Ohlin RT guys: front wheel/tire sizes/offsets

[mrgizmo04]

Off Topic: What setting are you guys running on Ohlins RT on the street? Still struggling to get the same comfortable feel I had when I ran Ohlins on my e92.

Per my testing with Shaikh on his shock dyno (years ago at this point), I run them on close to full soft (~20-22 clicks from full stiff), due to high amount of gas pressure and the curves we saw. No, I don't touch the knobs when I autox or track.

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[Exclusivs]

FWIW, I’m running an 18x8.5 et 32 on 245/40 PS4S without issues.

Off Topic: What setting are you guys running on Ohlins RT on the street? Still struggling to get the same comfortable feel I had when I ran Ohlins on my e92.

18s especially 40 series shouldn’t struggle to be comfortable on street - stock top hats? That’s disconcerting if the case with this chassis. Ohlins from all I hear is comfort plush soft riding joy.

@giz - is that setting because of upped spring rate?


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[LSB4Me]

Per my testing with Shaikh on his shock dyno (years ago at this point), I run them on close to full soft (~20-22 clicks from full stiff), due to high amount of gas pressure and the curves we saw. No, I don't touch the knobs when I autox or track.

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Very interesting. Thanks for the info. Tough to argue with shock dyno data.

Do you the same turns in the front and rear? If not, do you recall the offset?

[LSB4Me]

18s especially 40 series shouldn’t struggle to be comfortable on street - stock top hats? That’s disconcerting if the case with this chassis. Ohlins from all I hear is comfort plush soft riding joy.

@giz - is that setting because of upped spring rate?


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Agreed. Pretty sure I’m in a very small minority of unhappy Ohlins users, so something must be amiss. The setup on my e92 felt like a dream. Compliant, stiff and capable … all at once. I am chasing that same feel that I remember well.

I think my setup is underperforming due to installer error. After much driving and more adjustments than I can count, I have traced the issue to the rear shocks feeling overly compressed at rest or simply not having enough travel to dampen properly. Doesn’t matter what the rears are set to, the back end is jittery, unsettled and just plain busy. We will be adjusting/lengthening the rear shock next week and checking to ensure the bump stops were cut.

Currently running 12/18 (clicks from full stiff/closed). Oddly enough, it is the most balanced the car has felt and rotates beautifully. It’s just moving about too much in the rear.

Edit: Yes, stock top hats and OE rubber bushings everywhere. I wanted a comfortable daily driver …

[Slideways]

Agreed. Pretty sure I’m in a very small minority of unhappy Ohlins users, so something must be amiss. The setup on my e92 felt like a dream. Compliant, stiff and capable … all at once. I am chasing that same feel that I remember well.

I think my setup is underperforming due to installer error. After much driving and more adjustments than I can count, I have traced the issue to the rear shocks feeling overly compressed at rest or simply not having enough travel to dampen properly. Doesn’t matter what the rears are set to, the back end is jittery, unsettled and just plain busy. We will be adjusting/lengthening the rear shock next week and checking to ensure the bump stops were cut.

Currently running 12/18 (clicks from full stiff/closed). Oddly enough, it is the most balanced the car has felt and rotates beautifully. It’s just moving about too much in the rear.

Edit: Yes, stock top hats and OE rubber bushings everywhere. I wanted a comfortable daily driver …

My guess is that the E92 is a more comfortable chassis in general and like more modern cars, it is better isolated from NVH in the cabin. The Ohlins on the E46 are more suited for track than street TBH, even though the product states "road and track" (maybe the roads they are referring to are in Germany lol).

What is the current ride height set at in the rear (measured from the bottom of the wheel rim to the top of the fender and subtracting the radius of the rim)? Following Ohlin's guide, the rear is typically too low at 12.75" from the center of the wheel to the fender. Lengthening the rear damper, without raising the ride height, will cause the rear damper to lose bump travel and might engage the bump stop sooner. From memory, Ohlins instructions don't say to modify the length of bump stop, only the dust boot.

[LSB4Me]

My guess is that the E92 is a more comfortable chassis in general and like more modern cars, it is better isolated from NVH in the cabin. The Ohlins on the E46 are more suited for track than street TBH, even though the product states "road and track" (maybe the roads they are referring to are in Germany lol).

What is the current ride height set at in the rear (measured from the bottom of the wheel rim to the top of the fender and subtracting the radius of the rim)? Following Ohlin's guide, the rear is typically too low at 12.75" from the center of the wheel to the fender. Lengthening the rear damper, without raising the ride height, will cause the rear damper to lose bump travel and might engage the bump stop sooner. From memory, Ohlins instructions don't say to modify the length of bump stop, only the dust boot.

