Adjusting Your Drive Ratio – Changing Your Sprockets for Maximum Performance

Adjusting Your Drive RatioAre you gearing up? Adding teeth? Or are you simply stuck in the stock compromise you’ve been given? Okay, maybe that’s not fair. But chances are, you can do better – and for less money than you think.

When you bought your motorcycle or ATV, it was full of compromise. It had to be. It didn’t really know you, or your abilities, or your physical size, or where you ride. This “compromise” is most evident in the stock tires and wheels, as well as the chain and sprockets.

All of these – except maybe wheels – are “wear” items that eventually need to be replaced. Tires may be the most evident of these. But did you know that a simple sprocket swap could do even more for your bike? We’re not just talking about when the original wears out. So we’ll explain gearing and sprocket sizes, as well as applications, and we’ll show you some of our favorite sprocket products.

Gearing Up

Sprockets, or
This may sound like you’re prepping your gear for a trip to the trails, but we’re talking about something else. You “gear up” or “gear down” by changing sprockets, front or rear, to different sizes. Because you can change either front or rear sprockets, it’s best to begin by determining their relationship.

Sprockets, or “chainwheels” more literally, are measured by their number of teeth. To determine the final drive ratio, divide the rear sprocket size, say 49 teeth, by the front or countershaft sprocket size, say 13 teeth (like a new Yamaha YZ250F). In this case, the Final Drive Ratio is 3.77 – the front sprocket revolves 3.77 times to make one complete revolution of the rear sprocket.

The final drive ratio on a motocross bike will likely stay close to 4.0. For street bike guys, there’s a much bigger spread of ratios depending on sportbike or standard. For sport ATV riders, the stock final drive ratio will generally be lower, around 3.0 or less.

Back to that YZ250F. If you replace its 49T rear chainwheel with a 52T – and that’s a big change – your final drive ratio is now 4.00 (52 divided by 13). You just “geared down.” That may sound backwards, but the relation is always to the front or countershaft sprocket, and in that relationship, you geared down. This number is most important when you’re changing gearing. It’s easy and beneficial to be scientific about this. And when you want to make a change, you should be scientific. Make one small change at a time, document it and test it before considering further changes.

Why Change the Drive Ratio?

Gearing up, like with a smaller rear sprocket, decreases the final drive ratio and adds more top speed to your motorcycle or ATV. Want the short answer? Gearing down by installing a larger rear sprocket (like with our YZ example) increases the final drive ratio and reduces top speed, but can increase acceleration.

Gearing up, like with a smaller rear sprocket, decreases the final drive ratio and adds more top speed to your motorcycle or ATV.

Short answers never tell the whole story, of course. Setting the gearing for any motorcycle or ATV presents a trade-off between low-end power delivery and top-end speed. If you like a nice blend of the two and are happy with the power delivery of your vehicle in stock form, then leave the drive ratio alone. Just keep an eye on your sprockets (and chain) for wear.

If you want better top-speed or stronger acceleration – and it’s not easy to get both – then gear up or gear down, and you can do so for $100 or less (sometimes way less).

If you’re a beginning rider, you might consider gearing down. Low-end power delivery and more effective acceleration will serve you better than top speed. Expert riders may already know how to get the best low-end delivery, and might want to gear up a vehicle for improved top-end power. But let’s look at specific applications to give a better answer.

ATV and Off-road motorcycle

ATV Gear UpA technical track or trail loop with deep soil, sand or elevation changes will require Gearing Down. This will give you strong acceleration out of corners, and let your bike or ATV better use power to pull through the soil or up hills. You may have to shift more often, but you’ll get the strong pull you needed.

If your favorite track or trail is hard-packed with big sweeping turns, then you may want to Gear Up and make the most of your machine’s top-end power delivery. You will lose access to some low-end power, and may have to use more clutch for low-rpm control. In exchange, you’ll get more of what you want at higher rpm in improved top speed. You can also gear up if you’ve made other modifications to your bike or ATV that improve acceleration.

Dirtbike Gear Ratio Ride a Suzuki LT-R450 and want even better low-end power? Gear down. Switch that stock 36T rear sprocket for a 37T or 38T.

Ride a Kawasaki KX450F and want more top-end? Gear up. Switch that stock 50T sprocket for a 49T.

Street Motorcycles

If you ride a sportbike on certain technical roads or race tracks, perhaps, you can gear down for best acceleration and low end power delivery.If you ride a sportbike on certain technical roads or race tracks, perhaps, you can gear down for best acceleration and low-end power delivery.

For street riders specifically, changing gearing can help you tune your bike to a desired cruising rpm. For example, if your bike rolls down the freeway at 6000 rpm at 65 mph, you could gear up to lower that cruising rpm, reducing vibration and improving fuel mileage.

Changing gearing on street bikes can be more complicated than with a motocross bike or ATV. If you change the front sprocket, your street bike’s speedometer will very likely read incorrectly. You’ll need to correct that. Also, changing sprockets on a track-riding sportbike can change the effective wheelbase of the bike enough to affect handling. Those effects are not as pronounced on a dirt bike or quad.

