Suspension opinions needed - race ht SC

MJM911SC · 02-22-2005, 06:07 PM

I am trying to nail down the ride height and corner balance on my car and I am having a little controversy with my mechanic friend.

Specs - 1982 911 SC track car 2450lbs race load with driver and gas. Trying to finish this project (diet and body+paint) and this is the finishing touch. Pictures to follow this weekend.

Corner balance comes in pretty good (within 8 lbs of ideal per Thom's spreadsheet), but to me the balance could be a bit better and the ride height is off (rear too high).

Here are the numbers:
LF 24.5" 460lbs
RF 24.5" 450lbs
LR 25" 800lbs
RR 25" 740lbs

Questions:
1. What will happen to the balance if I lower the rear? Will that move weight forward?
2. How will the car handle with more rake, higher than spec rear?
3. Remind me the rule of thumb for moving weight around, for example if you lower the LR, it will lower the LR weight and raise RF weight, etc.

I did a decent search and answered most of my questions, except the ones above. Thanks in advance for the help.

ipapilot · 02-22-2005, 06:43 PM

Mike, i think you have the relationship backwards on weight transfer. For example, raise the right rear and it increases weight on the left front. At 2450 race weight, you must be on the rigth track for lightening! Are you planning on doing PCA stuff or with another club?

dickster · 02-22-2005, 11:38 PM

i dont know the answer to the rake but believe that the setting is important. mine is in the shop at the mo being setup and they have asked me to change my front tyres sooner than expected because if i waited and changed them further down the line it would mess up the rake they had set (new tyes have lower profile).

i didnt realise it was THAT important.

IROC · IROC's Garage

Lowering the rear will not "move" weight anywhere as obviously the F/R distribution is set by the configuration of the car (CG location relative to the centerlines of the wheels). You can lower the rear as much as you like, but what you'll have to do is play with the left/right distribution to get back to the corner balance you desire.

I am of the belief that rake isn't that important. Until I went to massive tires in the rear, I had my car set up with little or no rake and it was great. I've known mechanics who set up cars this way (little or no rake) also.

Also, within 8lbs is great. Go drive it around the block and put it on the scales again and it'll change anyway...

Mike

dickster · 02-23-2005, 04:08 AM

mike

but lowering front/rear does alter the f/r weight distribution.

IROC · IROC's Garage

Quote:

Originally posted by dickster
mike

but lowering front/rear does alter the f/r weight distribution.

You're probably right, but I don't understand why. I've done lots of corner balancing, but mostly just went through the motions without doing a rigorous examination of what I was doing.

Crap, now you've got me thinking and that's a dangerous thing... :>)

Mike

Wil Ferch · 02-23-2005, 05:31 AM

Raising one corner will increase that corner's "weight" ...as well as the opposite diagonal.

Any *two adjacent* wheels will ALWAYS stay yhe same ( combined) weight...no matter what you do ( example...total of LF+LR...or LF+RF....or RF+RR...or LR+RR).

also...short form for proper corner balance...LF/LR should = RF/RR.

If you wish...do a search on Chuck Mooreland or my name ( especially on those threads we engaged together)....for more details.

Wil

Bill Verburg · Bill Verburg's Garage

Quote:

What will happen to the balance if I lower the rear? Will that move weight forward?

The weight doesn't actually move, but the normal static component acting through the rear wheels will increase when the rear is lowered. Dynamicly there will be less forward weight transfer during braking(you will want more rear bias) and there will be more rear weight transfer during acceleration. Aero will be FUBAR w/ more lift at the front and rear.

Quote:

How will the car handle with more rake, higher than spec rear?

w/ the posted #s you have a little bit of forward rake, which is good for static and dynamic weight as well as aero considerations, a little more forward rake to a point will improve these #s, but there is a point beyond which strange things will happen. stay w/ the #s you have.

stlrj · 10:11 AM

Quote:

How will the car handle with more rake, higher than spec rear

If you lower the front it will thow your alignment further out of spec which would be detrimental to handling depending how far out wack you go.

You might ask yourself how much front end push can you tolerate? Bumpsteer? Ride harshness? How much do you enjoy bottoming out?

If none of this is an issue then by all means...

Cheers,

Joe