This article is about motorcycle “gearing”. It will explain:
- What is gearing?
- Why motorcycles have gearing
- Why you might consider changing the gearing on your specific motorcycle
- How you might do that
- How you can select new gearing
- What improvements can you expect?
- How much might it cost?

What is “Gearing”?

“Gearing” is a short way of describing the relationship between how quickly your engine is rotating (“revolutions per minute” or “rpm”) versus how quickly the drive (rear) wheel on your motorcycle is rotating (“road speed”). This relationship determines how fast you travel down the road at each given engine rpm in each gear, and, even more importantly, how much thrust force you have to overcome the effects of mechanical friction, aerodynamic drag, and hills, and still have thrust force left over to accelerate (as when passing another vehicle!)

There are 5 components on motorcycles that work together to create your overall gearing:
1. The rpm range in which your engine likes to operate
2. The numerical primary drive ratio (the ratio between engine rpm and clutch shaft rpm)
3. The 5 or 6 gear set ratios in your gearbox (1st gear, 2nd, 3rd, etc to “top gear”)
4. The final drive ratio (ratio of rear sprocket size versus countershaft sprocket size)
5. The overall diameter of your drivewheel tire

Why Motorcycles Have Gearing

Motorcycles have gearing for 3 reasons:

• Reduce engine rpm down to a usable wheel rpm
• Provide “leverage” for the engine to rotate the drive wheel against road loads
• Engines are only happy in certain rpm ranges

In general, in the gearing component list above, items 2,3, and 4 are all numerically “greater than 1”, so they have the effect of reducing an engine rpm that might run in the range from say 3000 to 15,000 rpm to a final drivewheel rpm ranging from a minimum of about 200 rpm to an absolute maximum of around 2800 rpm (about 200 mph for a typical modern motorcycle wheel).

In other words, the first reason for having gearing is that it “reduces” engine rpm down to a practically usable wheel rpm. If your typical Japanese 600cc superbike engine ran at 13,000 at peak power without gearing, it would be trying to turn the bike’s rear wheel at the same rpm, which would translate to about 867 mph! Not only is that road speed unsafe with present human technology, the engine simply does not make enough power to achieve that road speed, so the engine would stall!

Another very important reason for having gearing is that it provides leverage as your bike’s engine is trying to rotate the bike’s drivewheel. Just as with a car jack that is based on leverage, the more leverage you have, the easier it is to turn that drivewheel, but the more rpm the engine has to turn for each rotation of the drivewheel. Less leverage means an engine has to work harder to rotate that wheel a full revolution, but it can also turn at a lower rpm while doing so.

It’s easy to tell a low leverage bike: the numerical drive ratios in components 2,3, and 4 above tend to be small numbers. For a high leverage bike, those same drive ratios tend to be numerically larger.

Harleys in general have low leverage gearing because they do a lot of work with each engine revolution and operate at low rpm. Japanese 600 sportbikes in general have very high leverage gearing, because they do smaller amounts of work with each engine revolution, but they rotate those engines at much higher rpm to compensate (13,000 versus 5000 rpm!)

Both approaches are valid. It’s like two men shoveling sand. One is a small man who picks up 10 lb of sand with each shovelful, and does 10 shovelfuls per minute. The other is a big man who picks up 20 lb per shovelful, and does 5 shovelfuls per minute. Each is doing an identical amount of work (100 lb of sand being moved per minute). One is a “high revver” and the other is a “low revver”.

And, if anyone tells you that a low revver engine will accelerate a bike faster than a high revver engine of equal horsepower, they are wrong! All that matters is how much power is available at any given road speed, and with the right gearing, both bikes will accelerate identically! The high revver engine will simply be spinning faster while doing it. However, see comments below on how that high revving engine might unhappy at low rpm cruise conditions.

