2 Up 1 Down - Motorcycle Gearing
No we are not talking about some lopsided house here but in fact referring to a common modification riders like to make to the gearing of their motorcycles. This is something we get asked about quite a lot so thought it might be worth producing a little guide.
Changing Your Final Drive Gearing
Now sprockets might not be the sexiest things in the world but they have a big effect on how your motorcycle performs. As standard from the factory most bikes tend to be geared 'high' for reasons like ride-ability and fuel economy.
Now what we mean by high or low relates to the ratio between the number of teeth on the front sprocket compared to those on the rear. By altering the number of teeth front and rear you change the ratio of the final drive i.e how many times the front sprocket needs to turn in order to turn the rear.
To make things clearer lets use an example of a bike that has a 15T front a 45T rear as standard. To work out the ratio you divide the number of teeth on the rear by those on the front eg
45/15 = 3:1 Ratio
So if we wanted to lower the gearing on this bike we could add a couple of teeth to the rear sprocket giving us a new ratio :
50/15 = 3.33:1
And Conversely we could gear the motorcycle higher by fitting a 43T on the rear and this would give us the following ratio
So What Does It All Mean ?
Boring mathematics aside what does all this mean in real World ? Well put in very simple terms it is as follows
Higher Gearing = More Top End / Slower Acceleration
Lower Gearing = More Acceleration / Less Top End
You can affect these changes by adjusting the gearing on either one or both of the sprockets. Referring back to the title a very common approach that a lot of riders like to go for is '2 Up on the Back' and '1 Down on the Front'. To use our fictitious it a lot more bottom end punch and faster throttle response.
This is a popular alteration as most riders do not need or get to use the top end speed of their machine unless on a track day or on a German Autobahn ! In the real world you will make your bike feel a lot faster as you spend more time in stop / start traffic of on slow twisty roads meaning the improved acceleration will transform how your bike performs.
Points To Consider
There are a couple of final points worth making before you think about changing your bikes final drive gearing:
1) Do not think by fitting higher gearing your 125cc will suddenly be able to do 150mph. Remember you have not suddenly increased the power of your bike and if you gear it too high you will not even be able to pull away on it. Think what it is like to ride a push bike and try setting off in 21st gear !
2) Do not gear it too low as you will be bouncing off the rev limiter and your fuel economy will go out the window. You should always look to find a happy balance between top end and acceleration
3) Changing one tooth on the front in either direction is about equal to changing 3 on the back. Plus front sprockets are cheaper than rears so this is the most cost effective way of altering the ratio
4) If you are looking at changing the sprockets make sure your chain is in good condition. You could end up fitting brand new sprockets and a knackered chain will make mince meat of them in no time at all.
5) If you make just minor changes then you will be able to use the same length chain as standard but if for example you go and fit a monster 53T on the rear you will also need to buy a longer chain to accommodate the new rear sprocket.
Final Thoughts ..........
At Motorcycle Parts UK 95% of the kits listed are for standard gearing, if you want to change the gearing of you bike get in touch with us and we will be able to let you know what options there are. As ever if you are unsure feel free to ask, we are here to help