Offset confusion

[jesterwalker69 0]

Basically I'm getting a little bit bored with my ABT's and thinking of getting some new wheels.

The thing that makes this difficult is the Porsche brakes on the front.

I have currently got 10mm spacers on the front so my wheels clear the callipers but they ONLY just clear and i dont want to put bigger spacers on as the tyres are literally in line with the arches - any more and they will be an MOT fail!

I dont want to end up faffing on buying wheels then finding out they don't fit over the calipers etc!

I think (one for the wheel whores out there - BEN!) that its the ET of the wheel that will determine whether they fit or not?

My current wheels are 17's ET30 (i think?!)

If i stick with the same size wheel and ET for my new wheels should they just pop straight on without any clearance issues?

Searched explanation of ET numbers etc and came out just as confused (blonde!)

I have also considered dropping to 16's as i think they MIGHT just squeeze on but again what ET would i need to achieve this?

Thanking you kindly!

[binliner 0]

It's not just the ET that will affect it, the style of wheel will as well. The offest is measured between the centre of the wheel and the mounting face but the shape of the spokes is also a factor and that can only really be tested by fitting the wheel.

The other thing you don't mention is the wheel width... In theory the same size wheel and offset would fit if it's the same width (but like I say, not guaranteed) If you went for a wheel with a higher offset you could get it to fit by using different sized spacers (or you could go for an offset a few mm lower with no spacer)

[jesterwalker69 0]

Ah sorry, width is 7.5

Ok...think i get ya. Maybe just have to be trail and error then

[legvw 0]

Try this site to work out wheel offsets etc.

http://www.1010tires.com/WheelOffsetCalculator.asp

[Ben Seabrook 4]

Mate as Justin says if you stick a wheel on with the same size, offset, width etc you would expect it to fit although the shape does have an impact obvisouly when cleaing brakes. Standard VR ET is 35 mate so your current wheels at et30 and with a 10mm spacer means they are effectively et40 which is why they fill the arches nicely so you can get some rims with a smaller et and then use bigger spaces or bigger et on a standard fitment and use no spacers depends what you are after although as running standard you might be better off selling the pimp brakes and putting the money towards some new rims ! ;)

[Rikki 2]

Et30 with a 10mm spacer makes them et20.....smaller et = further out they sit. You will have to test fit first...i got porsche brakes with 312mm disks and tt' comps have more room than it looks like in you sig and they are around et37 (i think)!

[Ben Seabrook 4]

am confused now !! I always thought spacers added to an et not reduced it as they increased the distance between the effective hub and the centerline of the wheel ?

[Rikki 2]

The less the number the more they poke. Et is the distance of they center of the wheel what mounts to the hub to the back side of the rim!

[Ben Seabrook 4]

yeah I know that about smaller et's poking more mate just always thought it was the other way round about et's changing with adaptors !! muchos confusion !

[gavinvr6 0]

he distance is measured from the centre line of the wheel to the wheel mounting face, by putting 10mm spacers on your effectivley moving the mounting face 10mm closer to the centre line, so reduces the et by 10.

if a 30 et then you fit 35 mm spacers althought you'd be a twat, it becomes negative et -5 because you have crossed the centre line by 5mm

simply find a decent wheel shop and find what you want then ask em to trial fit some over ya front brakes, if they fit then ask em what size and et they are then tell em you'll be back and go find some the same cheaper on the bay of e or something

[Ben Seabrook 4]

Just found this Ollie and it explains it pretty well I think and yeah I now get it :)

A positive ET figure eg ET35 means the hub face is 35mm OUTSIDE of the centre line of the wheel. So it's likely you'll foul suspension components and bodywork INSIDE the wheel and on trying to turn corners with the fronts.

So when you fit ET55 wheels then the offset now moves the centre line of the tyre INWARDS on the car. See if this helps

Code:

+-- wheel to hub face

| +-- centre line of tyre

| |

V V

+----------+

| |

\ ________/

|

| this is exagerated to show the different lines

|_______

/ \

| |

+----------+

The distance between the 2 points are the ET. If the centre line is outside the hub line then it is a negative offset number.

So, the HUB face is a fixed point, so the ET moves the centreline of the tyre in and out for + or - et VALUES. So a LARGER postoive ET value means a larger distance between the 2 points and the centreline of the tyre moves inward ( because the hub is fixed ). Equally a small ET moves it out. For negative ET values it works the other way round. Just keep sketching the above diagram with the different ET values and look where the tyre ends up - remember the hub is fixed.

So how to solve your ET55 problem ? Well, cheat and don't make the hub a fixd point. Simple spacers will more the hub face out by the thickness of the spacer. So for an ET35 wheel setup for an ET55 you want to add a 20mm spacer. BUT, make sure this is donw with professionally supplied bolts and spacers to ensure you don't over stress anything and it breaks.

By adding the spacers the centreline of the tyre returns closer to the point the suspensions is designed for and the "handling problems" I warned of are avoided. These problems occur becase as KE says you case the scrub radius to change having moved the camber and caster angles and aslo the ackerman angles for the steering. All can be bad news for safe and consistent handling.

The larger ET wheel with the same width of wheel means the centreline of the tyre doesn't quite return to the same place, to do that you also should go for a slightly wider wheel. Less of an impact as the outright ET change but still can have an impact on handling. Dependant on the wheels availabel you can juggle the ET sizes and wheel widths to better reposition the contact point. This is why any serious car will have fully adjustable rose jointed arms so that the camber/caster/ackerman can be adjusted for different wheels.

FINALLY you have to worry about bodywork and might need to give more space on the outside and the inside. In the works cases you sometimes contact suspens arms/track control rods etc. These all need to be thought befoer you buy-and-try Best advice is to find someone who has fitted the same and inspect for any rubbing or modifications and get to test the handling of the resulting car. In many cases added "better" rims can make the hadnling worse by compromising the stock (UNadjustabel) suspension

[jesterwalker69 0]

Wicked cheers for the Ben and cheers chaps for all your advice.

So essentially i need something with a lower ET as that would mean the hub face is FURTHER away from the spokes BUT just make sure the wheels don't sit too far from the arches....Anyone know of any decent arch rolling spots oooop north?!

[binliner 0]

Standard VR ET is 35

ET on standard wheels is actually 45 (or possibly 42 cant remember) but they're 6.5J wheels... that equates to about ET 32 on a 7.5

your current wheels at et30 and with a 10mm spacer means they are effectively et40 which is why they fill the arches nicely

As has been said adding a spacer pushes the wheel out further thus lowering the et

[binliner 0]

shouldve read page 2 before posting really shouldnt I!

[Ben Seabrook 4]

well personally had got this arse about face so to speak !!! but yes Ollie that's right mate as for arch rolling the only peeps I know of is this guys http://www.archenemy.co.uk/ not sure if there is anyone in your area but they do travel I believe