Agreed re different chassis. But I’ve got something wrong—the unsettled rear can’t be as intended. At certain settings in the 10-15 (from full stiff) range, the rear ended will bobble when I apply / releasing the throttle. Additionally, the rear shocks are all too excited to release compression when going over a ledge that allows the rear shocks to suddenly decompress, even at 18 clicks from stiff. It feels like the rears are outside their operating window and unable to dampen enough before hitting the bump stop.

Ride height is 13.5F / 13.0R. Tire pressures are 32F / 35R. The Ohlins guide was supposed to be followed very closely by my tech.

Any thoughts, tips or suggestions would be appreciated. I don’t want to swap the Ohlins but my 2010 GT3 is starting to feel like my comfortable car.

[Exclusivs]

Agreed. Pretty sure I’m in a very small minority of unhappy Ohlins users, so something must be amiss. The setup on my e92 felt like a dream. Compliant, stiff and capable … all at once. I am chasing that same feel that I remember well.

I think my setup is underperforming due to installer error. After much driving and more adjustments than I can count, I have traced the issue to the rear shocks feeling overly compressed at rest or simply not having enough travel to dampen properly. Doesn’t matter what the rears are set to, the back end is jittery, unsettled and just plain busy. We will be adjusting/lengthening the rear shock next week and checking to ensure the bump stops were cut.

Currently running 12/18 (clicks from full stiff/closed). Oddly enough, it is the most balanced the car has felt and rotates beautifully. It’s just moving about too much in the rear.

Edit: Yes, stock top hats and OE rubber bushings everywhere. I wanted a comfortable daily driver …

Sounds like the very specific preload adjustments weren't followed, or adhered to. Or maybe (because ive never owned and dont know) that's just Ohlins characteristics.

Do find it bit odd of a system; the "pre-load" specifications they refer to. Unless their definition of pre-load really is ride height.

Check that your rear shock body length (since that's where your busyness is coming from) - measures the 220mm length Ohlin prescribes

Pls report back

[mrgizmo04]

@giz - is that setting because of upped spring rate?


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Stock Ohlins rates are 400/628.

I run 350/672. But no, independent of spring rates. Ohlins are tightly valved, and compression/rebound graphs we looked at of force vs velocity made them perform "better" and less jarring at soft/full soft settings.


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[mrgizmo04]

Very interesting. Thanks for the info. Tough to argue with shock dyno data.

Do you the same turns in the front and rear? If not, do you recall the offset?

After spending time with Shaikh, I hate using knobs to adjust anything, but.

I'll keep it short. For flat ride to work you need soft (low hz) front spring setup relative to rear to give the front enough hang time so it settles with the rear once the rear goes over the same road imperfection. That means lower rate front springs, but then to control body roll you need a stiff front bar. I ran Turner (solid) front bar for a while on med setting and that was good and car felt neutral on track. I switched to Hotchkis (hollow) on full stiff and that was not enough to control oversteer on high speed sweepers on track (hollow, less torsional resistance, yes it is 9 lbs lighter than Turner, but if you crash because the rear lost grip first since the bar is just too small to load the front tires, who cares about 9 lbs. I had an interesting moment at thill t8 at 105mph experimenting with Hotchkis, but anyway). I had corner balancing and alignment done before I switched to Hotchkis bar, but to tame high speed oversteer with Hotchkis I had to "dial in" (via knob) 2 clicks stiffer on Ohlins front vs rear. I also had to drop rear tire pressure a psi or so in rear vs front to tame oversteer when running Hotchkis bar. In future I will redo the alignment to give me a few tenths of degree of rear negative camber and "undo" the clicks.

But it really depends on what the rest of your setup is, how you drive, where, etc. My testing is track/autox driven at the limit. My car is also nose heavy ~52%. There is no one size fits all answer. But to actually answer your question I just ran on track with the latest setup on Monday with 22 clicks off stiff in rear and 18 clicks off stiff in front. I don't change clicks from track to street to autox, but I dial in car handling on track and run that everywhere. I'm also still slowly experimenting, but soon I'll just run 25 clicks from stiff (or however many my setup allows, I think there were different versions with 25 vs 30).

Shaikh's guidance was to run full soft at all times on both front and rear, again, based on dyno results we saw from the gas pressure and force inherent in the valving, and maybe come in a few clicks from soft if spring rates were significantly increased.

