17/40 gearing on TT250

[RogerWFarrier]

Well since I can't leave anything alone and my riding is entirely on the pavement I decided to install a 40 tooth rear sprocket and I am actually pretty happy with the results. While it doesn't like the wind much on the top end when the wind isn't a factor it performs really well especially in city driving. Last night I took it on the freeway and without the headwind and in traffic it actually hit 73 mph at about 7300 rpm and was able to maintain 66-68 mph when I was alone in the gusty conditions which I think is pretty good since I weigh 250 lbs.

[Megadan]

I tried a 17/39 with my 120/80-18 tire (similar to a 17/40 on a stock tire). I had similar results to you, but I didn't find my bike to like steep hills very much, so I went back to a 43 rear. I guess that is less of a problem in Florida though. You should track your fuel economy with those gears to see if it makes a difference.

[RogerWFarrier]

It's been really windy here so I'm sure that has had an effect on things but I really only noticed it when I was riding into a head wind so it knocked it down to about 58 mph but on the return trip I was able to maintain 66-68 mph with a max of 73 when in traffic. When I took the secondary road with a 55 mph speed limit it easily maintained 58-60 mph with some throttle left so it will be interesting to see how it performs when it's not battling storm gusts. As far as mileage goes I've consistently gotten around 47-50 mpg with this bike since I've had it so it will be interesting to see if it has any major effect on fuel mileage. There may be more experimentation on the horizon because when I was browsing on amazon the other day I scored a 42 tooth sprocket for $10 with free shipping because I have Prime. At that price I had to pick it up even if I just save it for a spare....lol.

[culcune]

I had a TMEC 200 and went to a 40 rear (17 stock countersprocket). Not the best idea, thinking back. I never measured top speed on GPS, and the speedo was long broken, but I kept having to put it into 4th on windy days to keep up with traffic, or to not hold back traffic (50 MPH posted but cross-border traffic running at 60+). I would probably have preferred a 42 or 44. It seems like you are getting better results with your larger engine and any modifications. My 196cc Zongshen was bone stock.

[RogerWFarrier]

Originally Posted by Megadan

I tried a 17/39 with my 120/80-18 tire (similar to a 17/40 on a stock tire). I had similar results to you, but I didn't find my bike to like steep hills very much, so I went back to a 43 rear. I guess that is less of a problem in Florida though. You should track your fuel economy with those gears to see if it makes a difference.

Now that I have ridden with the 17/40 gearing for a bit I actually like it. For speeds up to 60 mph it has no problem at all even in the somewhat windy conditions that we've been having. When I have noticed a decrease in speed is on hills and especially if it is fighting the wind. I rode it about 140 miles the other day on secondary roads and some freeway and it actually did really well. It ran a steady 60-62 with no problem on the secondary highway and when I got on the freeway it ran a steady 65-68 mph unless the wind took over. The only time that it dipped below 60 mph was when I hit a strong wind and a rise at the same time on the freeway. When I was in a group of fast moving traffic it actually got up to 75 for a couple of minutes until I couldn't keep up with the faster cars. The fuel mileage is actually the same as I've been getting the whole time I've had the bike 47 mpg which is pretty good considering that the bike was at 6K rpm or higher for the majority of the trip. I think it's because I'm turning the same rpm as before I'm just going faster. On a side note I had called CSC to order a couple of O-Rings and just out of curiosity I asked what the gearing on the Café Racer is going to be and was told that it is going to be a 16/41 setup so which would be roughly the same as a 17/44 which just happens to be a ratio that I was considering at some point. At any rate I think that I can live with the 40 since it actually performs really well for the majority of my riding. I may go back to the 43 once this one is worn out or possibly go back to a more dirt oriented setup on the TT if I can get my Kz1000 Resto-Mod finished since that will be my main ride for the street.

[Megadan]

The 17/40 combination is definitely the most highway friendly gearing, but I still much prefer the 17/43 after having ridden both. I will sacrifice the 400rpm drop at 60mph for the slight little extra bit of pulling power. In any case, it sounds like it suits you and your needs very well.

[JerryHawk250]

Roger,
I'm running the 40 tooth on the rear. The 17 works great for just highway riding. I run a 16 tooth on front most of the time due to I tend to leave the hard roads for off road riding. 16/40 is a good all around combo especially if there are no hills. I switch to the 15 tooth if I'm running strictly off road and if on hilly trails. The front sprocket is a quick and easy swap compared to changing the rear. I would just buy a 15 and 16 tooth front and not mess with the rear sprocket.

[kirbo7106]

Originally Posted by JerryHawk250

Roger,
I'm running the 40 tooth on the rear. The 17 works great for just highway riding. I run a 16 tooth on front most of the time due to I tend to leave the hard roads for off road riding. 16/40 is a good all around combo especially if there are no hills. I switch to the 15 tooth if I'm running strictly off road and if on hilly trails. The front sprocket is a quick and easy swap compared to changing the rear. I would just buy a 15 and 16 tooth front and not mess with the rear sprocket.

When changing the front sprocket, do you have to change the chain length?

Enjoy the ride!

[JerryHawk250]

Originally Posted by kirbo7106

When changing the front sprocket, do you have to change the chain length?

Enjoy the ride!

No, due too there's not a big difference in diameter in sprockets.