How to calculate wheel offset for wider wheels

[Burdekin]

This seems to be one of those topics that I’ve never been able to find the correct answer. When choosing wider wheels for a car what changes to the offset are required. Anyone actually know? I've seen folk recommend; keep the back space the same, keep the front tyres outer width the same and keep the original offset.

 

[pedrobedro]

Have a read on Oponeo, you'll figure it out. If you go for more inset you might end up fouling the inner wing on full lock so need spacers to remedy it.

 

[colnerov]

widen them and you end up catching the outer wheel arches

That's what rolled arches are for and why they came about.

 

[Burdekin]

Have a read on Oponeo, you'll figure it out. If you go for more inset you might end up fouling the inner wing on full lock so need spacers to remedy it.

I've read that and the formula just calculates how to keep the wheel outer in the same position, so a wider wheel gets more offset. Means the wheel centre line is more inboard so not sure that is correct.

 

[Burdekin]

You could always keep the wheels as standard That's how they were designed after all.

Looking for specific advice. If you don't know then no need to comment thanks.

 

[hotponyshoes]

If all you want to do is change the look of the wheels then you can just keep the same offset as before.
Ie, if you swap 235x18" wheels for 255x18" then you will just end up with 10mm more tyre on both the inside and outside and the ride and handling will be pretty much the same as before.

Otherwise, it depends on what you are trying to achieve to work out what offset you need.

 

[Fastdruid]

This is where backspacing kind of makes more sense as a measurement.

In general if you keep the offset the same then at some point you will run into problems with clearance to the struts (assuming mcpherson strut) or other suspension/steering parts, generally you can manage a *small* increase but it's increasingly risky. If you measure your clearance then the widest you can go is 2x clearance for the same offset.

If you keep the offset *AND* the diameter the same (ie by going to a smaller aspect ratio) however you will also keep the scrub radius the same (on the front), if you change either then you will change the scrub radius, now generally in most cars you have to go quite some way to *really* upset things here but on others it's possible to go negative to positive (or vv) by changing the tyres.

If you want to keep the same clearance then go by the backspacing, in theory you can go as wide as you want as long as you keep the backspacing the same but in reality you'll run into clearance/arch problems on the other side!
You can increase the backspacing slightly to take up some of the clearance of course.

 

[carbon]

I used this site when I changed to wider wheels to find a tyre that had the same rolling circumference
Will they fit

 

[Bornfree]

I used this site when I changed to wider wheels to find a tyre that had the same rolling circumference
Will they fit

I've used this site it's very helpful

 

[Blobber]

Whats are they going on? many car manufacturers offer loads of different size wheels for the same model which would give you an idea

 

[Burdekin]

Whats are they going on? many car manufacturers offer loads of different size wheels for the same model which would give you an idea

1969 Volvo Amazon. They didn't really do anything wider. I can measure clearances that's not an issue, keeping the best patch contact etc is what I'd like to ensure.

 

[Rannsachair]

Just watch, changing offset can decrease wheel bearing life. I used to design hydraulic wheel motors and the centreline of the tyre relative to the bearings was used for bearing life calculations, probably ok given the limitations of wheel arch clearance, but not something everyone thinks of, worse on tractors where they fit twin tyres for soft ground.

 

[octo0072000]

seen amazons on banded rims before maybe 50mm on outer not sure on rear arches though google shows loads i like minilite rims

have a look at guy;s volvo

Guy Martin on his Volvo: the fastest car in Britain

The daredevil Guy Martin, Isle of Man superbike rider, engineer and holder of countless speed records, has had Porsches and Astons but says none can match his 1967 Volvo special

www.driving.co.uk

 

[8ob]

This seems to be one of those topics that I’ve never been able to find the correct answer. When choosing wider wheels for a car what changes to the offset are required. Anyone actually know? I've seen folk recommend; keep the back space the same, keep the front tyres outer width the same and keep the original offset.

@Rannsachair is on the money with keeping the wheel centerline the same. Move this outboard and you are effectively adding leverage to anything you clip a wheel on. Kerb it or run into a big puddle with a load of offset that shouldn't be there and the steering wheel will rip your thumbs off.

Bob

 

[Rrobson]

Offset is the relationship between the hub mounting face and the centre of the wheel.
If you increased the width of the wheel by 10mm but kept the same offset then the wheel width would be added equally to both the outside and the inside of the wheel.
If you had an offset of +40 and you wanted a wider wheel by 20mm but wanted the width only on the outside edge you would need a wheel 20mm wider with an offset of 30. Your offset needs to be reduced by half the difference because the centre line moves over by half the total extra width.
I’m quoting it I’m mm to avoid confusion, obviously most wheel widths are measured in inch but offset tends to be in mm for some reason.

 

[Nick DV]

You've not said how wide you wish to go, but these people are helpful and can build what you want https://www.imagewheels.co.uk/

 

[Burdekin]

You've not said how wide you wish to go, but these people are helpful and can build what you want https://www.imagewheels.co.uk/

They are but way too expensive.

 

[Nick DV]

They are but way too expensive.

They are indeed, but if you need something non standard...............

 

[Burdekin]

They are indeed, but if you need something non standard...............

I don't, see my first post. There's plenty of off the shelf options available whichever way I go.

 

[Nick DV]

I don't, see my first post. There's plenty of off the shelf options available whichever way I go.

Ok, but it's not clear from your first post, and was only trying to help but from your reply, I guess you don't really need it!