Spring Rates & Sway Bars (road racing)

[spxxx]

Hi all!!

Stoked to be back and excited for the 2020 track season. I only got on track 3-4 times in 2019 due to work and broken N54 things... I finally have the time to do a big refresh of the car and hope to do ~20 events next year with a new role at work in 2020.

With the limited number of E82 track cars out there I wanted to get a thread going to cover what spring rates & sway bars folks are running on E82s for road racing. I started tracking about 3yr ago and never really got my suspension dialed in (Essentially just asked more experienced folks and threw some springs in).

I'll start:

Option 1: #400/#750 + F/R Dinan Sways (M3 Bars)
Ran this for ~1.5yrs and recently started to bump up my rates as I added functional aero and got some advice from some faster folks. This was my fastest setup but I also had the most seat time.

Option 2: #450/#750 + Stock Front / Dinan rear sway.
- MAJOR oversteer on corner exit but less understeer even with the slightly stiffer rate up front. Impossible to drive at the limit
*** Lap time ~2 sec slower than Option 1 (2min lap)

Option 3: #450/#750 + Stock Front & No rear sway.
- Easier to put power down on corner exit but mid-corner understeer came back
**lap time ~1.5 sec slower than option 1

Option 4: #550/#800 + F/R Dinan Sways
- similar balance to 400/750 but turn-in understeer was back and bad in big sweepers... That being said, the car was more planted through Esses and easier to control during corner-exit.

Option 5: #500/800 + F/R Dinan Sways
- Yet to try this on track but have a good feeling that this will reduce front understeer and allow the car to rotate with less snap oversteer like option 2.


Let's hear what everyone else is running!

Also, any suggestions on adjustable sway bars?

[bbnks2]

Originally Posted by spxxx

Hi all!!

Stoked to be back and excited for the 2020 track season. I only got on track 3-4 times in 2019 due to work and broken N54 things... I finally have the time to do a big refresh of the car and hope to do ~20 events next year with a new role at work in 2020.

With the limited number of E82 track cars out there I wanted to get a thread going to cover what spring rates & sway bars folks are running on E82s for road racing. I started tracking about 3yr ago and never really got my suspension dialed in (Essentially just asked more experienced folks and threw some springs in).

I'll start:

Option 1: #400/#750 + F/R Dinan Sways (M3 Bars)
Ran this for ~1.5yrs and recently started to bump up my rates as I added functional aero and got some advice from some faster folks. This was my fastest setup but I also had the most seat time.

Option 2: #450/#750 + Stock Front / Dinan rear sway.
- MAJOR oversteer on corner exit but less understeer even with the slightly stiffer rate up front. Impossible to drive at the limit
*** Lap time ~2 sec slower than Option 1 (2min lap)

Option 3: #450/#750 + Stock Front & No rear sway.
- Easier to put power down on corner exit but mid-corner understeer came back
**lap time ~1.5 sec slower than option 1

Option 4: #550/#800 + F/R Dinan Sways
- similar balance to 400/750 but turn-in understeer was back and bad in big sweepers... That being said, the car was more planted through Esses and easier to control during corner-exit.

Option 5: #500/800 + F/R Dinan Sways
- Yet to try this on track but have a good feeling that this will reduce front understeer and allow the car to rotate with less snap oversteer like option 2.


Let's hear what everyone else is running!

Also, any suggestions on adjustable sway bars?

The more I mess with suspension the more I learn that spring rates and even sway bar tuning doesn't mean much if you're not considering the many others aspects that affect the cars handling. Springs are least important of all. I am a firm believer in running neutral balanced spring rates, that work well within your struts range and damping, and then tuning the car to handle how you like through other means. There are massively more important things to consider than changing the spring rates by 100lb.

I don't remember, but, don't you have a true rear coilover? Or was that Berns?