A third reason for having gearing is that a typical gasoline engine can only operate happily, or at all, in a relatively narrow range of rpm. The typical Harley for example can run decently only in the 2000 to 5000 rpm range. So, if you want that Harley to do 130 mph, and if it actually has the power at 5000 rpm to achieve that speed, it is going to be very unhappy at any speed below 2000 rpm which is 52 mph. This is inconvenient for city driving, and an impossible restriction if you ever want to actually go, say, 15 mph (577 rpm without any gearing, or lower than the engine will even idle!). But, if you gear the bike to give 2000 rpm at 15 mph, it will hit its redline of 5000 rpm at only 37 mph!

The high performance Japanese 600 has the same problem. Because it is much more highly tuned, it is happy only in the 5000 to 15,000 rpm range. So if you gear it for the 160 mph its engine power can achieve, 5000 rpm is going to be 53 mph, and again 15 mph becomes a real impossibility, as under load that engine will stall below 3000 rpm with that overall gearing. If you gear for 5000 rpm at 15 mph, you hit the 15,000 rpm redline at only 45 mph.

In both the case of the low revving Harley and the high revving Japanese 600, the motorcycle designer solves the problem by providing component 3 in our list: the 5 or 6 speed gearbox. This enables the rider to ride the 600 at 160 mph at 15,000 rpm in 6th gear, but also to ride the same bike at 15 mph and still show 4000 rpm on the tachometer in 1st gear. He simply selects the gear that is right for the speed and circumstances, since he has a choice of 6 gears.

Note that each engine can only handle a realistic load. That Harley engine in stock form will never hit 160 mph like the Japanese 600 will, because it just simply does not make enough horsepower to do so. If you gear it for 5000 rpm at 160 mph, it will actually not only not achieve the 160 mph, it will fail to even achieve its original 130 mph! This is because by “overgearing it”, you have given it insufficient leverage to turn the drivewheel against the frictional and aerodynamic drag forces present at high speeds. At 130 mph, it is now turning only 4062 rpm – far below the 5000 rpm range where it makes the necessary power to achieve 130 mph. It will run much slower than the original 130 mph. Moral of the story: each engine needs to be geared for the right amount of leverage.

There are a couple of important things to note and remember about gearing for the balance of this article:

1. If you change ANY of the 5 components numbered above, you are affecting your gearing.
2. Each engine is only happy within a certain rpm band
3. If you give an engine too little leverage, it’ll balk when you want it to turn that drivewheel under load conditions (e,g, the Harley at 130 mph with 160 mph gearing)

Why Would You Change Your Motorcycle’s Gearing?

By now, you may gotten the message that gearing is a bit complicated. Well, it gets even worse. And, it gets pretty hard to “please all the people all the time”.

In the previous section of this article, we talked about how a motorcycle designer has to take into account engine rpm versus road speed, the amount of leverage, and the power capabilities of the engine versus both of those.

However, the designer also has to take into account other factors. One is emissions testing protocols in different areas of The World. Often, the designer will skew the gearing away from optimized performance simply to help the bike pass a specific emissions testing protocol, even if that protocol is applicable in only one or a few places where the bike will actually be sold overall. If the state of California has tighter standards than Texas, the Texas rider may get stuck with the California gearing just because the manufacturer doesn’t want to produce and track different versions of bikes for different markets. Another example of this is bikes meeting stringent Euro standards being sold elsewhere in the same trim. In such cases, a gearing change might be in order.

The same thing happens for noise level testing. Harleys and Ducatis both for example are deliberately geared for lower rpm by their manufacturers to help minimize mechanical noise during certain noise level tests. This lower rpm gearing is very unsatisfactory at city speeds, where it necessitates a lot of clutch slipping. If the owner of the bike lives in a jurisdiction where this testing is not done, a gearing change is certainly in order.

Another issue that sometimes affects a designer’s choice of gearing is the engine vibration present at different rpm at under different load conditions. Sometimes a designer decides to gear a bike sub-optimally because it vibrates unacceptably (in his opinion) at certain road speeds with ideal gearing. Your weighting of the importance of vibration might be different than his, and you might be willing to accept some vibration to get better performance.