On stock Ohlins rates 400/628 it is a very pitchy ride, so I am not sure dropping the knobs to full soft will solve the poor ride quality. But you have to prescribe to flat ride philosophy of spring/bar choices.


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[Tbonem3]

Are ohlins double adjustable? Couldn't you find more harmony by slowing rebound (maybe called stiffer or +, but rebound should be thought of in terms of the speed of control of the spring's release of energy), but softest compression up front but softest/fastest rebound in the rear to get rear to catch up faster to front?

I suppose you can only do so much without actually changing spring rates.

Love your insights re flat ride, front sway and understeer Stas. Despite going from bilstein b6 with 325lb 7" and hotchkis on medium to MCS 400lb (6.25"), I liked the car's behavior less. I had to go down to soft on the bar to get enough grip/roll, but that has me doing the opposite of what you say Sheikh would say. And 400 fronts would have me run something like 750-800 in the rear which I really don't want to do

I've been meaning to increase rear rates per FR, but now I'm pretty sure I need to go back to something like 325-350 7" up front and go back to medium on the Hotchkis.

Max - I have to believe correctly installed, off the shelf ohlins would feel better than what you're experiencing.

[LSB4Me]

mrgizmo04 — Thank you for the detailed info re flat ride and adjustment settings. Perhaps I simply cannot run the RTs at or near the settings I ran on my e92 (11/13). I am happy with the balance at the moment and will have my shop inspect the rear shock length to figure out if something is wonky before going softer on the adjustment knobs.

I had considered going to Turner sways (soft or medium setting) to help the chassis cope with the stiffer suspension set up and might revisit this if I strike out on the above. This makes mechanical sense, but my gut says Ohlins should yield a comfortable ride off the shelf without requiring this step.

Tbonem3 — Unfortunately, the RTs are only single adjustable. My understanding is that the knobs predominantly adjust rebound, but that compression is changed to a lesser extent through the range of clicks.

As you say, I imagined off-the-shelf Ohlins would have me pretty happy. Suffice it to say, I have not been over the course of 5000 miles and, at times, knob changes every other day. It has been a process. Something must have been installed wrong. It shouldn’t be this hard.

[repoman89]

After spending time with Shaikh, I hate using knobs to adjust anything, but.

I'll keep it short. For flat ride to work you need soft (low hz) front spring setup relative to rear to give the front enough hang time so it settles with the rear once the rear goes over the same road imperfection. That means lower rate front springs, but then to control body roll you need a stiff front bar. I ran Turner (solid) front bar for a while on med setting and that was good and car felt neutral on track. I switched to Hotchkis (hollow) on full stiff and that was not enough to control oversteer on high speed sweepers on track (hollow, less torsional resistance, yes it is 9 lbs lighter than Turner, but if you crash because the rear lost grip first since the bar is just too small to load the front tires, who cares about 9 lbs. I had an interesting moment at thill t8 at 105mph experimenting with Hotchkis, but anyway). I had corner balancing and alignment done before I switched to Hotchkis bar, but to tame high speed oversteer with Hotchkis I had to "dial in" (via knob) 2 clicks stiffer on Ohlins front vs rear. I also had to drop rear tire pressure a psi or so in rear vs front to tame oversteer when running Hotchkis bar. In future I will redo the alignment to give me a few tenths of degree of rear negative camber and "undo" the clicks.

But it really depends on what the rest of your setup is, how you drive, where, etc. My testing is track/autox driven at the limit. My car is also nose heavy ~52%. There is no one size fits all answer. But to actually answer your question I just ran on track with the latest setup on Monday with 22 clicks off stiff in rear and 18 clicks off stiff in front. I don't change clicks from track to street to autox, but I dial in car handling on track and run that everywhere. I'm also still slowly experimenting, but soon I'll just run 25 clicks from stiff (or however many my setup allows, I think there were different versions with 25 vs 30).

Shaikh's guidance was to run full soft at all times on both front and rear, again, based on dyno results we saw from the gas pressure and force inherent in the valving, and maybe come in a few clicks from soft if spring rates were significantly increased.

On stock Ohlins rates 400/628 it is a very pitchy ride, so I am not sure dropping the knobs to full soft will solve the poor ride quality. But you have to prescribe to flat ride philosophy of spring/bar choices.


