So you are looking to put a new chain and sprockets on your dirt bike, and have a few questions. About sprocket size, and gear ratios.
In this article we will cover just that.
When talking about changing the gearing on a dirt bike. Or what is called the final drive ratio. It’s basically just referring to changing the actual size (tooth count) of the sprockets.
Though before, you work on your dirt bike, or change the gearing. Don’t forget you should always check in your owner’s manual. For safety guide lines, and specific recommendations.
Now,You can have a
Bigger, or smaller front or rear sprocket.
A bigger diameter sprocket will have more teeth,
And a smaller sprocket will have less teeth.
What does gear ratio mean?
When talking about the gear ratio here. We’re just referring to the diameter (size) of your front and rear sprocket, and how they correlate to each other.
For example, how many rotations does your front (counter shaft) sprocket make. To one full rotation, of the rear sprocket.
The gear ratio, will define how the engine rpm. Converts to rear wheel speed.
So if you add, or take away teeth from the sprockets. You will change the gear ratio. Which will either increase, or decrease. The rear wheel speed of the bike.
Why would you want to change the gear ratio?
By changing the gearing. You will have the ability.
- To gain more top end speed, but with the loss of low end torque.
- Or have better low end torque. With the loss of top end speed.
So, changing the gearing ratio. Will change the overall performance of the bike.
Ok, so how do you,
Find your current gear ratio?
First, count the teeth on your sprockets
You will need to divide the amount of rear sprocket teeth. To how many teeth you have, on the front sprocket
Lets say for example, you have 50 teeth. On the rear sprocket, and 14 on the front (countershaft) sprocket.
This means, the front sprocket will rotate 3.57 times. For one rotation of the rear sprocket.
Now, you may be wondering,
What does this number mean?
A higher numerical number, would be a lower (shorter) gear ratio. Or also called gearing down.
While a lower numerical number is a higher (taller) gear ratio. Also known as gearing up.
A gear ratio of 3.00, is higher (or taller).
And a 4.00 gear ratio. Would be lower (or shorter).
Something to think about.
The actual gear ratio, is what will determine how the bike will perform. So, you can go down or up (at the same time) in size. On the front, and rear sprocket, and just about keep the same gear ratio.
For example, lets say, if you had a 14 tooth front, and 50 tooth rear sprocket. Which is a 3.57 gear ratio.
Then went down to a 13 tooth front, and a 46 tooth rear sprocket. Now you have a 3.54 gear ratio. So, you are real close.
Which sometimes riders will go down in size on both sprockets. To lighten things up a tad bit. And or to help reduce the rotating mass. Of the sprockets, and chain as they spin around.
Though this article isn’t about that. So i don’t want to get too far off topic.
So, with all that being said. The main thing is be mindful, and don’t just randomly, change sprockets around either. Or you could end up. As you can see, with almost, the same exact gearing.
So, do your math, or reference a sprocket gear ratio chart. In any case, it just helps to know where you start, and where you end up at, with the gearing.
I should add, while all the gear ratios and numbers are helpful. It’s not needed, as long as you know the tooth count of the sprockets. On your bike currently, and know how to adjust them. To get the performance change you want.
Which brings us to the next point,
Understanding the teeth
So, if you want to,
Gear up (higher gear ratio).
- You will want less teeth on the rear sprocket.
- Or, you will need to add teeth to the front (countershaft) sprocket.
Gear down (lower gear ratio).
- You want more teeth, on the rear sprocket.
- Or take away teeth on the front sprocket.
So do you really need to,
Change the gear ratio?
So this might be a question you’re wondering, if you really need to change your gearing
This will ultimately depend. On the type of terrain, and riding you will be doing.
Whether you need a taller gear ratio. To give you more top end. On long open stretches like desert racing etc. Taller gearing also allows you. To lower top gear, cruising engine rpm.
Or, if you do slow trail, or technically type riding. You might want a lower gearing ratio.
Lower (shorter) Gearing “Gear Down”
Will apply more low end torque to the rear wheel. So you will have snappier acceleration. Off the line and out of the corners.
You will also have to shift quicker thru the gears As it brings the gear spread (gap) in the gearbox closer together.
