Understanding a motorcycle gear ratio can make a real difference in the world of motorcycling. A small change to the gear ratio can make a big difference when it comes to engine RPM. Not just on a race track, but in the real world of riding bikes every day. The standard gearing on a particular motorcycle might suit your riding perfectly. Every manufacturer spends a lot of time and money trying to make it as universal as possible, but we aren’t all the same and often our needs can be very different.
Maybe like me you weigh a bit more than you should or carry luggage regularly. Perhaps your bike wants to do a little more than the legal speed limit before shifting into top gear and you want to change up at a lower speed. You might want different gearing if you are doing a lot of track days, high speed miles or if most of your riding is around the city. Whatever the reason, understanding gear ratios can help you step beyond a trial and error approach to find the right final drive ratio.
First, What Is The Final Drive Ratio
You can calculate the final drive ratio of your motorcycle by dividing the number of teeth on the rear sprockets by the number of teeth on the front or countershaft sprocket.
For most motorcycles this will typically be between 3 and 5. This number represents the final drive ratio and shows how many times the countershaft sprocket will turn in order to turn the rear motorcycle wheel one revolution.
A higher number allows the engine to rev more. The countershaft sprocket will turn more for every rotation of the rear wheel.This is referred to as Lower Gearing.
A smaller number is referred to as Higher or Taller Gearing. This will allow the motorcycle to run at lower rev’s for the same road speed.
Adding extra teeth at the primary end, on the front sprocket, will make the gearing Taller. If you replace the rear sprocket for one with extra teeth you will lower the gearing.
Why Is The Final Drive Ratio Important On A Motorcycle?
Let me fill you in on a dirty little secret of the motorcycle industry….despite what many tuning shops and manufacturers might say, It’s Not All About Maximum Power figures!
Yes you heard that right. Even when racing, having more usable power for given conditions is much more important than absolute maximum top end power.
It is quite possible that the engine with the greatest peak horsepower will not produce the best acceleration. The driving force at the rear wheel might not be enough except where peak power is produced. Changing the number of teeth at the front or rear wheel can give you a much better spread of power.
If maximum power was all we were concerned about then motorcycle racing would be nothing more than a drag-race. It is acceleration that usually wins races and this is important on the road too!
Do yourself a favour, before spending thousands on high performance engine tune up’s, first, get your motorcycle gear ratio right. Make sure the gearing you have suits your weight, riding ability, and your intended use. If you change to a larger rear wheel or a rear tyre with a different profile this will also affect the final drive.
How To Choose The Best Motorcycle Gear Ratio For You.
First do an honest assessment of your weight, the weight of any passenger and luggage and the kind of use the bike will have in general.
Generally speaking, heavy riders or those carrying a passenger and/or luggage will have a much harder time maintaining momentum and will benefit from having more power at a lower rpm range of the bike. This will offer better acceleration and control between gears.
Heavy riders will find Lower Gearing allows the motorcycle to stay in the middle of the power-band much more easily. This leads to a much more enjoyable and relaxing ride. It can also suit riders who spend most of their time in the city or on slower roads.
Lighter riders who never carry a passenger or luggage will want the opposite. With a lighter load the taller/higher gearing will keep them in the sweet spot as far as the power band is concerned, and depending on the bike and its use, may give both a higher top speed and better fuel economy.
What Will Changing The Gear Ratio Do To The Motorcycle?
Lower Gearing will allow the engine to move through the gears faster, but that also means the rider will be shifting faster and more often. The bike pull harder, but reach its rev limit faster.
Taller Gearing will produce engine power in a more linear way. The bike will carry each gear for longer. This can mean you have to use of the clutch more to achieve a fast take off, but the maximum speed potential of each gear will be increased.
Note I use the term “maximum speed potential” here. This is because standard gearing on most road bikes will not allow the bike to reach the maximum potential speed in top gear. Actual maximum speed is likely to be quite different to the potential maximum speed.
Take Small Steps With Motorcycle Gear Ratio Changes
If you do decide to see if a change in gearing will be of benefit to you take it slowly. Never make more than a one-tooth change in gearing at a time and always keep a log of any change you make to the gear ratio with your comments about the results.
Motorcycle Sprocket Construction
Not all motorcycle sprockets are created equal. You will find different designs made from different materials. Hardened Steel will last longer and cost less. Aluminium is lighter, but will need to be changed more often and is more expensive so in general is more suited to racing. Anodized Aluminium is a good compromise offering a hard outer layer for better durability, while keeping weight to a minimum.
