23 replies to this topic

[pat slattery]

All cars 1990-1997 are permitted to use the “R” model tie rod ends part # N021-32-280A

Is this an advantage to put these on and why? How do I know if I already have them on my 92 car?

Thanks

Pat

[Bruce Wilson]

Probably not a disadvantage as it should help with the bumpsteer we get from lowering our cars so much. We're probably talking less than a 10th of a second on a really long track, so the advantage would get lost in the noise of minute (or not so minute) mistakes we all make during a given lap. The question is, are they worth 90 bucks or would I be better off spending that on more tires...

-bw

[john mueller]

The question is, are they worth 90 bucks or would I be better off spending that on more tires...

!!!! +1 !!!!

[Brandon]

The question is, are they worth 90 bucks or would I be better off spending that on more tires...

Or if you're already dealing with busted seals and all (along with bent tie rods, loose control arms....yeah, I managed to find some walls in 2010...)

[Bench Racer]

Pat, this is not aimed at you.

I really get a kick out of all this bump steer chatting. Shim it down, shim it up, shim it sideways, shim, shim, shim. Or spacer, which ever turns you on.

Everyone talks, but to date I've seen NO ONE post any numbers.

YES, as soon as it friken warms a bit I'm going to measure the bump steer on my 1990. For $60.00 I can fab my own 2 dial indicator bump steer gauge rather than buy one for $200.00

[Brandon]

YES, as soon as it friken warms a bit I'm going to measure the bump steer on my 1990. For $60.00 I can fab my own 2 dial indicator bump steer gauge rather than buy one for $200.00

It warm up there in Cheese-ville yet?

I'm curious to learn/know if there's much, if any difference. Don't forget to include how thick of a shim/spacer you use (I think the rule allows up to 12MM/half-inch) to achieve this mythical "zero bump-steer" scenario.

Thanks for the work David!
Brandon

[Bench Racer]

It warm up there in Cheese-ville yet?

Brandon, at the moment it's 34*.

Since my post a knowledgeable source (car builder/renter/sales org) made a comment that the 99 chassis is more about change of suspension pickup point locations/roll centers than bump steer. As the cheese thaws I will get to the bump steer.

[Qik Nip]

It warm up there in Cheese-ville yet?

I'm curious to learn/know if there's much, if any difference. Don't forget to include how thick of a shim/spacer you use (I think the rule allows up to 12MM/half-inch) to achieve this mythical "zero bump-steer" scenario.

Thanks for the work David!
Brandon

Brandon
I can tell you is that 1/2" will not offset all of the inclination of the tie rods. I'd guess that to do so will require the 1/2" of shimming plus the R tie rod ends.
Rick

[Brandon]

Brandon
I can tell you is that 1/2" will not offset all of the inclination of the tie rods. I'd guess that to do so will require the 1/2" of shimming plus the R tie rod ends.
Rick

Oh, right, of course. I wasn't implying the shim alone would eliminate bump-steer. I understood the rule to be such that shims are only allowed with the use of the R-package tie rod ends. No updated tie rod ends == no shims (whether they were useful or not).

Thanks!

[Motor City Hamilton]

It warm up there in Cheese-ville yet?

I'm curious to learn/know if there's much, if any difference. Don't forget to include how thick of a shim/spacer you use (I think the rule allows up to 12MM/half-inch) to achieve this mythical "zero bump-steer" scenario.

Thanks for the work David!
Brandon

I didn't see this 12MM/half inch spacer allowed in the SCCA rules. I am changing to the R-tie rods, but I don't think I am allowed to also shim the rod ends? Can someone please clarify for SCCA?

[Brandon]

The shims aren't for the tie rod ends themselves but rather to put the rack a few MM's away from the subframe.

After having my car setup for the first event I can see where/how the R-pack ends "might" be beneficial as my tie rods were angling ever-so-slightly upward from the rack.

And seeing this, I believe the shims are to ensure there isn't a chance of bind of the tie rod itself on the rack as the spindle/knuckle rotates through its range of motion.