Now, with lower gearing. You lose top end speed, and generally have to do less clutch work, but gain more bottom end.
A lower gearing might be needed. If you run steep hills, deep soil, sand. Or in muddy, tacky terrain. Which can bog a engine down.
Higher (taller) Gearing “Gear Up”
Will allow you to whined out the gears more. Before you have to shift. The gear spread (gap) will be further apart.
Keep in mind, if you go with a taller gearing ratio. You will lose some power. On the bottom end acceleration. So, it will be a bit more sluggish taking off.
Also, you might have to do a little more (feathering) clutch work. But the power is more manageable. And it gives you, the ability. To gain more top end speed.
So, it really just comes down. To where, and how you ride.
The stock gearing might be ok. For some riders, but if you need to. You can just dial it in a bit, for your needs.
Ok so to sum it up. When you have the optimum gearing for your needs. It allows you to keep the engine (RPM) in its sweet spot. For peak power, acceleration, traction and control. To help stay hooked up. On the track or trail.
Ok, so if you do decide. To change gear ratios to fit your style of riding better.
Just remember, to
Make small changes at a time
For example, a good place to start, is to change one tooth on the rear. Then see where your at and how it feels. If you need a bit more. You could try changing another tooth in size, and so on.
Or, maybe you need to step it up a notch further at first. Which would be to change a tooth, on the front sprocket. Then, if you need to, just fine tune it in, one tooth at a time. With the rear sprocket.
Changing the front sprocket a tooth. Can be a cheaper way. To change the gearing on your bike vs the rear sprocket. To help get a better feel. In the direction you need to go for gearing.
But just keep in mind. When changing the tooth count, on the front sprocket. It will change your gear ratio. By a bigger percentage, than the rear sprocket.
For every (+ -) one tooth you increase or decrease. On the front (countershaft) sprocket. Would be the same as, adding, or subtracting,
Depending on the type of gearing you have. Roughly (+ -) 3-4 teeth from the rear sprocket.
Also, in some cases you may have to change the front sprocket. To get the gearing you need.
But, I should point out. That it’s generally recommended. For a longer chain life. To not go smaller than the stock size (tooth count). On the front sprocket,
It will make a tighter radius (bend). For the chain to roll around. Increasing friction, and wear on the chain and sprocket.
So, with the chain and sprocket life in mind, and if you want to make. Very subtle gearing changes. It’s best done with the rear sprocket, in one tooth increments. Which most of the time is desired.
Now, keep in mind…
Sprocket size will affect chain length.
Changing sprocket sizes on your bike. By one tooth will affect chain length. So you will have to reset the proper chain tension (slack).
But by doing this. It will affect the length of the chain run, and wheel base of your bike.
So, you will have to move the rear wheel forward, or backward. To accommodate for more, or less, chain slack.
A smaller sprocket will loosen the chain. So, you will need to push the wheel back. To the rear of the swing arm (lengthen wheel base). To adjust for chain slack,
A bigger sprocket. Will push the wheel forward. To the front of the swing arm (shorten the wheel base). To adjust for proper chain slack.
So it’s always a good idea. To know how much room you have. In the slots of the swing arm, to adjust your chain. Before you change sprocket size.
- Go up in sprocket size too much. You will need a longer chain or,
- Go down in sprocket size too much. You will need a shorter chain
So, if you’re plum out of room. In the chain adjustment slots. Or in doubt how much room you have.
It’s best to….
Replace chain, and sprockets, at the same time.
If your chain and sprockets are already worn out. A worn out chain, will wear out new sprockets in no time, and vise versa. As those old components. Develop wear patterns together.
Also, last but not least. Is to keep in mind. That there is,
Sprocket size limits.
There are limitations, of how big and small you can go. With the front, and rear sprockets.
So, always refer to your owners manual.
Go too small on the front countershaft sprocket, and it could cause the chain, to wear into the swing arm.
Go too big on the front sprocket, and it could cause the chain to grind into your engine case. Or sprocket guard causing damage.
Too big or small with the rear sprocket, and it can cause you problems with the chain guide.
Ok now for some,
Also it might be a good idea. To look, and ask around to find other riders. That have the same bike as you. To get some sprocket combos they might use. That will fit your riding style.