On Fri, 14 Feb 2003 18:08:03 +0000 (UTC), Alex Graham <
[email protected]> wrote:
> Bazza De Looney wrote:
>> Now I know I should know the answer to this but I dont. The highway code shos speed limits for
>> vehicles but not for cyclists, now logically the speed limits should apply to us two wheel man
>> powered speed freaks but can anyone confirm or deny this please, and keep me out of trouble.
>>
>> My question is prompted by just having gone through a radar speed trap set to catch motor cycles
>> on the moors above Rochdale. The policeman in charge was not impressed by a mountain bike doing
>> 47 mph through his trap!
>>
>> Any answers via e-mail please, all would be appreciated.
>>
>> Barrie Winstanley
> Am I just slow or is 47 on a bike _very_ fast?
>
It's very fast. At these sorts of speeds there are almost no hills where terminal velocity isn't
less than this so you have to pedal to maintain the speed (Ducked down on my bike a 1:10 gives a
terminal velocity of around about 40mph - I've never actually measured this because I'm usually
pedalling like mad ;-).
IIRC, terminal velocity when tumbling in a fall is not much over 120mph. If I'm thinking straight
(which I might not be on a Friday night
this implies to me that a 50mph terminal velocity
(coast) will be achived on something like a 1:6 and 40mph on a 1:9 (which agrees with my experience)
Unless you have really big gearing you are pedalling like mad.
I've managed 49.9 but I just couldn't get the big 50. 23x700, 48 front, 13 rear. I've since changed
the front to a 52 so next time I get a long hill ...
(49.9 is 22.3m/s. So this is slightly more than 10 revolutions of the wheels per second. 48:13 is
about 3.7:1 so about 2.7 revolutions of the pedals per second or a cadence of over 160 - and it
felt like it as well ;-)
> I never expected a bike to be able to trigger a radar trap.... Theres one that flashes SLOW DOWN
> to people going at >30mph on my daily route - Ill have to sprint it at some point to see
>
There is a complication WRT radar traps in that the spokes at the top of the wheel are travelling
twice as fast (relative to the ground) as the bike. There have been stories of some radar traps that
can be triggered easily by bikes - I've never come across one - I've managed 41mph through a 30mph
limit one once and it still didn't flash (And I had to arrange a friend to stand a but further down
the road because there was no way I could make that speed through the trap and then take the next
bend on the correct side of the road so we had arranged that he would wave like mad if a car started
coming up the hill from the other end so although I might not have noticed the flash he certainly
would have seen it.)
--
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