Need a wheel expert to check my math....

Neveragain55 · Post by **Neveragain55** » Sun Sep 27, 2015 7:59 pm

I know the offset / wheel size questions have been beaten to death in here and in most BMW forums but I think it's because there's lost of people like me who just get confused by all of it no matter how much it's explained to us.

So I appreciate the weariness of the question, but I really need some help here.

I'm currently running a staggered set of M Parallel wheels.

The current rear wheels are: 18 x 9.5 with an et of 25, the current front wheels are: 18 x 8.0 with an et of 13, and they all fit perfectly with no rubbing or binding issues at all.

The new wheels going on the car after paint are: 18 x 9.5 with an et of 30 in the rear, and 18 x 8.0 with an et of 32 in the front.

If I calculated everything right, I'll need at least a 5mm spacer for the rear wheels, and a 19mm spacer for the fronts to make the new wheels sit where the current wheels are sitting now.

All I'm looking for here is a yay or a nay regarding my math.

If I am wrong please tell me which size spacers to use.

Thanks.....

Brucey · Post by **Brucey** » Fri Oct 02, 2015 6:45 pm

your maths is correct but the plan is fundamentally flawed in that the rear spacers (if 5mm) will almost certainly not retain the correct hubcentric wheel location, (or if they do, it'll be over just a few mm, depending on the counterbore in the wheel centre). This can lead to all kinds of problems.

Mind you it would be worse on the front.

I wonder if you shouldn't shoot for a 10mm spacer at the back; this will push the wheels out another 5mm but IIRC you can get 10mm spacers in hubcentric, which is what you probably need.

cheers

Da_Hose · Post by **Da_Hose** » Fri Oct 02, 2015 10:56 pm

I concur with Brucey. I also recall that 10mm is about the thinnest you can get and still have a hub centric fitment. A quick web search shows that 10mm is the thinnest that most people carry.

Jose

Neveragain55 · Post by **Neveragain55** » Sat Oct 03, 2015 2:26 pm

10mm it is for the rear then.......

Brucey, do you think the 20mm spacer up front is sufficient?

Brucey · Post by **Brucey** » Sun Oct 04, 2015 8:22 am

yes, in fact if the sizes are as indicated it is 1mm more than is strictly necessary....

cheers

Neveragain55 · Post by **Neveragain55** » Sun Oct 04, 2015 1:50 pm

True, and I looked for a 19mm spacer but there doesn't seem to be any in that size.

I did find a company that claims they can make them to any size you want but of course I wouldn't know if they are as reputable as the big guys like: H&R or ECS Tuning.

bpoliakoff · Post by **bpoliakoff** » Sat Oct 10, 2015 3:37 am

Da_Hose wrote:I concur with Brucey. I also recall that 10mm is about the thinnest you can get and still have a hub centric fitment. A quick web search shows that 10mm is the thinnest that most people carry.Jose

An issue I have run through my mind many times. What I have figured out is to buy a spacer with an integral hub centric and then turn the back side of the spacer down to the desired thickness. Thereby getting a thin one piece spacer with a hub centric.

Neveragain55 · Post by **Neveragain55** » Sat Oct 10, 2015 4:50 am

Good idea but ECS Tuning has us all covered.

They sell hubcentric spacers specifically for our cars that are precisely machined to fit our 72.56 hubs in almost every millimeter size you can think of.

They even go the extra step of making longer bolts stronger to withstand the extra load of the spacer.

My plan is to get hubcentric, 10mm "washer" style spacers for the rear, and hubcentric 20mm "bolt-on" style spacers up front.

That should put my new wheels exactly where they need to be and I shouldn't have any rubbing issues if I calculated everything right.

