Technical working out unknown offset

[ronnieronson]

Hopefully I have this right (but I await someone to correct me).

if we know that a wheel is 6j (152.4mm) wide, and divide that in half (76.2mm), that tells us the centre of the wheel.

If we then measure from the hub face, to the rib of the rim (which in my case measures 110mm), and deduct half the width from the new measurement that should give us the offset yes?

Here's my working:

152mm (rounded down)
divided by 2 = 76 (rounded down)

hub face to rib measurement = 110mm
minus 76mm
= 34mm

based on the assumption that they are indeed et34, and using the calculator (as found in the faq - cheers Custard ) here: http://www.1010tires.com/WheelOffsetCalculator.asp

...it would indicate that I need 4mm spacers - so here's the thing:

Assuming that all my working out is accurate, would I be best to go with 3mm or 5mm spacers? - not going to bother on the fronts for now, as clearance seems to be good enough to avoid any scrubbing on my gearbox, but obviously the clearance on the rear of a sei isn't so great, with currently only approx 3mm to play with on 175/50's (and I may wish to upgrade to a set of 195's next summer).

:chin:

 

[randomizered]

I put, ET 34 6J on mine. Think that was the spec anyway.

I have a rear disc conversion, but i think the offsets are the same.

With 3mm spacer, it would foul on the rear arm, i wouldn't go on on at all!

With 4mm spacer, it just fits! I have about 0.5-1mm! between the wheel and arm.

With it this close, the tyre scubs on;

the nearside rear outer arch lip
the offside rear inner

thats with 185/50/14 tyres

It only scrubs with people in the rear though, and i am on a 50-55mm drop.

Double check the wheel oofset of mine to make sure its the same spec as yours; oz racing superturismo.

If it it, then the above is all applicable

Kristian

 

[fingers99]

Whenever I try to work out offsets with that method I get really flakey results.

I find that 3mm works OK with 35et (with drum brakes) on a Cinq, Emz found the same with the Sei. No scrubbage at all with 195/45/14s, but GOK with those high profile things, especially with 15s.

The easy way (in the long run) is the hard way: pull the rear spring one side, pop studs in, start with a 3mm spacer and add washers. You can then test for clearance by putting a jack under the (unsprung) wheel. Obviously, you don't run the car till you've bought spacers of the correct dimension and re-fitted the spring!

I'd not run without front spacers. The car will sit higher and -- on skinny tyres like that -- it may not turn in at all.

 

[ronnieronson]

I put, ET 34 6J on mine. Think that was the spec anyway.

I have a rear disc conversion, but i think the offsets are the same.

With 3mm spacer, it would foul on the rear arm, i wouldn't go on on at all!

With 4mm spacer, it just fits! I have about 0.5-1mm! between the wheel and arm.

With it this close, the tyre scubs on;

the nearside rear outer arch lip
the offside rear inner

thats with 185/50/14 tyres

It only scrubs with people in the rear though, and i am on a 50-55mm drop.

Double check the wheel oofset of mine to make sure its the same spec as yours; oz racing superturismo.

If it it, then the above is all applicable

Kristian

Nice one - will check this out.

especially with 15s.

??? - staying with 14's Fingers - the car isn't lowered, and currently runs 175/50/14's, planning on just using these tyres until summer and then going for 195/45's.....

 

[fingers99]

I thought the MOs were 15"?

Assuming 34 et, 4mm at the back will do it. It'd be crazy not to use spacers at the front -- 10mm should do it. If you don't, I'm pretty sure you'll foul the TRAs and gearbox cover.

But, given that your calculations/measurements may well be out, and that 2mm is a lot, I'd actually trial fit with the rear spring out.

 

[AppleSei]

you can get them in 14'' as i thought that too fingers but performance alloy website stock 14'' of that wheel so must be available

 

[StoneNewt]

Compomotive MO5s go from 14x5.5 to 17x8 see their site (linked)

 

[randomizered]

I just checked for you and mine are actually 14x6 ET 36, not 34 as i though.

