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stopping distances car vs bicycle


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#51 Lee Nicolle

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Posted 28 September 2017 - 09:25

Rim brakes work well owing to the high relative velocity of the rim/braking material -- three or four times higher than for a disc brake. It is pretty straightforward to make a rigid system of lever, cabling and callipers. In theory a disc system will be better at all but very low bicycle speeds but it is much harder to design a rigid mount for the callipers.  

A rim brake is a disc brake, usually about 27" in diameter. But friction material made from rubber and a ineffective cable pull caliper and effectively no pad area is what the problem will always be. I am sure a decent calliper could be designed and use hydraulics' but oh, it will be too heavy!! The poor dears are frightened of weight.

And then the tyres have no grip anyway, and that on dry smooth bitumen so wet bumpy and dirt strewn roads you do not stop. Or in my case moss!



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#52 Charlieman

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Posted 29 September 2017 - 13:02

A rim brake is a disc brake, usually about 27" in diameter.

Small diameter disc brakes for bikes did not exist until recently. They are hard to design and you have to mount the caliper on a springy bit of the bike. They have a specific use case. Hydraulic mechanisms might work for expertly maintained bikes, but are impertinent for family bikes. 

 

Almost anyone can fix a cable operated brake. You can carry the tools in your bonk bag.



#53 Fat Boy

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Posted 29 September 2017 - 16:15

Small diameter disc brakes for bikes did not exist until recently. They are hard to design and you have to mount the caliper on a springy bit of the bike. They have a specific use case. Hydraulic mechanisms might work for expertly maintained bikes, but are impertinent for family bikes. 

 

Almost anyone can fix a cable operated brake. You can carry the tools in your bonk bag.

 

I guess you have to define 'family bike', but a coaster brake works if you're going slow enough. Modern hydro brakes are pretty damned impressive, and weight is really no longer an issue. Racers have to ballast their bikes to legal minimum.

 

https://sram-cdn-pul..._09_2015_en.pdf


Edited by Fat Boy, 29 September 2017 - 16:18.


#54 mmmcurry

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Posted 30 September 2017 - 12:14

Small diameter disc brakes for bikes did not exist until recently. They are hard to design and you have to mount the caliper on a springy bit of the bike. They have a specific use case. Hydraulic mechanisms might work for expertly maintained bikes, but are impertinent for family bikes. 

 

Almost anyone can fix a cable operated brake. You can carry the tools in your bonk bag.

 

Not sure about recently, I've been using them for nearly 20 years, recent in terms of how long bikes have been used, but not really recent.

 

If you're using a suspension fork then the rim brakes are on the unsprung weight anyway. For rigid forks, yes the rim brakes will be sprung. I think the only time I've had an issue with disc brakes is when the roads have been salted / gritted and they seized up after being left in a damp cellar overnight, which I've also had with rim brakes. They are pretty much fit and forget, pads are far easier to change than rim ones, no messing around with the toe angle.

 

Whether they're necessary is another matter, I'd not want to go back to rim brakes these days.

 

Steve.



#55 gruntguru

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Posted 01 October 2017 - 03:44

A rim brake is a disc brake, usually about 27" in diameter. But friction material made from rubber and a ineffective cable pull caliper and effectively no pad area is what the problem will always be. 

The actual problem is the disc (a bicycle rim). It has a "U" shaped cross section which limits caliper clamping force, needs to be lightweight, ie aluminium or composite, all of which dictates low clamping force and very soft pads to reduce wear of the rim itself.

- The mechanism could easily be designed for far greater clamping force - that is not the problem.

- The pad area is not a problem.


Edited by gruntguru, 01 October 2017 - 03:44.


#56 kikiturbo2

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Posted 01 October 2017 - 14:52

pad force is not a problem either... problem is high COG and if you hit the brake hard you will go over the handlebar..



#57 mmmcurry

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Posted 01 October 2017 - 17:15

pad force is not a problem either... problem is high COG and if you hit the brake hard you will go over the handlebar..

 

Hydraulic discs all the way, power and control.

 

Hopes for me have better power and modulation, though I am comparing Hope Mono M4s from 2004 to Shimano SLX from 2014.

 

Steve.