Coilover Spring Rates Question

Hello all. I have a quick question concerning spring rates for my car on the new Ohlins coilovers. I've had a bit of an adventure getting them installed, and now I'm finally ready to take the car in to TPC racing for final setup. I mentioned that I wasn't really entirely happy with the ride in my car, and asked about spring rates they normally use for street driven cars, as mine feels slightly too racy for some of my favorite roads and the front end still feels a bit bouncy. The Ohlins come from the factory with 7/8KG/mm spring rates front and rear respectively. TPC suggested 60/100 Newton/mm swift springs as a replacement option. I looked up a conversion, and it appears that that equates to 6.1 kg/mm for the front spring, and 11.2 kg/mm for the rear. So, they are suggesting a slightly softer front spring, and a much firmer (30%) rear spring. So my question to you guys is does this sound correct to anyone out there? It's a little hard to fathom that going up that much in rear spring rates could actually make my car ride a little better.

Maybe that spring combo works for Cayman Spec racing, but knowing you are not going to be racing, but want a car that can handle back country roads, I would stick to the 70f/80r Nm/mn, which is the recommended spring. According to the owners manual, the shock comes set to 7 clicks, which is noted in the install manual as lower end for track usage and in the center of the winding road rebound setting. If you are talked into the 100 Nm/mn Swift spring by TPC, they maybe able to revalve your rear shocks to adjust the damping force required for a stiffer spring. My installer used 7 clicks in front and 8 clicks in the rear to provide a balanced ride for daily driving. I intend to use a more aggressive rebound setting for Autocross next month. For me and my driver style, this setup is just about perfect.

I tried that setting and found it excessively stiff, as in punishingly so. Backing off down to 10 and 11 clicks respectively improved ride slightly, but reintroduced the bounciness in the front end, although to a lesser degree than before alignment. I'm also still wondering if I might not have some sort of issue with the dampers, as the car still displays a tendency to resonate after a bump, rather than absorb it once and done as I expected from past experience with their products. It's much better than it was with the alignment slightly off after the install, but it still doesn't feel right. It feels nothing at all like the Ohlins R&Ts I had on my previous car, and that makes me question whether it is behaving correctly and just stiffer than I prefer, or whether something is actually out of calibration. I really wish it was easier to have things checked out, especially as I have to leave for 5 months in a couple weeks, but these cars are a pain to do suspension work on, especially the rear axle. I have spoken to TPC racing a bit about it as mentioned, but I'm really not getting a good vibe from them at the moment. I understand that they didn't build the suspension and it's not their responsibility to fix it, but I was trying to gauge whether they think something is actually wrong with the setup that needs correction, as they were going to do the setup later this week and I wanted to give them the best chance of nailing it. I got a distinct vibe of not wanting deal with it over the phone, so I asked if it might be helpful to bring the car in for them to take a look and got a response along the lines of "normally people pay us for our advice, but I guess maybe we could do a "freebie" drive around the block". This was coupled with several mentions of "you should have bought our $5,000 setup instead if you wanted good ride quality". Coming from a company that has the balls to charge $1,700 for a pair of sway bars, I'm starting to think they might not be my kind of people.

TPC most likely will craft their recommendations around the JRZ product. Ohlin is a different product as we all know. A couple of thoughts re the preload setting, manual says 2mm or 1 round, while Cantrell gave me 4 rounds, or 8 mm of preload. Not exactly sure what this did to the linear spring rate, but I feel that it upped the working load of the spring a lot. So the shock needs more rebound, so the 7 front setting and 8 rear, which is in the track rebound setting from the mounting instuctions setup data. So, try 20 mm drop, 1 round of preload and 10 front and 12 rear to see how that works. The street range is 10-20 clicks from the owners manual. If the rebound is too lax in the back, then 1 click firmer. I will benefit from this experience as well, so let me know your thoughts. I will be combining my adjustable sways and wheel spacers which have an effect on the spring rates and damping. I am currently running 18 mm in back and 10 in front spacers, which put more pressure on the shocks and springs. I am also running 18 inch Porsche rims with Michlins PSS. I do not know the weight difference between my setup and your 19 inch wheels and tires . I did confirm that my camber is -1.6 front and -2.1 rear, toe out -.01 front , toe in .15 each side total toe in .31 rear. (Castor 8.4 left 7.6 right was not changed). This setup runs extremely well over rough bumpy back country logging roads that I experienced last weekend while passing a group of cars, getting to an Autocross in Packwood, Wa.