I am still running 6k/16k (336/896) with E92 M3 sways front and rear and I don't have any plans to touch that anytime soon. Car handled great last season. Ride height, rake, track width, alignment, bump stops, strut travel, corner balance, rear differential behavior, etc. are all other things I am looking at for 2020. Any of these things being different from someone else who replies to this thread can drastically change how their car "feel," or "handles" vs yours. No one on this forum ever wants to get into actual suspension tuning though it's just always "you have to run x spring rate because it works for me."

[amg6975]

This thread is great. Can we also include our diff set ups and how the car puts the power down? My biggest fear with doing sways is the impact on my poor open diff.

Last year I did three weekends at Watkins Glen and some various autocrosses with the following:

2.56 DCT open diff
Stock 135 sways
Springs: 550F 800R over JRZ RS2s
Camber 2.8F 2.1R

Car felt pretty neutral and rarely had issues getting full on the power at the apex. It had quite bad power understeer with the recommended starting damper settings, but I fixed that with damper settings and I'm super happy with out it exits now.

At a slower go kart type track there was still a wiff of understeer with an aggressive turn in but I suspect that's a front camber issue. Still no major issues putting power down with some restraint of the loud pedal.

I was debating the M3 bars but I think I'm just going to send it this year and see how it goes. I think I'm going limit this year's focus to weight reduction, safety, and improving the carbon unit.

[spxxx]

Originally Posted by bbnks2

The more I mess with suspension the more I learn that spring rates and even sway bar tuning doesn't mean much if you're not considering the many others aspects that affect the cars handling. Springs are least important of all. I am a firm believer in running neutral balanced spring rates, that work well within your struts range and damping, and then tuning the car to handle how you like through other means. There are massively more important things to consider than changing the spring rates by 100lb.

I don't remember, but, don't you have a true rear coilover? Or was that Berns?

I am still running 6k/16k (336/896) with E92 M3 sways front and rear and I don't have any plans to touch that anytime soon. Car handled great last season. Ride height, rake, track width, alignment, bump stops, strut travel, corner balance, rear differential behavior, etc. are all other things I am looking at for 2020. Any of these things being different from someone else who replies to this thread can drastically change how their car "feel," or "handles" vs yours. No one on this forum ever wants to get into actual suspension tuning though it's just always "you have to run x spring rate because it works for me."

Divorced rear on my car, yeah your rates do make sense with the low rear motion ratio and why I'm going to drop my front rate down closer to where it was previously.

Just tired of the splitter/bumper rubbing up front and the terrible camber curve of the front suspension with the lower rates, I'll likely stick with 500/800ish for the time being.

Mfactory helical LSD for me ^^^

[bchalks]

My fastest setup last season was:

Open diff, 350/700, e93 m3 front bar and no rear bar, -3.5 front camber -2 rear camber

I tried 350/600 stock sways and it understeered bad...Then I tried 350/600 e93 m3 front sway with oem rear and the car felt GREAT but still understeered (would like to try this setup again). Then swapped stock rear sway to uuc rear bar and there was too much oversteer to drive at the limit.

Went back to OEM rear and added 700lb rear springs and the car felt more neutral again. I wanted more oversteer so I did a e93 335i rear bar (15mm?) with e93 m3 front and this made the car extremely fun and easy to control throttle oversteer...

Finally, I settled on NO rear bar, e93 m3 front bar, 350/700 springs and the car handled like a real champ. Very confidence inspiring at the limit and I can coax oversteer when I want it. This setup was about 2 seconds faster than the e93 335i rear bar.

A lot of this could be my driving style, so take it with a grain of salt.

[tsk94]

Back when I ran a 135i for a season and a half it had the following setup:
200F/500R Swift springs on Koni Yellows
Front and Rear whiteline sway bars
Solid Subframe bushings
Rear ground control spherical arm set
BW front tension arm monoball and M3 control arm
MFactory Helical diff
255 square R-comps

Car setup was nice like this, minimal understeer but a bit soft for serious track duty. Great for bumpy tracks, riding kerbs or when it was wet. Koni's were full stiff front and back.

