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MG MGB GT V8 Factory Originals Technical - wheel offset for WW axel w bolt hub
|Have a 70 BGT with WW rear axel converted to bolt-on with 4 on 4.5 B hubs. Running 14 - 175's on rostyle stock wheels. Experiencing minor rubbing on inside of wheel house (behind the wheel when viewed from side of car).|
Would like to run 15 - 205 (60 series?). Assume this will require at least a 5.5 inch wide rim. Maybe 6 or 7? Does anybody know the necessary wheel offset? If possible please explain direction of offset in reference to some fixed datum, centerline of wheel?
Source for the wheels? Would like manufacturing and model if possible. The minilite and replicas would be OK, but are becoming rather common. Any alternatives?
|In fact it is precisely from the centreline of the wheel that the offset is calculated:|
Here is an explanation which I lifted from http://corrado-club.com/corrado/faq/offset.cfm
From Kevin Lau (Kevin.Lau@crestarsys.com )
Take a wheel off your car. Lay it on its sidewall so that the inside of the wheel (the side that faces the hub and brakes) faces up. Lay a straight-edge or something across the rim (not the tire). Measure up from the wheel's hub-mating surface to the straight-edge you laid across the rim. Subtract 1/2 the wheel's width from this measurement to get the wheel's offset.
A wheel with 0 (zero) offset has the hub mating surface exactly in the center of the wheel's width.
A wheel with a positive offset has the hub mating surface "offset" to the outside of the wheel (bringing the tire in
A wheel with a negative offset has the hub mating surface "offset" to the inside of the wheel (taking the tire away from the car and closer to the fender).
And also :http://www.edmunds.com/ownership/techcenter/articles/46431/article.html
Wheel Offset, Rear Spacing and Wheel Measurement
Rear spacing (or backspacing) is the distance between the wheel's inboard edge and its mounting pad. It can be measured by using a ruler and a straightedge set across the backside rim of the wheel.
Offset is the distance from the wheel center to its mounting surface. To find offset, plug the rear wheel spacing and width into this formula:
Offset = Rear Spacing — Total Wheel Width
If you have a "positive" offset, the mounting pad is in front (or outboard) of the rim centerline. This situation most commonly occurs on front-wheel-drive applications. To picture this more accurately, think of the convex design of many wheels found on front-drivers; the center of the wheel sticks out further than the edges of the wheel. If there's a "negative" offset, the mounting pad is behind (or inboard of) the rim centerline. This is typical for most standard rear-wheel-drive vehicles and "reversed" rims. Sometimes, this style is referred to as a "deep-dish" wheel.
For example, an 8-inch wide, 3-inch-rear spacing wheel would have a 1-inch negative offset. Conversely, if the same 8-inch wheel had a 5-inch rear spacing, it would then have a 1-inch positive offset. Finally, if the same wheel had a 4-inch rear spacing (which is exactly half its width) then the wheel would have what's known as a "zero offset."
There are loads of other explanations and also pictures on the Internet
|OK Marc, thanks very much for the wheel schooling.|
Now, anybody have thoughts on my car's application?
LHR is usually nearer to lip so I assume the RHR is rubbing on inner. This imbalance will vary from car to car but usually 195 are max without considering rolling lip.
The club are selling 5 spokes and split rims used on Supersports but you may find price is steep.
Marc uses Saab (7ins 32mm offset?), there is a web site with possible matches with right PCD.
Supersports used WW
|Paul - 30 offset.|
But what might be the offset for Steven's converted WW axle? Not necessarily the same. He needs to measure it specifically
|Typically, A 3/8" spacer on the driver side (USA) & a 1/2" spacer on the passenger side will give you close to the same track width with a converted WW axle, to match the front track. Both spacers 1/2" is more accurate, but may result in tire rub on the driver side.|
An hour or so of fiddeling with tire sizes using Datsun 260 Z spec 15" wheels resulted in 215/60/15 Yoko Avids in the rear & 195/65/15's in the front. The tire diameters are virtually the same, but the tread width is very different. These are 6 1/2" Sendol wheels, & the rear wheel arches have been radiused for clearance, but not rolled or flared.
Normally, 205/60/15 is about as large as you can go
with a 6" wheel. 6 or 6 1/2" is as large a wheel as you really need, but I have used 7" in the past, just because they were available.
Too wide a tire in the front will cause rubbing on the sway bar, if you have one. If not, you should add one for any spirited driving.
|Thanks Marc and agree needs to measure specifically.|
The offset I guess should be same (norm 22mm but no guarantees) but WW is narrower, as Jim points out a spacer can be used. The Supersports used diff offsets front and rear and squeezed 215's with a minor adjustment but was a new shell built to give max room.
Just what I was looking for.
Check out www.wheelspecs.com. Using a search for PCD 4x114.3 and various offsets here're a few examples that might work:
Volk Racing TE-37 14x6.5 15mm 205/60R14
15x5.5 35mm 185/65R15
15x6.5 20mm 205/50R15
15x6.5 35mm 205/50R15
15x7 15mm 225/50R15
16x7 25mm 205/45R16
BBS RGII Open 15x6.5 38mm
Advan Racing RG 15x7.5 21mm 225/50R15
16x7 31mm 205/45R16
Advan Racing Siena 16x7.5 32mm 225/45R16
SSR Type C 15x7 30mm
Sebring ITC 17x7 35mm 205/45R17
A positive offset greater than stock (22mm) moves the wheel centerline towards the center of the car. For example, a 15x6.5 wheel with 20mm offset might rub the fender lip. A 15x6.5 wheel with a 38mm offset might rub the inner fender well or sway bar. Lots of other stuff in the archives.
From the above responses you are likely on the right track, but while poking about I happened upon the thread, so...
My specific set up:
'74 B-GT (early model year chrome bumper)
Wire wheel rear with bolt-on hubs
Doug Jackson Panhard rod
Panasport 15x7 22mm offset Minilite replicas
Kumho 205/50/15 R compound tires
Seven whacks with BFH on inner fender above bumpstops
1/4 inch spacer LH side, 1/2 inch RH side
NO modification needed to fender - not even the lip
I have wondered if 215's could squeeze in with rolling the fender lip and seven more whacks.
|slightly off topic, and relatively irrelevant (can you say that?) but 225/40/18's will fit on the back of a steel wheel axle B with a 7" wide wheel and a 40mm positive offset with no flaring, no rubbing, and no bfh work. Car might not handle at its best, but hey, we're only running these things on 1/4 mile drag strips.... right?|
p.s. In all seriousness, I wonder if I couldn't get away with that tire combo with my IRS, and with Ted Lathrops redesigned front suspension....
This thread was discussed between 17/09/2003 and 03/10/2003
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