Another reason why factory gearing is sometimes inappropriate is that the manufacturer is trying to be competitive with other makes of motorcycles in the same displacement range on pure top speed, because this is what unsophisticated buyers use as a gage of a bike’s overall power. That manufacturer will tune his engine for a high but narrow power output, gear the bike for absolute maximum top speed under ideal conditions (flat road, no head wind, small sized rider, etc) and then advertise that top speed as the “come on” for buyers. What the manufacturer will not advertise is that this bike will now be impaired for normal use at lower highway speeds and under adverse conditions. If that same bike is regeared for a lower top speed, the overall performance will be greatly enhanced. In one specifc case in the Ducati lineup. Improvements of about 1/3 second can be obtained in the 0 to 60 and 0 to 80 mph times by a simple regearing to a more sensible top speed. That same sort of regearing on another Ducati model increases available horsepower in top gear at 60 mph by up to 45% while maintaining sensibly low rpm at that speed.

Another rather major complication is that each rider tends to want to use the same model of bike in a different manner! To use a particularly vivid example, Rider 1 may want to use his Ducati 748 as a track racer, and might therefor find the factory gearing reasonable for his/her purposes. But, Rider 2 who wants to use it as an all around sporty street bike will find the factory gearing rather bad when going less than 60 mph! Rider 3 who wants to use his/her Ducati 748 everywhere including downtown traffic will find the stock gearing totally unworkable in city traffic because at low road speeds, the bike will never be in its powerband. Both Rider 2 and Rider 3 should be re-gearing their 748s for their specific intended usage.

For another example, Japanese 600 superbikes will do 160 mph or more, but in top gear at 60 mph they are incredibly short on horsepower for passing, hill climbing, or carrying a passenger. Their small displacement, coupled with big top speed expectations and high states of tune, makes them real weaklings when they are forced to cruise at 4000 to 5000 rpm speeds far below their “happy” power band, which is typically in the 9000 to 15,000 rpm range. Those bikes should really be regeared for more normal speeds, if used primarily on the street.

In another example, someone using a typical sportbike for casual sport riding on windy hilly roads is going to be very unhappy with stock 160 to 180 mph gearing that has the engine well below its powerband at the 40 mph to 80 mph speeds he or she is spending most of their time at. With that “tall” gearing, 5th and 6th gears don’t have a lot of “leverage”, so your 6 speed bike becomes in practicality a 4 speed bike.

Another interesting example is that in the latest crop of 1000cc superbikes, 1st gear is good to almost 100 mph. This sounds sort of impressive until you realize what it means at city speeds: virtually no power at all, since these highly tuned engines don’t run too happily at 1500 to 2000 rpm, which is where they’ll be at city speeds with stock gearing. The cynical rumor is that the manufacturers deliberately geared these bikes this awkward way to ensure that squids don’t kill themselves by indiscreetly opening the throttle too wide at city speeds. This theory is supported by the prior generation Suzuki Hayabusa on-board computer which retards engine spark timing in the lower gears to reduce power there. That approach was easily defeated by an aftermarket electronic add-on for the Hayabusa, so bike manufacturers are making circumvention more difficult in the current crop of superbikes (internal gearbox gears are hard and expensive to change).

Finally, there are everyday practical issues to consider related to the rider as opposed to the bike. If for example you are a 225 lb rider, your bike will feel a lot different to you than the same model bike will feel to a 120 lb rider. Your gearing usually needs to be stiffer (more leverage) if you are a big person. Or, if you often carry a passenger on the back of your high rpm superbike, you are probably pretty unhappy in city traffic with the stock gearing.

All of the above are just a few examples of reasons why someone might want to change the gearing on his or her individual motorcycle to better fit his or her specific needs and wants.

How Can You Change Your Gearing?

You have to be practical when looking at how to change your gearing.

First, you can eliminate the idea of changes to components 2 and 3 in our gearing components list (primary drive ratio and internal gearbox ratios) unless you have a lot of both time and money to spend. Those kind of changes for street bikes are both complex and costly to do.

You might be able to change the power versus rpm characteristics of your engine via fuel, camshaft, or exhaust system changes, but those tend to be costly too, and to get really notable power curve changes, the costs tend to go pretty astronomic. On an existing street bike, it’s much more practical to adapt the rest of the drivetrain to the engine, rather than the engine to the drivetrain!