I now run a E92 M3 race car - while it's not directly comparable, the motions ratios are almost identical and weight is very similar to the 135i now that's it stripped and caged.
800F/1150R
Front and rear Hotchkis adjustable sway bars
Full spherical/monoball suspension
2-way 8 clutch Drexler diff

Initially this setup was very oversteer biased on turn in and mid corner - that was sorted with sway bar, alignment and damper adjustment. Spring rates only tell part of the story, I've taken a setup with the same spring rates, tweaked other aspects (alignment, sway bar settings, ride heights, damper settings), and went from a very loose setup to something very stable with a bit of understeer.

Basically what I'm trying to say is, optimal setup goes far beyond just wheel rates.

Get the Hotchkis adjustable set. I believe they work on the 135i as well.

[chris_flies]

I'm not in time trial or racing (yet?), but my car is huge amounts of fun on track. It's my only car, so it's not too extreme, but it's well beyond most people's tolerance for NVH.

Diff: MFactory 1.5-way with 3.73:1 ratio.
Suspension: Ohlins Road and Track with 1M-spec valving from 3DM Motorsport and 7k/16k (F/R) Swift springs.
Sway Bars: No front sway bar. ECS Tuning 12mm solid rear sway bar with Meyle HD end links.
Others: M front control arms, Dinan camber plates. M rear upper control arms and guide rods, Condor Speed Shop UHMW (solid) subframe mounts. 225/45-17 RE71R's all the way 'round.

One thing that made a big difference in how the car handles, was the alignment. My car is currently sitting at -2.1* camber and 0.2* toe out up front, and -0.8* camber and 0.2* toe in for the rear.

Deleting your sway bar may be drastic, but I actually looked at pictures of my car when I had an Eibach 28mm solid bar up front, and I was barely compressing the outside suspension, and was lifting the inside tire about an inch off the ground, which means there was a little more grip to be had. As a stop-gap measure, I removed the front sway bar, drove 7 hours to Mid-Ohio, ended up loving it, and haven't turned back. The deletion of the front sway bar drastically changed the behavior of the car. Even on the highway it felt so much better than before. Presently, it's definitely biased towards oversteer, but it isn't excessive. It really likes to come around at corner entry, which feels great, and if you catch it right you can get a smooth 4-wheel slide going through to corner exit, at which point all 250-odd horsepower stabilizes the rear end and you're off to the next Miata. I think an extra half degree of camber in the rear, or maybe deletion of the rear sway bar will neutralize it to perfection.

[The Wind Breezes]

Alignment (camber and toe) and the hardware to preserve it while driving hard is much more important than spring rate and sways.

[spxxx]

Originally Posted by The Wind Breezes

Alignment (camber and toe) and the hardware to preserve it while driving hard is much more important than spring rate and sways.

Yeah 100% agree, just interested to see the variance of setups across the board.

There's not much centralized info online for suspension setup with this chassis.


Thanks all

[joeo]

Running a TCKline setup with 505lb 7" swift springs in front and 900lb 10" hypercoil springs in the rear. Stock front bar, and UUC rear bar. Still using the open diff which does spin the inside wheel on even faster corners. Said wheel spin started when I switched out the rear bar, but I like the overall balance.
Camber is -3.0 front and -2.0 rear.
I think stiffer rear springs would help; it's still bouncing off the bump stops in the rear too much.

[ShortShift]

Running TC Kline DA shocks with Swift 392lbs front and 672lbs rear springs. Stock E92 M3 front sway bar with powerflex black bushings (26.5 all the way rather then stock E82 is 26.5 but tapers down in the middle ). Rear bar is Cobb 15mm which I believe is the same as a stock E93 335s.


as an avid track goer one thing I've learned is a lot of people set the cars up way too stiff. so I chose slightly less stiff springs and bars then most people have. I also drive the car on weekends and wanted a setup that would work on track and in the canyons.

[berns]

I ran a soft setup for a while. Seems to be the go-to recommended setup originating from Harold @ HP Autoworks days. I don't really understand the insanely soft rates on this nose-heavy and generally heavy overall car.

