1985 k100 rear tire

[TBN]

Hi All,

Sorry if this is a repeat question but I've pretty much exhausted my search looking through the depths of the internet.

I recently decided to get my wheels powder coated and put some new tires on. The bike is a 1985 K100 and the rear tire mounted before I took the wheels to get powder coated was a 160/60-17 radial. From what I've read this seems a little too wide for the wheel as the stock size is 130/90-17 (biased ply?). The 160/60-17 tire did lose some air before I removed it but I figured it just had a slow leak (it was the tire that was on the wheel when I bought the bike and despite looking in decent condition could be old/leaking/etc.). I'm also not sure if the rear rim was replaced from a newer bike as it seems like the different year k bikes have different rear wheels and tire sizes.

Anyways, does anyone know what size tires can go on the rear wheel of 85 K100? Can I put another 160/60-17 radial tire on it? These seem much easier to come by than a 130/90-17. Might seem like a dumb question since I've ridden probably 1k miles on the old 160/60-17 but I don't want to put a new tire on it that leaks air or has any type of handling/blow out/etc. concerns

Thanks in advanced,
TBN

[Scott_]

From what I have worked with on my 1100's, there are only a few things to consider.....

Will it physically fit the rim properly, ie does the bead of the tire have enough surface contact with the rim to seal, what size rim(width) was the tire designed to fit.
If you put a tire designed for a wider rim on a narrower rim, you risk not getting the proper bead contact between the two. Say nothing of being a PIA to mount and set the bead.... btdt.

When you put the tire/wheel combination on the bike, what is your clearance around the tire. Specifically at the final drive area. Sometimes with a wider tire you can run the risk of it rubbing against the final drive/drive shaft housing under certain conditions. This can make for a hazardous condition.

Be aware that a tire with too much difference in the outer circumference of the tire will throw off the speedometer calibration. Not a deal breaker by any means, but just a fact to be aware of before you hit the next LEO speed trap....

A tire with a different sidewall dimension can affect the bike when trying to park it on the center stand. A shorter tire will make it more difficult(not impossible) to put up on the center stand. A taller tire will make it easier, but if it's too tall, it may still touch the ground when the bike is on the stand.

You may have to remove the exhaust can to install/remove the wheel/tire from the bike. (You have have to anyway regardless of the tire size....depending on the exhaust system you have, I have to remove my Remus cans to change mine.)

[Laitch]

Anyways, does anyone know what size tires can go on the rear wheel of 85 K100? 

Post a photo of your current rear wheel. Stock '85 wheels are Y-spoke style. The later three-spoke styles comfortably handle wider tires, depending upon their width. What is the width between the outer and inner rims of your moto's rear wheel?

How old was the tire you replaced, according to the date stamped on its sidewall?

[TBN]

Thanks for the replies!
I'll have to measure the wheel when i get it back from being powder coated. It is the Y spoke wheel which I'm thinking is meant for the thinner tires but I thought  there could have been a wider Y spoke wheel released later. I also won't be around the old tire to take a look at the date on it for a little bit but I'll post when I get a chance. The old tire didn't seem to have any clearance issues with the center stand or final drive although I'm wondering in what scenarios will there be a problem with the final drive? Maybe I just didn't have any problems with it, I assume heavy cornering? The exhaust isn't a problem because i put an aftermarket exhaust on that's significantly shorter. I didn't ever have a problem getting it on the center stand and as far as the speedometer goes I'm using a phone app for speed...I'm sure that app has some problems of its own though lol.

[Laitch]

It is the Y spoke wheel which I'm thinking is meant for the thinner tires but I thought  there could have been a wider Y spoke wheel released later. , . . The old tire didn't seem to have any clearance issues with the center stand or final drive

It helpful to use a parts fiche for learning what stock parts have been used on the motos and what is available for them. According to MAX BMW's parts fiche, Y-spokes were offered only in 2.75 inch width and 160 width tires are generally not recommended for that width rim. A wide tire that barely clears the swing arm when its cold might rub the swing arm when warmed up so the wheel might need more offset using a spacer.

A tire that's too wide for the rim can leak. View the 17" rear tire/rim section of this chart to see how far your current setup varies from a recommend match.

[TBN]

Ahhh, thanks! This is what I was looking for. Also the old tire is from 2013 so it's a little old but I'm guessing at least part of the air leak is due to the width of the tire not being right for the width of the wheel.