Wheel Offsets and how to work out what you need

Iv noticed a few threads of late asking about how to work out what size of wheels and offsets they need and asking for help as they don't know how to work it out, well I have found myself with a free 10 minutes so i'm here to help...

The offset (seen labelled as "et" when ordering wheels for example 18x10et12 where 12 would be the offset or it could be a simple plus sign) is a measurement between the face of the hub and the centre of the wheel. Below I have used the knocked up a quick sketch of the same size wheel, tyre and hub setup but with a different wheel offset to show what I mean.

You can see that the 18 inch diameter and the 10 inch width is the same on both diagrams but because of the offset changing it has changed the dimensions of how far it sticks out from the hub... in this example we have an increased offset of 23mm (from et12 to et35) on the right hand diagram that means that there is 23mm more in distance from the face of the hub to the centreline of the wheel so as the centreline of the wheel is further inwards to the car than the face of the hub increasing this measurement by 23mm will bring the wheel 23mm inwards in the wheel arch. In reverse action you could have a wheel with a lesser measurement for the offset and this would bring the centreline of the wheel closer to the face of the hub which would bring the wheel out to stick further out in your wheel arch.

The example below shows that with an offset of 12mm in this size wheel the outside edge of the wheel sticks out 115mm from the outside of the face of the hub and where the same size wheel has an offset of 35mm it only sticks out by 92mm as it has been brought inwards 23mm by the centreline of the wheel being 35mm inside of the face of the hun rather than only 12mm inside the face of the hub.

When working out the size that you want if you can find out the size of the wheels with offsets of what you currently have on your car you can then measure how much you want your new wheels to stick out or go back in compared to your existing wheels and order the correct offset for your new wheels knowing that they will sit perfect in the placements that you want

There are plenty of handy links like this one here which is a tyre/wheel size comparison so you can see how your new wheels would sit in relation to your existing setup but it is nice to know the details of how this is worked out so you understand why you are ordering what you are ordering

Just to add to the useful information on this post the standard MKIV Supra wheel sizes are below just so you have a starting point to see if you have no idea what yours are:

Front 17x8et50 (with 235/45/17 tyres)

Rear 17x9.5et50 (with 255/40/17 tyres)

or

Front 16x8et50 (with 225/50/16 tyres)

Rear 16x9et50 (with 245/50/16 tyres)

And the tyres sizes to wheel sizes you want is depending upon what use you are using your Supra for but a guideline would be:

Remember that the narrower in this chart that you go the more "stretched" your tyres will be and the wider in this chart you go then the more "mushroomed" your tyres will be (the link above for the offset calculator also shows tyres sizes so you can use that link for tyres too).

Hope this helps a few people understand more about your wheel/tyre setup sizes and im always happy to answer any questions or help anyone out who doesn't understand

P.s. Mods I didn't know which section to put this thread in so feel free to move it to technical or FAQ's or wherever you see fit

To measure how much wider you can " get away with " you need a straight edge on your wheel arch / inner arch that is perfectly vertical, a spirit level is probably best. then measure from your wheel to the straight edge. this will give you a guide to what will and wont fit !!

Good right up

Might be worth mentioning that certain spoke designs won’t clear the larger OEM brakes or larger aftermarket options.

Might be worth mentioning that certain spoke designs won’t clear the larger OEM brakes or larger aftermarket options.

Thats the most important fact, offset, unless its ludicrous, has absolutely nothing to do with brake clearance. Spoke design has though

Nice one Shawn I’m even more confused now

Great that someones took the effort

Just a shame its such a confusing way its been explained lol

Offset is simple

Its just the relationship of the rear hub mounting face and the centreline of the wheel.

Positive offset moves the mounting face outwards toward the face of the wheel

Negative does the opposite and moves it inwards towards the inside edge

This has the effect of moving the inner and outer edges of the wheels outward for a lower or negative offset, accompanied with that sexy deep dish or concave look. Or inwards for a flat and boring style as the Supra tends to suffer from with standard ET's

All you do is start with the width of the wheel, halve it is the centreline = Zero offset ET, on an 8J rim this means 4" to each lip (actually its slightly more as wheel widths are measured to the inner edge of the lip where the tyre beads), if it was a +25 et the you'd have 3" to the outside and 5" to the inside using the rule of thuimb that 25mm=1inch, keep going up and eventually the inner lip will foul the strut on the inside. Go too far the other way and the outer edge will extend past the bodywork and you'll rub tyres and paint.

