I'm sure this is common knowledge to most of you guys, but I just noticed, and thought it was interesting - you can buy an 07 RX8 6 speed with 16" wheels. Are these smaller wheels to the benefit or detriment of autocrossing in B Stock?

I see benefits like this;
lighter
cheaper tires
minutely improved acceleration
lower center of gravity when using low profile tires

disadvantages;
don't know width - probably not good (deal breaker)
top speed in all gears would be less

 

Not worth it, 16'' models have smaller brakes and that'll have more of a detrimental effect then any of the positives you mentioned.

 

That's the 6-speed auto. The 6-speed manual still comes standard with 18"x8" wheels, so you can't use the 16" wheels on a manual transmission car.

Not that you'd want them anyway...

 

Having the biggest brakes available isn't necessarily a benefit for autocross. Lots of CSP Miatas in the past have backdated to the smaller brakes that came standard on 1.6L cars in order to fit narrower offset 13" wheels. I'm sure the smaller brakes on the auto RX-8 would be fine for autocross, but the tradeoff of a narrower wheel, a lower output engine, and an automatic gearbox would all outweigh any positives you'd get from a lighter 16" wheel.

 

I think the point of information, in the first post, was that the '07 RX8 can be ordered 6spd/16" wheel combination (as opposed to past years)...which could be interesting. I'm guessing the 16" rim would be 7" width? I can't find any specs anywhere on that dimension...

 

And that point of information would be incorrect. The only '07 6-speed RX-8 available from the dealer with 16" wheels is still the auto. Download the '07 specs and features brochure and look for yourself, or call your local dealer if you don't believe me.

 

^I believe you

I just wasn't sure you had read the first post carefully, but obviously you had and are stating that the information given was incorrect!

 

It must be a mistake in Mazda's web site. If you build a RX8, choose TRIM=sport, and TRANSMISSION=6 Spd Manual, and then choose no options, you will be shown a picture of a RX8 with the 16" wheels. And if I search inventory for an RX8 just like this, it shows me several like this...

LINKY

Hmmm. Anyway, thought it was an interesting idea.

 

Just to continue with the specifics of the now-disproved initial scenario:

Brake fade generally isn't an issue in autocross, so I agree with altiain that smaller brakes would be beneficial due to lower rotating and unspring weight. However, if the rims are indeed 16" x 7", then the loss of an inch of rim width would impose far more of a penalty than the gains from lower weight.

 

Take your link and click on "print window sticker":

Exterior:
18-IN ALUMINUM ALLOY WHLS W/LOCKS
225/45R18 TIRES

 

talked to a guy at work who was looking at buying an RX8.....he went down to a dealer and then spoke to me the next day. He asked what options I havd on the car, and whether I bought the upgraded brake package. I asked him toclarify what he ment about by upgraded brakes...from discussing it further, I guess the salesman was tyring to convince him that the GT package gave him upgraded brakes...he was looking at the MT....I didn't think the MT came with the small wheels and brakes...this thread makes it clear that they dont.

 

More info abou the trim and wheels LINK.

Also JDM Option did a test on some cars and the 16" wheels where best for the RX-8 when it came to grip and drifting: "Anything over 17" in the rear causes camber issues, causing difficulty to drift".

 

why would 16" vs. 18" wheels have an effect on camber? the wheels don't have any camber built into them, heh...

 

yo yo yo, never attempt to understand drifter logic ...

 

Lol

 

If you have a car with 16" wheels and you change to 19" what do you think will happen?

 

Nothing will happen to camber as long as you retain the same diameter and width.

 

Odd I went from 16" to 18x8 and before I got a wheel alingment it was off

 

Then your alignment was off before you changed wheels.

I should clarify also -- there's nothing inherent to different wheel and tire sizes that would change camber, for that matter, but if a larger tire package interferes with your fenders or some other part of your car, you might have to adjust camber to compensate.

 

Even changing diameter and width won't have an effect unless you introduce a change of rake. Even that would be minimal. It might have some dynamic effects because of raising or lowering the roll center relative to the contact patch. That's why they invented slide rules.