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Username Post: Wheel fitment/measurement        (Topic#337935)
53belair 
Frequent Contributor
Posts: 2376
53belair
Age: 62
Loc: Ellerslie, Georgia
Reg: 03-25-07
08-01-16 08:33 AM - Post#2643000    

I just found this old link and thought I'd post it. Seems like there is a similar question about wheels at least once a month.

http://www.hotrodhardware.com/pdf/steel_wheel_info...

1953 Belair Sport Coupe,350/350/Fatman/Dako ta Digital/American Shifter/Southern Air/Ciadella Interiors
1967 Chevelle 396 Muncie
2010 Camaro II-SS
2011 Camaro Pace Car
2012 Tahoe


Edited by Tony on 08-01-16 11:20 AM. Reason for edit: No reason given.

 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
08-18-16 12:25 AM - Post#2646345    
    In response to 53belair

Good info 53Belair. Just a couple of points I would make. Bolt spacing may also be referred to as Pitch Circle Diameter. (PCD) So you may have 4 on 4 1/2", 5 on 5 1/2", 6 on 6 1/4" etc which specifies the number of studs on the PCD used.
The second point I would make is there are two systems used for backspacing. The one you showed and the other uses the same outside point as where the rim width is measured to. Basically where the bead seats. Just make sure you use the suppliers style and you will be fine.
Another significant area for these fit sizing exercises is to know about the "aspect ratio" of a tire, which ultimately determines its rolling diameter.
The aspect ratio is the height of the tire from the bead to the outside tread compared to the width as shown in the previous post.
So a tire may be a 215/70 15 which means the nominal width is 215 mm but the sidewall height is only 70% of that, on a 15" rim.
By varying the aspect ratio you can fit a larger diameter rim say 16" vs 15" by using a 16" tire of lower aspect ratio to arrive at the same overall diameter. This is often done to allow bigger brakes to fit in, or to shrink the sidewall to increase its directional stability. A lot of cars that would have used 13" wheel two decades ago are now coming out with 15" rims and even 17" on sporty variants.
We used to call this process "D" profiling for going up from a standard spec. But be aware it makes the ride harsher in a trade off for directional stability. Mostly though its just an appearance reference to racing vehicles that helps sales.
Now for the trap that matters for our era vehicles when choosing tires.
A TIRE WITH NO ASPECT RATIO MARKING IS NOT 100%
It will be either 78% or 82% depending on the source market. So for practical purposes the standard tire should be considered 80%.
So if you are working out clearances or gearing then a 6.70 15, is actually a 6.70/80 15.
Cheers Kiwi

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 08-18-16 12:40 AM. Reason for edit: No reason given.

 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
08-18-16 02:05 AM - Post#2646349    
    In response to Bel Air kiwi

Hi Guys, another way to consider the backspace of a rim is to measure it as offset from the tire center line.This is the normal way that the OE designers consider the rim and its relationship to the steering and suspension.
Heavy negative offset

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
08-18-16 02:05 AM - Post#2646348    
    In response to Bel Air kiwi

Hi Guys, another way to consider the backspace of a rim is to measure it as offset from the tire center line.This is the normal way that the OE designers consider the rim and its relationship to the steering and suspension.
Heavy negative offset

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
08-18-16 02:05 AM - Post#2646350    
    In response to Bel Air kiwi

Hi Guys, another way to consider the backspace of a rim is to measure it as offset from the tire center line.This is the normal way that the OE designers consider the rim and its relationship to the steering and suspension.
Heavy negative offset

Attachment: Offset.jpg (10.73 KB) 65 View(s)




48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
08-18-16 03:20 AM - Post#2646356    
    In response to Bel Air kiwi

Heavy negative offset wheels are usually only found on semi-pro and pro drag cars which run full-floating hubs as a safety feature and consequently have two big taper roller races which easily support the extra load.
Heavy positive offset is a common feature on front wheel drive where the bulk of the driving and steering hub require the offset to get the wheel center line back over the bearings.
The area on 49-54’s effected by this are those with stock front suspension and aftermarket disc adaptions. Typically the new rotor face mounts the wheel between 3/8” to 3/4” further out from the original. This affects both bearing load and steering geometry.
To correct this you simply take that amount off the wheel offset and everything goes back to cherry. This is the same whether you widen the rim width or not.
If you stay with stock rim widths then you can also just take the amount of change off the backspace, but if the rims are wider you need to add back half of the rim width change back on.
Cheers Kiwi


48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


 
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