Once everything is on I'll do a follow up....

hornhospital · Post by **hornhospital** » Sat Oct 10, 2015 4:51 am

Won't work, Bert. The hub (back) side of the spacer is going to have a counterbore I.D. to fit the hub (72.56mm), but it will neck down a short way in. Enough that the hub fits through it, and the counterbored location part of the hub mates up, but it has to get smaller to allow any strength and thickness for the O.D. of the hubcentric neck part that fits in the wheel, which is also 72.56mm. If you face off the back side of a thick spacer, you'll lose the 72.56 counterbore, and it won't fit on the hub.

m6dave · Post by **m6dave** » Sat Oct 10, 2015 8:33 am

The easy fix for the rear is to fit E32 rear trailing arms as they come with the vented disc brake set up. In order to accommodate the thicker disc the hub sticks out 9mm further each side so you get a brake upgrade and the wider track without needing spacers and keeping the standard hub centric arrangement.

Neveragain55 · Post by **Neveragain55** » Sat Oct 10, 2015 2:13 pm

Hornhospital (interesting user-name by the way)

I'm not sure if I explained myself correctly, my apologies. I'm not facing off, machining or turning down anything. All I'm going to do is buy two rear 10mm spacers (that are "supposedly" already designed to mate up to both the hub bore and the wheel bore without me having to touch anything)

Here's the link to the ECS spacers, click on the link where it says: "Fits These Cars", and read the "Product Details"

https://www.ecstuning.com/BMW-E24-635CS ... /ES205204/

I have to tell you that I find it really hard to believe that any company making wheel spacers wouldn't calculate all of this stuff we're talking about, or design a spacer that doesn't work out of the box.

They would all go out of business pretty quick if we all had to do lots of fabricating "past" what they've already done. Please look over the link and get back to me, I'm curious as to what your opinion on these spacer are.

m6Dave....................."easy fix"???? dude you don't like me?

What you suggested definitely doesn't sound easy to me but I'll consider it if the spacer thing ultimately doesn't work. Thanks for the suggestion.

hornhospital · Post by **hornhospital** » Sun Oct 11, 2015 3:53 pm

Neveragain55 wrote:Hornhospital (interesting user-name by the way)

This will explain it:

www.airhornhospital.com

Neveragain55 wrote:I'm not sure if I explained myself correctly, my apologies. I'm not facing off, machining or turning down anything. All I'm going to do is buy two rear 10mm spacers (that are "supposedly" already designed to mate up to both the hub bore and the wheel bore without me having to touch anything)

Here's the link to the ECS spacers, click on the link where it says: "Fits These Cars", and read the "Product Details"

https://www.ecstuning.com/BMW-E24-635CS ... /ES205204/

I have to tell you that I find it really hard to believe that any company making wheel spacers wouldn't calculate all of this stuff we're talking about, or design a spacer that doesn't work out of the box.

They would all go out of business pretty quick if we all had to do lots of fabricating "past" what they've already done. Please look over the link and get back to me, I'm curious as to what your opinion on these spacer are.

Those will work fine with the correct longer-than-OEM bolts.

I was replying to bpoliakoff's posting about facing off the back side of a set of spacers, not your choice of spacers.

I've both bought spacers and made my own from scratch for specific cars to achieve a particular offset. My '85 635 is running a set of Beyern 5s that came as E36 fitment (high offset...45). I made a set of 25mm hubcentric spacers to bring them out to an effective 20mm offset.

Neveragain55 · Post by **Neveragain55** » Sun Oct 11, 2015 4:56 pm

Cool..............

My late uncle (may God rest his soul) was a truck driver and an insanely good mechanic. Looking at your web site brought back some cool memories.

I appreciate the reply's, they really help.

I also have a pic of my 89 in the rain, and I love your rims.....question though?

From the picture it looks like your front end is a pinch higher than the rear. The front clearance from the fender to the top of the tire looks like it's wider that the clearance in the rear.

Is this the case or is it just the angle of the picture?

I'm asking because after all of my suspension work (that I'm very happy with) the gap between the front fender & tire looks like it's a few mm wider than the rear gap and my OCD has already kicked in wondering how I can reduce it.

Thanks for sharing all the info about the spacers.........you guys are the best.

Here's a picture of mine taken several years ago in the rain.