I run MCS 2ways with 700lb front and 550lb (true rear, divorced equivalent is 1000lb)

Car is planted and a riot to drive. Will work out corner exit oversteer but the car finally rotates, and I'll take that. Just need to put the power down better but I'm making about 470whp at redline, so it's a lot for 275s to handle. Still have some initial understeer at turn in that I have made progress dialing out with damper and alignment settings.

Sway bars are Eibach front and rear, 28mm/15mm.
I tired the M3 rear sway once (21.5mm I believe) and couldn't put power down out of any turn. Assuming the M cars, 1M included, achieve better traction with the M rear subframe and staggered tires. I believe my bar was also installed a bit twisted which meant too much preload and a technically stiffer bar. no bueno either way, but the smaller eibach bar feels 10x better out back.

I have a wavetrac LSD which seems to do well and takes the abuse I throw at it constantly. I ran one on my e90 also, without issue.

Should be said -- ALL of the fast E9x cars run rates similar to what I'm running.

But, who know what works here. I also run a proper front splitter and 3d style APR wing. I suppose without aero, you could knock these rates down quite a bit. Will always come down to what your dampers were designed for.

[joeo]

Berns - would love to see your suspension setup! Very curious if you had the Wavetrac installed with the M3 bar; if it was able to put the power down? I've recently decided to give the wavetrac a shot - have high hopes. The going wisdom is that clutch style LSD's are the best for track work, but yeah - the maintenance on them!
Thanks.

-Joe

[chris_flies]

Originally Posted by joeo

I think stiffer rear springs would help; it's still bouncing off the bump stops in the rear too much.

Check out the Dinan rear upper shock mounts, it increases travel before the bumpstop by over 10mm. Helps greatly with the "rides on the rear bumpstops" feel of these cars.

[bbnks2]

Originally Posted by berns

I ran a soft setup for a while. Seems to be the go-to recommended setup originating from Harold @ HP Autoworks days. I don't really understand the insanely soft rates on this nose-heavy and generally heavy overall car.

I run MCS 2ways with 700lb front and 550lb (true rear, divorced equivalent is 1000lb)

Car is planted and a riot to drive. Will work out corner exit oversteer but the car finally rotates, and I'll take that. Just need to put the power down better but I'm making about 470whp at redline, so it's a lot for 275s to handle. Still have some initial understeer at turn in that I have made progress dialing out with damper and alignment settings.

Sway bars are Eibach front and rear, 28mm/15mm.
I tired the M3 rear sway once (21.5mm I believe) and couldn't put power down out of any turn. Assuming the M cars, 1M included, achieve better traction with the M rear subframe and staggered tires. I believe my bar was also installed a bit twisted which meant too much preload and a technically stiffer bar. no bueno either way, but the smaller eibach bar feels 10x better out back.

I have a wavetrac LSD which seems to do well and takes the abuse I throw at it constantly. I ran one on my e90 also, without issue.

Should be said -- ALL of the fast E9x cars run rates similar to what I'm running.

But, who know what works here. I also run a proper front splitter and 3d style APR wing. I suppose without aero, you could knock these rates down quite a bit. Will always come down to what your dampers were designed for

When I watch the video I see a car that is under-steering and then you get back on the gas early as you're still dialing in additional steering angle to hit your apex. Getting back on the gas early while still turning the wheel to steer more then results in power oversteer. With the way my car is setup, if I try to get back into the gas to power out of a corner while still dialing in steering angle I am getting sent into a spin lol.

@ 00:26 - I think this is an example of the above. You get back into the gas a split second early while you're still dialing in steering angle. Rear kicks out and you have to count-steer out of the turn.

@ 1:55 - Looks like an example of terminal understeer. The car doesn't look willing to turn and you get back on the gas early again to rotate the rear.

