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Author Topic: Maximum spacer size?
W. Bonsell
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There are several spacer sizes on the market. What is the maximum spacer size for a 30 offset wheel??

Thanks...
Bill

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William Bonsell
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Chris Haldeman
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5mm

Ron Alan Made Donation to Website
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The goal is 25mm(max offset). I believe the max spacer is 13mm regardless of wheel.

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W. Bonsell
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Year : 1991
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I believe there is a maximum track width which you can not exceed. What is the maximum size of wheel spacer you can use with a 30 mm offset wheel to achieve maximum track width without exceeding SM rules? I am sure spacers are used with 25mm wheels so 5 mm can't be the correct number. And 13mm spacer may exceed the max track width, yes?

Thanks again...

Bill

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William Bonsell
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Chris Haldeman
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in theory spacers can not be used with 25mm offset wheels and stay within the track width limit.25mm is as wide as you can go there for 5mm is the largest spacer you can use with your 30mm offset wheels.

Ron Alan Made Donation to Website
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1st...assuming you are using 15x7 wheels 25mm offset is the perfect number on a miata to hit the max.track width that has been set in the rules as Chris said. There is a number but I don't know it off the top of my head.

So when you use a spacer on a wheel you have to subtract it's thickness from your offset on the wheel. 30mm-5mmspacer=25mm offset...perfect. But if you have a 40mm offset wheel the largest spacer you can use legally is 13mm which would put you at 27mm...best you can do.

Offset is measured from the C/L of the wheel to the mounting surface. At 0 offset the mounting surface is C/L of the wheel which puts more wheel to the outside of the car. Sorry if you know how this works...this got me confused when I asked the same questions you did and someone explained it to me.

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-RA


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davew Verified Driver Made Donation to Website
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As one of the people who measured a couple dozen cars to get the specs:

The max allowable tread width is designed for a 25mm wheel with no spacer. If you have a 30mm wheel, you are allowed a 5mm spacer per wheel.

The spacers must be the same per axle. In other words if you have 5mm spacer on the right front, you must use a 5mm spacer on the left front. You are allowed to use a different or no spacer on the other axle.

This is designed to eliminate 10mm on one side and none on the otherside, thus creating an offset chassis.

Maximum allowable spacer is 13mm thick.

Only one spacer per wheel.

dave

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W. Bonsell
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Ok...thanks everyone for clearing the fog which often surrounds me...Looks like I will be purchasing 4 - 5mm spacers to use with my 30 offset wheels...(also looks like my son bought the wrong size spacers).

Thanks,
Bill

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William Bonsell
SCCA/ICSCC #26
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Ron Alan Made Donation to Website
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quote:
Originally posted by W. Bonsell:
Ok...thanks everyone for clearing the fog which often surrounds me...Looks like I will be purchasing 4 - 5mm spacers to use with my 30 offset wheels...(also looks like my son bought the wrong size spacers).

Thanks,
Bill

Bigger is better theory just went out the window [Big Grin]

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-RA


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Johnny D Verified Driver Made Donation to Website
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You may need longer studs (than stock) if you don't have them already.
J~

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CP Verified Driver
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So a wheel with a 38mm offset (5.5" backspacing) would need a 13mm spacer to be barely legal per the ruleset?

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quote:
Originally posted by CP:
So a wheel with a 38mm offset (5.5" backspacing) would need a 13mm spacer to be barely legal per the ruleset?

The rule says not to exceed the track width. So you can run the 38 offset just as it is, your track will be 26mm under. With the 13mm spacer you will be at max track.
J~

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Brandon F. Verified Driver
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quote:
Originally posted by CP:
So a wheel with a 38mm offset (5.5" backspacing) would need a 13mm spacer to be barely legal per the ruleset?

You aren't "barely" or even "over" the offset allowance with a 13mm spacer: you're exact. Maximum spacer size is 13mm and when used on that 38mm offset wheel you are at the maximum track width allowed.

Going to a 14mm spacer would put you "greater" in width (by 1mm) if used with the same wheel.

It's counter intuitive but adding spacers deducts from a wheel's offset which in turn puts the outside edge of the wheel further away from the vehicle's centerline thus widening it's track.

38mm offset wheel == 13mm spacer == legal width
30mm offset wheel == 5mm spacer == legal width
30mm offset wheel == 13mm spacer == illegal width
25mm offset wheel == 0mm space == legal width

I'm even having trouble visualizing what I'm trying to write and have it make sense!

   

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