From: noel shelley (noel@shelley1722.freeserve.co.uk)
Date: Fri Mar 12 2004 - 06:46:10 PST
Dear Fred and List,
Further to your question on the length of
brake shoes , enquiries to one of the leading manufacturers has resulted in
following answer ! The lining length will be arrived at using various design
criteria and also the preferences of the individual designer .
Obviously weight , speed , type of usage , operating environment , drum
size , and lining material type will all be factors . The leading shoe in
forward motion may be longer and also thicker since this shoe will do most
of the braking , with factors of 3 or 4 not uncommon over the trailing shoe
,{single leading configuration }, meaning that a twin leading set up in
reverse may only have 25% of it`s forward efficacy .
Another point worthy of note in the context of braking is the principal of
weight transfer and it`s effect on stopping the machine . Under braking the
load on the front wheels dramatically increases resulting in the front end
doing about 75% of the retarding , obviously if the balance of front to rear
is not correct then a very dangerous situation is created where one end will
lock up . In commercial or load carrying vehicles where the load varies this
is often compensated for by using a load sensing valve on the rear .
To sum up , there is no simple answer to the initial question !
Done my best Noel
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