im trying to decide which size rims i should get for my autocross/track car. either 15x7 or 16x7, and ive noticed most of you guys here prefer 15in. may i ask why?

 

cheaper & lighter

 

Smaller diameter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eee Pee &raquo;</TD></TR><TR><TD CLASS="quote">Smaller diameter.</TD></TR></TABLE>

not necessarily, overall diameter with tires are usually about the same

 

Do an internet search on rotational inertia or moment of intertia. Also, a 15" wheel and a 16" wheel can have the same OVERALL diameter and circumference (when including the tire) so that is not the answer. Hint: Deals with weight and where it is placed.

 

wouldnt larger wheels with thinner tires perform better ?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2*Integra &raquo;</TD></TR><TR><TD CLASS="quote">wouldnt larger wheels with thinner tires perform better ?</TD></TR></TABLE>

Nope

To answer your next question of 'why are 17+" wheels on racecars' its to clear big *** brakes.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">

...big *** brakes.</TD></TR></TABLE>

for lack of a better term

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2*Integra &raquo;</TD></TR><TR><TD CLASS="quote">.....and ive noticed most of you guys here prefer 15in.</TD></TR></TABLE>

Not all of us prefer 15in. Personally, I'm shopping for 13"

 

Sometimes, it's due to class specifications, based on who you're racing with. With IT in the SCCA, there are designated allowed rim diameters based on what came stock on the car.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">
To answer your next question of 'why are 17+" wheels on racecars' its to clear big *** brakes.</TD></TR></TABLE>

Or to satisfy a sponsor or spec tyre requirement.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2*Integra &raquo;</TD></TR><TR><TD CLASS="quote">im trying to decide which size rims i should get for my autocross/track car. either 15x7 or 16x7, and ive noticed most of you guys here prefer 15in. may i ask why?</TD></TR></TABLE>

"DC2*Integra," eh?

I don't race, I just drive on track. In my case, sticking w/15" wheels for the track has to do with the overall availability of tyres in the 205-50-15 and 225-45-15 sizes.

EVERYbody makes a good 205-50-15, and many of them in 225-45-15.

With the DC2 in 16" you'd end up shopping for weird sizes like 215-45-16 and 225-45-16 and your offset would be in the +45 range, right? I guess you could go for the cheaper 225-50-16 and then just manage the ride height.

But the overall availability and price of the 15" tyres just makes it a better choice for amateurs, IMHO.

 

You might wanna consider what tire you want to run, and how competitive you want to be. I for one ended up going with 16s because I'm in STS and the best tire currently is the Falken Azenis. Since they only have a 205 in 15s, I went with the 215/45/16. Of course my car really needs 235/245s, but that would be STX

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2*Integra &raquo;</TD></TR><TR><TD CLASS="quote">wouldnt larger wheels with thinner tires perform better ?</TD></TR></TABLE>

It depends. What are you actually doing with the car?

I am going to 16" (was considering 17") wheels because I can get more tire selection in that size. With a 15" wheel, you are severly limited in most tire width selections, unless you can use Hooseirs which come in a 225/45/15. But you honestly need at least a 8" wide rim to make those suckers work because they are sooo wide.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BlueR &raquo;</TD></TR><TR><TD CLASS="quote">cheaper & lighter</TD></TR></TABLE>

 

I wouldn't bank on the lighter in smaller wheels all the time. My freind is running 17" racing harts on his type R with khumo MX's mounted, a rota slipstream in 15" with azenis comes in just over 5.5 lbs heavier. Food for thought

 

I prefer my 14s over 15s.

Tires are cheaper. Rims are lighter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CRX-RX &raquo;</TD></TR><TR><TD CLASS="quote">I wouldn't bank on the lighter in smaller wheels all the time. My freind is running 17" racing harts on his type R with khumo MX's mounted, a rota slipstream in 15" with azenis comes in just over 5.5 lbs heavier. Food for thought </TD></TR></TABLE>

And uhhh, how much more do those 17 wheels and tires cost compared to the Rotas with 15" tires?

 

5.5lbs each wheel is 22 lbs of total rotating mass. But at least that 22 lbs is further away from the hub..

Do some acceleration testing, and I *garuntee* the lighter 15s win every time.

