TheOtherEric

Let the games begin! Now we have a genuine disagreement. Has anyone checked how the pressure changes when on the ground versus unloaded?


Could you elaborate on why "feel" has worked better? Are your adjustments having little effect on the graph? Do you prefer a setup having an asymmetrical graph? I'm contemplating adding position sensors just to experiment with.

Veloce Raptor

Correct. Or all wheels off the ground. But nothing in between. Pick one methodology and stick with it.

Larry Herman

I agree. I think that absolute numbers mean little. It is the relative pressure as compared to the current shock settings. I found that when I changed canister pressures on my Motons, everything changed (HSC, HSR & LSC), but to differing degrees. Right or wrong, I want to know what my pressures are with the car sitting on the suspension. I do not jack my car up to check the tire pressures either, though that probably makes little difference.


Oh yeah, how many of you set the canister pressures and tire pressures before you corner balance the car? Think about that.

Veloce Raptor

Yup, relative pressure. James Clay, who runs Bimmerworld's World Challenge program, checks canister pressures with the car up in the air, so I have adopted that method, but as you said only for relative pressures.

And yeah, when I have noticed a change in the performance of the car, that is when I have found one or more canisters have lost some pressure. Even 10-20 psi is noticeable!

Accelerator

[QUOTE=TheOtherEric;6302519]Let the games begin! Now we have a genuine disagreement. Has anyone checked how the pressure changes when on the ground versus unloaded?


this is a new set up for me but as best I remember when I checked it on the ground it was 20-30 lbs of increase. Lex at the Moton US distributorship just told me that I should take the weight off the dampers when measuring canister pressures. That's the end of the games for me and my set up.

Geoffrey

Doesn't everyone?

It's not like you can just plug in a computer and you get the perfect setup. As with most things, there has to be a deliberate approach about how you collect the data. I tend to look at the suspension histograms as a lap in total and then drill to individual corners if necessary. I have found that laps with different times and lines will produce different suspension histograms, so unless you are carefully collecting the data, it may not mean much. This means that when a change is made, you need to look at a lap time similar to before the change and yes, one click here or there will show up on the histogram. This includes high and low speed compression and rebound. If you adjust strictly by the histograms, you will end up with damper adjustments that are asymertircal corner to corner. I'm on the fence about what to think about that and have experimented both ways and keep comming back to an asymertrical setting. However, I don't know for sure if that is the right way to approach it. I've heard arguements both ways, but keep comming back to what the data shows and if asymentrical adjustments show a symetrical graph, then...If you don't have a data analysis software package like MoTeC, you will only get damper positions and depending on the level of math functions, you may or may not be able to calculate things like roll angle, roll rate, damper acceleration, etc. If your software cannot do that, then damper position sensors are probably a waste of time.

You cannot ignore the driver's setup preference which is why I say I go back to the "feel". For example, the driver can force a car to understeer or oversteer in the same corner just by where and when he turns it, so you have to take that into consideration.

Premier Motorsp

It does not matter how you check the damper pressure, as long as you do it same each time.

However, the damper pressure is critical to consider when you are figuring out which helper springs to use. The calculations obviously need to done with wheels on the ground.

In my experience the canisters never lose pressure unless there is an oil leak or an obvious nitrogen leak. The pressure changes with ambient temperature (especially if the canisters are mounted in the engine compartment). It is actually impossible to check the pressure without affecting it. Putting the gauge on causes a large pressure loss. You can set the pressure with the gauge on, but that is the only time you will see the actual pressure.

In my opinion, the canister pressure itself has next to no influence on tuning. The canister pressure's interaction with the spring(s) may or may not have an effect on tuning. The nitrogen acts as an additional spring that is helping the other spring(s) hold the car up. The force the nitrogen spring exerts is small compared to the rate of a main spring, but it is significant compared to the rate of a helper spring. The spring rate of the nitrogen spring is strongly progressive as well.

Chris Cervelli
Spline Technologies

Veloce Raptor

Right or wrong, the rule of thumb I have used is to assume I am losing 10 psi every time I check the pressures. Thus, when I add N, I add an indicated 10 psi extra in order to get my desired target pressures.

wanna911

This is starting to sound like a maintenance headache. How do you add and remove pressure from the cannisters and how often do you have to do it?

PatK-Mpls

Rebound tends to control roll more. Similar to bump, the less rebound the more grip and the more roll - also the slower the car is to transition. The more rebound, the more platform and less grip.

Rebound also does other less obvious things. For example, if you want more early turn into mid turn front end bite you can run higher front rebound. It works as follows: When you come into a corner and brake hard the front end will compress (via bump). If the rebound is high the front end effectively gets strapped down for a bit giving more front end grip.

Veloce Raptor

It's not, but it helps to buy a N canister/regulator, or have a friend with one!

Accelerator

[QUOTE=Larry Herman


Oh yeah, how many of you set the canister pressures and tire pressures before you corner balance the car? Think about that.[/QUOTE]

I would expect the answer would be all of we who understand the importance of same.

Accelerator

[QUOTE=Geoffrey;6303061] If you adjust strictly by the histograms, you will end up with damper adjustments that are asymertircal corner to corner. I'm on the fence about what to think about that and have experimented both ways and keep comming back to an asymertrical setting. However, I don't know for sure if that is the right way to approach it. I've heard arguements both ways, but keep comming back to what the data shows and if asymentrical adjustments show a symetrical......

Could the rightness of the asymetry have something to do with the left-side weight and the cross-weighting of your car? Most of us aren't ideal in that arena and asymetry would make a lot of sense if there were some wedge or lack thereof.

wanna911

Good stuff, makes sense.

Seems like it would help trail braking as well. In a car that power understeers like mine, all the front grip you can get is always helpful.

Accelerator

+1. A great point that should be understood by all. Took me a while to really get it. Too little rebound makes for a sloppy transition into the corner. Too much rebound will jack it down and the ride will get a bit harsh (straps it down a bit too long) which is also uncomfortable.