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| 09-05-2021, 11:25 AM | #1 |
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Suggestions for Dialing in suspension
Suspension/Chassis Mods:
-Ohlins R/T mi00 revalved for 400/685 lb/in springs -Stock sport front and rear sway bars -Dinan Fixed camber plates -m3 front control arms -Megan racing adjustable pillow ball toe, camber, and upper trailing arms in the rear -Whiteline rear subframe bushings -apex arc8 17x8.5 et40 with 235/45r17 Nexen sur4g tires -car has about 100lbs weight removed from interior -stock diff Alignment/setup front -2.5 camber with +-0 toe rear -2.9 camber with +- 0 toe lowered about 1 or 1.5 inches front and rear Purpose of the car -Temporary daily -Goal is to have a car that will carve through corners on both canyon/backroads and the track Current issues/characteristics -Good initial turn, but the car doesn't want to rotate -rear end doesn't feel close to wanting to step out, unless under braking or intentionally flicking the rear end combined with a clutch kick -The front end pushes on mid-corner and exit -Car darts around when going over bumps, feels like this is mostly coming from the rear -Tire wear in the rear is relatively even, but the front still experiences more wear on the outside edge -Also have an issue with getting the tires to fit in both front and rear. The front fender lip is basically rolled completely flat and it still rubs a little when I hit a bump under brakes or mid-corner. Also, the front tires are practically touching the front springs but don't actually rub. The rear doesn't rub but that's only because I had to add 2.9 degrees of camber for it to not rub. The rear fenders are rolled but there is still a rather large lip -minimal 1 tire fire action, but the car is currently at somewhere around 170whp if I'm lucky since the drivetrain is stock and I'm at 6000ft elevation at the lowest What I have planned -Vorshlang camber plates to help with front end grip, tire wear, and tire clearance. Not sure how much camber I would achieve but hopefully somewhere at or a little over -3 degrees -shaving/cutting the rear lip in the rear in order to run less camber. Ideally, id be somewhere around -2 degrees -clutch style LSD Questions Will the following mods to balance out the camber be enough to increase the front grip of the car to make it easier to rotate? What should I do for sway bars? Leave them stock, add a stiffer one to front and rear, or just rear? Would a 245/40r17 be able to fit in the front since it has a slightly smaller diameter than the 235/40r17(25.3" diameter vs 24.7" but .3 inches wider) What toe settings are people running since after looking more on the forums people recommended I add some toe-in at the rear to help the car feel more stable over bumps? Since I'm currently running a 7inch inch springs upfront and have an inch of adjustment to raise the car an inch, would changing to 6-inch springs in order to get more clearance have any negative effects? Last edited by dmytro98; 09-05-2021 at 03:38 PM.. |
| 09-07-2021, 02:04 PM | #2 |
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For starters, I can't understand why you'd need -2.9* to fit that wheel and tire combo in the rear. I've run 18x8.5 ET48 with a 255/35R18 and -1.9* with no rear rubbing issues. So we have similar offsets, but you're running a tire 2 sizes smaller. Are you sure the rear was rubbing and not the front?
I think that's step 1. Because right now your alignment is far from optimal and will be contributing to your problems. Next, go to the 6inch spring. That will help your tire clearance up front. The other option is to run a 3mm spacer up front and add some negative camber while leaving the current spring in place. That will fix the issue of your fender and strut clearance. I also suspect that more negative camber will also give you more mid corner grip, and it will fix the outside tire wear. A camber plate should give you up to ~-3.5*. Every car will be different. Worst case scenario, if you need more then plate allows you to get, slot the strut tower holes for some additional adjustment. 400/685 is pretty front biased for spring rates. The easy solution would be to go to a stiffer rear spring, as they are easy to swap out. Since you can probably only go so much stiffer on your current valving, the next step would be to add a bigger rear sway bar if the spring rate increase is not enough. Since you're struggling with so much understeer, do not touch the front sway bar for now, that will only make matters worse or cancel out any effects of a stiffer rear spring/sway bar. The car darting around is just the nature of an aggressive alignment. Running as much negative camber as you are in the rear, coupled with 0 toe, will have the rear end reacting to any pavement imperfections and result in a less stable/planted feel. In your case since you're struggling so much with rear rotation, 0 toe might be okay. In general, almost everyone tracking this chassis runs toe IN in the rear - something to keep in mind. Anywhere from a 1/16" to a 3/16" toe in per side is the norm. Yes, a smaller diameter tire will make fitment easier. You should be able to get that size to fit, but sort out your current fitment first is my suggestion. That will then give you a better idea of what it will take to run a 245/40R17. Last edited by tsk94; 09-07-2021 at 02:09 PM.. |
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| 09-08-2021, 09:56 AM | #3 |
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As said above, you need to stop using camber for tire fitment and realize it impacts handling. Try reversing those camber numbers... 2.9* up front and closer to 2.0* out back...