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Interesting insights. I've been running with the front 5 from soft and rear 8 from soft, and with square tires it is close to neutral and easy to drive but slightly oversteer-biased around fast corners. (with 350/325 driver/passenger in the front and 628 rear, CSL front bar/stock rear bar). Maybe going softer in the rear than in the front on the shocks will push it that much closer to perfectly neutral. Either way with my stock CSL-sized staggered setup it's understeer, which makes sense.

[Tbonem3]

As you say, I imagined off-the-shelf Ohlins would have me pretty happy. Suffice it to say, I have not been over the course of 5000 miles and, at times, knob changes every other day. It has been a process. Something must have been installed wrong. It shouldn’t be this hard.

I would set the rear dampers to the weakest settings, and I would play with increasing the front off full slow/soft. Since they're single adjustable (I would assume all rebound, or maybe a bit of comp like MCS does it, like you said) that will slow the front down and allow the rear to catch up a bit faster so it's less "pitchy" as Gizmo put it. If nothing more than to see if that makes the car feel better. Different springs would be the better wa to do it tho.

I wouldn't increase your front bar if you're going to stick with 400lb front springs.

You want some roll, and the 400lb springs don't allow that much, so don't increase the bar imo. For me, it just introduced so much understeer. Other than making sure the set is installed corrrectly, and putting the rear dampers down to the weakest settings, the next best thing you could do, it seems, is lower the front spring rates and/or increase the rears. I really liked 325lb up front vs 400lb except in a few situations in the canyons.

Remember, the rear 628s are actually like 365lb (I don't have the exact math - Gizmo could do it) because of their location inboard on the control arm.

And then, the car's weight (with us in it and whatever fuel amount) affects spring rate. So people's damper adjustments will differ not just for other setup reasons, but for weight since a 400lb spring on a 3400lb car is not the same thing as the 400lb spring on a 3100lb car.

[Exclusivs]

mrgizmo04 Appreciate your posting, and real world accounts. To challenge that (respectfully) - isn't what you describe switching back to stiffer bar just essentially spring rate? Not in the direct sense of the word - but try to see where Im coming from. Is not touching the knobs philosophy , locked in because it would "disrupt" flat ride? Or is flat ride always there on set spring rates throughout the full dampers adjustment range.

Tbonem3 Ohlins "double adjust" through 1 knob, simultaneously. What rates do you run on your MCS 1WNR vs B6? Know you did lots of changes/trials on the B6 setup which was great to see. Interested to hear your accounts on the MCS...I need to toss my on already.

LSB4Me Definitely report back on your findings. Sounds to me like somethings off with the rear setup.

[Tbonem3]

I went from 325/550 on b6 which could barely control the front (rear was fine as stock rear goes up to 685 - remember rear rate is almost halved due to location on control arm) to 400/600 on MCS. I'm going to probably go to 350 F & 600 or 628 or 650 in the rear next. Then probably go back to medium on hotchkis bar from the softest setting I'm on now. I hesitate to go up to the 700lbs in the rear I'm probably supposed to for flat ride because I try to straddle the line between performance and comfort since the car is 100% street and a bmw (luxury car) at the end of the day. But since it's only used for canyon driving these days, I'm more likely to increase the rear. But that's a personal thing.

Regarding swaybar and spring rates. Sway bar increases the rate so to speak during cornering, limits roll (anti-roll bar). Hitting a bump evenly causes no increase as the bar is fixed to the housing of the strut which does not move, in relation to the wheel, and is free to rotate in its bushings which are captured on the car's body.

A stiffer sway can allow you to keep lower spring rate for comfort, but limit roll for more responsiveness I believe. I think bigger sway bars got popular amoung enthusiasts, especially early in a car model's run (before we all start doing more hardcore modding) when added to stock or stock like suspension (h/r or Eibach pro-kit, for example).

But as people started buying these cars used, for less money, and spent more money on racecar parts, they probably didn't evaluate if they should be still be using a bigger bar or stiffer setting when they went to coilovers.

I think the issue coincided with the popular opinion at the time that we should be running 500/500 or 600/600 rates like was so common with tck and groundcontrol kits, for example. At least, that's my memory from later 2000s, early 2010s. The only reason I've come across for such high front rate was to combat nose-diving in corners.

Now we're realizing we want compliance, softer front rates (remember, stock is only 143lb!) PLUS remembering that the rear spring rates are not actually what they're rated, but effectively much lower due to their location as I've said.

Imagine, you had 500/500 rates, that's actually like 500lb/300lb or so lol. If anyone doesn't remember or believe me - go look at M3Dragon's journal he's rebuilt, and go back to 2009 or so when he started doing mods. Think he started with 500/500 then went to 500/600.