Please help me measure the offset of this whee

[wemorgan]

I'm feeling like a bit of a blonker here. I took some information on trust and now something has gone horribly wrong.

Following my cracked alloy saga I bought a new alloy. A Rota Slipstream 15x7 ET28. (this is the size I thought they were, being the same as used in the Ma5da series)
I had this fitted and all was OK, or so I thought.

Today I was checking the wheel nut torques in preparation of my track day tomorrow and noticed that the socket sat at a different depth in the new alloy.
I checked again and yes it's now clear that the offset of the new alloy is different from the old ones. (I presume it's the offset causing this)

So off came the new alloy and stamped on the hub inside face was ET28.
Off came an old alloy and there was no ET number stamped on it. I checked the others and they were the same too.

So how do I now measure the offset of my current alloys?

Thanks.

Old alloy

New alloy

In theory the available options are:


15” x 6.5” 4x100 / 4x108 ET40
15” x 6.5” 4x95.25 ET7
15” x 6.5” 4x95.25 ET10
15” x 7.0” 4x100 ET28
15” x 7.0” 4x100 / 4x114 / 5x114 ET40

 

[Dieselman]

Measure the width of the rim then place a plank/block across the inside of the wheel and measure the mating hub from the rear rim.

If the mating face is exactly half way through the wheel the offset is zero, any deviation is then the offset.

 

[wemorgan]

Thanks Will. I've just had a go at this. It's not as easy as I hoped.

The wheel is ~205mm wide. Outer rim edge to inner rim edge. Though holding the ruler steady and looking vertically downwards with my face up against the wheel arch was awkward.

The tyre sits proud of the rim edge, so I held the piece of wood up against one rim, but then it angles out resting against the tyre wall on the opposite side.

Excuses, excuses I know. But what I'm getting at is that I think I measured a ~10mm difference between the old and new alloy. So I think I needed an ET40.

Both alloys were roughly the same width. I say roughly as I was not so steady of hand. I presume 7" is the width of where the tyre sits inside the wheel?

 

[Dieselman]

Placing a block of wood across both the inside and outside tyre sidewall should reveal the same result as using the wheel rim, but can then be measured easily.

 

[wemorgan]

Ah, TWO blocks of wood.....the inventory is growing!

 

[wemorgan]

I've been out again, now with 2 pieces of wood and it's a lot easier

My measurements were now within 1-2mm accuracy.

So the old wheel is ET40 and the new one I confirm is ET28.

BUGGER! Nothing quite like flushing good money away.

A few medicinal beers required.

On the plus side though, I have a very good reason for why I will be slow at tomorrow's track day.

 

[grober]

The standard offset for the W208 CLK for a 205/55 tyre on a 7J wheel seems to be ET37 except for a staggered set up where the rear can be ET36 or even ET30

 

[wemorgan]

Thanks Graeme. Sadly though, I sold my CLK a few years ago now. I'm ashamed to admit I've been longer outside a Mercedes than inside.

 

[Dieselman]

You could use a wheel spacer to adjust the offset.

 

[wemorgan]

Now you're talking a language beyond me.

Help this fool out please. What size spacer do I need to make a ET28 wheel comparable with a ET40, or is it vica versa? I presume I will need three 12mm spacers? But then will the wheel nuts still fit correctly?

This is a whole new world to me.

New ET28 wheel

Old ET40 wheel

 

[wemorgan]

The place I bought the alloy from sells 3 and 5 mm spacers at £9 each.

So even if I could get 12mm spacers, I would need 3 each for 3 wheels. That's £81, which is not much cheaper than the wheel itself at £110.

 

[Dieselman]

You need a 12mm spacer to give the old 28mm wheel a similar stance to the new wheel. That would space the rears the same amount.

A new wheel would be ideal though.

 

[Dieselman]

Did you buy the wheel as a mail order part, if so return it as they are bound by distance selling rules.
The seller would be likely to offer a replacement of the correct offset rather than a refund.

 

[wemorgan]

The problem is that it was my mistake.

He delivered the wheel which I asked for. I simply ordered the wrong size.

 

[Dieselman]

The problem is that it was my mistake.

He delivered the wheel which I asked for. I simply ordered the wrong size.

Still, Distance Selling Rules apply as you couldn't check the goods before purchase.

 

[Doodle]

I was about to suggest potentially machining the hub face, given how Rota's are constructed. But tbh that will probably also cost as much as a new wheel.

 

[sspeed]

I would buy 1 more wheel for the rear...
I think the new wheel looks better with it being a wider stance..
Leave the front as they are and widen the rear..

I think it very likely that spacers would mean you need new bolts !

 

[wemorgan]

I quite like having equal wheels on all four as it allows me to rotate. The tyre wear is not so even due to track use, so this is quite handy to do.

I'll call up on Tuesday and order the correct wheel this time.

 

[ghouluk]

buy a new wheel, spacers are a world of pain .... especially when you don't need them

1. unsprung weight - you're using on track right?
2. balance and handling suffer
3. even with hubcentrics (which won't need longer bolts/studs and will locate as good as possible) you're looking at odd sizes which means silly money, or stacking spacers making 1 & 2 wors

ok for looks alone, but stump up for the new wheel if you want to go quick

(there - i knew my wideboy skyline history would come in useful for something )

((by the way - nothing against anyone who chooses to use spacers, personal opinion only as someone who does a lot of track days ))