V brake pads - why 70mm?

[- Baz -]

Looking to replace my V brake pads which haven't lasted very well, despite only moderate use. Kool Stop pads seem to be a clear winner by a long shot, but why do 70mm pads have the fixing bolt offset from the centre? Ashima do some 55mm ones with a centre bolt which, to a numpty like me would seem to give more efficient braking power in relation to brake pad length. Anyone used these?

Could someone enlighten me - what's the thinking behind 70mm pads with an offset fixing?

 

[Gerry Attrick]

When the pads contact a moving rim, the friction creates a turning force about the pad fixing bolt with the result that the rear end of the pad is forced further towards the rim, whilst the front end tends to be forced away from the rim. The type of pads with a longer rear are an attempt to make these forces more evenly spread along the length of the pad and thereby even out pad wear. It can also serve to reduce chatter, which is the cause of brake squeal.

 

[- Baz -]

Aha! Makes sense. Thanks for a clear and well explained answer.