Greetings guy's, can anyone please tell me what the maximum size of the rear tyre on an 1986 BMWK100RS, I recently took my bike to the shop and got some new tyres put on, now this is where it gets annoying, the manual states 130/90 and the shop gave me 130/70, I didn't notice it then, but when i got the bike back home I checked it out and it looks like i am riding on a rear bicycle wheel, I need to get the tyre replaced but I need you guy's to please advise me what the maximum size for my bike can be or should be.

The rear Y spoke wheel should be able to handle a 140/80-17 without dramas, and the stock 130/90 size, but never a 130/70. That is a wanker move on the part of your tyre changer. Did they not read the tyre's sidewall? I'd be knockin' on their door first thing telling them they need to remedy the situation. A 70 series tyre is what's commonly used on a much lighter motorbike than a typical K100.

Thank you for the quick reply and the dimensions, I will be taking it back to the shop and telling them how stupid they are, I really thought if I had a 130/90 installed why in the living hell would they throw on a 130/70, just stupid I'm guessing.

12 years ago I was riding south through Cairns having spent a month fiddling about where I could get to in far north Qld. My K100RS needed a new rear sneaker very bad. I stopped in a shop and all they had was a 130/70-17, but it was good 'n' cheap like me at the time. It lasted from Cairns to Beenleigh. It was frightening to ride on with camping gear and the usual moto travel kit at motorway speeds and in corners, any corner. It was my choice. It was my money. I accepted it. I would never do it again.

tassoni wrote:Greetings guy's, can anyone please tell me what the maximum size of the rear tyre on an 1986 BMWK100RS, I recently took my bike to the shop and got some new tyres put on, now this is where it gets annoying, the manual states 130/90 and the shop gave me 130/70, I didn't notice it then, but when i got the bike back home I checked it out and it looks like i am riding on a rear bicycle wheel, I need to get the tyre replaced but I need you guy's to please advise me what the maximum size for my bike can be or should be.

The tyre should be fine, I run 140/70 but you can use 130/80 130/90 140/80 if you prefer. It can deend on your preferred tyre choice too. 150 does not have side clearance to fit.

You need to pump it to 42psi for solo riding.

Tyre size options are dependant upon how stock you wish to be. 
On my 1983 K100RS I decided to make various changes and have successfully fitted a Pirelli radial 160/60 R18 to a 3 spoke K1100 18" x 4.5 rim. This has been done in conjunction with other upgrades and modifications. 
Centre Stand Modification: I modified a K1100 centre stand by widening it. I then fabricated a steel plate which fits between the centre stand mount and the base of the engine block (the K1100 has different mount hole positions to the K100 one).These centre stand modifications have made it easier to lift the bike onto the stand. 
Exhaust System Modifications: I have fitted an aftermarket exhaust collector and a carbon fibre muffler for weight reduction. To get muffler clearance with the left side of the tyre I machined an aluminium spacer that fits onto the left foot peg plate.
The above mods were done with 2 objectives: benefit from a radial rear tyre with improved performance; reduced weight.

160/60 is the correct size for a K1100 18" rim. It,s for K1100RS but the 18" rim also fits a K1100LT and there is clearance for the 160 on the K1100LT and RS.

K1100LT rear rim is 17" and you are back to 140 because of the rim size, not because of clearance issues.

92KK 84WW Olaf wrote:160/60 is the correct size for a K1100 18" rim. It,s for K1100RS but the 18" rim also fits a K1100LT and there is clearance for the 160 on the K1100LT and RS.

K1100LT rear rim is 17" and you are back to 140 because of the rim size, not because of clearance issues.

150/70 works fine on the 17" 3-spoke rear. I run 150/70-17 rear radials on the 17" 3-spoke - K75, K100 and K1100LT.

I run 130/80-18 radials on the Y-spoke rear. 110/80-18 radial in the front.

redrockmania wrote:Tyre size options are dependant upon how stock you wish to be. 
On my 1983 K100RS I decided to make various changes and have successfully fitted a Pirelli radial 160/60 R18 to a 3 spoke K1100 18" x 4.5 rim. This has been done in conjunction with other upgrades and modifications. 
Centre Stand Modification: I modified a K1100 centre stand by widening it. I then fabricated a steel plate which fits between the centre stand mount and the base of the engine block (the K1100 has different mount hole positions to the K100 one).These centre stand modifications have made it easier to lift the bike onto the stand. 
Exhaust System Modifications: I have fitted an aftermarket exhaust collector and a carbon fibre muffler for weight reduction. To get muffler clearance with the left side of the tyre I machined an aluminium spacer that fits onto the left foot peg plate.
The above mods were done with 2 objectives: benefit from a radial rear tyre with improved performance; reduced weight.

Not sure I understand this. I have put the complete K1100 stand assemblies on all my 2v Ks and its a straight change, same gearbox mounts etc. . "


Centre Stand Modification: I modified a K1100 centre stand by widening it. I then fabricated a steel plate which fits between the centre stand mount and the base of the engine block (the K1100 has different mount hole positions to the K100 one).These centre stand modifications have made it easier to lift the bike onto the stand".

