What now? Go to 14" / 15" or keep are 13" wheels?!?

[cpa7man]

I'm sure most of you have seen the new FastrackNews for November. Were now free to go to 14x7 or 15X7 in our ITA first gens. I'm just curious as to what all you guys are thinking about this.

I'm not sure if I should call a Panasport dealer right now or see what happens next year.

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Paul Pineider
ITA 05 (Soudiv)



[This message has been edited by cpa7man (edited October 05, 2004).]

[dickita15]

I would rather buy 15 x 6's and move to ITB

seriously in the front it would allow thicker turn in spacers like the one susko sells for E Prod, but in the rear I am not sure i could get the car back dow to preferred ride height.

dick

[titanium]

Originally posted by dickita15:
but in the rear I am not sure i could get the car back dow to preferred ride height.

dick

If you are currently running a 205/60-13, in a Kumho, it has a diameter of 22.3 unshaven. If you change to a 205/50-15, the diameter increases to 22.8 inches.
That 1/2 inch difference in diameter will raise the car just 1/4 of an inch.
Tire Rack has all the dimensions on their site.
FYI: They have a 225/45-15 available also at the 22.8 diameter.
*************************************
Rodney Williamson
#93 IT7
www.titaniummotorsports.com (http://www.titaniummotorsports.com)

[mustanghammer]

I would rather buy 15 x 6's and move to ITB

I second that thought, Dick.

It seems to me that the issue of Diameter and Width needs to be considered. There are some 14 and 15 tires with some meat on them but will they fit?

It looks like there may be some rules relief in regards to fitting larger wheels. See the Fastrack discussion.





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Scott Peterson
KC Region
IT7 #17

[Mike Cox]

The major problem I am finding is the offset. According to Tire Rack the offset on their 15" x 7" K-1 wheel is 4.65". This creates a major inner clearance problem. The only way to run these wheels are with a 1/2" to 5/8" spacer to clear the spring.

Diamond does not offer a 14" x 7" wheel in the right bolt pattern or a 15" x 7" at all.

5/8" inch spacer means longer studs and a safer condition? I'm not so sure thats the right way to go.

Plus according to them, the K-1 weighs 14 lbs.

[This message has been edited by Mike Cox (edited October 05, 2004).]

[lateapex911]

Well, thats the other side of it, isn't it? The 15" wheel weighs 14 pounds, but a 13" Panasport or Revolution weighs about 10-11. Run a higher aspect ratio tire on the bigger rim, and save....?

In the end, I think the net/net is the 13" combo is lighter.

Also, here's another height comparo.

225/50/13 = 21.8" dia., tread of 8.2"
225/45/15 = 22.8" dia., tread of 8.6"

So, 1/2" higher, and 4" or so circumference (gearing) change, but you get a wider tread by 1/2"......

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[dyoungre]

Wider IS better - but you can also increase the tire contact patch area by going to a larger diameter, which also improves feel at the limit (longer path to maximize slip angle, so more gradual break - away). My personal choice will be to stay with 13" so long as competitive tires are available; Suspension travel is a good thing - and maximized with the smallest tire diameter. There sure are a lot of different things to think about (including Dick's front suspension comment, weight, etc etc)

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Dave Youngren
NER ITA RX7 #61

[Greg Gauper]

Then again there is a reason last year's E-prod national champ (Brakke) ran 13" rims on his Miata instead of 15", and why there was a mad rush amongst most front runners this year to have custom 13" rims made to fit (requires forged centers w/spun rims in order to clear the brakes)......

They wouldn't waste the money at the top national level if it wasn't faster!!!!!!!!

[JeffYoung]

Guys, I'm in same boat as you all so I'd like to participate in this one. I have an ITS car with 13" rims, Panasports that I spent a LOT of money on.

I also have gearing issues in that any taller gearing is bad for me, so I plan on staying with the 13s for now.

But, I am thinking about getting a set of 15X7s for fairly cheap to use as rains. My thoughts/questions:

1. Taller aspect means taller gear which is probably beter in the rain right?

2. What decent and cheap 15X7s are out there right now?

Thanks guys.

