Wheel Diameter - 14 or 15?

With the option of a OE 14" car going up to a 15", would you do it and why?

For the record, its an ITA Miata.

What are the advantages/disadvantages of the increased wheel size at 15"? On paper it seems to me that the smaller diameter will be a lighter wheel & tire, and more specifically, will have a smaller moment of inertia. However, are there handling differences that get created by the different wheel size that would offset this rotating mass advantage?

While we're at it, 205 or 225 width?

Thanks
Matt

I used to run 225/50-14 on 14x7s, I swapped to 225/45-15 on 15x7.

The *exclusive* reason I did this is because I came across a very good deal on two sets of very lightweight Volk TE-37 wheels (minus ~2-3 pounds per corner from where I was) and Hoosier made a 225 tire in the same diameter. Had neither of those been true, I would have stuck with 14s for all the reasons you state.

I run 225s because I am able to get them up to the proper temperature range; I was overheating 205s. I would choose tire size based on temperatures achieved.

Two other considerations -- as Greg hints at a change will affect gearing. Going from 225/50 to 224/45 (both on a 13" wheel) change my shift points by a couple hundred RPM. So, watch your overall wheel diameter when changing wheels sizes. Can be a plus or a minus obviously, in any event it is cheap gearing change.

Second, I'm going from 13" to 15" primarily to get more room for brake ducting. Something that may or may not be important to you.

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For the record, its an ITA Miata.

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Matt....... Are you coming to swim in the ITA pond this year??? That will make things interesting...........

If you have a choice, go with the 15.

I have a feeling that 13 and 14 sizes (both rims and tires) will get less manufacturer support in the future.

If my tire of choice is available in 14" and a shorter tire is an advantage at the tracks I race I'd go with the 14"

A 15" will open up more compound and wheel options. IF the overall tire diameters are the same/reasonably close, the shorter sidewall on the 15" tire will generally be stiffer, therefore will give quicker response.

Matt,

Tell us the following:

Sprint or Enduro car?
Tracks you will run
Weight of the 15's you would buy
R&P you will run

Here is where I am at:

Sprint
LRP/NHIS
9lbs
4.3

My 4.88 would be better at different tracks than we have out here.

Andy:

This is for an enduro car. So a slight weight gain in return for being a bit more rugged is probably hte better choice.

Summit & Nelson

We are running a 4:30 and like it, we don't quite hit the rev limit going under the bridge at Summit. The slightly taller gears does do some good things for fuel economy though.

We have 3 or 4 sets of 14's but there's an internal discussion amoungst us about which would be faster. I knew some people had made the switch once the rules allowed it and was curious why and what gains they found.

So far it seems like it comes to price, weight and availability of tires.

Matt