Hello!

I have 1987 BMW K100RS wich have 5 speed transmission.
My question is.
Does anyone know if there is any transmission with six gears, which could fit it in my 1987 BMW K100RS?

Thank you.

A K1200 transmission and bell housing will fit on the K100 / K75 block, however you're going to have to modify the frame to adapt it to the transmission, figure out how to adapt the K1200 hydraulic clutch to a cable operated K100 clutch, figure out how to adapt the sprague clutch mechanism on the K1200 to the main drive on the K100, buy a complete K1100 paralever rear end to replace the K100 monolever..  It's been done, but it'd be cheaper to get rid of the K100 and buy an early K1200 to get the 6 speed gearbox you're after.

Plus I believe the starter and alternator cannot be easily removed from the K1200. On the K75/K100/K1100 you can do them while breakfast is cooking.....

We have debated the 6 speed gearbox fit quite a bit but the modifications are severe if you are starting with an 8 valve engine and Monolever rear end. If you have to do it start with a K1100??

Put me in the "Why bother?" camp. K bikes are designed to run at high RPMs so although it may seem like the RPMs are high it is not going to hurt the bike. (It's not a Camry.) Plus you get more torque in the highest gear with a 5 gear trans.

If you're after a taller (higher) cruising gear you'll find there won't be a great deal of difference.
Top (6th) gear and FD ratios are not much different to the K100RS.

K100RS 5 speed GB and FD
FD ratio            2.82
5th gear ratio    1.666
At 100 kph you're engine would be doing 4100rpm*

K1200S 6 speed GB and FD
FD ratio            2.82 (I think its the same as the RS)
6th gear ratio    1.582
At 100 kph you're engine would be doing 3900rpm* Just starting to get a bit too low for cruising imo.
*these are rough calculations.

The K100 has only about 60% of the bhp of the K1200S and so not as capable to handle a taller top gear anyway.

Top gear on a K100 would be about normal when compared to other bikes in its class. The power band cuts in at around 6k rpm so you're better off keeping the revs up in my opinion.

Thank you guys!
I'm just asking is that possible and I know, on this world is anything possible  .
I think this modify is too much for me and I will pass.

I have another question.

Wich tires do you have on your BMW?

Thank you again.

bolka13 wrote:
Wich tires do you have on your BMW?

Pirelli Sport Demons for me every time. Lots of threads on the forum about it. 

Like this thread.

Hi Bolka13

This is great fun. We love    when someone opens up the tyre debate.

88 and myself live not too far from each other...about 3 hours. We go on trips together......We don't get much snow here and not a lot of frost but would have road surface temperatures quite low in winter.

He swears by the Pirelli Sport Demons, rides all year and in all weathers.

I am happy with Bridgestone Batlax BT45, 110/90/18 front at 38 psi and 140/80/17 rear at about 42/45 psi on the rear. Using them for quite a few years but as I use the bike a lot 6-8 months would be a good lifespan for me.

We ride on similar roads and we are both happy......so to some extent its personal choice/price whatever.

And you will find others on the forum using different tyres.

All I can say is see what is best used locally to you. I live with about 1500mm rainfall a year so plenty wet weather riding. 88 has much the same up his way.