Changing the diameter of the drivewheel tire is not hard – just buy a smaller or larger diameter tire – but that change also affects the geometry and handling of the bike a fair bit, if the change made is large enough to really be detectable in terms of gearing. There’s also a hidden flip side here: if you change your tire diameter, you are making a small change to your gearing. Normally, this might not be dramatically important. But, if your gearing is already too “low rpm” at city speeds, and you make the tire larger, the problem gets worse!

The easiest, most effective, and by far least costly, way to change gearing is to change component 4, the final drive ratio, by changing either the countershaft sprocket, or the rear wheel sprocket, or both. In the worst cases, where the desired change is substantial or the range of chain adjustment is small to begin with, you might have to buy a longer chain.

How Do You Select the “Right Gearing”?

Ok, so you are unhappy with your gearing, or you simply like acceleration and want more of it, and now realize that stiffer gearing = more leverage = faster acceleration, all other factors being reasonably equal. How do you figure out how much to change it, and in which direction?

There are a number of ways of selecting the right gearing, and they range from simple trial and error all the way to getting help from someone who has access to performance modeling software. Let’s look at them in order of accuracy and effectiveness.

Trial and Error

Trial and error is the most basic method. You talk to buddies, or just start swapping countershaft sprockets and see what seems to work and what feels good. This can work, especially if the factory gearing is way off what you need for your circumstances. But it is time consuming (typically lots of error before success), and can be rather costly, because worthwhile gearing changes seldom are as easy as drop 1 or 2 teeth on the countershaft sprocket.

Dropping one tooth on a typical 15 tooth countershaft sprocket is making only a 6.6% change, which is pretty inconsequential on a motorcycle. Dropping 2 teeth is not a good idea, because at 13 teeth, you start to run into stuff like cyclic chain speed variation, the chain rubbing on the swingarm, and rapid chain wear. Going in the opposite direction – larger sprocket on the rear wheel - is really a hit or miss option in this trial and error mode as the “right” number of teeth there can be anything from 37 teeth to 50, depending on the individual bike. You might have to try several sprocket sizes, and at $50 to $80 each plus the work to make the swaps, this is not cheap or fast.

You can copy what a buddy did on their same model bike, but then, if they did it by trial and error too, you are just ensuring that you make the same bad, ok, or superb change they did, without ever really knowing if you have really done the best you can, and worrying that maybe you really made things worse. And, unless they are the same weight and size as you are, and ride at the same speeds and under the same conditions, it’s a shot in the dark to copy them anyway.

This method has potential for error, but it can work if you are patient enough and don’t mind making a few errors along the way, spending perhaps more money on hardware than you need to, and being satisfied when you have something better, and not worrying about whether it’s the true “best” for you.

With the vast majority of bikes on the road today, trial and error will result in some improvement.

Matching Peak Engine Power to Top Speed and Factoring From There

This slightly better method begins with matching the known rpm at which peak engine power occurs to the maximum realistically expectable road speed for that power. Then, the next step is calculating what sprocket sizes will give you that road speed at that rpm in top gear (takes some math!).If you are targeting getting the maximum top speed out of your bike, this is where you stop.

However, if you instead want lower cruising rpm for touring, you increase countershaft sprocket size and/or decrease rear sprocket size, doing some more math along the way to get the rpm at cruising speed to where you want it.

If you instead want more acceleration, or more passenger or luggage carrying reserve, you “factor” the gearing to increase your “leverage” by decreasing countershaft sprocket size and/or increasing the rear sprocket size, doing more math along the way.

You can even test the validity of your initial horsepower versus top speed assumptions by finding a place where you can actually get the bike up to top speed (you need at least a mile of dead flat and arrow straight surface to do that on most bikes) and see if the bike actually is capable of hitting the rpm you assumed for top speed.

