I am looking to increase the gearing on my F4i. Has anyone put a 17 tooth up front. They are available but I have not seen anyone do this mod. I am looking to drastically increase the gearing(bike is used strickly for commuting).. What is the smallest I could go out back without the chain rubbing the swing arm.. Would a 17/40 setup work?

Thanks!

 

17/40 not sure about and dont know why you would go that low on the teeth anyways.

But a 17 on the front, you should get better gas mileage because you have lowered your rpms slightly by doing this. In conjunction, you have also increased your top end. Just my 2 cents.

 

A 40 rear seems a bit drastic, no? lol

If anything, just try the 17 for now, and if you think it could use a bit more, try it out.

 

--edit--- doh....made a mistake!

 

Try doing +1 in the front and -1 in the back, i wouldnt do anything more drastic than this.
this is a 600cc bike and it doesnt have enough low end to pull you in 6th gear, doing 80mph at 4k RPM. (which im assuming you are trying to do).

 

as was mentioned in another thread, aerodynamics the reason a bike is at higher rpms than you would think in 6th gear at only around 70mph. A 17 toothe front sprocket is a freakish change that I would imagine would make the bike almost unrideable. When your geared that high you have to rev a lot more to start from a stop. My ducati has a 16 tooth front sprocket and its a pretty awkward bike in that respect. You really have to slip the clutch while revving a lot to start off, definitely not what you want for a commuter/daily rider imo.

Aerodynamics are also a huge factor. A motorcycle's top speed stock may be limited by gearing so changing the gearing may allow for a greater top speed but at a certain point the motorcycles power is not great enough to overcome the aerodynamic drag. The same principal applies at lower RPMs and speeds. Its the reason that in many bikes the top gears will be at around the same RPMs at say 60-80mph. Being in 6th gear will theoretically allow the bike to be at a lower RPM to maintain the same speed but in reality the lower RPMs are not enough to overcome that wind resistance and maintain that same speed so the bike has to rev a bit more. I do not believe that running such high gearing will allow you to run at lower RPMs at freeway speeds in 6th gear and as I mentioned earlier it doesn't make for good stop-and-go commuting either so I would not suggest doing this.

a small change might help (still not sure it would do anything in 6th gear but it might in the first few), you could try a 600RR stock rear sprocket. Its 3 teeth smaller in the back (I've got my old stock F4i sprocket on my RR for the opposite effect lol). 3 teeth is a pretty decent change, its possible it won't fit depending on how much range of adjustment you have in your axle. If its pretty close to the back of the adjusters it probably won't fit but if its closer to the front, its possible. I'm sure you can probably find them on ebay for almost nothing though.

imo you would be better off having your bike dyno tuned for gas milage and trimming some weight off the bike, maybe adding a DB windscreen if you don't already have one

 

I do 17 and 60 but not 17 and 40, but that's me.