Let's do some math, it will be worth it, I promise.
Lets assume that your engine has a 10t gear on the engine crankshaft, 41t gear on the clutch, a engine output sprocket with 10t, and you have a 40t rear sprocket.
THEN:
Gear Ratio = (41/10) * (40/10) = 16.40:1
Soo, with the 10t sprocket, we have a gear ratio of 16.4. Cool stuff. Let's keep making assumptions..
Now, let's assume your engine spins 6000 RPM. At that 6000 RPM with a 26" wheel, your speed will be:
Speed = (RPM) / (Gear Ratio * (Some Factor which is a function of wheel diameter))
I don't feel like doing the math, so I used a calculator, the speed ends up being 28.3 mph. Feel free to do the unit conversion if youd like; I didnt like.
Sooo we have:
Speed = (RPM) / (Gear Ratio * (Some Factor which is a function of wheel diameter))
Speed = (6000) / (16.40 * (Some Factor which is a function of wheel diameter)) = 28.3 mph
Lets solve for the factor so it can be used later:
==> ( Some Factor which is a function of wheel diameter) =12.93. This has some weird units along with it, Ill leave those of because Id like to. Id also like to just ignore any error which might show up as a result of rounding that down, so I will.
Anyways, now we finally come to the whole point of this mental exercise:
So you want to know what happens when you change the engine output sprocket to 11t?
Lets just plug it into our handy formula we derived..
Speed = (RPM) / (Gear Ratio * (Some Factor which is a function of wheel diameter))
Speed = (6000) / (( (41/10) * (40/11) ) * (12.93))= 31.1 mph.
So, if your setup happens to be the exact same as the one described by the above assumtpions, then by switch to the 11t gear you will increase your speed at 6000 rpm by about 3 mph.
Can we learn anything from this to prevent doing math ever again?!I would sure hope so. Play with the formula, note that:
1) The change in speed is about equal to current speed * a ratio of rear gears changed.
or, New speed = Current Speed * (Old rear cog teeth count / New rear gear cog count)
2) The change in speed is about equal to current speed * a ratio of front gears changed
or, New speed = Current speed * (New front cog teeth count / Old front cog teeth count)