Sprockets/gearing

[Ash]

Any recommendations or references for general gearing theory?

Specific example: Ninja 300 with stock gearing (14/42) at Shannonville Long. The bike has a power commander and pulls all the way up to the 13k rev limiter. I'm currently only using 4 gears (2-3-4-5), getting near the redline in 5th on the back straight, and hitting the rev limiter hard in 3rd before T4a/b (the double apex lefts).

It's really just that stretch between T3 and T4 where the gearing isn't working for me any more. 3rd gear is too short, but if I shifted into 4th I'd only be there for a second or so before having to shift down again into T4.

As a winter diversion, I started punching numbers into www.gearingcommander.com and www.blocklayer.com/rpm-gear-bikes. My first thought was to just go a bit taller on the gearing (14/41, let's say) and gain a little bit more room on the top of 3rd gear. But 14/41 only buys me an extra 3km/hr in 3rd, and I strongly suspect everyone goes shorter with their gearing, not taller.

So generally speaking, what do you aim for with your gearing? As low as possible, as long as you're somewhere close to the power peak in top gear on the back straight?

 

[TK4]

Shorten it way up so you're only using 1st off the line (if at all), then worry about your fit from 2nd through 6th.

 

[Brian P]

Get it so that you are using 6th. I'll guess 3 more teeth on the rear sprocket (and a longer chain) and have on hand sprockets with one more and one fewer than that for fine tuning.

The higher gears are closer together. Means you can be closer to optimum in any given situation.

Sometimes it is necessary to go one tooth bigger or smaller to get away from an in-between-gears situation in one particular corner, and force the decision one way or the other.

 

[boyoboy]

or one tooth off the front, is ~ the same gearing as adding 3 to the rear sprocket. keep your chain if its good..

 

[boyoboy]

if its td's you are doing, not racing - live with the stock gearing, and spend the savings on more td's and really really good tires ..

 

[Ash]

if its td's you are doing, not racing - live with the stock gearing, and spend the savings on more td's and really really good tires ..

Yes, I'm just doing TDs in the short term. I agree, for the past couple of years I've just dumped my money into TDs and tires and time on the SuperSonic minibikes. I have a set of Q5 for this year ready to mount once I burn off the Q3+ that are currently mounted. In the grand scheme of things, sprockets are pretty cheap, and I'm mostly just looking at them as part of the learning process.

The other part is to gauge whether I want to get serious about making plans to go racing in a couple of years. My current reference is the LTWT Production class at Shannonville. I'll never be fighting for the lead, but dropping 4 or 5 seconds off my lap time still seems attainable (not just from sprockets, although I'm sure they would help). That would put me in a place where I could make a respectable showing in the back half of the field.

 

[Brian P]

Adding teeth to the rear sprocket allows fine-tuning in finer increments than subtracting teeth from the front sprocket ... and it puts less stress on the chain, and reduces the tendency for the chain to rub on the guides on the swingarm depending upon suspension movement (it keeps the path of the chain further away from the swingarm). (The latter adds friction, and the forces involved interfere with suspension movement)

 

[boyoboy]

pretty cool. good outlook !