As said, you just start with stock rims and ET, measure roughly where you want to be and add or subtract accordingly. It gets more confusing when also going up widths of wheels, and then when you are getting good you can start to add tyre stretch, geometry and other tricks to get that deep set of Works rims looking HellaFlush !!!

Can I get your view on these xxr 968 I'm looking at 18x9 et35 or et20 available at front and 18x10.5et20 rear (only et20 rear available) I've seen few pics of them on supras but no info really on fitment with that aggressive offset I've rear rolled arches and coilovers not lowered will they fit under with a 285 tyre at back? fronts should be spot on!

Can I get your view on these xxr 968 I'm looking at 18x9 et35 or et20 available at front and 18x10.5et20 rear (only et20 rear available) I've seen few pics of them on supras but no info really on fitment with that aggressive offset I've rear rolled arches and coilovers not lowered will they fit under with a 285 tyre at back? fronts should be spot on! https://jza80.mkivsupra.net/imports/2018/05/69.jpg

 

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may be pm safcdixon it seems he has the same offsets you want.....

 

http://www.mkivsupra.net/vbb/showthread.php?335694-What-offset-clears-uk-brakes&highlight=xxr968

Thank you bud that's perfect!

may be pm safcdixon it seems he has the same offsets you want.....

 

http://www.mkivsupra.net/vbb/showthread.php?335694-What-offset-clears-uk-brakes&highlight=xxr968

Thank you bud that's perfect!

 

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the most you will be able to run comfortably on the back is a 255 tyre, this would require a little bit of a " stretch " which is nothing in dangerous in my opinion, and a 235 on the front with a ET20.

He got back to me saying that he didnt get them as they wouldnt fit after researching would need wide arch kit to run even with a stretched tyre would have rubbed sad times:(

He got back to me saying that he didnt get them as they wouldnt fit after researching would need wide arch kit to run even with a stretched tyre would have rubbed sad times:(

 

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I currently run 18x9 ET20 up front and 18x10 Et20 rear with the tyre sizes ( 225/40 Front & 255/40 Rear ) a roll on the back, lowered on Eibach springs and the only time it scrubs is when I hit a bump hard

Do the rears stick out much bud? Do you think it would work ok? I won't be lowering my car either just don't want buying them then realising they wont work

I currently run 18x9 ET20 up front and 18x10 Et20 rear with the tyre sizes ( 225/40 Front & 255/40 Rear ) a roll on the back, lowered on Eibach springs and the only time it scrubs is when I hit a bump hard

Do the rears stick out much bud? Do you think it would work ok? I won't be lowering my car either just don't want buying them then realising they wont work [\QUOTE]

 

They will "work" but they will protrude the arch and you will have to run a stretch, I would personally do it as I am BPU and have no issues with traction. I will see if I can dig up a picture but your wheel will stick out 6mm more.

Thank Matt appreciate it

Do the rears stick out much bud? Do you think it would work ok? I won't be lowering my car either just don't want buying them then realising they wont work [\QUOTE]

 

They will "work" but they will protrude the arch and you will have to run a stretch, I would personally do it as I am BPU and have no issues with traction. I will see if I can dig up a picture but your wheel will stick out 6mm more.

 

 

Thank Matt appreciate it

 

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Just found this Wonder what sizes are

came on here for this thread, great write up.

However I'd be interested in peoples experiences of wheel fitment & LS400 calipers, kind of discussed here.http://www.mkivsupra.net/vbb/showthread.php?343738-Ls400-calliper-clearance&highlight=ls400

I've got some dished wheels & currently have to run 15mm spacers all round (to clear the LS brakes at the front and for a properly lined up fitment on the rear).

Guessing the LS brakes are narrower than the UK specs?

Any thoughts on the above?

Yep,

Flatter spoke designs often have trouble clearing bigger calipers, case in point - the pretend 3piece Rota Kyushu rims wouldn't clear my Wilwood 6pots on my drift car without at least a 12mm spacer.

So wheels like those XXR which are tryoing to look like Work Equips will have the same problems the Equips do with not clearing larger calipers, suck it and see usually although some dealers like Driftworks can send you a spoke design "cross section" you print on paper and cutout to see if its going to be feasible or not.

Just thinking there would taking wheels to a machine shop to take some material off the backpad of the wheel would higher the offset help fitment in some wheels? Anyone done this

You can do it,

Certainly depends on many factors, primarily how deep the seats are for the nuts/bolts !!