This method gives you a better shot at getting good results than the trial and error method, but has its own potential pitfalls:

• You may not have an accurate net (not gross) peak power figure for your specific bike, and if you are off appreciably, the errors will be magnified as you factor, especially if you do like most riders do and optimistically assume you got “one of the better engines”, and you also optimistically forget that you are built like a linebacker and therefor present a formidable “brick wall” to aerodynamic efficiency.

• Your local traffic police officer will not recognize the scientific merit in what you are doing when he clocks you at triple digit speeds and tickets your for reckless driving, and drag strips are NOT long enough to get up to true top speed.

• You can move a known and accurate power curve up or down the road speed range, but you still have no idea how much of that net power at the rear wheel is left for acceleration or for hill climbing or for overcoming a headwind, because you have no data on friction and aerodynamic drag. So, you might have improved power in, but you have no idea what the net hill climbing, headwind, or acceleration capabilities are that result from your change.

Overall, this method is better, but still very far from great.

Optimizing quarter mile performance

Another tried and true technique is to maximize quarter mile performance by trial and error at the controlled conditions present at a dragstrip. Basically, you play with sprockets until you get the lowest quarter mile time. Since you are doing it under controlled, same-each-time conditions (within reason), you are basically experimenting in a controlled ¼ mile long laboratory.

Notice that I said lowest time, without mentioning “highest trap speed”. This is because nothing you do with gearing (unless you go REALLY bizarre) is going to change your trap speed. Trap speed is determined by horsepower and to a much smaller extent by net total weight of bike and rider. When you play with gearing in a quarter mile setting, all you will affect appreciably is your elapsed time.

The neat thing about this method is that if you play with sprockets until you get the absolute lowest elapsed time, you will positively have the best gearing for pure acceleration in the range of zero mph to your trap speed.

The bad news is that that is all you will have optimized. Your horsepower at any given speed in top gear (e.g. 60 mph) will not be optimized for that speed. If your trap speed is lower than what you want as your maximum available speed, you are out of luck, as this method leaves your engine rpm somewhere between your horsepower peak and the rev limiter, at your trap speed, so you can’t go any faster. Your cruising rpm at say 80 mph might also be way too high.

This method is a good reliable way to build a pure street racing machine, but beyond that, it has lots of negatives.

Manual Plotting of Power Versus Gear Ratio Versus Road Speed Data

In this method, you manually plot engine power at each rpm, in each individual gear, versus road speed.

You might even be able to find a web-based tool somewhere where you feed in your horsepower or torque curve laboriously one point at a time, along with your 5 or 6 numerical gear ratios, and get a manual or semi-automated graph of horsepower, torque, or ideally tractive force versus road speed.

If you take enough time to do this accurately, and if your horsepower or torque data versus rpm is truly accurate and representative of your specific motorcycle, you can get a pretty accurate graph of power or tractive force available at each road speed.

What you don’t get though is the other half of the critical information: the mechanical friction and the aerodynamic drag present at each of those road speeds.

So, again, you can improve the amount of power and tractive force availabe over given speed ranges, but you can’t measure the effectiveness in the real world, because you don’t have the “drag” data,

This method Is also clearly pretty time-intensive.

Graph of Actual Versus Ideal Tractive Force

This method is a sophisticated refinement of the method above.

With this method, you begin by manually generating an ideal tractive force versus road speed graph, using the known accurate peak horsepower of the engine. This graph’s construction is way beyond the limits of this short article, but conceptually, it represents the tractive force that this engine would generate at each road speed if you had perfect, infinitely variable gearing that changes dynamically as road speed increases and keeps the engine at its peak horsepower no matter what the road speed is.

In real life, the only road vehicles I know of that even approach this ideal are the lowly scooters that use centrifugal clutches and infinitely variable v-belt drives. They basically keep their tiny engines screaming at peak power rpm at any speed from almost zero to whatever maximum road speed they are capable of. This is why their on-road performance seems so impressive given their modest power. Honda also has one Civic car model car that has something like this.

Before you going looking for a centrifugal clutch and infinitely variable v-velt drive setup to transplant into your motorcycle, be aware that such drive systems have a lot of other limitations and disadvantages that are too lengthy to discuss in this short article.