Great driving and a fast lap. Not trying to diminish that AT ALL. But, you might be chasing your tail if you go looking to solve a "corner exit oversteer" issue if it's driver induced and a function of inherent understeer. Stickier tires will help put the power down. Part of it could be spool and boost onset being too aggressive. That torque hit can upset the car. You can hear the turbo spooling up right before the tires crack loose.

[berns]

Originally Posted by bbnks2

When I watch the video I see a car that is under-steering and then you get back on the gas early as you're still dialing in additional steering angle to hit your apex. Getting back on the gas early while still turning the wheel to steer more then results in power oversteer. With the way my car is setup, if I try to get back into the gas to power out of a corner while still dialing in steering angle I am getting sent into a spin lol.

@ 00:26 - I think this is an example of the above. You get back into the gas a split second early while you're still dialing in steering angle. Rear kicks out and you have to count-steer out of the turn.

@ 1:55 - Looks like an example of terminal understeer. The car doesn't look willing to turn and you get back on the gas early again to rotate the rear.

Great driving and a fast lap. Not trying to diminish that AT ALL. But, you might be chasing your tail if you go looking to solve a "corner exit oversteer" issue if it's driver induced and a function of inherent understeer. Stickier tires will help put the power down. Part of it could be spool and boost onset being too aggressive. That torque hit can upset the car. You can hear the turbo spooling up right before the tires crack loose.

No offense taken, it's all good! The car does still tend to understeer more than I'd like. It was worse on this lap because the tires are past their prime and I was pushing hard, figuratively and literally.

:26 - This turn is called off ramp. It is notoriously a huge pain in the ass, because it's slow, tight, and has an off camber exit. Yes the car breaks loose for a second because I got on the throttle too early, yes the tires are screaming up front, but the car is relatively quick through this section all things considered. I would love the low speed understeer to be better but the car has really always done this here, though it works the best now vs all the other setups and spring rates I've run in the past.

1:55 - Oh boy, this is just embarassing. It's really difficult to get this thing stopped in time on street tires with aggressive pads, 3200lbs, 133mph top speed into this super difficult turn. USUALLY, I turn in early, clip the curbing, bounce into a power-on oversteer, lose time and cross the finish. This time, I couldn't get the car slowed and turned in time, which resulted in me hopping off the brakes and turning in, and praying for enough front grip not to go off, and to finish the lap. The car understeered here because of me, I didn't fuck the turn up because of the understeer, if that makes sense.

Will continue playing around with damper settings, going to add more front aero, will try stickier tires soon too (A052) and go from there. If the car is still not doing what I want, I'll see about softening the front rate some.

Double also -- going to swap to E9x M knuckles up front too.

[bbnks2]

Originally Posted by berns

No offense taken, it's all good! The car does still tend to understeer more than I'd like. It was worse on this lap because the tires are past their prime and I was pushing hard, figuratively and literally.

:26 - This turn is called off ramp. It is notoriously a huge pain in the ass, because it's slow, tight, and has an off camber exit. Yes the car breaks loose for a second because I got on the throttle too early, yes the tires are screaming up front, but the car is relatively quick through this section all things considered. I would love the low speed understeer to be better but the car has really always done this here, though it works the best now vs all the other setups and spring rates I've run in the past.

1:55 - Oh boy, this is just embarassing. It's really difficult to get this thing stopped in time on street tires with aggressive pads, 3200lbs, 133mph top speed into this super difficult turn. USUALLY, I turn in early, clip the curbing, bounce into a power-on oversteer, lose time and cross the finish. This time, I couldn't get the car slowed and turned in time, which resulted in me hopping off the brakes and turning in, and praying for enough front grip not to go off, and to finish the lap. The car understeered here because of me, I didn't fuck the turn up because of the understeer, if that makes sense.

Will continue playing around with damper settings, going to add more front aero, will try stickier tires soon too (A052) and go from there. If the car is still not doing what I want, I'll see about softening the front rate some.

Double also -- going to swap to E9x M knuckles up front too.