feeshta, in simplistic terms, the spring rate determines how much distance the suspension travels for a given loading. So a stiffer (higher) spring rate will deflect less than a softer(lower) spring rate for the same loading (e.g. a 1-g steady state turn). The damper (aka shock absorber) controls the time it takes for the spring to fully deflect (compress) and recover (rebound) from this loading. If the car is "pogoing", it probably needs more rebound damping to control the release of the spring energy. My feeling is the spring rates are too stiff for your driving preference. I'd follow Ohlins ' recommendations, since you're already paying for their expertise. They'll get you sorted out eventually. I don't fault TPC for not wanting to step in the middle of your car's development if you're using a competitor's product, although a little goodwill can sometimes go a long way. Alas, such is the fate of the trailblazer... Sent from my XT1650 using Tapatalk

I'm currently at 10 front, 11 rear, and it still has the resonant behavior. Actually, it's much more noticeable on this setting than it was at 7 and 8. At the stiffer setting, the car simply felt way too stiff. Part of me is starting to wonder whether the behavior is actually the result of something else shifting in the car? Maybe the transmission mounts are bad or something? The thing is, it was looked over a few months back by a shop with a license to go nuts and find everything wrong and get payed full price for it. It was still under extended warranty at the time and the shop raved about how great my extended warranty was because they got payed same day without questions. They had it for three days and only found an issue with the engine mounts and front control arms, both of which they replaced. Then they found that the shocks were bad when that didn't fix the issue. Could there be something else they missed?

I think I might try stiff in the front, and leave it softer in the rear tomorrow. Seems like the front is the problem child. Could also make sense to try a softer spring up front only, which is a whole lot less work than the rears. I don't fault TPC for being leary of another company's problem, but they certainly could have handled it with a bit more professionalism. I was asking them whether they felt there was a problem with Ohlins spring rate choices, or whether they believed it was something else they could correct with setup, i.e. make money. If you are confident in your spring rate choices, it shouldn't be too hard to make a call here I wouldn't think. I think they are a bit too accustomed to dealing with the richer folks who just give them the car and a bunch of money and tell them to make it right. I'm much more hands on, and I will not pay someone $200 an hour to do what I can do myself, because it's insulting to my intelligence to do so. Shops don't seem to like folks who do any of their own work.

Feestha, please give us an update on the thread

feestha, maybe take out most of the preload in front, set up manual calls for 1 turn or 2 mm, back to 1/2 turn, then try 9-10 clicks in front. You should have a small amount of preload and the weight of the car, so going over a bump that unweights the front should not result in a noise from the spring becoming completely free. 9-10 clicks will give you a good amount of rebound/compression and the reduced preload will effectively lesson the spring rate some. Ohlin rear spring rate is about 460/80 Nmm in linear. PSS9 rate their rear progressive spring at 366 average, Fronts are 280 for main spring and 80 for helper. Rears are progressive, 170/180/295/380 (that is for 1", 2", 3" and 4" travel mark) I have spring tester and measured them. Starting point was 1/2" preload. Posted from an older thread. In the Ohlin Product news, 3/30/2017, they highly recommend the spring that is indicated for this shock, Öhlins Road & Track team has extensively tested a wide variationof springs to nd the right balance between road and track use.By testing in different conditions on road as well on track, the listedspring rate is what we strongly recommend you to use.

Sorry to hear that the spring rates are too stiff for your liking. You should get the Bilstein PPS9 set, very compliant ride, yet great damping and control on track. Call Bilstein and ask them what are the rates of their springs, then swap that onto your car.

