The Ultimate Street & Track Torsion Bars, Shocks, Bushings and Ride Quality Thread

[oh snap]

Originally Posted by panzerfaust

im very interested what you will end up with. my lighten and stiff m491 is pretty understeery with 225f 245r. i have to confirm what TB's are in the car. the dampers were revalved much stiffer at the bilstein at there place in SD according to the build sheet.

be wary with guys with normal narrow body cars. there geometry are different and dont have the added anti dive in front giving it unersteer. rear pick up points are relocated too.

perhaps chasing a 930 set up would be more appropriate for m491 cars? i driven my buddies 930 with full on elephant set up with ASP and it drives like no other G bod 911. it makes my old 930 seem like a lazy sloth. the kicker is his car is maxed out on TB and tire size but rides much much better than my two factory wide bodies with softer TB's.

my personal opinion is dampers are often overlook compared to the attention given to TB's and bars selection. the digressive valving seem to work pretty well but proper 2 or 3 way dampers may be the way to go though they are $$$$. my penskes dampers on my racecar was 6k for a set :-(

in my experience dampers have a much larger effect on ride quality than springs rates for those of us trying to build a DE street car. 3 ways would help a lot since u can tune the hi and low speed frequency separately. kinda like having your cake and eating it too. what you probably dont want to hear is race type dampers with there precise valving need frequent servicing.

cheers

Interesting points. I assumed the spring rate changes on the 930 was due to the added weight over the rear. The front to rear ratio of 21/30 is close to the stock 930 ratio though. Does the M491 have anti-dive? What does it look like? If its thicker spacers in the front a-arm mounts mine look like the normal 911 ones.

Ill post in here when I get the car back together. When I get to do some DEs it will probably be with a friend who races a 996 GT3R so Ill let him take it for a lap or two and see what he thinks. His opinion will be more valuable than mine.

[tshebib]

Another point we need to discuss is how spring rates differ using Rebel or Elephant poly-bronze bushing versus rubber bushings. My car has rebel bushings with 31mm T-bars in the rear and a similar car (both of us have 3.6l) here at the local track has 28mm rear T-bars with rubber bushings. My rear compresses more than his (that sounds weird ). Point is, it would be nice if there were some real numbers with regards to effective spring rate using different bushings.

[panzerfaust]

M491 chassis is same as 930 sans the tie rods. Im not sure what the ratios are between the narrow bodies vs 930 from the top of my head. The geometry in front is pretty much invisible since most of the parts are the same. Its how the A-arms are mounted to a different front pan that truncates the leverage reaction to the CG. A clue is that the steering rack is closer to the sheet metal pan than the NB were it prevents u from running a large spacer to help with bumpsteer.

For most part I agree with most people here that the stock set up bias towards the safe side for I feel the 930 has even more of an understeer than NB unless u keep your foot in it for some intended hooliganism. This may be due to the anti dive and increase scrub radius over the NB.

How you set up your car is mostly preference and how you intend to use it. If u autox, set the thing up loose unless you like to be spanked repeatedly by a stock miata. Javadog makes a great point. I find entering a corner at over 75-85mph the car turns in much much nicer with heavy areo influence at the rear and less scrub radius effect. Remember turn 8 turn in point at willow springs is 110-115mph. Its REALLY hairy flat tracking around it with your elbows flying around. fun as hell but with successive laps your tires will feel greasy. Its a true widow maker of a corner!

Jack enters at 131mph! he passed by me like I was painted on the tarmac…
Bobby Cee's Racer's Edge: Driving School: The Track

my 2cents pf

[glennmathias]

I have the same car, but I have coilovers in the rear. The car is a point A to point A street fun rod.

I just went from 22mm front torsion and 250lbs/in rear to 22mm front and 300lbs/in rear. I have Bilstein Sports in all fours and OEM sway bars.

I think that the 250lbs/in spring rate in the rear was too soft. When I went around corners, I would have to slow down because the inside of the nose was lifting up. When I went to 300lbs/in springs in the rear, the car felt more neutral. I could accelerate thru corners, and the nose was staying more planted.

250lbs/in ~ 29mm torsion bar
300lbs/in ~ 30mm torsion bar

Hence, I have 22mm front and (sorta) 30mm rear. I think it is awesome. Very little body roll and very neutral. Some bumps are tough, but I think I still need to revalve the struts, replace bushings, and raise my spindles to fix that issue.

Glenn