Track forum general chit chat.

[omgzirra_exe]

Originally Posted by RalliartRsX

Because it takes a little thought to fit 18x11 and 295s.

Its just easier to buy and fit a 275 and a 18x10.5 because the information is readily available.

luckily 275 is the ideal size for 10.5 lol

[omgzirra_exe]

Originally Posted by pirategenes

This is pure gold. Thanks so much for the helpful feedback!

This aligns well with what I was tentatively planning, and I hope it all works out as you described. I'd really like to keep the helper spring up front since I frequent Grattan Raceway and there's a jump feature there where the suspension becomes fully unloaded.

I have lots of spacers from previous tinkering episodes, so should be all set if the 295 RE71RSs are too meaty.

I'll get the install started this weekend, but will take my time and not complete for probably a week or two. Then head to corner balance shop with the aim of arriving at close to GTS ride height, which is 14.4" front and 13.9" rear measured fender to wheel center, if anyone is playing along. Happy to share the outcome if it might be helpful to others.

Cheers!

I try my best.

With 295s I think setting GTS ride height is a good base line, before you decide to lower it more / corner balance.

but make sure you are doing the "race" ride height of the GTS, I believe they use a c clamp to raise the car when not on track, and remove the c clamp to lower the car more before going on track. Although not a huge drop in height but something to be aware of when going GTS ride height.

[tsk94]

I've started to run 275's on 11's myself. I think 295/30 is too short for these cars, after using many many sets of them.

GTS height of 14.4" and 13.9 sounds quite high imo.
KW recommends around 330-340mm (12.9-13.4") front, and 325-335mm (12.8-13.2") rear. Measured from wheel center to fender as well. I use that as my baseline. I'm a bit lower then that...

[RalliartRsX]

As an engineer, it drives me nuts when people mix units lol

Anyone have a corner balance heights for 275 and a 5 lbs battery in the RR?? With me being 220 and a 5 lbs battery, it seems in order to get anything reasonable in terms of even balance across the axle, all four wheel heights become wonky

[tsk94]

Added freedom units

I'm so used to working with mm's for ride height on these cars I didn't even think to include in inches lol.

[omgzirra_exe]

Originally Posted by tsk94

I've started to run 275's on 11's myself. I think 295/30 is too short for these cars, after using many many sets of them.

GTS height of 14.4" and 13.9 sounds quite high imo.
KW recommends around 330-340mm (12.9-13.4") front, and 325-335mm (12.8-13.2") rear. Measured from wheel center to fender as well. I use that as my baseline. I'm a bit lower then that...

it's more or less to make sure the 295s can clear the fender first lmao.

[tsk94]

Originally Posted by omgzirra_exe

it's more or less to make sure the 295s can clear the fender first lmao.

The ride height you mean? I would take a lower ride height and narrower tire, over the wider tire at a higher ride height. For both aesthetic and performance reasons, lol.
From the testing I've done with my own cars, I'm fairly confident a lower ride height with a 275 (assuming same tire on same width of wheel) will be faster then the 295 at a higher ride height. Assuming we're talking about a significant enough difference in ride heights, ~20mm or greater (0.75"+)...

[omgzirra_exe]

Originally Posted by tsk94

The ride height you mean? I would take a lower ride height and narrower tire, over the wider tire at a higher ride height. For both aesthetic and performance reasons, lol.
From the testing I've done with my own cars, I'm fairly confident a lower ride height with a 275 (assuming same tire on same width of wheel) will be faster then the 295 at a higher ride height. Assuming we're talking about a significant enough difference in ride heights, ~20mm or greater (0.75"+)...

it's what they want, who am i to tell them no

I personally would do 275 and just have my car dump to the floor

[kolosy]

Originally Posted by F4rmost

100% remove your helper. My coilover does not have one and that may be the difference.

Edit: I am curious what offset those wheels are too though. They look tight to the coilover body with those 15mm spacers. It could just be the pictures though I can't recall how tight mine are.

I put the et 25 wheels on last night with the 10mm spacers for ~15mm offset with the 295s. I will drive it tomorrow to the alignment shop, but it might rub the fender compared to the et 22 Apexs with 5mm spacers for ~17mm offset. I didn't think the 2mm would make that big of a difference, but it appears so. PS4S tires also have a pretty square sidewall. Will update.

Edit again: I just saw those are 11's - that could be the inner barrel distance problem you are encountering. I am on 10.5 wides. Bern knows about 11 wides on the front. You will need 5 inch springs and no helpers at the least.

Btw — heard back from forgeline, they were able to look it up by the serial number. F80 fitment, 18x11 et 30.

[kolosy]

talk to me about understeer. driving the GTS on track made me realize how plow-ey the E90 is right now. I don't think it's weight balance since they're both sitting at about 53% front right now. GTS is on stock suspension and just SPL arms. E90 is on Ohlins Dedicated Track with 685 front / 1k rear springs, and HR blue sway bars front and rear. I just bought a set of MCS 3 ways that'll come with 800 front / 700 rear. It's a true rear coilover so if Claude's math is right it's roughly the same effective spring rate split front to rear.

the HR bars aren't adjustable. I don't want to deal with dropping the rear subframe to swap out the rear bar. Should I throw in an adjustable front bar and play around with settings as part of the new coilover install? or just do the coilovers and see how they do first? any other advice?

[bigjae1976]

Originally Posted by kolosy

talk to me about understeer. driving the GTS on track made me realize how plow-ey the E90 is right now. I don't think it's weight balance since they're both sitting at about 53% front right now. GTS is on stock suspension and just SPL arms. E90 is on Ohlins Dedicated Track with 685 front / 1k rear springs, and HR blue sway bars front and rear. I just bought a set of MCS 3 ways that'll come with 800 front / 700 rear. It's a true rear coilover so if Claude's math is right it's roughly the same effective spring rate split front to rear.

the HR bars aren't adjustable. I don't want to deal with dropping the rear subframe to swap out the rear bar. Should I throw in an adjustable front bar and play around with settings as part of the new coilover install? or just do the coilovers and see how they do first? any other advice?

I find that most BMWs are setup with way too much front spring or not enough rear. Could also be a ride height issue where the roll center is screwy because the ride height is too low. Running a lot of front sway bar will add understeer.

Most of the mods people add pushes the balance to more understeer.

And driving can be a big contributor. The hardest part is to be aggressive but smooth on AND off the brakes.

[former 240 s14]

Originally Posted by kolosy

talk to me about understeer. driving the GTS on track made me realize how plow-ey the E90 is right now. I don't think it's weight balance since they're both sitting at about 53% front right now. GTS is on stock suspension and just SPL arms. E90 is on Ohlins Dedicated Track with 685 front / 1k rear springs, and HR blue sway bars front and rear. I just bought a set of MCS 3 ways that'll come with 800 front / 700 rear. It's a true rear coilover so if Claude's math is right it's roughly the same effective spring rate split front to rear.

the HR bars aren't adjustable. I don't want to deal with dropping the rear subframe to swap out the rear bar. Should I throw in an adjustable front bar and play around with settings as part of the new coilover install? or just do the coilovers and see how they do first? any other advice?

My initial response without driving/seeing the car since October is that ride height could be a cultprit. As the previous poster mentioned BMW integrates understeer from a design function from the factory, this is to help reduce risk for novice drivers (novice drivers typically handle understeer better than the opposite oversteer.)

The OP mentioned "too much spring" which is another way of saying IMO that the front is too high compared to the back. Once I was able to get my ride height dialed in I did a good alignment and the car slices and dices.

I'll send you my alignment specs via text, hopefully that can be useful after you get the ride height dialed.

Rubin