Introduction to Gearing
One simple way to understand motorcycle chain wheel ratios is to consider a 10 speed bicycle with 5 chain wheels at the back and two at the front.
Selecting the smallest chain wheel at the front and the largest chain wheel at the rear, the cycle is very easy to move off from standstill and climb hills. However not much speed can be achieved and the riders’ legs soon cannot operate quick enough to effectively push on the pedals. Effectively the riders leg “rev out” or reach their rev limit.
Selecting the largest chain wheel at the front and the smallest chain wheel on the rear, the cycle is slow to move off with and slows on a hill. Effectively the riders’ legs are labouring. However on the flat or down hill much speed can be achieved and the riders’ legs can operate effectively pushing on the pedals with the cycle achieving great speed.
The same principles apply for motorcycles. Reducing the front chain wheel and/or increasing rear chain wheel size will increase acceleration, but may limit top speed. Increasing the front chain wheel and/or reducing the rear will reduce acceleration and increase top speed provided the engine is strong enough to drive the bike to that speed. Of course on a motorcycle we cannot change the rear ratios while riding (that’s why we have a gear box), so selecting the right chain wheel ratios before racing is all important.
Basics for selecting the chain wheel gearing.
A rider on a new track may need to adjust the chain-wheel ratios to get the best performance out of the bike.
- If the rider finds they never get into top gear on the fastest section then the gearing of the bike is significantly over tall. This can be rectified by significantly increasing the rear chain wheel size or reducing the front or both. (Common when converting a road-bike for track use).
- If the rider finds they are getting into top gear but the bike is not pulling up to just a fraction over peak power revs on the fastest section, then the gearing of the bike is slightly over tall. This will likely be rectified by increasing the rear chain wheel size slightly.
- If the rider finds they are getting into top gear and the bike is bouncy off the rev limiter on the fastest sections the bike is geared short. This can be rectified by decreasing the rear chain wheel or increasing the front.
As a rider becomes more familiar with a track or as conditions vary, this process may need to reviewed again and again.
It is worth recording the gearing found to work at each track ridden. This will allow the bikes gearing to be set up for the track prior to arrival allowing track side set-up to focus one other areas of the machine or more on track practice time
For a more comprehensive explaination of gearing check out "gearing explained".Gearing Explained | Gearing Ratios