There are more expensive alternatives such as Stainless Steel or Titanium. They offer some advantages but are not often used.
I would say always use a high quality Case Hardened Steel front countershaft sprocket. This is a high wear item and its small size means the extra weight is minimal.
Some manufacturers like Renthal and Supersprox offer 2 piece rear sprockets such as Renthal Twin Ring and Supersprox Stealth. They offer the best of both worlds. They have an aluminium inner mount plate with a hardened steel outer sprocket. This gives you the weight advantage of aluminium with the durability of steel.
New Motorcycle Sprockets Means New Motorcycle Chains
It makes no sense to change to fresh motorcycle sprockets if the motorcycle chain is no good. Running a new sprocket with worn motorcycle chains costs power and causes faster wear on the sprockets.
Do yourself a favour, when you change the gear ratio by fitting new sprockets, make sure you fit a new chain too. A good quality motorcycle chain and sprockets will drastically reduce the wear on your entire drive train. Make sure you service your bike properly and regularly.
Motorcycle Chain Construction.
There are essentially two types of chains used on motorcycles. Conventional and O-Ring/X-Ring designs. Conventional motorcycle chains use steel pins with a press-fit soft metal bushing to form each link. These chains use a mechanical seal to protect the link, meaning there is minimal clearance between the rollers and the link.
O-Ring or X-Ring chains use a ring to seal lubrication in the link and keep dirt and water out. These motorcycle chains are much more durable. They are a little more expensive and heavier, but they are much better from a maintenance perspective.
Sealed O-Ring or X-Ring chains do not require cleaning or adjustment as often as a conventional chain.
Proper Motorcycle Chain Adjustment.
The condition and adjustment of the drive chain has a significant effect on both the handling and engine performance of a bike. The simple chain-and-sprocket is still the most efficient way to transfer power from the engine to the rear wheel.
It can be dangerous if the chain adjustment is wrong. If it is too tight, too loose, or the wheel is not aligned properly in the swingarm it can be unsafe. At best it will result in excess wear. An experienced rider may notice the difference, but it is easy to miss. Improper setup or poor chain/sprocket condition can absorb serious horsepower at the rear wheel on the average bike.
To set the chain adjustment first start with a perfectly clean chain to get a truly accurate reading. Next check to see where the tightest point of the chain is. Find the centre point between Primary drive (gearbox) sprocket and rear sprocket. Check the manual and adjust the chain to the manufacturers specification.
Next, make sure the sprocket alignment is right. Use the swingarm markings as a guide but in production there are slight tolerance differences in these marking which can make a difference. Most mechanics use a lazer alignment tool or an alignment gauge. These fit into the centre of the rear axle and swingarm pivot bolt. You will make back the cost of the tool by a reduction in the cost of wear and maintenance of bearings and other drive-train components.
A Real World Example Of Changing A Motorcycle Gear Ratio.
You will find plenty of people with advice on this subject. If someone has been racing or even doing track days at different circuits they may have more understanding of how changing a motorcycle gear ratio can affect performance. Having said that, their needs and criteria might be very different to yours. Below is an example from personal experience.
I have owned a Suzuki DL650 Vstrom for ten years now and bought it just before a touring holiday into the highlands of Scotland. By the time I returned, I had decided I wanted a little more acceleration than I had when I had luggage and a pillion on board. So I decided to lower the gear ratio slightly.
Sacrificing A Little Top Speed Will Help Acceleration
Sacrificing a little top speed in favour of a shorter ratio for better acceleration wasn’t a problem for me, so I went one tooth down on the front sprocket and left the rear the same.
As well as giving me better acceleration the lower gear ratio was great for slow speed off-road riding. When riding solo it made a huge difference to acceleration and as the little Vstrom couldn’t hit the rev limiter with standard gearing, It actually increased the overall top speed.
This all suited me great at the time. I spent a lot of time off-road and even took the Vstrom on a few track-days. The extra acceleration meant it surprised a lot of people riding much faster bikes.
The only down side was increased fuel consumption, especially if I was generous with the throttle. Now, I have slowed down a bit, and I ride more on the road, so I switched back to the standard gearing. I enjoy the more relaxed ride just as much now as I enjoyed the extra acceleration back then.
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