After manually generating this graph, you then use a trial and error method where you try a given final drive ratio (rear wheel sprocket teeth divided by countershaft sprocket teeth), and plot each gear’s tractive force graph against the ideal curve. You optimize the overall final gear ratio by finding an overall ratio where the combined total of all the gears tracks as closely to the ideal curve as possible, and where the inevitable “gaps” between the actual and the ideal are (a) minimized and (b) not at road speeds critical to your happiness.

This method is pretty good, but still has two big shortfalls:

1. It is very time consuming to do and requires a fair bit of knowledge to do correctly

2. It still looks only at net tractive force available, without looking at all at the friction and aerodynamic drag that must be overcome, so it cannot predict real world performance.

Computerized Performance Modeling

This is by far the most sophisticated method to determine optimized gearing, and the only one that can actually accurately predict the effects of changes before you spend the time and money to try them physically.

In this method, you use computer performance modeling software to assist you in doing ALL the above methodologies, all simultaneously, with the ability to dial in closer and closer until you find the ideal gearing solution for a specific rider on a specific motorcycle – stock or highly modified – under whatever circumstances the rider has specified as being important to him or her. With this methodology, you also dynamically compare the tractive force available at each road speed with the friction and air drag loads present at that speed.

What you do, greatly simplified, is you model the motorcycle and its rider in an electronic computerized environment as opposed to physically on the street. This allows you to iteratively try a lot of different gearing solutions, in an accurate and absolutely repeatable setting, very rapidly and without spending any real money. Gearing that gives good results is saved and reported, and gearing that gives unsatisfactory results is discarded. This is a very powerful approach.

Furthermore, it is not restricted to just gearing. It is relatively easy to add or take weight off the electronic model of the bike (or rider), or to add on virtual models of lightweight low inertia driveline components, and see what effects these changes would have too.

And, you don’t need to be restricted to “stock” engine power curves. If your engine has been modified, and you have a copy of its actual dyno curve, that curve can be used instead of the stock curve.

This approach requires a pretty strong and accurate computer software package backed up by a database of accurate actual motorcycle power curves and specifications (weights, gear ratios, coefficients of drag, etc), and a skilled operator who understands the physics involved.

The combination of software and skilled use means that the power curve of the bike, the weight and size of the rider, and the relevant specifications of the bike, and any accessories, can all be “what if”ed many different ways without spending any actual money on parts and modifications until you get the electronic results you want. Then, you do only that specific set of parts and modifications that you know in advance will be successful.

Obviously, this is not something you literally do yourself. You go to a specialist who has the software, the database of actual motorcycle data, and the skillsets to use them. This can be inexpensive or expensive, depending on what you are trying to do. If you are simply trying to optimize the gearing on your stock street bike by getting new sprockets, it can be pretty inexpensive (in the case of GEARING GURU Performance Modeling, as inexpensive as $29). If you are trying to build a custom killer street or track machine with lots of nifty features, it can cost hundreds of dollars. If you are preparing a race team, it can cost thousands.

Let’s look at one example.

Here is an actual example of a tractive force versus road speed graph, generated via performance modeling software, for a Ducati 748 with stock gearing, that the owner wants to use on the street rather than on the track:

Imagine this is your bike.

This graph compares your bike’s actual gearing to “ideal” gearing that would have the engine operating at its peak power rpm no matter what the road speed of the vehicle is.

The lightweight curved line represents the tractive force created by perfect, or “ideal” gearing. It is truncated at low speeds because the tire can only transmit so much force before it starts to slip instead of grip. Any force above this truncation line (just under “700” lb of force in this case) is superfluous at these low speeds.

The heavier line represents the actual gearing. You can never make it “perfect” unless you have an infinitely variable transmission. The sharp drops in this line represent shift points where you shift into the next higher gear because it provides more force at that speed than the previous gear. The force at each such point is well below the ideal line, because the engine rpm has dropped as a result of the shift to an rpm where the power output is lower. However, if you had not shifted, the power at higher rpm in the lower gear would be lower yet (i.e. you are enough past the peak to be lower than the power available in the next gear). The performance modeling computer software calculates the best shift point automatically.

