SPS

i have a `95 twin cam wagon and i want to put some 15x7" rims on it...what back space is best?i am thinking about running in STS and will be daily driving it also......thanks,steve.

Admin moved this post to the S series forum 07-19-08.

Do you mean 'backspace' or 'offset'?

I'm guessing you mean offset - which is the distance between the center of the rim and the outside of the hub at the base of the lugs (where the wheel sits against the hub).

This is usually a positive number - meaning that the hub edge is to the outside of the center of the wheel (or the center of the wheel is to the inside of the hub edge). Though there is also such a thing as 'negative offset' where the center of the wheel is to the outside of the hub edge. (Remember in the early 1990s when the 'skateboard wheel' look was popular? That was a negative offset.)

The stock offset is 50mm. So the center of the wheel (aka: the center of the tire) is 50mm to the inside of the outside edge of the hub.

I don't think that you would ever want to use an offset larger than 50mm because:
1. I'm not sure there is such a thing
2. You would probably not have room - since this would put the inside edge of the tire very close to the strut body
3. This would reduce track width and thus have an adverse effect upon handling

As a rule, an offset smaller than 50mm can have some advantages. Such as:
1. It increases the track width - which will result in a reduction in body roll and an increase in cornering traction, holding all else constant
2. It increases the amount of clearance between the inside of the tire and the shock body - allowing you to use a wider tire and/or wheel
3. It looks better

The potential disadvantage is that, holding all else constant, it will result in more load being applied to the bearings and hub spindles - which will increase the rate of wear and tear on these parts. (You will replace hubs and bearings more often.)

As to what is the 'best' offset, well, that depends. As far as I know, any given wheel in a 15x7 size and a 4x100 bolt pattern is probably only going to be available in one offset. And the wheel weight is probably more important than the offset.

So if I were choosing between a 15 pound wheel with a 35m offset and a 12 pound wheel with a 42mm offset, I would probably opt for the 12 lb wheel - even though it has more offset.

Holding all else constant, I would go for less offset. Less weight and less offset.

If you are using 225mm tires or certain 205mm tires that run extra wide (like the Hoosier R compounds), then you may need a smaller offset (like maybe 45mm or less) because you might run out of clearance between the tire and the strut body. This is not a problem with most 205mm street tires though, so any offset 50mm or smaller will be fine, in that case.

Also, it seems to me that most aftermarket wheels use offsets smaller than 50mm. 42mm is about the largest I have seen, not that I pay that much attention to it these days.

I'm pretty hungry and tired at the moment, so hopefully this makes some sense...

thanks jay- back space is an "old" word i cant get out of my vocab....offset is what i was asking about.
so less +offset is better-how much can the stock fenders takei
i will be using a 205/50-15 and i think a +42mm offset is better for fender clearance issues....thanks for your feedback-and good racing!

On the ITA car, I used a 35mm offset plus 5mm spacers - hence the equivalent of 30mm offset - with H&R springs and had no fender issues at all.

James used even larger spacers and had no issues.

Technically, the rules in Improved Touring say that your tire cannot extend beyond the fender line. I'm pretty sure that James would have exceeded this rule if not for the -2.5 deg of camber that leaned the top of the tire back under the fender and created a visual illusion that we were in compliance.

i just put a set of +30mm 15x7 rota rb`s on my `92 civic si and i had to roll the fenders-they still scuff just a little under full bump...so i was checking to see how things were on the saturn,and to chat with a saturn racer...

i met this spring,a fellow from up north that runs a ssc saturn. he was at kershaw,sc and won despite getting hit hard by a civic...he was gonna run at roebling rd and i tried to make it down there to see him-but didnt have the cash for the trip. are you still running the ita car?

i recently bought a crx that has tom fowlers old carrera suspension under it and walt puckett is gonna set up the suspension for a vir event i am running at the end of august....thanks again for the feedback,steve.