George A

Does anyone know what's the max nitrogen pressure the moton club sports can handle? I know the brochure gives a starting point of 185psi on the struts and 275psi for the shocks, but what is the max I can put in without causing internal damage?

George

95m3racer

Why do you want to know the max, are you running that high of a spring rate?

The pressure in the Canister will vary depending on spring rate, which also means it will vary with different shock/motion ratios.

You should contact your Moton distirbutor for detailed information to see how your shocks were valved and what Pressure range will fit your specific application.

There is NO "best" spring rate or "best" pressure, it takes testing.

Hank Cohn

George,

I have been looking for information on the range as well. If you find out something, please let me know or post it here. I have a set on my 993 and I have been running 150 psi in the front (struts) and 175-200 ps iat the rear (shocks). From which brocure did you get the starting point information? I didn't get anything with mine that I am aware of.

Thanks,
Hank

95m3racer

What spring rates are you running? Do you know the motion ratio and wheel rates?

You want to tune your can pressures, there will be no set pressure that will for sure work in all conditions.

Whomever you bought the shocks from, you should contact them and get support.

You most likely will never get close to maxing them out on a porsche, as its close to 300psi (usually the range is 5-20bar which is 294psi).

If you do not already know how the shocks and canister pressures work, I Highly suggest researching them, either through moton, or through another company that has a similar shock (jrz/protrac, the other NL companies). Look at how they work, and how each change affects the shock, and ultimately how it will affect the handling.

I'm assuming you have off the shelf valving, and generic spring rates for your application...in that case 160-225psi is the range I would guess you will want to test in. Since there are so many variables that are part of this "equation" you really just need to test.

A small nitrogen bottle is pretty cheap, and the guage/filler is like $125 or so.

George A

I'm running springs in the upper range of what the CS support. I just don't want to blow the shock internals. My first time out in it, it felt better the stiffer I went on rebound and compression so I decided to add some nitrogen and went to 210psi and 300psi. It felt great but I was a little nervous. I sure would like to see what even more would do.

Hank, you can see it in the attachment on adjusting them. It's at the bottom of the last page.

George

Hank Cohn

George,

Thanks! I have seen that brocure - I forgot that pressures were listed. Do you know the maximum Spring rate the shock and struts will support with stock valving?

95m3racer, you are, of course, correct about testing. I am not sure what generic springs would be. I am running 1000 lb/in at the front and 1200 lb/in at the rear. I'll be testing tomorrow afternoon. Any other suggestions would be appreciated.

Thanks again,
Hank

George A

Hank, I'm in the 1700~1800 lbs range with stock valving. I've been told that's about the most you want to go. It does work, so you have plenty of room to spare.

George

95m3racer

Not sure if this applies to any of you, but realize, that these spring rates are for coilover applications ONLY. If the spring is in a differnt location you have to calculate its rate at the shock.

What are your wheel rates? (and motion ratios if spring is not in a coilover position)

if you are at 1700+ # you might want to have the shock revalved for your application, it'll help dial in the car and not have to max out any of the adjustments.

Also, do any of you guys run tender springs?

George A

95m3racer, our cars use the standard coilovers, so we are talking about wheel rates. And yes, I'm running tender/helper springs (I always get the two mixed up). I actually had them rebuilt before I put them on and was told by Lex not to revalve them. I've really only had one weekend to play with the setup and it really wasn't complete (they just threw it together for me to play around with at a DE). I've since had it lowered/corner balanced/aligned/etc. and really don't want to use my prior settings as a starting point or even a guide. I've got a race this weekend (with the BMW CCA CR) and it will be my first real test with the setup. I just want to know what I can and can't do.

Hank, I would really like to hear what you get out of testing tomorrow.

George

chris walrod

Higher CP's will work your shimstacks harder. If you are revalving, keep the same pressures simply for the purposes of back to back testing. I would pick a number a stay with it. Presures can increase with heat, which depends where you have the canisters mounted.

Alan C.

I ran 125 - 150 front and 150 - 175 rear on my CS's. Spring rates were 700/900 F/R. I liked the settings, worked for me with some room for bumpy tracks and my own mistakes

95m3racer

Yea, I was thinking everyone in question had true coilovers, just wanted to make sure for other readers

Tenders are the ones you want Droop is ciritical for your suspension to work properly. Tenders are fully compressed at stationary rideheight, making a technically infinite/solid spring rate. There are different spring rates available for the tenders, and if you ar really dialing in your chassis, they will be key.

