EP/FP Miata 7x15 Wheel Backspace question

O

Old Goat

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Hoping a Miata racer could go out and measure their wheels for me. I am looking to have a new set of 15x7's made. I am wondering what the backspace is for your typical EP/FP Miata 7"x15" wheel? I've run some calculations but would like to double check against actual wheels being used. if you can list Manufacturer, Style and backspace I would really appreciate it. I will be running 215/580/R15 Hoosiers and my calculations show 3 3/4" backspace. Am I close to what is typically used? If you have a set of say Spinwerks or others you want to sell, please PM me. I would be interested in used if available.

Happy New Year
 
I would check any of the SM sites, since they run a 15x7 rim, that should work with your car.
 
My wheels are Team Dynamics 1.2. On my Spec Miata they are 30mm offset (I believe they are positive offset), anyway they have a back space of 5 1/8 inch, mounting surface to outside edge of rim. I know of an F production Miata car that uses these same rims with spacers. Spacers are another tool in the set-up box.
 
This is not for a Spec Miata application. Currently we run 15x10 Spinwerks with Hoosier FA slicks for autocrossing. The car is a wide body similar to an EP/FP Miata. The 15x10 run a 5 1/2" backspace which makes them a 0 offset. I would like to keep the track width about the same. Using Hoosiers information for sectional width of the 23.0x9.5Rr15 slicks we are using Hoosier states 10.7". The 215/580/R15 Road Racing Radial Slick shows 9.7 for the sectional width on a 7" measured rim width. I already have a set of Team Dynamic Pro Race 2's with a 5" backspace. I have lots more room to increase the track so that is the reason for the question.
 
I understood, it was not a Spec Miata application. Miatas are Miatas other than for production cars mzay add wide fenders at your pleasure. Point was 15 x 7, 5 1.8 back space are used for Spec Miata and production with DOT or slicks. Please note the Prill narrow body F car. Info only, nothing more or less. :D
 
David popping on spacers are an option if you want to use wheels which are of the incorrect offset for your application. Since my plans are to have wheels built with the correct offset I was simply asking what the prod guys are running for backspace. I know there is a wide assortment of wheels which prod racers use. They vary from custom built with the correct offset like Spinwerks, Pannasports, etc or as you mentioned using off the shelf Team D's, Kosei K1's and I'm sure others with spacers. Since I am looking at custom wheels I am simply trying to verify my calculations. If I can't get some information here I can always have Bassett build me a relatively inexpensive test fit steel wheel and then fine tune it with the 5mm spacers until I find the correct fitment. I'll run up to Delevan to pick up a 215 after stopping at Burlington to pick up the rim and go from there. But getting a starting point backspace for the Bassett would be helpful. At this point I'm debating between a 4" or the 3.625" backspace. What would you Miata Production racers recommend?

As you see from the autocross set up my son runs the flares give us the opportunity to push the FA's outwards a good amount. I want to match this with the 215's when I start taking him to road courses this summer.

 
I don't have measurements for you but, it should be easily calculated out.

Miata Maximum track width is given in the PCS. You know what your current track width is with the 15x10...just some math that doesn't require trials and spacers....
 
Go with 3.625 if you want to fill out those flares. That would be a good number with spinwerks wheels for backspace on an EP car.

Good luck. I'm assuming this is Rich Haimlech?
 
I've run the calculations but just wanted to get a real world backspace dimmension to verify my 3 3/4" backspace calc. The problem with the calc is that my 23.0x9.5 on the 10" rim has very little sidewall bulge. The the tread width is almost the rim width. You guys run a wide slick on a narrow rim which I assume has quite a bit of bulge. Might be mistaken but according to the info given by Hoosier your tread width is 9.7" for a 215. I have taken that into account in the calc even giving myself 1/2 cushion. I was hoping I wouldn't have to re-invent the wheel (wow that pun applies here :) ) since there should be someone in the prod community who could verify it for me. Just looking for a little bit of help with a ruler and a wheel.
 
Hey Jessie you guessed right. Too bad that Spinwerks is gone. Talking with a different manufacturer but once I get the backspace hammered out they will let me know what they can do.

Thanks and Happy New Year.
 
JP figured it out but re-arranged the spelling of the last name around a little. Alo known as the father of the young stuborn billy goat in the picture.
 
You might find a used set if you post a "wanted" ad for the wheels, and dimensions you are looking for.

Somebody may have a set they had not yet considered posting for sale.
 
spinwerks isn't "gone", really. Diamond racing wheels bought them out and moved operations to wisconsin. They are now building wheels again, just call diamond
 
Thanks Adam. I heard from the distributor I bought my 15x10's from earlier this year, that they were gone. But that was probably mid summer. Wisconsin boarder is about a half hour away so even better then when they were out west.

I will post in the Wanted Section if anyone has an older set of 15x7's they want to move. PM me.
 
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