9.5" Up Front + 5mm Spacer = Shimmy!

HadE55NowM5 · 13th April 2002, 08:44

Earlier today, I installed a pair of new OEM 9.5" x 18J wheels combined with 275 35 ZR 18 Michelin Pilot Sports up front and 5mm H & R spacers and lug bolts.

When leaving the tire shop, I immediately noticed an unbearable front end shimmy only in the 40 - 60 mph range. I returned to the tire shop thinking that it was a problem with wheel balance. After re-balancing the front wheels, wheel balance turned out to not be an issue). We even rotated the rear wheels/tires to the front with no reduction in the front shimmy.

I started thinking that maybe the cause is either excessive front wheel bearing runout, or abnormal wheel runout. I've since eliminated these as the possible culprits. I also thought about changing the front alignment by increasing the front toe-in about 1/16" (so as to offset the natural tendency of the heavier and wider wheel/tire assembly to pull outward).

I think that I've settled on the real culprit! When looking at the wheel hub, the hubcentric "register" protrudes (visual estimation) about 12mm outwards. But with the 5 mm spacer, the effective amount of register which goes through the wheel center hole to locate the wheel, diminishes to about 7mm.

The problem seems to be that the 74mm diameter of the wheel center hole is not entirely consistent the whole way through! It seems that about 5mm worth of this hole (starting from the inside surface of the wheel center where the wheel mounting pad contacts the hub) has a non-flat conical contour, seemingly to make the wheel easier to slide on and off the hub register.

The remaining 7mm of register (i.e. the spacer thickness takes up 5mm worth of the register) does not fit snugly in the wheel center hole due the mostly conical shape of the hole at the point where this 7mm of hub register makes contact. Therefore, the wheel is only really located by the five lug bolts, which makes for a wobbly situation.

What can I do? I think that the smallest spacer thickness available which has a built-in register is 15mm (due to the fact that such a spacer with integral register has to clear the entire length of the OEM register which is built into the hub itself).

Should I try to have the registers on the front hubs machined shorter (or even removed entirely) so that I can have custom 5mm spacers made with with integral registers? I refuse to run the 15mm hubcentric H & R spacers because (a) they will change the offset too much that was designed into the wheels, and (b) the tires will end up rubbing against the outside bodywork.

Is there any way to fabricate a small piece of metal/aluminum that I can firmly (if not permanently) insert into the inside of the wheel center hole so as create a uniform 74mm diameter that will eliminate the offending conical contour? I think that if I can do this, then even the remaining 7mm worth of hub register will be sufficient to locate the wheel in a stable, non-wobbly and non-shimmying fashion.

DZeckhausen was correct and absolutely spot-on when he warned of the shimmy problems associated with 5mm non-hub centric spacers! However, there must be a sensible solution to rectify this problem.

DZeckhausen · 13th April 2002, 14:30

I though you were running the StopTech brakes which clear the factory wheels without spacers. Or is it because of the wider tires that you need the spacer?

H&R's smallest hubcentric spacer for the E39 is 15mm thick. However, there is another company in Germany that makes a 10mm hubcentric spacer. It's more expensive than the H&R. Steve at Ultimate Garage carries them.

I have two sets of them left over from before I modified my Style 66M wheels to fit without spacers. I would be happy to mail a set for you to try out. Send me a PM if interested. Perhaps they will cure your problem.

I started out with 15mm H&R spacers and noticed a big difference when I dropped down to the 10mm spacers. The shimmy was gone except for just the slightest hint during hard braking on certain off camber turns. There was a noticable reduction in tramlining when I put on the modified Style 66M wheels and eliminated the 10mm spacers.

atomic80 · 13th April 2002, 17:18

DZ does it again! Looks like he's one of our many technical guru's here. I'll be coming to you when the time comes to upgrade my wheels + brakes!

greg · 13th April 2002, 17:37

I'm sure you are right in your diagnosis. Shame on the engineer and supplier of that 5mm spacer - that is plain bad design.

Note that it is indeed this system that truly locates the wheel to the hub. This is NOT the function of wheel bolts, whose job is to clamp the two pieces together. Failure to adequately locate the wheel can put huge shear stresses on the lug bolts - you should inspect them very carefully and if there is even a hint of any damage, scratching, nicking, thread distortion, you should replace them. This is cheap insurance against a potentially expensive catastrophe.

