Please explain wheel OFFSET.

AlanS · Post by **AlanS** » 29 Jan 2024, 12:08

Another quick Wheel question: Looking now at aftermarket wheels- TireRack. My 2006 xc70 is 17". The wheel that I would like is 17x7.5 offset +40mm Does that seem right? Just making sure of the #'s. IS there an optimum offset for my car?

Post by **BlackBart** » 29 Jan 2024, 12:52

The ET or offset is the distance from the centerline of the wheel to the plane of the wheels mounting flange, which is also the plane of the hub mounting surface.

A positive offset means the wheel centerline is located inboard of the hub. A negative offset number (rare except on race cars) means the wheel centerline is located outboard of the hub.

AlanS · Post by **AlanS** » 29 Jan 2024, 13:02

Is there an OPTIMUM offset for my application? There are many wheels available, but with different offsets- mostly in the 40's range.
again- 2006 xc70 Ocean Race 17"

Post by **Blacklab467** » 29 Jan 2024, 14:04

The offset on the factory wheels is 50mm. You don't want to get too far away from that otherwise you run into problems with steering and suspension geometry and to a lesser extent clearance issues. The optimum offset is the one the Volvo engineers designed into the factory wheels........which is 50mm.

AlanS · Post by **AlanS** » 30 Jan 2024, 13:21

Also....width? 7, 7.5, 8? Will it matter? Darn... What happens when one uses wheels with lesser offset, etc?

Post by **BlackBart** » 30 Jan 2024, 14:55

Look up your specific year's car specs, it should list the OE wheel size.

Or go to Tiirerack.com and enter your car and year in a tire search. It should tell you what the OE wheel size is, and will ask if you have an optional wheel size. My '94 850 search will tell me a 15" wheel size, as well as the T-5 16" wheel.

A tire that sticks too far inboard may rub on the strut or the inner fender when you turn the wheel to the stop. A tire that sticks outboard too far may rub on the fender opening, may spray slush all over your car because it's outside the fender, may cause "tramlining" or pull the wheel outwards on rough roads. A stock width tire on the wrong offset can do the same things. A half inch is probably no big deal, but you'd better check that first.

Post by **BlackBart** » 30 Jan 2024, 16:27

: tirerack.jpeg (131.32 KiB) Viewed 302 times

This shows 17x7.5 ET 49
https://www.getallparts.com/Volvo-XC70- ... gJTEfD_BwE

This one is 17x7 ET 49
https://autorimshop.com/products/2006-v ... gKe7vD_BwE

17x7 ET 49
https://www.hubcaphaven.com/p/10621/aly ... 14880.html

17x7.5 ET 49 (Is this the Ocean Race wheel?)
https://autorimshop.com/products/2006-v ... gLUHfD_BwE

So it seems they're all in that 49-50mm range like Blacklab said. A 7.5" wheel with the same 49mm offset will sit a quarter inch farther in and out than a 7".

So....a 40mm offset will sit 9mm or about 3/8" farther outboard on the car.

Post by **MoVolvos** » 30 Jan 2024, 22:29

AlanS wrote: ↑29 Jan 2024, 12:08 Another quick Wheel question: Looking now at aftermarket wheels- TireRack. My 2006 xc70 is 17". The wheel that I would like is 17x7.5 offset +40mm Does that seem right? Just making sure of the #'s. IS there an optimum offset for my car?

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Having a 40mm wheel is like adding a 9mm shim to the stock wheel pushing it outward towards the fender lips. Most cars will be fine with a 20mm shim and not rub.
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All the stock rim sizing for a 2006 XC70.
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https://www.wheel-size.com/size/volvo/x ... 7-25t--207
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https://www.wheel-size.com/calc/
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