track or autox without much normal driving I generally don't suggest going too high.

Watch them do the adjustment if possible. The toe arm is easy to adjust since it's a cam bolt, but seeing how much it cross talks to camber might be useful.

I'll start with this! Thank you!!

 

[razorlab]

Hopefully I'll get resourceful enough to do my own alignments lol. But I appreciate the advice. I don't really daily my car but I'll take it out any chance I can. So I guess same boat.

Since it's not really your daily I would also look into way more negative camber in the front or you are just going to annihilate tires.

 

[Rta95]

Since it's not really your daily I would also look into way more negative camber in the front or you are just going to annihilate tires.

Oh yeah that's what I plan to do next. Camber plates and sway bar end links cause I feel like I should have done those before anyways.

 

[Subydude]

You basically have no toe-in in the rear so that is why it wants to kill you. On power, the oem bushings will basically flex enough to toe out the rear and you get drifito machine dynamics.

I run about 2.5mm toe-in in the rear. Not sure what that translates to degrees. I do my own alignments and use a mm ruler.

Even with that setting, I get even tire wear and I drive to/from events and on the street, but not a daily.

The calc is tire diameter * 3.14 (gives circumference). Divide that by 360 to split that circumference into radians. Then times that value by your toe value in degrees. I do this math regularly since I'm used to doing my own alignments on strut cars, and will generally do toe adjustments track side if I need to with a tape measure that goes to 1/32. I end up double checking those with an alignment rack session once a year or so. I just hate doing it to multilink or SLA suspensions since there's so much cross talk

A good example using the oem tire height of 26.6" would be:
26.6 * 3.14 = 83.524
83.524 / 360 = .232
.232 * .2 (total toe I have) = .046
Or roughly 3/64's of total toe in

For your 2.5mm (assuming that's total toe), you're talking about .098 (3/32) inches of total toe in, or roughly .4 degrees total. I run .4-.5 total toe on my autox car, and have run what you do on other cars with minimal wear. I will say, once you go over .4ish degrees total toe in you will likely see some inside wear over 3-4k miles (also assuming -2.5 or up for camber). In this case, that's why I generally suggest starting with mild toe of .1 per side and seeing how it feels. For those that track a lot, the tires are used up before that anyway so it doesn't matter.

One other thing we didn't discuss is using spacers to help track width. If you added spacers to the front, but not as much to the rear you're effectively changing track width which will affect the balance of the car. I don't think it's something to consider until the OP has added rear toe in to start though.

 

[Rta95]

The calc is tire diameter * 3.14 (gives circumference). Divide that by 360 to split that circumference into radians. Then times that value by your toe value in degrees. I do this math regularly since I'm used to doing my own alignments on strut cars, and will generally do toe adjustments track side if I need to with a tape measure that goes to 1/32. I end up double checking those with an alignment rack session once a year or so. I just hate doing it to multilink or SLA suspensions since there's so much cross talk

A good example using the oem tire height of 26.6" would be:
26.6 * 3.14 = 83.524
83.524 / 360 = .232
.232 * .2 (total toe I have) = .046
Or roughly 3/64's of total toe in

For your 2.5mm (assuming that's total toe), you're talking about .098 (3/32) inches of total toe in, or roughly .4 degrees total. I run .4-.5 total toe on my autox car, and have run what you do on other cars with minimal wear. I will say, once you go over .4ish degrees total toe in you will likely see some inside wear over 3-4k miles (also assuming -2.5 or up for camber). In this case, that's why I generally suggest starting with mild toe of .1 per side and seeing how it feels. For those that track a lot, the tires are used up before that anyway so it doesn't matter.

One other thing we didn't discuss is using spacers to help track width. If you added spacers to the front, but not as much to the rear you're effectively changing track width which will affect the balance of the car. I don't think it's something to consider until the OP has added rear toe in to start though.

I have some rays gramlights that are .5 inches wider than stock, more more aggressive offset. Essentially gained some track with there right?

 

[razorlab]

I have some rays gramlights that are .5 inches wider than stock, more more aggressive offset. Essentially gained some track with there right?

Yes. I run 13mm spacers in front on 18x11 +40 and it def helped front end bite and dialed out some understeer. I would encourage you to get everything else setup correctly before tweaking fine tuning adds like spacers, bars, preload, etc.

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