But what do I know? I just put new boots on my ends and kept the R-pack ones in their baggies...

[Motor City Hamilton]

The shims aren't for the tie rod ends themselves but rather to put the rack a few MM's away from the subframe.

After having my car setup for the first event I can see where/how the R-pack ends "might" be beneficial as my tie rods were angling ever-so-slightly upward from the rack.

And seeing this, I believe the shims are to ensure there isn't a chance of bind of the tie rod itself on the rack as the spindle/knuckle rotates through its range of motion.

But what do I know? I just put new boots on my ends and kept the R-pack ones in their baggies...

I didn't see that in the GCR either. Just want to make sure that I didn't overlook a valuable tune.

[Brandon]

Oh! I see what you were driving (heh) at.

No, I don't/didn't see it in the GCR either but it may be due to a delay in getting various fast track updates incorporated.
You may have to go digging into the 2011 FT releases for the specifics on what's allowed.

My "quotations" earlier in the thread were from memory only and not a reference back to any specific rule(s).

I'm surprised we haven't heard from either a DaveW or a MCollins yet on it with chapter/verse.

[Bench Racer]

I'm surprised we haven't heard from either a DaveW or a MCollins yet on it with chapter/verse.

How about a note of legality from David D.

From SCCA June Fastrack Prelim minutes for 2011.

Spec Miata:

2. #4676 (Larry Mendez) Steering Rack Shim question
Shimming of the steering rack is not permitted. The rule is correct as written.

[Brandon]

Dave D works too. *thumbs up*

Does your reference cite a specific rule or FT update Mr. Mendez was writing in about?
I think that's where MCH & I are a bit lost.

Thanks!

[dmathias]

Hmmmmmmmm, not permitted eh. I'm gonna have to look under Deerwester's car this weekend - I'm smelling protest!

[Bench Racer]

Does your reference cite a specific rule or FT update Mr. Mendez was writing in about?
Thanks!

What you see is what there was.

[Motor City Hamilton]

I have read and re-read the GCR and Fastracks back to January of 2010. I race against Mathias and he has a stack of protest papers hanging from his rear view mirror just to remind us to be law abiding citizens. Just wanted to make sure I didn't miss anything.

[dmathias]

Keith, you know I'm not the GCR cop - just giving Rick some crap.

I'm with David D. No one has presented any real data regarding shimming the rack. Must be another 'gray area secret'.

[davew]

Some of this is first hand knowledge some is conjecture.

A couple years ago when I was on the SMAC, we concluded that the R Model tie rod ends where legal for all Spec Miatas.

From GCR "n. All cars 1990-1997 are permitted to use the “R” model tie rod ends part # N021-32-280A." So legally 99+ are not allowed the R-model tie rod ends. Jim, Mike etc, is this what we wanted? I thought we approved it for all years??????

The R-model car ran Bilstein shocks and had lowering springs from the factory. The designers made the stud slightly longer to help with bump steer. This has been a very common Showroom Stock "upgrade".

The SMAC considered, but never approved the shim under the steering rack. We did not feel there was any need for it. Since according to everyone that sent letters to the CRB (concerning crossmember updates) stated that the 1.6 cars where the best handling cars and did not need help in that department. And, we had just allowed the 94-97 cars to use the 1.6 sway bar.

NASA decided to allow a rack shim. I can not say if they did any testing or just pulled it out of thin air (like their weight and plate choices for 99s). To the best of my knowledge, noone is selling these shims, so my GUESS would be that no testing was done. Since I have plenty of races in my area with Regionals, Nationals, Midwestern Council and the occasional vintage event, I do not particpate with NASA. So I have no reason to investigate the rack shim.


Bump steer is effected by camber, caster and toe settings. So bump steer should be measured and adjusted at every allignment. Just saying you need a shim "this" thick will not do you any good. Even setting it once and forgetting about it is not a good idea. On the Trans-Am cars, we adjust bump steer with machined washers that are 0.015" thick.

My 2 cents
Dave