You said the radius of the wheel section that mates with the locating ring was there "seemingly to make the wheel easier to slide on and off the hub register." That is a side benefit, but the real reason is that good engineering radiuses everything - sharp corners are huge stress raisers and lead to premature failure. By reducing the contact area of this locator the spacer not only created the problem you witnessed, but also could significantly increase the stress on this area as well.

A proper spacer ought to completely replicate the location ring so that there is as much surface area protruding into the wheel, and machined to the same tolerances, as the OEM fit.

PhilSeastrand · 13th April 2002, 20:55

Quote:

Originally posted by greg
A proper spacer ought to completely replicate the location ring so that there is as much surface area protruding into the wheel, and machined to the same tolerances, as the OEM fit.

This isn't possible when the spacer is thinner that the location ring.

I don't think you want to grind down the existing location ring because then you'll never be able to get a good center again. The spacer itself will not center the rim. I wonder if your ring is more beveled then mine since I'm not having this problem. The only other option I can think of is to add some sort of wedge between the rim and the ring -- it would have to be the same on at least three sides to keep the rim centered.

HadE55NowM5 · 13th April 2002, 21:27

Quote:

Originally posted by PhilSeastrand
This isn't possible when the spacer is thinner that the location ring.

(1)

I agree with you!

I wonder if your ring is more beveled then mine since I'm not having this problem.

(2)

The hubcentric register/lip isn't what's beveled -- it's the wheel center hole (ring?) which has some beveling on a portion where the register first begins to engage this hole.

The only other option I can think of is to add some sort of wedge between the rim and the ring -- it would have to be the same on at least three sides to keep the rim centered.

(3)

That's what I'm thinking -- boring out the 74mm hole in both the wheel center and in the spacer, so as to insert a larger custom-fabricated "wedge" (that in turn have a 74mm inner diameter)) that will then travel through the spacer and engage/grab/attach to the ENTIRE length of the OEM hubcentric register/lip.

Does anyone think that this is do-able? I hear that some company in Germany makes a 10mm hubcentric spacer. I'm just worried that a 10mm spacer will space out my 9.5" x 18J OEM wheels with 275 35 ZR 18 tires too much (to the point where the tires might rub against the outer bodywork during hard cornering). For purposes of clearing the front strut, I really need a 2mm or 3mm spacer.

DrJimM5 · 14th April 2002, 00:32

I think you may have a faulty tire or rim. Max and I have run that same set-up for a long time now without any problems. Since the rub is minor, I'd suggest putting the wheel/tire on without the spacer and go for a ride. Avoid extreme high-G cornering and you won't have any problems. If the shimmy is still there, then it's the wheel or tire. You can figure out which one then by rotating one front to back in this set-up. I once had a defective tire that resulted in a shimmy. If the shimmy isn't there w/o the spacers, then ask the manufacturer for a new pair. There is enough internal rim sitting on the hub with a 5 mm spacer to center it. It is NOT THE BOLTS doing the centering. Good luck,

Jim

Bart Carter · 14th April 2002, 02:05

Quote:

Originally posted by DrJimM5
I think you may have a faulty tire or rim

This would be easy to check without going to all the trouble of changing / checking / comparing. And a lot more measurable.

Jack up the front wheel to be checked and use a dial indicator. (You can find a basic one for very little)

If you don't have a dial indicator, fix a piece of aluminum wire (soft enough not to scratch).

Now place the end of the indicator (or wire) at a spot on the wheel or the center of the tread and slowly rotate to see if any out of round exists.

If you find a high spot, loosen the wheel bolts and see if you can reposition the wheel to be concentric. If you can, the wheel is not centering on the hub. If you can't, the wheel or tire is out of round.

There have been others on the board that have used the 5 mm spacers with good results.

I am making a set of 3 mm spacers within the next couple of weeks and will be measuring everything. Dick Roberts gave me some details and from his measurements there seems to be no problems.

If anyone would like to have some 3 mm spacers, the first one (setup) is always the most expensive. Additional ones should not be that pricy.

DrJimM5 · 14th April 2002, 05:31

Bart, let me know on those 3 mm's. Although I'm not having any problems with my set-up, I'd rather have more rim/hub engaged if I can. Drop me a line @ DrJimM5@aol.com

Jim

Bart Carter · 14th April 2002, 17:43

Jim, I'll probably try to negotiate for several more sets at a better price. I'm sure several others will want to take advantage of these.