Any rules of thumb to follow when adjusting height & dampers?

[vodka]

Hi all,

I just install the SPAX RSX 580 on my 2004 MINI ONE. This kit offer 28 stages of dampers adjustment and maximun lowering is 320 (F)/325 (R) mm, minimun lowering 340(F)/340(R) mm - http://www.spaxperformance.com/owner...ndbook-580.pdf

Is there any rule of thumb to follow when lowering the car? For example, the front should be lower than rear by x mm or both font and rear should be lowered at same height? How about the dampers setting? Front softer than rear or both should be the same?

Currently the car is lowered at 330(F)/335(R) mm and the dampers setting is 6(F) / 15 (R) click/stages. It seem like rear is stiffer than the front, all this setting is given by the mechanic. Please help/teach me to find the best combination. I'm looking for comfort and once a while drive, cornering hard.

Sorry if the question is being asked before, newbies here

Thank you very much

[meb]

The answer to that question can fill a text book.

Things affected:

Center of gravity - lower is better but comes with some trade-offs...

Roll center hieght - mini's rear RC is 50mm higher than the front in stock form. A higher RC height relative to the height of the Center of Gravity will load the tires more quickly but with less wieght - think transient. A lower RC height relative to C of G will load the tires more progressively but with more ultimate weight - think steady state. I higher rear RC will make the mini turn in faster.

Instant Centers - defines the arc the suspension moves thru and this affects the next line below...

LCA orientation (Mac Strut end) - possible scrub problems in bound and rebound, camber compensation etc. LCA should basically be parallel to avoid scrub problems. This by itself will determine front ride height...then the back if you retain the 50mm difference.


There is more...

[andyroo]

meb have you plotted or seen the cog and roll centers plotted?

i'd be interested in having a look.

[meb]

I had several conversations with the fellow heading suspension design and development for BMW when they owned Rover...he no longer works for BMW. The Mini was under his watch.

I was given some information but anything else I asked for is considered a secret, seriously.

I'll post what I have tomorrow. I was looking for C of G hieghts and all went quiet...unfortunately, those are the most ellusive elements. I discussed the stock LCA bushing, the electronic steering pump and a few other details about theory but nothing major. We shared a few anecdotal stories about track time and racing...he owns a nicely set up Lotus - didn't say which one...

[andyroo]

I'll take anything you got. PM is fine too.

Was bump travel confirmed to be something like 2.5 inmches at stock ride height?

Thanks!

- Andrew

[meb]

Yes, in front...but remember that the mini is a bumpstop active car...the bumpstops make the suspension progressive even if linear springs are installed. There is tuning potential in those bumpstops - IMO

[andyroo]

Yup...and that's one reason why lowering the car on stock struts is absolutely nuts IMO. It seems like a lot of cars are going that way these days. My company's new springs for STI lower the car just 5mm, but with a substantial increase in spring rate and shortened bumpstops....they rock. Otherwise they'd suck. The valving is quite good on that car though (finally).

I agree you can find some potential in the bumpstops, but it sure is a lot easier to tune if you're staying off them. With the stock struts your bump travel limited, so you could run high spring rates (and shortened bumpstops)....but the struts probably can't handle it.

Sorry for hijacking the original post!

- drew

[andyroo]

To the OP....i would start by dropping the front and rear the same amount. A milder drop is probably a better idea, but it depends on your spring rates and you can alter the balance of the car by lowering the front and rear different amounts. Good if you know what your doing, but a simple 1 inch drop is probably a nice starting point.

For damper settings, i would start at full soft and go up until you find a setting that doesn't crash over bumps and that is comfortable. Do this separately for front and rear. Don't try and alter the balance of the car with the damper settings yet....they can help corner entry and corner exit, but in a steady state turn, the damper does not affect balance.

Remember that a super stiff feeling car doesn't necessarily mean it's handling better. For a lot of good coilovers I use, the street setting isn't far off of the track setting. The stiffness of the valving also doesn't affect how much body roll you have, just how quick the car rolls. Body roll is from springs and swaybars

- Andrew