At really low speeds, the thick (actual) line is well below the thin (perfect) line, because you are running at low rpm in 1st gear. You can raise the actual force to the traction limit by slipping the clutch as you apply lots of throttle, but that wears your clutch quickly and introduces a dangerous lack of control for street use. A drag racer would use this technique to overcome the “hole” in tractive force at low speed.

The thick line goes horizontal in this graph above a certain speed. This is the speed at which your bike’s available power is no longer high enough to allow the bike to accelerate (i.e. your top speed), or when you bump into the rev limiter.

You can see that in this specific case, this Ducati 748 is clearly not geared well at all for street use. It’s geared for track use. Because it has a rather bumpy and peaky torque and horsepower curve, it never follows the “ideal” line really well, but it does its best at higher road speeds of 80 mph and up.

In the critical speed range of 0 to 60 mph for street use, it’s pretty horribly geared, with huge gaps between the actual curve and the ideal curve, and it never even gets close to the traction limit of 700 lb force. At 20 mph, where it is particularly weak, it can deliver only a bit more than half of the force that the tire can transmit before slipping. This bike would not be much fun in the city.

Don’t despair though. A good session of computerized performance modeling can help quite a bit, in adapting this track tool of a bike to the needs of a street rider owner, as the next section of this article will show.

What Improvements Can You Expect?

Regardless of the method you end up using, the amount of improvement you can get depends on such things as:

• How good or bad your factory gearing is

• The bike’s “as designed” degree of match or mismatch to your needs and wants

• How typical or how unusual your needs and wants as a rider are

• The power curve shape for your bike’s engine (peaky curves are harder to optimize, but often give proportionately dramatically better improvements over stock)

Here, for example, is what was achieved for the Ducati 748 seen earlier in this article:

Notice that:

The bike now generates enough tractive force in 1st gear to cause tire slippage above 40 mph.

Even at 20 mph, it now creates almost 75% of the tractive force required to cause tire slippage.

The big drop in force at the 1st to 2nd gear shift is now moved lower in the mph range, from 65 to 55 mph, where the lower drag forces are easier to overcome and therefore make this drop less catastrophic to forward acceleration.

These changes make a huge difference in actual street performance. The actual measurable improvements achieved in this specific example, identified via the computerized performance modeling, include:

0-60 mph time reduced by 0.72 second

0 to 80 mph time reduced by 0.81 second

Horsepower available at 60 mph without a downshift increased from 26 to 33 hp (27% better)

Average horsepower available in the 0 to 100 mph range increased from 59 to 64 (8.5% better)

Crawl speed (lowest speed at which you can apply full throttle without slipping clutch) went from 18 to 15 mph, which translates in the real world into much less need for clutch slippage around town.

Top speed declined from 146 mph to 140 mph, not that much of a loss given the other improvements.

Most bikes don’t respond quite that dramatically, but a surprising number do.

How much might it cost?

Gearing changes are among the lowest cost, highest impact changes that you can make to your motorcycle.

A countershaft sprocket might cost anywhere from $30 to $40, and might need perhaps a half hour of shop time to install if you cannot do it yourself.

A rear sprocket is more expensive at $50 to $80, and requires more labor, but is still pretty inexpensive compared to almost any other modification.

If you make a substantial enough change to require a longer chain, add $80 to $150 plus a bit more labor.

So, the range is anywhere from $30 to an absolute maximum of $450 if you need the most complex solution and use the best quality parts.

Add $29 and up if you want some help from someone with performance modeling capabilities.

Looking at the potential benefits, the benefit versus cost ratio for gearing changes is particularly attractive.

Caution!
Any gearing change that improves acceleration and response also increases tendency of the bike to wheelie. Unicycles do not steer well and do not brake at all well, as most of your braking ability comes from the front wheel.

A re-geared bike can also break traction easier, as there is more torque being applied between the tire and the road surface. This is especially possible when the road is wet or has dirt or loose material on it.

If you implement any gearing changes, be very careful in where and under what conditions you apply throttle, especially when doing so suddenly!!