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The TR6 Procedures Page - Maintained by J.B. Zimmerman - Content by the SOL!
You wrote:
> Hi,
Howdy.
> While changing the front bushings, and after reading Puhn's book "how
to
> make your car handle", I noticed that none of the front A-arms are
> parallell to the ground. Both upper and lower arms are pointing
to
> ground viewed from the pivoting points. According to the book, at
least
> one A-arm should be level, and so should the outer tie-rod, or at
least
> it should line up with the steering rack (On my car, the outer tie
rod
> is drooping). Theory aside, anyone knows what the proper set up for
a
> TR6 should be handlingwise, or anyone with experience in lowering
the
> front end? If so, with what effect?
A couple of notes...
Don't forget that the suspension reference in Puhn's book is for "loaded suspension". So, don't shorten things too much in there. The suspension component should be parellel when is has wieght on it... not when you have it up in the air!! And be careful that you don't make things so low that your roll center is below the ground!
Note that the standard height front springs need to be shorter if you go to a higher spring rate. I wouldn't screw around with the spring perches unless you really want to do a lot of calculating and then trial and error to make sure that things are okay.
FWIW, I know that folks do play with the rack mounts to eliminate bump steer effects - but I cannot offer any actual data.
In short, if you want to lower and you want to do the job right, then you need to calculate, you need to make changes and you need to make measurements (accurate measurements, no less) to see what effects the changes have on the process.
Now, don't get discouraged. Let me continue.
The easiest way to lower a car is to go with lower profile tires. With a TR6 and 225/45 tires, you lower the car by something like 1.5 inches. That's a lot, believe me. You didn't say how you intend to use your car, but in the 'States, using Hoosier DOT radials 225/45-15 will get you into the ballpark. I happen to use 225/55-15's and they lower the car a lot too, though not as much as the 45's.
If you are running slicks, a 9.0 X 23 - 15 is about equivalent to a 45 series tire (it's actually close to 47.5 profile, if memory serves, but check with a tire place).
> Remember to have read somewhere that the TR6 was raised in the front.
> There is supposed to be a tall shim in the suspension tower located
> above the spring. It seems that cutting down on that shim would lower
> the front. Anyone tried to do something to that shim?
Okay. The factory had "performance" springs available. The uncompressed height of the springs is considerably shorter than the stock spring. That fact, plus the fact that you can change the swivel brackets and other stuff up front means that in certain cases that if you unload the suspension, the spring could pop out. Also, if the spring was really short, you could have too much negative camber - hard to believe, but it is possible. Anyway, the spring spacers give you gross adjustment of the camber/castor range. But they also give you the possibility of jacking the corner weights around - if you get really serious, you may want to do this.
Now, I found from poking around that the Moss performance springs offer the best of both worlds. The spring is shorter (uncompressed) than stock and that with that spring and no spring pad bushings, you can easily dial in about 1 degree of negative camber on the fronts. Using the spacers for the brackets you can dial in more negative camber or even remove some. For the ultimate in adjustability, you can saw off the ends of the upper a-arms and weld in some threaded inserts and use heims joints to give you even more adjustment. Using this method, you can maintain the relationship between the upper and lower arm that the factory gave you but still get a bit more negative camber and if you play around enough you can add or remover positive castor (just make sure the castor is the same on both sides!
Moss has part numbers 670-138 (front) and 670-148 (rear) which I like a lot. Also, Richard Good's springs are he "correct height" to lower your R. Good also sells "stackable" spacers or different thickness.
Now the last word is: if you start playing with the suspension geometry, be prepared to spend a lot of time sorting things out. Give the folks that initially designed the things some credit - they most likely did a lot of work to get what's there. Remember that everything is a compromise, so if you tweek one thing, you will upset other things and you need to make consessions in order to get gains. And you should probably look around for some suspension analysis software to help you dial things in.
That is all.
rml
Bob Lang
TR6's
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