Wheel offset -- WTF?

[R31Nismoid]

Now... i relly dont understand this at all cause im a bit stoopid.

I've got an R31 with a 5-stud conversion.

And it currently has R32 GTR wheels on it.

I went to put stock R33 wheels on it last night, and they sat WAY inward, so i took them off as it didnt feel right on the car.

So firstly... can someone please explian (in basic terms) what offset is ?? and how it works.

Second... I'm getting a set of R34 GTR wheels...

Is there offset or whatever different to R32 GTR wheels ????

... and if so, what will i need to do to get them on my car.

Thanks in advance

ash

[Warpspeed]

As you already know, wheel offset moves the wheel rims in or out with respect to the plane of the wheel flange and studs. This effects several things but mainly front scrub radius and wheel bearing loads.

The most important is scrub radius. When you steer the front wheels there are a couple of ball joints that act like a hinge and allow the wheels to steer. If you draw a line through these two ball joints it will hit a point on the ground somewhere within where the tyre patch contacts the road.

The actual point on the ground where the tyre pivots will never be exactly at the centre of the tyre contact patch on the road, also the axis of turning is never exactly vertical either.

Now the guys that have designed your front suspension have worked out all the geometry, and the front end alignment settings to give the car good steering feel and handling characteristics.

What you want is good self centering, so the car does not wander at high speed, sufficient feedback through the steering wheel when cornering without the steering loading up and becoming too heavy, and ability to handle a flat front tyre or blowout without ripping the steering wheel right out of your hands.

Sometimes they decide to change some front suspension parts and they might change the wheel offset to improve the handling or feel after a lot of testing. If you want to fit odd aftermarket wheels just for looks, be prepared for some changes to either the handling or how the steering feels.

Changing the wheel offset by huge amounts can also change the stresses on wheel bearings and wheel studs. As these are so heavily over-designed, I doubt if either will ever give trouble, but it is something to think about as well.

[floody]

Stock R33 GTS wheels are a numerically higher offset than R32 GT-R wheels, and so will sit in further because the distance from the CENTRELINE of the rim to the THE HUB FACE (flat bit that mates to the hub/disk) is further. GT-r wheels are what, 16x8" and +30 offset, where the others are 16x6.5? and more like +35-38 offset (can't remember exactly) So they are narrower, and the flat bit is further toward the outside, so when you bolt them on they will be a long way further in, I'd guess what, 1.75" or so?

Lower the offset number, the further they stick out, higher the number the closer inside.

I think Most of the GT-R rims are about the same offset its just widths that change. R34 rims are what, 18x9"?and about the same offset as the GT-R rims. I think they'd just fit , but you'll just have to try them on I guess.

cheers,

floody

[PHaT MR30]

Ok i am just trying to figure this out too

My car has had some extensive work done to the suspension, (adjustable everything). as opposed to my mates identical car which is stock.

we tried to put his wheels on which are supposedly the right offset for the car(don't know the offset of them, how can i measure), onto my car. first of all my steering arm hit the inside of the rim, causing them to rub when i rotated the wheel, ok then they just didn't look right.

i had simmons on it previously which sat just in the guard (not rolled, didn't quite touch) but had to remove them for a little brake clearance problem.

now i have 17x7" with a +38 offset these clear the strut by ~7mm but sit in the guards a little.

how can i figure out what offset is right for my car?

if i go to say a lower figure will that bring the wheel out more into the guard?

HOW TO MEASURE WOULD BE SWEET!!!

[R31Nismoid]

mmm, i am in the same boat.

nothing on my suspension is stock

Adj strut tops... coil overs etc etc.

[floody]

Measuring is fairly easy. The distance you need is from the centre of the rim's width, to the hub face (the round flat back bit of the rim that mates to the brake disk/hub). It is hard to get a totally exact figure, but roughly it goes like this.

Get your rim width in mm e.g 7x25.4. Divide it by

There are 2 ways to measure the distance from hub to centre.

A) sit wheel flat on its face on a smooth level surface and measure from the surface up to the flat of the hub face, accounting for tyre overhang, and then deduct the measurement from 1/2 the rim width.

B) measure from hub face to back of rim, deduct half rim width from the total figure (hub to backside of rim).

Hopefully one of those will give you an idea.

Cheers,

floody

[PHaT MR30]

hmm im sorta getting it but still having trouble, could you possibly put it in lay mans terms for us dummys

'Looks for dummys guide to fitting wheels!!'

[floody]

Thought I did!

Umm which bit are you having trouble with?

cheers,

floody