33 replies to this topic

[James York]

With regards to Sean's comment on spacers, I'm having a little dejavu...didn't this assertion get disputed? GCR says if spacers are used they have to be equal per axle. Is axle the correct terminology here or should it be hub? If you cant run different offset wheels to stagger or square the car, why would you be able to do it with spacers...what am I missing? If running 30mm up front(and 30mm in rear) with 7mm spacers squares the car, would only seem logical you would be able to do the same with different offset wheels if that was the goal? My point being I didn't think you can only run 2 spacers?

Yes you can run just two spacers...... on the same axle. You can run 0, 2 or 4 spacers (not 3, not 1), and pairs must measure the same on an axle. And you can't add up to a total offset of more than what a 25 mm offset wheel would provide for track. Pretty simple.

[DrDomm]

Ahhh. Cool.

[Ron Alan]

Yes you can run just two spacers...... on the same axle. You can run 0, 2 or 4 spacers (not 3, not 1), and pairs must measure the same on an axle. And you can't add up to a total offset of more than what a 25 mm offset wheel would provide for track. Pretty simple.

Certainly don't dispute this as it does say axle...I guess i never associate a Miata with having axles(or axle) in the front. But I guess then I just wonder about the logic of not being able to run different offset wheels on different axles?

How you explained it above would be very clear if it was written that way in the GCR!

[James York]

Ron,

Maybe I need to lobby for a job on the SMAC! lol. Or the GCR editor..

[davew]

According to the GCR " All four wheels must be the same dimension including offset." and "If spacers are used they shall be no greater than 13mm and equal per axle."

Someplace along the wat the requirement for only a single spacer per wheel has been lost. SMAC?????

The purpose is to eliminate an offset car by putting a bunch of spacer on one side and a low offset wheel on the other side. Still creating the same total track, just not centered on the car.

Dave

[Bench Racer]

Might the intent be of the words "per axle" (Glossary axle shaft)be as one front axle & one rear axle.

Yup, I know what I can do with the word intent.

[DrDomm]

I've created a monster.

[Ron Alan]

Well, with a little help, I figured out track width. Man was I confused(and wrong!)! Maybe the spacer thing can be written more clearly?

[jpsomner]

Mazda built the Miata from the factory with the rear track wider than the front track to induce understeer so that when Grandma on the road panics and hits the brakes the car will push instead of spin. If you go with 25mm offset wheels all around then you are just making the situation the same but wider. I personally like to "square" up the car so that the front and rear track is the same (perfectly legal with spacers), or in some cases make the front wider so that it turns in better. If you go with 25's then legally you can not do this.

There are numerous theories on this and it is up to each driver and their preference, but the bottom line is that spacers are tuning aids. Just like air pressure and bar changes and ride height etc, etc, etc. Spacers as tuning aids are not going to be noticed by everyone, especially if they are not doing the prep needed to run up front. For my cars, they get a complete set up every race and in most cases differently for every track we run. With wheel spacers we can make minor adjustments easily and at least start life with a square chassis.

As with everything in SM, ask lots of questions, use common sense and logic and do what you think makes sense, not what someone on an internet forum tells you to do. If you are just starting out I highly suggest getting all of your wheels with the same offset so that there are no surprises in tech if you have a crew member accidentally grab the wrong wheel in a hurry.

Keep in mind as well that many wheels only come in (1) offset, so you might not be able to get the offset you want with every wheel design.

Thanks...... Sean

 

Hi, 

 

Running 25mm offsets, what size spacers up front are required to square the chassis?

 

Thanks.

[Glenn Davis]

Hi, 

 

Running 25mm offsets, what size spacers up front are required to square the chassis?

 

Thanks.

If you are at 25mm already, no spacers can be used.  Spacers can only be used to get you to 25mm.

[Ron Alan]

There are track width #'s in the GCR you can look up. By memory I believe the rear is 10mm wider(factory)

[Alberto]

What Ron said

 

Linky:

http://www.scca.com/...t.cfm?cid=44472

[Johnny D]

 

http://www.youtube.c...h?v=YHh3DN1EZW4

 

J~

[Kyle Disque]

To address the Don's original question, the tool you would use to measure track (which Jim described) is called a trammel.

 

It's a long tube with "L" shaped points mounted to sliders with lock knobs to secure it.  You put one tip of the "L" against the inside of one wheel at the center (height wise) and you adjust the slider until the other is just touching the outside of the other wheel.  Toe affects this measurement, so you have to either compensate for that mathematically or you have to zero the toe before you measure track or measure both the front and back sides of the wheel and average (assuming you can get to both sides).

 

You don't see trammels like this for sale often.  I made mine.  They are also useful for measuring wheelbase.  In a GT car, all of this is adjustable, and thus needs to be set as a part of the setup.

 

If I'm not explaining myself well, let me know and I'll take a picture of one and post it here.

 

-Kyle