What that means in practical terms, im not sure, i still haven't got this offset stuff

 

[ronnieronson]

I thought the MOs were 15"?

Assuming 34 et, 4mm at the back will do it. It'd be crazy not to use spacers at the front -- 10mm should do it. If you don't, I'm pretty sure you'll foul the TRAs and gearbox cover.

But, given that your calculations/measurements may well be out, and that 2mm is a lot, I'd actually trial fit with the rear spring out.

10mm on top of the 10mm spacers already on the fronts?

 

[ronnieronson]

I just checked for you and mine are actually 14x6 ET 36, not 34 as i though.

What that means in practical terms, im not sure, i still haven't got this offset stuff

on a 6j wheel the target offset to stick to OE measurements would be et30 - so based on the fact that you have only 4mm spacers and still have clearance should mean that if mine are actually et34 then 4mm ones should be plenty for me.

Did you use spacers up front, or just stick with the fiat 10mm ones?

 

[randomizered]

I just run the fiat 10mm ones on front. I have big issues fouling the gearbox, but that because its a 6 speed. From what rallycinq was saying, his didn't foul the 5 speed box at all

Kristian

 

[ronnieronson]

I just run the fiat 10mm ones on front. I have big issues fouling the gearbox, but that because its a 6 speed. From what rallycinq was saying, his didn't foul the 5 speed box at all

Kristian

sweet - just what I wanted to hear

Spoken to Richie about some spacers, but he only does them in 3mm or 5mm - where did you get your 4mm's from?

 

[randomizered]

they were off ebay...but looking into the offset thing a bit, you should be fine with 3mm I'd not go for 5 as they will sit too far out, and you won't have much of the cetering ring left.

Kristian

 

[ronnieronson]

they were off ebay...but looking into the offset thing a bit, you should be fine with 3mm I'd not go for 5 as they will sit too far out, and you won't have much of the cetering ring left.

Kristian

I suppose I can always get some 3mm ones, try em for a week and if I need to go bigger, buy some at a later date

 

[fingers99]

10mm on top of the 10mm spacers already on the fronts?

First time you've mentioned any on the front!

Again, if you don't know the et, do it properly instead of buggering around with a tape measure. Takes 5 minutes to take a rear spring out! :bang:

Or you might hurt the wheels!

 

[ronnieronson]

First time you've mentioned any on the front!

Again, if you don't know the et, do it properly instead of buggering around with a tape measure. Takes 5 minutes to take a rear spring out! :bang:

Or you might hurt the wheels!

The standard fiat ones that came with the car

Will treat her with the utmost care, to ensure that her new shoes fit nicely

...just finished giving the last one a quick respray, and all four are getting a little low gloss laquer to protect them - new centres and decals should turn up tomorrow, then it's off to TyreMen on Wednesday to get measured up (and hopefully fitted) - rang them today, said they can accurately sort out the offset and even have laser machined spacers made up same day for me if need be

Wooot! :woot:

 

[fingers99]

I was forgetting it was an Abarth!

If you get the chance, a good idea to put some decent penetrating fluid on all the studs -- I know of 2 cases where the studs have corroded into the hub so firmly on Abarths that the threads were wrecked on extraction. I doubt if they'll even touch the spacers, but if they do, they'll use an air gun on the studs. Ouch!

 

[ronnieronson]

I was forgetting it was an Abarth!

If you get the chance, a good idea to put some decent penetrating fluid on all the studs -- I know of 2 cases where the studs have corroded into the hub so firmly on Abarths that the threads were wrecked on extraction. I doubt if they'll even touch the spacers, but if they do, they'll use an air gun on the studs. Ouch!

I'll try to do that tuesday night when I get in from work - got some penetrating oil in my room somewhere (no joke, the bedroom looks like a garage at the mo ) - though I do recall having the studs off before and having no trouble...