TXC449 Gearing

[Bunny007]

Stock gearing is 15 tooth countershaft and 51 tooth rear sprocket. To gain more speed for road travel (to trails) or straight aways would it benefit me to change either the countershaft to 16 or sprocket to 49? Does this make much of a difference? Maybe just leave it alone. Any advice or experience with this would be appreciated.

 

[OlderHuskyRider]

1 tooth bigger on the CSS or 3 teeth less on the rear sprocket will reduce your RPMs in 6th gear by 500.

 

[7point62]

Ok, so let's increase your 15t front to a 16t while assuming that your cruising speed at a particular rpm is 50mph. The maths is hopefully not too daunting and we'll take it as read that a bigger front sprocket (or a smaller rear) increases speed at a particular rpm.

For our bigger front the increase is (16/15) x 50mph = 1.067 x 50 = 53.4mph.

So it raises speed (or lowers revs at a particular speed) by nearly seven percent. Thats 67 rpm per thousand.

Let's do the same with the smaller rear, dropping it from 51 to 49:

(51/49) x 50 = 1.041 x 50 = 52.0mph

So changing the rear by two teeth has much less effect than changing the front by one. A rule of thumb way of working it out is that in your case the rear cog is about three and a half times bigger than the front, so a one tooth change up front is worth 3.5 on back. Remember also that the chain is in touch with *about* half of each sprocket, so changing the rear sprocket by (say) four teeth will affect the chain tension by about two links, which means you have to pull the rear wheel back / forward by about a link length's worth of travel (which means you may even run out of adjustment), while changing the front cog by one tooth will have nearly the same effect on gearing, but will have far less of an affect on chain tension. Front sprockets are also a bit cheaper.

"This math is great and all," I hear you say "but what does this mean for me?"

Well, it depends. When you're riding on the dirt do you find yourself in first gear all the time, slipping the clutch in the tight stuff and clenching your butt cheeks every time you have to tackle a steep descent? If so, then raising the gearing might prove a struggle. But if not then a one tooth increase on the front isn't a huge jump (and on tarmac it's about the minimum jump that's worthwhile anyway). I change fronts all the time depending on where I'm riding that day thanks to the close ratio gearbox thing. In fact I had a very similar convo with Motosportz on TT a while ago about gearing and he assured me that although swapping cogs on the 449 / 511 is a bit more complicated than on a "conventional" bike it's still a snap once you've done it a few times. Maybe he'll be along to advise in a while as he's a guru on these bikes.