Wednesday 21 March 2012

Medium Gear 25 (72") - 24th March 2012

This Saturday's event is the Medium Gear 72" so time to dust down those single speed machines or get busy with a screwdriver. 

Frank will be there with his tape measure to verify gearing, so no trying to sneak a couple of extra inches! First rider off at 8:30am so please arrive by 8:15 am on the start line between Southill and Ireland (Route here). Entry on the line, £2 HNCC members, £3 non-members.

Notes from Frank: If using single speed with 700c x 23/25 wheels the following chainring/sprocket sizes are appropriate for the medium gear.

46-17 --- 71’7”
48-18 --- 70’7”
51-19 --- 71’1”

With multi-speed gears the machine must be set to prevent the selection of a ratio higher than specified. The ratio selected can be determined by using the following calculation. Number of teeth on ring divided number of teeth on block multiplied by 26.5 (700c x 25).

Alternatively, hold the machine with one crank vertically down, mark the point immediately below the pedal, wheel the machine BACKWARDS in a straight line until the same pedal is at the bottom, mark the second point. The distance between the marks must not exceed 18 ft 10 ins (5.74 metres).

It may be possible to achieve this by adjusting the limit stop on the rear mechanism to prevent the higher ratios being selected and/or adjusting the stop on the front mechanism to prevent the large chainring being selected.