Tire to swing arm clearance

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Zombie Master
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Tire to swing arm clearance

Post by Zombie Master » Mon Jun 04, 2018 2:38 am

1984 R100S

So it's time for new rubber. Many years ago, I shimmed the rear wheel over the left to provide room for a wider rear tire. When recently servicing the rear wheel splines, I noticed a second notch on the hub splines, due to the modified position of the wheel splines. Also a small area of the rear brake shoes is not contacting the the brake hub. Brake works well as is, and there is no problem with the splines. I have the original top hat spacer, so I'm thinking I should be able to reverse the modification. Does that make sense?

So I could not reverse the mod and continue on with the same size tire I have been using, or reverse the mod and go back to the original size tire.

Any thoughts? :ugeek:


This sound right?
BMW R100RS Tires. Tire sizes for the R100RS are the 3.25-19 front and 4.00-18 rear. Modern size replacements are 100/90-19 front and 120/90-18 rear.
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barryh
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Re: Tire to swing arm clearance

Post by barryh » Mon Jun 04, 2018 4:51 am

Going back to the standard spacer means it's going to take a while for the brakes shoes to bed in again and for the splines to wear off that step but it's the right thing to do in terms of wheel alignment. BMW issued a service bulletin that said wheel offset should be checked whenever the wider spacer was fitted and that it should be no more than 4mm.

Splines are in great shape. That must be relatively low mileage if original. Either that or very well maintained.
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Zombie Master
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Re: Tire to swing arm clearance

Post by Zombie Master » Mon Jun 04, 2018 9:55 pm

barryh wrote:
Mon Jun 04, 2018 4:51 am
Going back to the standard spacer means it's going to take a while for the brakes shoes to bed in again and for the splines to wear off that step but it's the right thing to do in terms of wheel alignment. BMW issued a service bulletin that said wheel offset should be checked whenever the wider spacer was fitted and that it should be no more than 4mm.

Splines are in great shape. That must be relatively low mileage if original. Either that or very well maintained.
I sanded off the ridge on the brake shoe. There was very little to sand. If BMW made those those top hat spacers available, would it still be an alignment issue?

Those are the original splines with 60K klms. I do grease them at around 30K klms.
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barryh
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Re: Tire to swing arm clearance

Post by barryh » Tue Jun 05, 2018 4:33 am

Zombie Master wrote:
Mon Jun 04, 2018 9:55 pm
If BMW made those those top hat spacers available, would it still be an alignment issue?
The wider spacer only adds 1.5mm so it's not a big deal. Perhaps the scope for adjustment on the swing arm bearing means that with the additional 1.5mm it's then possible to exceed the 4mm maximum and that's why they mention it.
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Chuey
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Re: Tire to swing arm clearance

Post by Chuey » Tue Jun 05, 2018 10:35 pm

Re, the wider vs stock size rear tire: Was the rear tire losing traction under hard acceleration? Was it slipping out in corners? Seems to me that the wider tire has enough downsides that I would stick with the stock width.

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Re: Tire to swing arm clearance

Post by Zombie Master » Wed Jun 06, 2018 1:52 am

Chuey wrote:
Tue Jun 05, 2018 10:35 pm
Re, the wider vs stock size rear tire: Was the rear tire losing traction under hard acceleration? Was it slipping out in corners? Seems to me that the wider tire has enough downsides that I would stick with the stock width.

Chuey
I did the conversion 30 years ago and it was recommended by a factory trained BMW mechanic. It was a mistake.
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ME 109
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Re: Tire to swing arm clearance

Post by ME 109 » Wed Jun 06, 2018 4:46 am

It's not too big of a step on the fd spline, but the wheel spline will run up on that step with the smaller spacer.
Is it a problem? It will be the only contact of the splines unless the wheel spline cup can twist to accommodate the step?
I'd imagine the step will wear down and the wheel cup will reciprocate.
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Re: Tire to swing arm clearance

Post by Zombie Master » Wed Jun 06, 2018 3:55 pm

ME 109 wrote:
Wed Jun 06, 2018 4:46 am
It's not too big of a step on the fd spline, but the wheel spline will run up on that step with the smaller spacer.
Is it a problem? It will be the only contact of the splines unless the wheel spline cup can twist to accommodate the step?
I'd imagine the step will wear down and the wheel cup will reciprocate.
So would you go back to the original spacer, or just keep it the way is and order the fatter (current) rear tire? I wonder if the added engagement area of the splines is significant? The rear brake seems to work OK, just that it lives a tinybit of a ridge on the brake shoe.
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ME 109
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Re: Tire to swing arm clearance

Post by ME 109 » Wed Jun 06, 2018 4:20 pm

Added engagement can only be a good thing. I don't think it will create a significant issue by reinstalling the shorter spacer.
Skinny tyres rule, and the skinnier the tyre, the more the sports bikes squirm when they get a view of it.
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Re: Tire to swing arm clearance

Post by Zombie Master » Wed Jun 06, 2018 8:36 pm

ME 109 wrote:
Wed Jun 06, 2018 4:20 pm

Skinny tyres rule, and the skinnier the tyre, the more the sports bikes squirm when they get a view of it.
This..... is a very important consideration! Embarrassing modern sport bikes is a noble pursuit. :P

Other than exchanging the top hat spacer, are there any other adjustments required?
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