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Is anyone able to help me with the biggest back space allowable in a standard rear wheel arch with standard spring placement.
I would like to run a 215x65x15 which has a tyre section width of 221mm.
If I put the tyre on a 7" rim with a 3.5" back space am I correct is saying 44% of the total width is back space and 56% dish.
The above percentages were worked out considering a 7" rim is measured to the inside edge of where the tyre bead sits and back space measurements are to the outside edge of where the tyre bead sits.
Therefor a 7" rim is actually about 8" wide (outer to outer) - so 3.5" back space leaves 4.5" dish which equals 44% back space and 56% dish
3.5x25.4=90mm, 4.5x25.4=114mm - add 90 and 114 to get total rim width of 204mm
204mm x 44% is 90mm and 204mm x 56% is 114mm.
Therefor getting back to the 215x65x15 with a total section width of 221mm if on a 7" rim I would need 44% of 221mm backspace and 56% dish - ??
221 x 44% is 97mm and 56% of 221mm is 123mm.
Therefor I ASSUME I need 123mm + ??mm for clearance from front face of brake drum to outer guard and 97mm + ??mm clearance to the inner guard/leaf spring.

I currently have 90mm between brakedrum face and outer guard and 150mm to inner guard ( I assume a standard wheel arch is about 250mm inside guard to outer guard), diff is a 10 bolt with HZ stud pattern- measurement provided by mechanic installing the diff, V8 etc.

I am trying to work out what the widest rim and deepest dish will fit and have concluded I need to cut the housing down about 40mm each side if I wnat any dish at all.

If anyone can understand my rant, have I worked it out properly and how much can I narrow the housing before the rims will rub on the inner guard or springs?

I am along way from my car and unfortunately cant jump under to have a look, If anyone has any advice or tips let me know.

Is there any advantage to running 14" rims over 15".

Thanks Mark

Borrow a rim and tyre and try it mate ...........the only way to be sure ....my diff is shortened by 25 mm each side ....I have 7 inch x 15 rims fitted with 215 tyres with a 80mm back space and they just fit .....If and when I mini tub it....I should have enough room to fit 8 inch x15 rims with a 100mm backspace with 225 tyres ....hoping anyway but just looking at it , it should all fit up well ..........Fingers

Cheers fingers, appreciate your help. I guess I purchase the rims and tyres and cut the diff down to suit.

Marko wrote:Cheers fingers, appreciate your help. I guess I purchase the rims and tyres and cut the diff down to suit.

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Or find some wheels that work with what ya got mate ..........Theres a guy in melbourne that makes steel rims to any specs and offsets to suit your application ....Phillip at Ajax Wheels Cnr Exley Drv & Ewar St, Moorabbin, VIC 3189. Bayside VIC, Southern Melbourne Tel: (03) 95557737...........Fingers