Sprocket Construction

The best steel sprockets use hardened and heat-treated steel.Most sprockets are made from either steel or aluminum, or maybe even a mix of the two. Steel sprockets are generally less expensive, and better for longevity. Countershaft sprockets are often made of steel; they need to be durable and their small-size means weight is usually not an issue. The best steel sprockets use hardened and heat-treated steel.

Sprockets made of aluminum are significantly lighter, but have a shorter life span, and are more expensive than steel. For race bikes or ATVs, the weight savings can be huge, often a couple pounds. For added durability, aluminum can be anodized, but sprocket life span is not an issue for most racers.

A Couple of Our Favorites

A Couple of Our Favorites JT Sprockets makes more sprockets – about 18 million annually – than any other manufacturer in the world.

In recent years, JT has begun using more durable C49 steel with a high-carbon content. For competition-quality sprockets, JT uses 7075 T6 aluminum. Its high strength-to-density ratio makes it ideal for racing applications. JT’s countershaft sprockets are made of full heat-treated chromoly SCM415 steel. Many other manufacturers simply “surface harden” their countershaft sprockets.

JT has fitment for more than 95 percent of bikes and ATVs in use today.

You may think of Renthal primarily as a handlebar maker, but the company’s chainwheels are chosen by hundreds of champion racers. Renthal makes sprockets for off-road and road applications, mainly from 7075 T6 aluminum. The company’s unique Twinring off-road chainwheel features steel teeth on an aluminum inner ring for a product that is lightweight and durable.

All of Renthal’s chainwheels are CNC machined for precision, and to provide a combination of lightweight and strength. Renthal front chainwheels are made from nickel-chrome-molybdenum alloy steel, and are case hardened.

You Need to Know This

When changing your sprockets due to wear, you will also need to replace your chain.When changing your sprockets due to wear, you will also need to replace your chain. The chain and sprocket relationship is best when the two wear together. Mixing an old chain with a new sprocket – or vice versa – will shorten the life of either. Not a good idea. And if you make a big change in sprocket size, you may need a shorter or longer chain.

Changing one tooth on the countershaft sprocket has a more significant impact on the gearing than changing one tooth on the rear sprocket. Plus, countershaft sprockets cost less. But, it’s most often best to make changes with the rear sprocket. You get more fine adjustments, and that’s generally desired.

Avoid using a smaller-than-stock front sprocket. On a smaller sprocket, the drive chain must turn a tighter radius, which increases friction and decreases the life expectancy of the chain.

    • http://www.chaparral-racing.com/blog/ Eric Ellis

      What size sprockets are you running right now?

  • Salim Alhasim Salim

    What is the best combination gearing for a long ride on my YZ 250 , i currently have 14 front n 47 rear sprockets on. 18″ rear wheel

    • Eric Ellis

      Hello Salim, it depends on what you want to do, do you want a faster top speed or more torque? For faster top speed you can step drop a few teeth on the rear, for more torque jump up a few teeth on the rear.

  • Pingback: 400ex Rear Sprocket - Honda ATV Forum()

  • J.

    I have a stock sym fiddle 125 cc looking to up the top speed. What’s the best idea?

  • dalton

    I have a 09 ttr230, I have 13 in the front and 49 in the back, I would like to know where to order a 52 for rear and 11 for front but can not find where to order them from to make sure I get the right ones

    • Eric Ellis

      Hi Dalton, can you please email me and I will provide you with some part numbers to help get you headed in the right direction to find what you are looking for. Thanks. edellis@chaparralmotorsports.com

  • Jeremy Windsor

    I need help with a gearing issue, have a 2000 warrior 350, not the fastest but want it faster. Tires were dry rotted and went down to 20×10-9’s but am going up to 23×10-9’s. Stock front is 13T and rear is 40T. What kind of difference would a 16T do to the front? And where can i find a rear less than 40T? Plz any input would be good

  • brayden

    My pit bike goes 110km top speed with a 41 theeth sprocket I’m going to change it to a 37 theeth how much faster will it go

    • Safwan Mansoor

      121.89 km/hr given your pit bike has enough torque so that doesn’t get affected by drag at high speeds!!

  • Safwan Mansoor

    Mr Jagjeeth Singh,
    more accelaration would mean lower top speed and mileage!!
    so it depends on how much more accelaration you want from your bike!
    if you want twice the accelaration from your bike, go for a 88 (44*2) teeth rear sprocket but also see if the new sprocket have sufficient clearing from all other parts of the bike!! but given it being a 150 cc bike i wouldn’t recommend changing it to 88teeth sprocket as it would not climb more than 20 km/hr(,assuming your bike goes 40 km/hr with stock sprocket) on the first gear at full rev!!
    this would also cut your mileage to half!!
    but if stunting is your priority then go for it after checking clearance of the sprocket from other parts!!

  • Bernard

    Im wondering what size sprocket can i change on my kx 85 for racibng

  • mohammad aamir

    my bike is a yamaha rxz for drag race its tyre size is 2.50/18rear, and 2.25/17 front so what should be the sprocket size