...when using a 160/60R18 tyre & wheel from a K1100RS, as well as a K11 centre stand, it is necessary to modify the stand to clear, when fitting these to a 2V  K. On mine it was only massaging a few mm's off the inner edge of the left foot.

Two Wheels Better wrote:...when using a 160/60R18 tyre & wheel from a K1100RS, as well as a K11 centre stand, it is necessary to modify the stand to clear, when fitting these to a 2V  K. On mine it was only massaging a few mm's off the inner edge of the left foot.

Isn't the root cause of this the fact that a monolever rear end is shorter than a paralever rear end? (So the rear wheel is farther forward on the monolever setup.) I'm pretty darned sure that if you put a paralever rear end on a K75/K100 then no mods would be required to run a 160/60-18 with a K11 center stand.

Yeah, that makes sense. It was only the edge of the 'wider' tyre making contact. A grind here n there made it clear. A Paralever gearbox & swingarm on an Monolever K would seem to pose no clearance issue with the '160' tyre.

redrockmania wrote:The above mods were done with 2 objectives: benefit from a radial rear tyre with improved performance; reduced weight.

A 4.5x18 weighs more than a 3x17.  Not only that but the heavier 4.5 rim is farther out so it has even more inertia and therefore will not accelerate as fast as a bike with a 3x17.

The 3x17 also requires less lean angle and has a tighter turning radius so the bike is more nimble in turns on a 3x17.

Wider tires do have a larger contact patch and better traction but I can scrape pegs on a 3x17 with a 150/70-17 radial and don't need any more traction than that. If K75 and K100s had more torque then it might make sense to run wider tires but neither bike has enough torque to spin up a tire coming out of a turn.

The wider tires also hydroplane more easily. My K1100RS hydroplanes at about 70 MPH but my K1100LT gets up above 75 before it starts to hydroplane.

Those are the reasons that I think a 3x17 makes more sense performance and weight-wise on a K75 or K100.

JM02, YMMV

Riding various K75, K100, K1 and k1100LT since 1997, I've tried various combinations of rims, with the K1100RS specs (17 inches front, 18 inches front) and mixed configurations (17 inches everywhere and 18 inches everywhere). 
My conclusion is the wider the rims are, the worst is handling. 
I never found any improve on grip with wider rims. But the ground clearance is then reduced with a 17 inches front wheel, and the bike is  more difficult to handle and to lean in cornering. 
Both 18 inches rims gave interesting results, but still with the resistance to lean due to the wide rims. 
The OEM rims set on the K1100LT is amho the best choice that allows to ride fast on twisty roads a 300 kg motorcycle with no fatigue. It's natural, safe and effortless, whereas the K1 is much more demanding on the same roads. 

Wide tyres is a stupid fashion, completely unnecessary.

jbt wrote:Riding various K75, K100, K1 and k1100LT since 1997, I've tried various combinations of rims, with the K1100RS specs (17 inches front, 18 inches front) and mixed configurations (17 inches everywhere and 18 inches everywhere). 
My conclusion is the wider the rims are, the worst is handling. 
I never found any improve on grip with wider rims. But the ground clearance is then reduced with a 17 inches front wheel, and the bike is  more difficult to handle and to lean in cornering. 
Both 18 inches rims gave interesting results, but still with the resistance to lean due to the wide rims. 
The OEM rims set on the K1100LT is amho the best choice that allows to ride fast on twisty roads a 300 kg motorcycle with no fatigue. It's natural, safe and effortless, whereas the K1 is much more demanding on the same roads. 

Wide tyres is a stupid fashion, completely unnecessary.

When I built my K75 Frankenbrick it ended up essentially being a K1100RS with a K75 motor. I decided on using the K1100LT wheels and it isn't a "pig" in the tighter turns like my K1100RS or K1 can be. (But I still enjoy riding the 4V bikes with wide wheels.)

jbt wrote:Riding various K75, K100, K1 and k1100LT since 1997, I've tried various combinations of rims, with the K1100RS specs (17 inches front, 18 inches front) and mixed configurations (17 inches everywhere and 18 inches everywhere). 
My conclusion is the wider the rims are, the worst is handling. 
I never found any improve on grip with wider rims. But the ground clearance is then reduced with a 17 inches front wheel, and the bike is  more difficult to handle and to lean in cornering. 
Both 18 inches rims gave interesting results, but still with the resistance to lean due to the wide rims. 
The OEM rims set on the K1100LT is amho the best choice that allows to ride fast on twisty roads a 300 kg motorcycle with no fatigue. It's natural, safe and effortless, whereas the K1 is much more demanding on the same roads. 

Wide tyres is a stupid fashion, completely unnecessary.

I have both the RS and LT wheels for my K1100LT. I too have tried the various combinations and most definitely the LT wheels [18 front /17 rear] make it much more nimble.