 

I started running 15's this year on my civic ex in hc due to the Kumho contingency and the lack of availability of 710s in 14" sizes. I prefer 15's over the 14's due to wheel availability and the fact that I believe the further you get your wheel away from your calipers, the more consistent your tire temps will be and the better your brakes will cool.

Also, I actually ran some 16" Konig Tuners, which weigh about 15 lbs each with kumho ecsta 205/45 16's for practice at a race weekend recently at Road Atlanta and to be honest my lap times were not much different from when I ran my 15 inch Kosei TS's (10.5lb wheels) with 225/45 hoosiers. Also, I actually liked the responsiveness of the lower profile tire, even though contact patch was not as wide. The overall diameter (and circumference) was exactly the same. In a pinch, I would not hesitate to run the 16's. As far as weight and rolling mass goes, if you get a 12 lb 16" wheel and a 10 lb 15" wheel, they will probably end up being the same weight once you mount the tire.

You are definitely right to question the masses in this department, but the main reason I run them is the fact that tire size availability is better with the 15's. Also 10 lb Kosei TS's are easy on the wallet.

 

Didn't see this but for Hondas more sizes in 15" performance tires are made than 16s.

If you are referring to autocross 205/50x15" fits much better than 215/45x16" Azenis. Plus it throws off the gearing and makes the car feel sluggish.

The other thing is 15" tires are cheaper than 16s and so are wheels.

 

I'm on 14's right now, they put me in STX this morning but I should of been in STS, I'm running a harder street tire (Falken Ziex 512's). I want to go with a 15" wheel, either a Falken or the Konig Heliums, because there is more tire selection. You can get a competition tire (either Khumo or Hoosier, don't remember) in a 205/55-14, but other than that I'm stuck with a 195/60-14.

 

15 is a good tire size for both R and street compounds, especially for lighter cars.

205/50/15, 225/50/15, 225/45/15 are all available in these sizes and at a significant discount compared to similar OD/tread width 16 and 17" tires.

azenis 205/50/15 ~$64/tire
azenis 215/45/16 ~$80-90/tire
azenis 225/45/17 ~$110/tire

BFG KA T/D 225/50/15 ~$135/tire
BFG KA T/D 225/45/17 ~$165/tire

and so on.

15's aren't as convenient for heavier A/X cars in street tire classes though, since i have yet to find the right compound in an acceptably wide TW in a 15" rim size for something as heavy as my prelude, with 225/50/15 BFG's being the only choice it seems. more importantly, azenis' only 15" size is a 205, and still grippier in that width than most others in a 225. the problem is, with other cars in the class running the same width tire with 200 lbs+ less weight to carry around, i am at a disadvantage. at this point i would consider a 16" or a 17" wheel so that i could run a 245/40/17 or even the 215/45/16 azenis, but to this point i am happy with my 15" wheels.

for road racing/r comp auto-x cars, considering how much cheaper r-comps are for 15" rims, and how many sizes are available in that size it's very popular.

 

I have a question along a similar line then.. obviously the move to a wider rim would mean that a wider tire could be used, but let's say you keep the same width of tire.. is there a difference moving from 15x6 -&gt;15x7 (besides weight)
I know that when selecting rim diameter, ideally you would choose the smallest size that fits over your brakes.. would it be the same for tires, you choose the skinnies rim to fit the width of choice?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sil &raquo;</TD></TR><TR><TD CLASS="quote">I have a question along a similar line then.. obviously the move to a wider rim would mean that a wider tire could be used, but let's say you keep the same width of tire.. is there a difference moving from 15x6 -&gt;15x7 (besides weight)
I know that when selecting rim diameter, ideally you would choose the smallest size that fits over your brakes.. would it be the same for tires, you choose the skinnies rim to fit the width of choice?</TD></TR></TABLE>

well, as a general rule, the wider the wheel the better, granted it's not too wide and you get that ugly VW stretch thing that's so popular with the "euro-scene."



(i love teasing the "kids on the short bus" over at the Vortex ...)

a 225 on an 8" wheel behaves much better than a 225 on a 7" wheel in terms of sidewall rigidity and response. but keep in mind that the increased weight of wider rim width will have an impact on your corner exits, so there is a happy medium somewhere.