Gear Chart - Why bother
Whether you are running a full race replica Lambretta with every tuning option or a standard 150cc, having the correct gearing makes the most of the machines available power.
Many aspects of the engine, the rider and the road or track will determine the optimum gearing for a given bike. Talking to any successful race rider you will find they have a number of gearboxes and sprockets, ready to be swapped over to give them the best for the day.
For road use we have to choose the correct gearing or close approximation for all intended use of that machine, as it is unlikely to be changed on a regular basis.
The factors that play the biggest role in selecting the correct gearing are: the type of exhaust fitted, the type of cylinder being run and the rider.
Exhaust: Standard exhausts and the clubman offer a wide distribution of power making the scooter very easy to ride and allowing a large variation in gearing without problem. Expansion systems on the other hand have a much narrower power band making the choice of gearing much smaller. Also different expansion systems power bands cover different areas of the rev range so gearing has to be chosen to reflect this.
Cylinder: The capacity of the top end you are running and the state of tune will also determine the amount of power available on a given set up. To this end two bikes running the same exhaust and carb one with a 175cc kit and the other running a TS1 will want different gearing.
Rider: The weight of the rider will play a part, as a Jockey living in the Salt Flats will be able to ‘pull’ higher gearing than a Sumo in Switzerland. The use of the bike ‘Around Town’ ‘Rallies’ ‘Motorway’ ‘Fast A Road’ is also important. Finally the type of rider: be honest with your self about what you want from your bike then be honest with your local dealer. A knowledgeable dealer will be able to recommend a good set up after discussing with you what you hope to gain.
Gear Chart - How to use
The chart should be straightforward to use as a quick reference once you are familiar with the layout.
From the top down on the left hand side (the gearbox column) all the most common gearboxes are listed and colour coded. If you are in doubt as to which gearbox is fitted in your bike you will have to count the number of teeth on the gear cluster to identify which one is yours from the list.
At the top on the right hand side the Chain selection boxes allow you to identify which size of chain will fit with a chosen primary drive (F. sprocket and Crown Wheel).
At the bottom on the left hand side is a guide (Recommended Final Drive Ratio). Based on the average rider, the preferred Final Drive Ratio on each of the most popular set ups is listed. If you do not find yours there or are in doubt, speak with your local dealer or the dealer who supplied the parts on your bike and find out what they recommend.
Once armed with the desired Final Drive Ratio refer to the ‘How to obtain the desired final drive ratio’ box on the bottom right. Locate the Correct Final Drive Ratio and find the listing colour coded with your gearbox.
Now you know the recommended primary drive ratio that will allow your gearbox to provide the correct final drive ratio.
Gear Chart – What is ‘Final Drive Ratio’
The Final Drive Ratio is a ratio of the number of revolutions of the crankshaft to one revolution of the rear wheel when the bike is in fourth gear.
I.e. On a standard GP200 in fourth gear the crankshaft will make 5.22 revolutions for each single revolution of the rear wheel.
As such at 9000 rpm a GP200 rear wheel will rotate 1724 times in a minute. If this final drive were set to 4.8 the rear wheel would rotate 1875 times in a minute and will have travelled further in that minute. The lower the final drive ratio the taller the gearing of the bike.
Disclaimer: Rayspeed hope that you find this information useful and informative, but point out that this is intended as a guide only and not a replacement for the knowledge and experience of your scooter dealer. We do not accept responsibility for any costs and damages you may incur as a result.
The Gear Chart supplied here is intended to act as a quick guide. As such it is not perfect. If you find any mistakes or you think there is any information that should be there that isn’t please email us and let us know.