The goal is 25mm(max offset). I believe the max spacer is 13mm regardless of wheel.
-------------------- -RA
"Happy birthday, I didn't get you a present...Oh, mom got you one? Well, that's from me then too, unless it's shitty." 9:52 AM Sep 14th, 2009 via web http://twitter.com/shitmydadsays
Region: NWR/Oregon
Car #: #26
Year : 1991 Posts: 334
Status: Offline
posted
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
-------------------- William Bonsell SCCA/ICSCC #26 SM/ITA
Region: texas
Car #: 71,72
Year : 1990,1999 Posts: 166
Status: Offline
posted
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.
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.
-------------------- -RA
"Happy birthday, I didn't get you a present...Oh, mom got you one? Well, that's from me then too, unless it's shitty." 9:52 AM Sep 14th, 2009 via web http://twitter.com/shitmydadsays
Region: chicago
Car #: 72 and ?
Year : 90 and 90 Posts: 1051
Status: Offline
posted
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
-------------------- Advanced Autosports, The Midwests leader in Spec Miata Service, Parts and Rentals 608-313-1230 Authorised Spec Miata service center www.advanced-autosports.com
Region: NWR/Oregon
Car #: #26
Year : 1991 Posts: 334
Status: Offline
posted
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
-------------------- William Bonsell SCCA/ICSCC #26 SM/ITA
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
-------------------- -RA
"Happy birthday, I didn't get you a present...Oh, mom got you one? Well, that's from me then too, unless it's shitty." 9:52 AM Sep 14th, 2009 via web http://twitter.com/shitmydadsays
Region: NER
Car #: 7
Year : 1999 Posts: 636
Status: Offline
posted
So a wheel with a 38mm offset (5.5" backspacing) would need a 13mm spacer to be barely legal per the ruleset?
-------------------- -Cy Supported by LTD Racing & Speed Shack - New England's Premier Auto Accessory Store Rt1 AutoMile - Norwood, MA http://www.speedshackonline.com
Region: SFR
Car #: 88 SM
Year : 99 Posts: 367
Status: Offline
posted
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~
Region: NNJR
Car #: 48
Year : 1996 Posts: 191
Status: Offline
posted
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.
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