Effects of Gearing Change

[Chili]

We made a gearing change to my son's bike this year when we put on the new sprockets and chain. Part of the change was concious and part was a mistake on the stock specs on my part. I now have a couple of questions regarding this gearing.

Stock was supposed to be 14/50 but I mistakenly thought it was 14/49, either way a local wrench told me that it was to tall and to change it to 13/49 which is what we did as we were looking for more jump out of the corners. I understand the ratio's of going up and down teeth on each end to affect the performance what I'm not sure about is when you gear it for more low end torque I know you are sacrificing some top end now is this sacrifice only at 6th gear tapped right out top end? or is it affecting from mid into top and making the bike have to be quick shifted a little more? The reason I ask is that it seems lately in his races alot of kids seem to be able to pull up on him in the straights and I was wondering if we have sacrificed too much at one end for the other?

 

[SpectraSVT]

Changing the front down one tooth is the same as moving up 3.5 teeth in the rear. With the -1 sprocket out back you geared the bike 2.5 over stock in the rear. This is a dramatic change. This will help on tight tracks as you will have boosted the bikes low end. The top end loss will come in every gear. It will require him to shift more frequently on faster tracks. If he needs some low end and most of his top end I would suggest 14/51. If low end isn't an issue and he needs top speed then use 14/49 gearing.

 

[Nevada Sixx]

i have low gearing now, so now when im on the fire road, im in fifth gear instead of third like i used to be. i have to shift thru the gears alot faster on straights now, but it will lug at low rpm in woods alot better.
to keep a two stroke in the power band, you have to ride at a high rpm, but if you gear too low, you will find yourself having to ride a gear high, with puts your bike at to low of an rpm again.

 

[atc3434`]

Basically, unless he is running topped out in 6th, you gearing isn't why he's pulled on the straights, unless of course he's slower coming through the gears. On most smaller engines, having tight gears, and shift all the time, is part of the equation for extracting maximum power. 1, 2, 3, and 4 are the gears most tracks require. If there is more than one or two spots were your getting into 5th, or even 6th, your probably geared to low and could pull a more gearing. Conversely, if you never get up to 3rd and 4th, your probably geared too tall, and arn't going to be on the pipe everwhere, or you'll be wasting the clutch all over the place. I want to speak to SpectaSVT's comment on a top end loss will occur in every gear, in effect yes, each gear will yeild less top speed then before, but your really only going to notice quicker shifts from gear to gear, and loss in your top speed pontential in 6th, tapped out. My YZ is geared about 4 more teeth than stock on the rear sprocket. The effect was first gear pulled better at lower speeds, the gears were all closer, which means I usually have the right gear for every situation, and I lost about 15 - 20 mph in top speed. The top speed loss wasn't important to me, with the stock gearing the bike would easily travel 75 - 80mph. (Yes, we actually tested that.) Now my top speed lies right around 60, and I have much better pull through the gears.