As far as the nitrogen pressure changing with heat, it won't change much, negligble. If you feel the cannisters after racing they'll be hot, but the side with the nitrogen in it (where the valvestem is) won't be affect too much, but its just another minute variable that comes into play when you are really getting deep into suspension design and optimization.

How are you guys, in general, picking spring rates? Do you mimic what the factory prepared race cars use?

Do any of you go test on the skidpad to determine your best spring rates?

Hank Cohn

George,

You’re running some serious spring rates. You must be attending the Chris Cervelli school of “There’s no such thing as to stiff.” Seriously, thank you for the information you’ve provided. Lex actually lives here in Atlanta. I’ve met him a few times. He is a hell of a nice guy and very knowledgeable. I ran a few Speed World Challenge races several years ago and he helped us out with some JRZ settings.

I was at Road Atlanta three weeks ago and we just started working on the suspension there. It was a private test day sponsored by Kinetic Speed Source and I was lucky enough to work with a race engineer named Lars. Nic Jonsson drove the car and was able to provide the kind of feedback that Lars could actually work with. We took the car as far as we could with the springs/bars that were on it. The car was much more drivable, but still not doing its fair share of the work. At the end of the day, the bars and most of the shock settings, save the canister pressures, were maxed out. As per Lars’ suggestions, I have added a stiffer spring to the rear and bigger sways. We’ll see what happens as long as the good weather holds tomorrow. The car has a lot of oversteer on corner entry followed by understeer just before the apex. It is difficult to put power down after the apex because of oversteer again. I don’t have the skill I once had (or thought I had) to drive around those problems very effectively. My car only has a bolt-in roll bar, and, as such, the diagnosis is that chassis flex is most of the problem. We are trying to “stabilize the platform.” I will let you know the outcome. I suspect that my car is very different from yours. It is still somewhat of a street car with full factory exhaust, cats, mufflers and A/C. Lars wants me to reduce the weight in the back as he thinks that would help a lot. The idea of my car was to follow the philosophy of the 993 RS, a car that you could drive to the track and one that would perform competently there.

95m3racer,
It sounds like you have a lot more knowledge than I do about this stuff. I appreciate your insights. I have raced 993s on and off (mostly off) for about 8 years. I built a car similar to this one several years ago and am using my experience with that car as a starting point. That is how I picked the initial spring rates. In my case, I am trying to rely on the experts to help get the car to a place that fulfills my goal stated above – drive it to the track and have fun there. If I were being honest with myself, I would realize that a street car can never be a racecar and vice versa. In truth, I want a car that you can drive around town and one that kicks butt at the track. I guess that’s not going to happen. By the way, I know that wheel rate is a mathematical combination of spring rate and the lever that it acts through that is the geometry of the suspension, however, I have no idea how to calculate that nor what it would mean even if I did.

Chris and 95m3racer,
I don’t actually know what the canister pressure does. I thought that it was a semi-substitute method of increasing spring rate. I did try upping the pressure at the rear from 175 to 275, but it seemed to make the rear worse – not better.

Alan C.,

I think you're on to something. My initial spring rates were 900 and 1100. It is a long story, but the car was pretty perfect with that setup for one day. We made some changes when we switched tire brands and could never get back to the balance of that day. If I were smart and weren't so deep into this spring swapping thing I would go back to that setup and try to get it back to where it was.

I think that tomorrow, at a minimum, I’ll have another data point if nothing else and more things to try for the next test.

Thanks again to all,
Hank

George A

Hank,

I actually got the setup from Cervelli........... I drove an RSA with a similar setup that he did and fell in love. I have to say that in my brief outing in my car, it felt incredibly smooth. I was expecting bone jarring effect but there were none, it felt great. I actually couldn't get the smile off my face. The only problem I experienced was oversteer at exit, entry and apex were perfect. I just couldn’t get the power down. Everyone told me to soften the rear so I stiffened it up session after session (I've learned to do the opposite of what "they" say). Anyway, at the end of the day, the car was beautiful. I need to thank Chris for that.

I'm not sure what it will feel like with it lowered and properly aligned but if it's anything like it was before, I'll have a blast figuring it out. I tried to call Lex today to see what he would recommend about pressures but their phone system was messed up. I do remember him telling me that I should add 20 to 25psi more pressure because of the rates I was using but I don't recall a max.

Please do let me know what you find out tomorrow.

George

Hank Cohn

George,

Tell me a little about your car if you don't mind. Weight, items removed, roll cage/bar, etc.

Thanks,
Hank