I don't have the ohlins but started out with the standard PSS9's on my daily driven CS for some time before upping the spring rate to 70NM F 80NM R which I believe is the same as the Ohlins rate. I have similar thoughts on the resonance with the 987 as I have previously driven on nice coil overs which really absorbed bumps nicely using a 16k F 14k R set up (N1 spec spoon) on an Integra type R. Even driving the standard E92 M3 has a nice feel on it. Originally, I felt the PSS9's didn't control the weight really well, felt slow to respond, bopped a bit to much in corners compared to my other cars. I thought it was the dampers then had them rebuilt (found them to be about 9% out of spec), shortened, with the higher rated springs. It's smoother but resonance is still there. With my limited experience, I'm starting to assume it's actually a normal characteristic with 2.5d camber because the grip is there, just not the feel (like when the tire is stickier than the rates of the coilover, they can be worked harder) so would be interested to hear from others. I even started to think, maybe its my seat giving me the extra bounce . I'm also learning that driving style influences the feel. ie. The way we drive, the rougher we drive can magnify the oscillations of the suspension. With the BMW you get quite aggressive and can easily transition into oversteer. With the Cayman , if you get on the gas to early, it lifts and you get understeer but if you feather the throttle, you stay more neutral and smoother in the corners. The one thing that does change the characteristics a lot is the tire pressure. 30 to 32 F lb and 32-33lb R seems to be the street range for me. This is on 19" sizes on Michelin PSS.

I noticed an extra jittery bounce from the rear after I adjusted my rear sway bar to the max hole to reduce understeer. I did not adjust the rear Ohlin from 8 clicks to a lower number (stiffer rebound), which I will on my next autocross. So, sometimes its not only the spring but the bar that the shock needs to absorb. I have 18 mm rear wheel spacers that also cause some additional torque on the shock, further out means the shock needs to work harder to smooth out the rebound. I am interested in your rear spring set up now, do you still have helper springs on top of the higher rated 80nm R after the shock rebuild? Also do you know if your spring is linear or progressive?

Sorry that I have been a bit absent from the thread for a little while. I got really sick this past week due to a combination of things that all hit at once. Acid reflux, seasonal allergies, and sinus and ear infections was the final tally when I went to the doc. I also have been busy preparing for a temporary duty trip for work. I'm leaving Friday afternoon for 5 months, and I can't take the Cayman because I can't get everything I need to fit. I also found that one of the rear tires is in danger of complete failure, with cords showing through, so I don't feel confident driving the car until that is addressed, but unfortunately I just haven't had time or energy this week. So, unfortunately it appears that correcting this will have to wait until after I'm back.

Get well soon, and safe travels! The car will be there when you return, and perhaps stepping away from it for a while will give you time to clear your mind and help you to decide a path forward. Sent from my XT1650 using Tapatalk

I already feel much better. Just still coughing up a bit of phlegm at this point. Thanks for the well wishes though. Next challenge is the tires . I am seriously considering downsizing and going to an 18" wheel though. 19s look nice and all, but I don't like the way they ride, or the tire prices. Given the fact that the factory sport wheels seem to command a decent price used, it's an attractive option to me to go down in size. Going to post a thread looking for options on that front, as oddly I'm not finding much via search. It seems like virtually every thread must mention wheels or something, because search doesn't yield many threads that actually concern wheels.

You are on target with 18 inch wheels and that very few makers are producing quality, high performance wheels in that size that will fit our cars. A set of 18 in wheels are on my short list that needs to be light weight, strong, in offsets that reduce the need for wheel spacers (additional weight), and wider base than OEM, like 10 or 10.5 inch in rear and 9 inch in front. Safe travels and take care.

Hey mate - assuming you're asking me 5NM helper F 20 NM Help R - Linear F & R. For rear PSS9, you have to get a new top mount to fit the linear springs. Currently sitting on setting 3 from soft all round. Everything else suspension wise is OEM except my GT3 LCA 's.

addicted2wasabi, you may be correct with using a softer multi spring for feeshta, seems that different people can have completely different uses for the same equipment. A softer progressive spring with a helper spring maybe just what is needed here. I have some other uses that makes harder spring rate (the standard Ohlin rate spring) more valuable to me along with larger sway bars. So I have decided to go above OEM ride compromise of shock/spring compression rebound to a much firmer ride. No looking back for me. Just trying to figure out how to utilize the 30 mm drop, adjustable sway bars, Ohlin shock controls, wheel spacers, 18 inch wheels and tires .