The stock rear bar is also tiny on these cars. Maybe bump the rear spring rate up a bit more. And yeah... 2.0+ camber up front and 0 toe will pull into grooves/crown in the road. zero to negative toe is a compromise you make for crisper initial turn-in. negative camber also negatively impacts straight line braking performance but again it's a compromise you make for better mid-corner grip by keeping the tire contact patch in a more optimal operating range. You can also take a look at rake if the alignment changes don't help enough. Maybe raise the rear a little. Measure rake from the jack points... I run 1/2" rake (rear higher) but many people are running closer to 1" of rake even without AERO. Moving to a 6" spring may result in COIL-BIND. a 7" swift spring in 400lb rate has a usable stroke of 3.7" and a maximum (bound) stroke of 4.7". Moving to a 6" version of that same rate spring would result in having only 3.5/3.9" respectively. You lose .8" of maximum stroke. The Ohlins have a little over 4" of stroke before contacting the bump stop and something like 4.5" of total travel so you will more than likely end up binding the spring constantly. The answer to running a 245 up front would be a small spacer. The diameter of a 235/40 vs a 245/40 is damn near the same. The added width of the 245 will put you into the collars. Does your car sit very low? any contact on the fender liner? you might consider increasing the strut length a the knuckle which will move the tire away from the collars but will raise ride height a little. Last edited by bbnks2; 09-08-2021 at 10:09 AM.. |
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| 09-08-2021, 06:32 PM | #4 |
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Fitment
I knew that running that much camber in the rear would sacrifice performance and mess up the balance of the car, but I was honestly just impatient and frustrated with trying to get the car not to rub since I already had my fenders rolled so the easiest solution was to just add camber. I know the main problem for the rear is getting them either re-rolled or shaved by a shop that has worked with e9x/e8x fenders since they seem unique compared to most other quarter panels. Also, the rear was definitely rubbing since I could see bare metal on the lip of the quarter panel and marks on the tires. For the front, I'm hoping that just maxing out camber with vorshlang camber plates will solve my problem. The car is also not very low but the red circle is where I'm rubbing on my fender even though the lip is completely flat and slightly pulled so I have no clue how it's rubbing based on other people's experience with fitment. Handlings I have not thought about adding rake to help with understeer but that will definitely be added to a list of things to change since I have a decent amount of room to raise the car. I'll have to talk to 3dm to see what would be the highest spring rate they would recommend based on the valving, but assuming I can compensate with proper valving what sort of spring rates would be recommended? Also would it be possible to only install a stiffer rear sway instead of doing springs or am I better off running stiffer springs and only going to a stiffer bar? |
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| 09-09-2021, 12:16 AM | #5 | |
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Quote:
Like bbnks mentioned, playing around with the rake will help too. Raising the rear of the car will make it want to rotate more for sure, and it's a pretty easy thing to do as well. There's no definitive answer to soft springs and stiff bars or stiff spring and soft bars. Both can work, so if you prefer to start with the sway bar then do that. |
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| 09-23-2021, 02:26 PM | #6 |
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Based on your photo, your ride height is set too low in the front! I have a Ohlins setup optimized by HP Autosport and my front struts have double the preload as yours with the same spring setup.
On the track my setup still rubs with ~20 mm preload and -3 camber on 18x8.5” ET45 235/40. It rubs on heavily pulled/rolled fenders and sometimes at the top of the wheel well in certain corners. It can actually use more preload / higher ride height, but then coil bind becomes a serious issue. We are stuck with a very small window to get ride height just right for this car. If you care about good handling, raise your overall ride height. A 1.5” drop is too low for the rear. Aim for .75” and no more than 1”. The fuel filler pipe on the passenger side is also a concern. Even though my rear is lowered less than 1”, my 265 street tire rubs it badly with the 18x9.5” ET58 wheel on the track with -2 camber. Start with a rake of 0.5” - 0.75” (higher in the rear). Stick with 7” front spring to minimize coil bind. For rear toe, set it no less than 0.08” each side. Try 1/8” or 3/16” first. Last edited by Bullitt; 09-23-2021 at 02:33 PM.. |
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| 09-24-2021, 10:49 AM | #7 |
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I actually just ordered a set of 10mm lower strut spacers from fe1rx to increase ride height without having to increase preload, but also it moves up the adjustment spring higher to give additional clearance for the tire. Also, this is another picture of the ride height which I thought wasn't too low and don't know what the actual drop is since I had an alignment shop set my ride height.
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| 09-26-2021, 09:41 AM | #8 |
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Yeah…your ride heights are too low. Geometry and roll center are compromised, which explains why you are experiencing issues with handling (and rub).
Fe1rx’s spacers will help, but you’ll still need 10-15mm of additional height if you plan to push the car and have optimal performance. If you’re only driving on the street, you can leave it as is. |
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