What should I consider when buying wheels with different offsets or widths?

[IXMandalorianXI]

My r33 Skyline currently has:

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Front:

• 18 x 8.5
• Offset 30

Rear

• 18 x 10
• Offset 35

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As I shop for new wheels, I am finding these exact wheel size/offset combinations to be a bit more uncommon than I expected. If I purchased wheels with a different offset, what do I need to consider? Is there a threshold of +/- X offset different that wheels can be without major modification? What about downsizing the rears from 18x 10 to 18 x 9.5?

The wheels in question I am interested in buying are:

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Front:

• 18 x 8.5
• Offset 35

Rear

• 18 x 9.5
• Offset 38

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Any advice would be appreciated.

Thank you

[GTSBoy]

If you can't do the calculations in your head, you can use an on-line offset calculator to show you how far the inner and outer edges of the rim will move with changes in width and offset.

For example, done in my head, your change from 10" +35 to 9.5" +38 will have the following effect, which I will describe in steps so you can follow it.

The width is 0.5' less, so that's 12.7mm. Call it 13, because near enough. If this was the only change, both inner and outer edges would be an extra 1/4" (6.35mm) further in towards the centre of the wheel, giving that much more clearance both sides.

But, with your change in offset from +35 to +38, which moves the hub face towards the outside of the wheel, you will move both those rim edges by 3mm. So your outer edge will now be about 9-10mm further into the guard, and the inner edge of the rim will now be ~3-4mm further away from the suspension.

You gain more clearance everywhere, but it is biased away from being evenly shared by the change in offset.

On the front wheels, you're only changing offset. The wheel rim will move into the guard by that 5mm. On an 8.5" rim, I would be worried that the tyre will foul the upright. I have 8" +35 on my R32 (so, yes, different suspension pieces, but the same basic design, so what is true for R32 may or may not be same same to the mm as R33). I have absolutely bugger all clearance from the tyre to the upright when sitting at ride height. That's with 235/45 tyres. If I want to go wider at the front, say to an 8.5", then I need the entire additional width to be on the outer edge, which would mean pushing the offset down to +28 (technically +29 would do it, but....who's ever heard of a +29 wheel?). That would leave my inner edge where it is and push the outer out by the extra half inch.

Having said that last part, apparently R33 GTR wheels, which are 9" +30, fit on an R32. I can't see that happening on my car because it would use up 8mm more clearance. Maybe the way to do it is to stretch a 245 tyre onto them instead of using a tyre that will fit the 9" better and have a more upright sidewall. This aspect of selecting tyres to make less appropriate wheel choices fit remains an option.

In your case....you have the car. you have the wheels fitted. Drive all 4 wheels up onto some blocks of wood so you can slide underneath it and have a look at all the clearances yourself. You will learn a lot and understand what happens when you change things. You can get someone fat to climb in the boot and see what happens when the rear suspension compresses. Do the same by having them sit on the radiator support panel at the front.

[Kinkstaah]

I mean to do it right you need to measure. 

The only thing really to consider is where the wheel will be sitting relative to your current wheel, and whether you will have clearance for brakes.

Your front wheels will sit 5mm further in-board than your current rims. (offset 35 vs 30).

The rears will sit 9.4mm further in-board from the outside of the car, and give you 3.4mm more clearance on the inside. It's smaller on both sides because it's a slimmer rim (10in vs 9.5in)

willtheyfit.com is a great resource to use to determine where one set of wheels will sit relative to another future set. If you really really like your new design, you could put a 5mm spacer up front, and a 10mm spacer at the rear, and they'll sit where your current wheels sit.

No idea if spacers are legal in the UK. I'd still argue it's best to find wheels that do fit.



I'm confident whatever this is, is also on the money.

[niZmO_Man]

9.5" +38 rear is Nismo RWD size so it'll fit fine.

I don't see any downsides as the wheels will fit better. 10 +35 seems too stretch/stancenation to me (I like meaty tyres).