4 replies to this topic

[bmarshall1]

I was talking to our local builder and asking if he could add the brace from the door bar to the rocker panel.  He stated he doesn't do them. I questioned why and he stated it's possible to get the car too stiff-  I asked him to expand further on that.

 

He stated one time he bought one of his old cars back and after prepping it he could not get it to handle.  After repeated attempts he realized the only difference was the additional cage bars giving additional stiffness.  He said he cut the bars out and viola', instantly better.  Sebring is our home track if that would make any difference.  

 

My friends car has the 'angle bar' from passenger footwell to rear section and the dash bar (under dash connecting side to side).  He recommended to cut those out.  Has anyone else experienced this? (mine has neither so to me it's a moot point)

I can conceive of the added flex of the body being beneficial, but always assumed stiffer = better.

 

Secondly, another racer I know wanted to put poly bushings on his Miata and I recommended against it as old bushings are stiff anyway.  I also recall reading somewhere (maybe here) that the rubber bushings give certain movement to the suspension for added stability (perhaps rear toe under cornering or braking, something like that).  In other words, does the additional compliance of rubber bushing help in any way or would the stiffness of poly be best.

 

I would also imagine in a small hit to the wheel the rubber would give maybe saving a bent control arm, plus the additional compliance of rubber would save some fatigue cracking after a while.

 

Lastly, once tightened, the rubber bushings act as torsion springs, how would eliminating this affect handling. Thoughts?

 

Has anyone tested both and what was the result I want to be right but have no way to back my claim.

 

This is more of a mental exercise than anything and trying to satisfy both my curiosity and theories.

 

 

 

[bmarshall1]

Come on, SOMEONE has to have some input on this, anyone? Satisfy my curiosity, unless it's a secret...

[Alberto]

I'm just another schmuck on the internet but I'm not buying the stiffness thing at all.  I've raced against plenty of SMs with the bars you seem to refer to and they handle just as well during the race.  Go somewhere else that focuses on Spec Miatas for that work.

 

Poly bushings are not allowed in SM but there is more compliance in the stock rubber bushings and I speculate that it will help in impacts.

[Michael Novak]

Cage--You need to talk to others but some parts might not be legal for the class And I would argue cage design is some of the reason why you pay race shops like East Street to cage/ or fully build a car for you. 

 

Bushings -- you have to use the Mazda version. It can be part of the tuning of the chassis but I believe most setup their cars in the neutral state--- car on ground sitting at correct level then tightening all of the alignment bushings. 

[TylerQuance]

Novak is spot-on for the bushings installation question. Using a rigid offset upper control arm bushing is one opportunity for us in SM to get rid of 4 rubber torsion springs. Allows you to run the car closer to level front & rear.

I can comment on the poly bushing question since it sounds like your friend is not using his car for SM. I agree with you, I would also advise against. Polyurethane is not a suitable material for sliding suspension bushings for a couple reasons:
1. Polyurethane has a slip-stick tendency where it wants to hold on to the steel sleeve until it starts moving, then it slides free. This causes unpredictable handling. You can grease them to remedy this, but polyurethane unfortunately is excellent at pushing the grease out. =mess.
2. Polyurethane is not strong enough a material to withstand high loads without breaking or deforming. E.g. Lower control arm bushings on a race car

Lots of poly out there because it's cheap to manufacture, but it's not good enough for race/track use.