Hopefully, NOT another tire thread!

[ShutterPilot]

Ok Gurus, I ran into a head scratcher.
And really, I have done all this before ...really! I've been wrenching on bikes for 20 years, But this bike has put me so far back into noob status I'm continually running into more "fun" stuff.

I fitted a rear 120/90-18 Metzler Lasertec, as I've seen listed many times on searches in the forum. But dang if it doesn't rub hard on the swing arm as soon as I bolt up the axle.

I'm reticent to fit different top hats, as I'm afraid it'll push the wheel too far off the splines. And I don't find a 110 in a lasertec rear.

While I read that most have been able to successfully mount a 120, any ideas on why I can't? I do have a 110-18 BT-45 in the garage I was getting ready to fit on the GB500, but am timid about mixing BT-45 rear with a lastertec front.

I'd love to hear anyone else's experiences, and yes - its ok to pile on with  ribbings as well.

[Bob_W]

Max BMW shows 36 31 2 301 737 sleeve to be used with the 120 tire.
Bob

[nhmaf]

Also, are you sure that you didn't end up with the tophat spacer for the left&rights sides swapped?   The part Bob W mentions does provide a few mm more offset, though I've decided to either stick with 4.00x18 sizes -OR- use a 110/90 rear sizef as I know that even with the variations among manufacturers, all tires of that size should fit and be easier getting the wheel on/off.

[Barry]

Just for the record what is the mounted width of the 120 Lasertec. Manufacturers data says 125mm which I know would be too wide for mine. I reckon on 120mm measured width as the maximum. That may vary though between early and later models as they have different swinging arms.

[montmil]

... I fitted a rear 120/90-18 Metzler Lasertec, as I've seen listed many times on searches in the forum. But dang if it doesn't rub hard on the swing arm as soon as I bolt up the axle.

I'm reticent to fit different top hats, as I'm afraid it'll push the wheel too far off the splines. And I don't find a 110 in a lasertec rear...

Guessing the rub is forward near the swingarm pivot? If the tire is rubbing near the rear axle, I'd be concerned about any attempts to spread the swingarm while maintaining axle preload.

I run Bridgestone S11 Spitfires on my '81 R65 in a 110 size on the rear and there's just barely enough clearance. No way would a 120 fit either of my R65s. Variances between manufacturers and their size specs could also be in play here.

[ShutterPilot]

I'm not sure if my top hats are the 36 31 2 301 737, Bob W, but I'm guessing not since I don't have clearance. And I left 'em in place when unmounting old/mounting new tire.
That doesn't mean they weren't switched previously and I just inherited it.
And yes, Montmil, the rub is at the swing arm pivot. More of a complete "hard-against-the-swingarm-and-not-moving" rub, BTW.

Stupid thing is, I never thought to check tire sizes of either the new Metzlers, or the old dunflops that were on there, as the PO provided the new tires with the bike and I just "assumed" they were correct. That'll learn me. But now I understand all the fussing it took me to get that wheel with the new tire back in place.
sigh.
So, while I'd rather find a 110 in a Lasertec, like I said, I DO have a set of 18" BT45s on hand ready to go on the GB500. While I don't think the 120-18 Lasertec will shoe up on the GB500 in a swap, it sounds enough of you ran BT45's that these would work fine on the r65.

[montmil]

BT45's are good tires. Just a bit more bucks than the S11's.  

[ShutterPilot]

Thanks to Barry, I rechecked Lasertecs and I see a 4.00x18 bias ply rear offered. Some sources place this as equal to 110/90-18 or MN90-18.
Can anyone confirm this?
I'll put a caliper on the 120 Lasertec, and BT45 110 I have later tonite to check width at inflation compared to the available swing arm space.

[Tony Smith]

I fitted a rear 120/90-18 Metzler Lasertec, as I've seen listed many times on searches in the forum. But dang if it doesn't rub hard on the swing arm as soon as I bolt up the axle.

I'd love to hear anyone else's experiences, and yes - its ok to pile on with  ribbings as well.

Wife has a 120/90 (not lasertech, but for present purposes that is irrelevant) on the rear of her R65/80, it is a bear to get on and off the bike, but it does fit - just. I cannot mount her wheel on my 1985 twin shock R65, it rubs on the swingarm.
 
As others say it is perfectly permissible to offset the rear wheel a bit, but my thoughts are why bother. One of the sweet things about the R65 is its relatively (for an airhead) spirited handling and a very nice ability to effortlessly "tip-in" to a corner. From ridign my wife's bike I know that fitting larger front and rear tyres degrades the "pleasant" aspects of the bike's handling - although I must also say that the outer limits, should you wish to explore them, are probably improved.
 

[msbuck]

So, I currently have a 120/90 CS Hi-Max on my rear tire (it was the only available tire in the town where I had my flat last time).  I have just ordered up a Pirelli Sport Demon in the 110/90 size.  I know that the local BMW shop put the extra spacer in when I originally swapped to the 120/90 size.  I'm guessing it now will need to be removed to put back the 110/90s?  

okay, i just looked at the fiche for the tophat and it looks like I need a different size one for the 400 tire.  Hmmm....I know they didn't give me the old part back, so will I have a problem putting the smaller tire on using the parts I currently have in place?   :-/

[Bob_Roller]

No, you should have extra clearance with he narrower tire .

[msbuck]

Thanks Bob!