When I watch videos of my driving in retrospect it always makes me cringe. I was 1/72 cars at an autocross and when I replayed the run it was easy to tear apart every little thing I could've done better/differently etc. Just didnt want you to take the comment the wrong way because as soon as you put something into text it always seems to be read as hostility lol.

Have you seen this build? He ran 1:47 at buttonwillow but on 305 pirelli slicks. His weight, power, aero, and suspension make it a similar comparison to where your car would be at with better tires. I think torque is a big issue. 135i has a much fatter torque curve. It's a battle every time I roll into the throttle regardless of suspension setup. In the same corner you can hear him apply maintenance throttle mid corner and then doesnt really squeeze onto the gas until corner exit. Just plain easier to do with an NA car but maybe some tuning could help.

https://www.m3post.com/forums/showthread.php?t=1158445

[berns]

Originally Posted by bbnks2

When I watch videos of my driving in retrospect it always makes me cringe. I was 1/72 cars at an autocross and when I replayed the run it was easy to tear apart every little thing I could've done better/differently etc. Just didnt want you to take the comment the wrong way because as soon as you put something into text it always seems to be read as hostility lol.

Have you seen this build? He ran 1:47 at buttonwillow but on 305 pirelli slicks. His weight, power, aero, and suspension make it a similar comparison to where your car would be at with better tires. I think torque is a big issue. 135i has a much fatter torque curve. It's a battle every time I roll into the throttle regardless of suspension setup. In the same corner you can hear him apply maintenance throttle mid corner and then doesn't really squeeze onto the gas until corner exit. Just plain easier to do with an NA car but maybe some tuning could help.

https://www.m3post.com/forums/showthread.php?t=1158445

Knew who you were talking about before clicking, ha.
Yes, I know Gabe, and his car. He is serious about data, and runs Pirelli DH slicks... Not cheap!

Would be cool to try some DH scrubs some day, I do imagine with a better lap, I could click off a 1:47/48 there on those tires.

It's fun working with the challenges of street rubber, though, and it'll only help me become a better driver. My torque curve isn't nearly as fat as a stock turbo car, but still, it's pretty easy to overcome 275s and 200tw. The car will see some help in the grip department soon. All trial and error. I'm getting faster every time I go to the track, so to me, that says seat time and small tweaks. Despite the issues, the car is definitely working!

[cwlo]

So my contribution is only in the planning stages right now. I'm getting all the parts together, and will be running a Fat Cat Motorsport coilover set. So far, by calculation, we are closing in on 6k/16k spring rates....which look to be identical to bbnks2. That should put us at 2hz front, 2.1 rear. That is before any adjustments for sphericals which I plan to run. Anyway, Fat Cat is finishing up on the spreadsheet with the calcs, and I will be glad to share it if there is any interest.

[spxxx]

Originally Posted by cwlo

So my contribution is only in the planning stages right now. I'm getting all the parts together, and will be running a Fat Cat Motorsport coilover set. So far, by calculation, we are closing in on 6k/16k spring rates....which look to be identical to bbnks2. That should put us at 2hz front, 2.1 rear. That is before any adjustments for sphericals which I plan to run. Anyway, Fat Cat is finishing up on the spreadsheet with the calcs, and I will be glad to share it if there is any interest.

Interested in that info for sure, those are some fancy shocks.

What's the cost for their different setups? I know it's very customized.

[cwlo]

He lists pricing on the website. Anyway, from my perspective, there are so many variables with suspension tuning that getting a turn key solution designed exactly to my needs has a lot of value, and will probably be cheaper in the long run.

Its also interesting reading through the threads on this forum, and also FCM's video's, that much of the stuff out there is tuned for understeer, or other characteristics that may feel fast, but are really slower than an optimized neutral setup.

Once I get the spreadsheet, I'll post it, and see if Shaikh can comment on its design. He did one for the e46 chassis, and there's a thread out there with good explanation.

[ajsmithvmi]

You should know what my suspension setup is since it was yours last year!

And the one before that was yours two years ago.

Stop selling me parts!