Gearing explained for the track

Written by Chris Wood

520 or 525

First lets cover the 520 or 525 question (it refers to the width of the chain, by the way) - racers tend to convert to 520 as its slightly lighter and you can gain a few bhp without compromising strength. The downside is you'll have to bin any sprockets you've got at the mo, as you have to match the width of the sprockets with the width of the chain.

Gearing Ratio

Gearing ratios is a whole science by itself, but I'll have a go at explaining. Think in terms of top speed and acceleration - they contrast, so you cant have max top speed and max acceleration at the same time. Its on a sliding scale; you give up one and gain on the other. The plus side is that you can get loads more acceleration through the range by giving up 20mph top speed that you probably don't use anyway (you'll be amazed what a difference it can make to your bike!!).

A fast road bike is geared for top speed, and most circuits in the UK simply don't have a long enough straight to get there. You may already be finding that you don't use the top gear or top half of the rev range in top gear. So the theory is you set the gearing so that you have just enough top speed for the circuit (at maximum revs), which means that you are then getting the most acceleration you can get from the bike on that circuit.

The combination of front and rear sprocket sizes dictate how far up that 'speed/acceleration' scale you go, with the front sprocket making the bigger difference:

  • More top speed / less acceleration = increase size of front sprocket or reduce size of rear e.g. a 15/46 will give you slightly more top speed than a 15/47. A 16/47 will give you a lot more
  • less top speed / more acceleration = reduce size of front sprocket or increase size of rear e.g. a 15/50 will give you loads more acceleration than a 17/43.
For example, if you have a sports 1000 it may be geared up for 180mph with say a 17 tooth front sprocket and 43 tooth rear (17/43). Chances are you wont get anywhere near that 180mph on most circuits, so you might drop down 1 tooth on the front (to a 16) and go up 2 on the rear (to a 45). This will go you loads more acceleration, and probably still be enough top speed for the straight. This is a typical mod for racers and track dayers.

We could go into 'ratios' here, but don't wont to swamp you with info.

Chain Length

Chain length - once you have a range of front and rear sprockets to choose from you'll discover that you need a chain length that can cope with the different combinations at the extreme at either end i.e. your max acceleration (shortest) gearing and your max top speed (longest) gearing. You'll have to figure that one out, but counting links is the best way to start!

It might sound like a bit of a pain but if you're currently running road gearing, dropping down 1 on the front and upping 2 on the rear will make it feel like you've gained 30 bhp!! It's worth it.

Personal Touch

After that, its a lot down to personal taste; some set their gearing up to get max drive out of an important corner and are willing to compromise a little on top end to get this. Others set their gearing to only use 5 gears on a modern sportsbike, as you're getting pretty much all the power/speed you need in those gears anyway. Personally, I set up for max top speed on the straight, and get as much acceleration as i can have. Horses for courses.