Jeff

[MaxEnergy]

A month ago I got a set of the Kosei K-1 for $89 each from tirerack, they are +38 offset which requires spacers up front but they are under 14lbs. The Rx-7 convertible rims are under 12 lbs but they are only 6.5" wide. I'm not sure how the 225s would perform on them.

[Greg Amy]

<font face=\"Verdana, Arial\" size=\"2\">What decent and cheap 15X7s are out there right now?</font>

A LOT! Spec Miata runs 15x7 wheels with a 13-pound minimum weight. Given the alrge numbers of those little snots out there, several companies are catering tho their needs...

Search out the guys selling to SM jelly beans and you'll find some good bargains.

[gran racing]

I've been giving this option some thought as well. Unfortunately the 13" rims I bought do not fit with my current studs. And with my car, it is a real pain in the butt to put new longer ones in.

With Hoosiers, the tires that would work for my car actually have the same overall diamater for 13" and 14" tires.

Here is my other thought though. Tire cost. The 13" tires are cheaper then the 14" (don't have the exact prices in front of me) but enough that after a season it starts adding up. Before buying the 13" rims, I even contacted Hoosier to get a feel for what their sales volume is like in the 13" size. I could just see them starting to discontinue 13" tires as soon as I bought the rims. Yes I know, this may be a bit strange but I did it anyways. According to them, they have no concerns.

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Dave Gran
NER ITB #13
'87 Honda Prelude si

[Banzai240]

Interesting discussion guys...

Funny, while this rule was created with the intent to allow everyone the same options, it kind of looks like the real benneficiaries are going to be those running 13x7 or 14x7" wheels...

Those of you on 13 or 14x6's sound like you are already pretty happy with what you have.

Either way, the option is open for everyone.

I'm pretty sure that, had we passed this rule with 7" rims allowed in ITB/C, this discussion would likely be much different!

I'm equally certain, however, that a lot of you would be really pissed off at having to go buy new wheels just to keep up with those that opted for the wider widths...

Hopefully, most are happy with this rule the way it was implemented. Feedback, as always, is encouraged...

Enjoy!


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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
http://home.comcast.net/~djjordan/Web/DJ_AV1.jpg

[dyoungre]

Darin,
Yup, happy with the rule, as written. The rule allows old(er) cars with old(er) technology to keep racing AFFORDABLY without having to mothball a perfectly good race-prepped car. I believe it was a smart way to avoid the cost creep I see in the production classes, much of which is caused by the scarce parts availability for the competetive marks.
Great job!

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Dave Youngren
NER ITA RX7 #61

[Jim Susko]

I think the 13 inch tire and rim, particularly the Hoosier 225/45R-13, is the best.

A larger diameter tire reduces the mechanical advantage of the brakes, so braking is improved.

A larger diameter tire and rim increases unsprung weight and overall weight significantly.

A larger diameter tire and rim significantly increase the rotational inertia of the assembly because all the additional weight is at an even larger diameter, further taxing braking capability.

A larger diameter tire increases effective frontal area and raises the center of gravity which reduces lateral grip.

A larger diameter tire increases clearance problems.

I have no issues with the short contact patch and my car is easy to handle and responsive. As a former manager of a tire research group it has always been my belief that a larger diameter tire lengthens the tire patch but doesn't increase its area. I would think the area of the contact patch relates more to the tire pressure and carcass stiffness, not to the diameter.

If I didn't have all these reasons to stay on the 13's, the $2400 I have invested in my new panasports would be the best one.

Jim Susko

[Banzai240]

Originally posted by Jim Susko:
A larger diameter tire reduces the mechanical advantage of the brakes, so braking is improved.


I'm assuming you mean that braking is REDUCED, which is true, because the larger diamter would have greater leverage (longer lever arm)...

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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
http://home.comcast.net/~djjordan/Web/DJ_AV1.jpg

[This message has been edited by Banzai240 (edited October 18, 2004).]