Boxerworks.com

If you are running a 120/90-18 rear tires, according to the parts diagram, it says that part #5 should be removed.

Can somebody explain why?

I can't see what difference it will make. The swingarm has to be centered no matter what.

I'm baffled yet i also haven't tried to mount that size tire with those spacers...yet. But I did assemble my swingarm with them and I am going to mount one of those tires so i may find out the hard way... or i can always pop off the dust covers and remove them.

Removing #5 will make a great difference. That is the part that transmits the squeeze to the taper bearings. Without that part, you won't have a solid swing arm and the bike will be a complete mess. I suspect that you read something off of the Internet, or some really bad article.

In any case, that part has nothing to do with allowing a change in width of tire.

Why in the world would you wish to use a wider tire? The whole bike geometry was designed to use a certain tire and any change will be a loss someplace else. At a minimum, you will lose neutral handling.

The other thing that a wider tire does is to make it VERY hard to get the darn thing out of the swing arm. I've bought some bikes that came with the wider tires and I can't feel a deterioration in handling from them but I also can't feel any advantage. I have yet to consistently slide the tires on my bikes. I would assume the wider tire is supposed to put a bigger patch on the road to increase traction. I've slid a bit sideways quite a few times but it's usually a result of something slippery on the road. A wider tire won't help that.

I would think that if you want to move the wheel/tire to the left so it doesn't hit the swing arm, you would have to re-space the hub and not the swing arm.

Chuey

Maybe i am misreading the parts diagram on MAXBMW.com's fiche.

In the part description for that part, #5, it says "Used when using a standard 400-18 rear tire."
That led me to believe that it isn't used for wider tires or there is a different spacer used for wider tires.

And yes, I am aware of wider tires and what is designed for the bike. I had a hard time finding the Bridgestone Battleaxe tire in the correct size. It seems they only sell it in Europe sized (4.00 x 18)for our bikes and can't get them in the USA. According to the specs, they are pretty close to a 4.00. My next set is going to be the standard size, different brand and I can't wait to compare them.

Chuey wrote:
I would think that if you want to move the wheel/tire to the left so it doesn't hit the swing arm, you would have to re-space the hub and not the swing arm.

Chuey

BMW actually sells a spacer that moves the tire away from the swingarm a wee bit. I am sure they did it because of the limited availability of standard size tires.
I think there are only 3 or 4 tires to choose from that have standard sizes. Avons, ContiGo! and Metzlers.
Other people like Bridgestone stay they make them in standard sizes but they are unavailable in the USA.

Seems to me you could mount the swing arm as far right as possible with the supplied hardware. That would give you about 3/32" or maybe an 1/8" offset, then a top hat that much taller on the inboard side of the wheel would give that much more clearance for a larger tire. Not that I would do that, just sayin' it could be done...

Ahh.
i figured it out. Mystery solved as to my own boneheaded confusion.
The wheel spacer that i am referring to is the last piece in the wheel hub, that sticks out of a dust seal, where the hub mates with the final drive.
There are two sizes for those spacers, one for a standard tire, one for a wider tire.
The standard size is the same part number for the spacer that fits in with the swingarm bearings. So it has the same part description referring to a standard sized tire.

Thanks for those who chimed in on this.

BMW sells a spacer, as mentioned above, that would allow fitting a 120 series tire.
I believe that these were stock issue on the post /7, 2-shock RS ...
Considering a tire wider than a 120 ?
You will be focused upon fashion rather than function
and I will have nothing to say about that.

The stock spec rear tire (/7 & up, anyway) is not co-linear with the front tire, not even in factory trim.
Using the BMW spacer to fit a 120 increases that wheel offset –
Increased offset affects handling characteristics.

One can compensate for this increased offset and return to stock spec
(but only within the load bearing / mechanical limits of the SA bearings and pins)
by "un-centering" the swing-arm in the frame.

Un-centering the SA, moving it left or right in the main-frame,
does absolutely nothing to change or increase the space needed for 120 tire clearance within the SA.
Most 120 tires will contact the drive-shaft side of the SA without an appropriate spacer.

No No... not considering a tire wider then 120 and yes, those spacers are strictly for moving the rear hub away from the final drive a wee bit so the 120 tire can clear the inside of the swingarm.

However, Are you saying that a /7 and up has a front and rear tire that is not lined up? That seems very un-BMW.

And, I thought un-centering a swingarm between the frame was a big no-no. I know it can be done... but that would be wrong.

jjwithers wrote:I thought un-centering a swingarm between the frame was a big no-no. I know it can be done... but that would be wrong.

Drive shaft clearance would be the deciding factor.