Boxerworks.com

Hi all

New tyres fitted this afternoon, rear is a Bridgestone BT46R Tour 4.00x18 which I believe is correct.

Poking about this evening in the garage I notice that there is zero space between the sidewall and the shaft drive housing. The tyre will spin by hand but is binding enough to lightly scuff the surface. I didn't notice it riding back the 7.5 miles through the city to my home

Previous tyre, a Pirelli Sport Demon 110/90 18 61H was ok.

The tyre fitters are a well known London establishment but they don't get many old bikes through.

Is there something in the process of fitting the wheel which has gone awry? Or something out of alignment? Will speak to them in the morning.

Pic below:

Actual tire dimensions vary quite a bit. However, the previous 110 type is nominally 4.3 inches in width. Now the 4.00 tire doesn't fit. Something seems wrong. Or the 4.00 tire is not really what they say it is. Maybe someone has experience with the Bridgestone.

Kurt

Thanks, back at the tyre fitters for much head scratching, they're trying to find the original Pirelli to put back on as their current thinking is despite the numbers being model correct, the Bridgestone is just too big...

There is a fair bit of axle on the non drive side exposed, from searches on here and further googling it looks like there are a lot of bits and spacers to the rear assembly. Is it something that is easy to mess up?

This comes up for the 60/7 anyone know if it is the same parts for the 100/7?

https://oem-bike-parts.com/en/parts/bmw ... id=1&pid=1

Edit.. assuming that all the above linked bits live in the wheel and the axle just slides through? They can't get the wheel back to front as there is a disc bolted to one side.

Could something be misaligned with the swingarm and frame?

There is a standard size sleeve in the bearing stack part 36314038142 and is about 9.2mm thick. Another sleeve can be inserted part 36312301737 which is 10.7mm thick. It effectively moves the tire to rider's left a small amount to help with fitment of larger tire. But this doesn't seem to be your problem, unless the tires in question are not within nominal specs.

Kurt

Kurt in S.A. wrote: ↑Fri Jul 18, 2025 5:49 pm ...Or the 4.00 tire is not really what they say it is.

There are no 4.00 tyres that I know of which are only 4" or 100mm wide. From the figures I have the mounted width can vary between 108mm - 125mm.

One reason for the larger measurements is that the manufacturer may have used the same mould to produce both a tyre labelled 4.00 and a tyre labelled 120. They just change the lettering inside the mould. For example, from figures I have a Bridgestone BT45 is exactly the same mounted width of 120mm in both a 4.00 size and a 120/90 size

If you can measure the mounted and inflated width and post it here, it will help others to know what will fit without rubbing and what won't.

Not all Airheads models are exactly the same in what will work but in general anything over 120mm is potentially a problem and the wider spacer only gains 3mm in acceptable tyre width plus it reduces the rear wheel spline engagement which is not ideal.

Plus it makes installation/removal harder.

Kurt

They put the older tyre back on which is 110/90 and it fits. I didn't get chance to measure the Bridgestone. They are going to find something to fit Monday and call me.

Cheers

Ade

This is me being picky but if possible I avoid 110/90's because they are always smaller in diameter than the correct 4.00 fitment. It's only a small difference at typically 655mm instead of 675mm but it does have a 3% effect on the gearing. Finding 4.00 tyres isn't getting any easier though. If they fit, 120/90's are fine on diameter.

Barry -

I will never go to metric tires again if I can help it. I ran 4.00x18s on my /7 for the longest time, then switched at some point to say 90/110s front/rear. I noticed that due to the shortened height profile (that's the "/90" in the tire spec) it dropped my bike lower to the ground. The result was that my side stand was nearly unusable as the bike sat nearly straight up...a puff of wind would blow it over. And using the center stand was harder, too. So, back to 4.00s for me.

Kurt

110/90 Bridgestone BT46 R fitted yesterday - it looks silly small compared to the 180 I used to have on my R1100S but seems to ride ok and importantly clears the swingarm...