800 chain and sprocket set up on 650?

[Malcolm Leick]

After 20,000 miles I think it's time to replace the original chain and sprockets on my F650GS.

Given that TT now offer a range of front and rear sprockets would I gain much advantage from losing one tooth on the front and adding one at the back? This would be a similar set up to the F800GS.

I know it would lower the speed a tad, but I'm not too bothered by top speed as the TKC80s keep me to 95mph anyway. Would it make that much improvement to off-road performance and on the down side, would it increase fuel consumption significantly?

90% of my riding time is on-road so I don't want to compromise this too much. But I also want to get into more off-road stuff.

Reading the other threads on chains and sprockets it sounds like a chain upgrade is definitely the way to go. I'm due for a tyre change soon so will probably get it all done at the same time.

If you read this Tim C, what are your thoughts? I know you have done a lot of miles on all terrains on your F650GS. Have you ever considered changing the gearing?

 

[Tim Cullis]

The problem with the gearing is that BMW took the close-ratio gearbox from the 800S/ST and stuck it in the F-GS range without altering the ratios. Ideally both the F650GS and the F800GS should have a MUCH lower first gear, especially for hill descents where the combination of a smooth revving engine and high first gear is sod all use for braking. Putting the 800GS sprockets on will improve things slightly but nowhere near enough.

 

[Malcolm Leick]

Thanks Tim.

Is it worth going all the way from 15 on the front to 47 on the back?

It sounds like you are saying the main problem is 1st gear only. Messing around with the sprocket and chain ring will obviously alter all of the ratios which may have it's downsides I suspect.

Malcolm

 

[MBronskill]

While agreeing with Tim's assessment, I still think dropping one tooth on the front sprocket produces a better overall compromise package on the F650GS.

Mike

Thanks Mike. Is this something you have done? Did it help?

Malcolm,

I replaced the original 17-tooth front sprocket with a 16-tooth sprocket supplied by my dealer last spring. It improves city driving and makes throttle response less abrupt, particularly useful when off-road. The increased rpm at motorway speeds is not objectionable. Only a minor chain adjustment required.

Mike

Thanks Mike. That's very useful to know. I'll give it a go. I presume you stuck with the original size chain ring at the back.

Malcolm,

Yes - kept the same rear sprocket.

Mike

 

[Malcolm Leick]

Fitted the 16T sprocket this morning Mike and I think your right. A good compromise. Smoother take off in the lower gears in town and nicer more controllable handling off road. A more relaxing ride all round.

At 70mph I was going for 6th and then realised I was already there! I'll try it at 80-90 next mph but I'm already sold on the sprocket. Don't think I would want go any lower though as it would make the bike too revy for me at high speed.

Still on the original chain and chain ring but will change when I get my next set of tyres fitted. Judging by the tyre slide I was getting in mud today, that will be sooner rather than later!

Thanks for the advice.

Cheers. Malcolm

 

[Malcolm Leick]

Decided to go for the 42 on the back when I replaced the chain with a DID X ring. With the 16 on the front I had much more grunt off road yesterday in mud, rocks and snow and better control on the downhill sections.

Also had better mid range acceleration for overtaking on the motorway on the way home. The engine is now running at 5000rpm at 80mph in 6th gear.

I'll probably get a spare 15t sprocket from TT for sustained off road riding and a 17t for long runs where fuel consumption is an issue.

Now have to work out how to straighten my bash plate which got rammed back when I hit a stone block. Everyone else on the TRF ride out were on nimble little 250-450 trials bikes yesterday so my GS was a bit of panzer tank. Width was an issue in some of the deep ruts especially when there were stone blocks either side. The folding gear lever was a god send!

Several people commented that they were amazed how far I got as the lanes got more nadgery. I think it was just about the limit for the bike and my current level of off-road skills. An F800GS with more ground clearance would probably cope better, but then my feet wouldn't reach the ground!

Chain and ring came from Motorworks.

 

[armstrg]

Does anyone know if making this mod would invalidate BMW warranty?

 

[chas820]

I doubt any BMW dealer would count the teeth on yer sprockets.

 

[windsurfer]

F650 gs twin 18t front sprocket

Might sound contrary but I have sought, without success, for an 18t front sprocket to reduce revs at speed. Carried out the same mod on a Honda transalp using an Africa twin front sprocket and dropped the rear by a couple of teeth to give really long legs. All achieved with the original chain length.
Any pointers for an 18T for the 650 twin??

 

[Smythson]

It's very very tight in there - you would have to mod the slider/guide/thing that protects the swing arm from the inside of the chain. However i was considering it as the guide is both thick and wide so could spare a thinned out channel section to allow the sprocket through.

From memory TT do a 18T.

Best,

S

 

[windsurfer]

18T front sprocket

Cheers Smythson, definitely looks worth a coat of looking at. I recall the large sprocket on the Transalp required some material removal on the plastic guard sitting over it.

Kenn