Two sets of brakes?

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LittleGreyCat
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Re: Two sets of brakes?

Post by LittleGreyCat »

Just looked at my Spa Wayfarer.

The rims are tapered inwards and are also a nice glossy shiny brown. Not ideal for brake pads to grip on.

They don't look as though they would happily take to V brakes, for example. In my limited experience rim brakes have a flat surface to work on and the rims have a roughly square section.

I was told that the canti bosses were to allow the emergency fitting of a braking system if the discs failed somewhere away from spares.

I think that if you were to have permanent dual braking systems then you would need to specify different rims with a non-glazed surface and probably more metal.

The idea is tempting - I think I have already mentioned it briefly somewhere on here - but I think I am in the usual position of "If I was going to do that I wouldn't start from here!" assuming that my current rims really aren't suitable.

ISTR that the general design of a wheel with disc brakes is different because of the difference between braking forces at the hub and at the rim. However I could be wrong.
scottg
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Re: Two sets of brakes?

Post by scottg »

We can start a petition for Sturmey to make a disc/drum combo hub for the front.
and a disc/coaster freewheel [7s] hub for the back. :D
Special CTC models.
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Mike_Ayling
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Re: Two sets of brakes?

Post by Mike_Ayling »

Brucey wrote:
Mike_Ayling wrote:Another consideration:
Rims designed for disc brakes have less metal and are not always machined on the surface where rim brake pads apply the friction to operate.
Rims designed for rim brakes have more metal than disc brake rims because the rim brakes wear the rim away over time.
This is an imaginary disadvantage in the rim brakes versus disc brakes debate.....


FTFY

-unless folk suppose that having rims about 30g heavier (and stronger to boot) is a big deal on a touring bike?

cheers


Hey Brucey,

You can probably answer this without any research:

How does the 30g difference in rim weight compare to the difference in weight between a rim brake and a disc brake?
I hope that the disc brake including rotor is more than 30g heavier.

Mike
pwa
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Re: Two sets of brakes?

Post by pwa »

LittleGreyCat wrote:Just looked at my Spa Wayfarer.

The rims are tapered inwards and are also a nice glossy shiny brown. Not ideal for brake pads to grip on.

They don't look as though they would happily take to V brakes, for example. In my limited experience rim brakes have a flat surface to work on and the rims have a roughly square section.

I was told that the canti bosses were to allow the emergency fitting of a braking system if the discs failed somewhere away from spares.

I think that if you were to have permanent dual braking systems then you would need to specify different rims with a non-glazed surface and probably more metal.

The idea is tempting - I think I have already mentioned it briefly somewhere on here - but I think I am in the usual position of "If I was going to do that I wouldn't start from here!" assuming that my current rims really aren't suitable.

ISTR that the general design of a wheel with disc brakes is different because of the difference between braking forces at the hub and at the rim. However I could be wrong.

I wouldn't put a rim brake on a rim intended for disc only. If you were thinking of putting a rim brake on (which seems to me to be a good idea for touring in mountainous areas) a new wheel might be a wise purchase.
Brucey
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Re: Two sets of brakes?

Post by Brucey »

Mike_Ayling wrote:
Hey Brucey,

You can probably answer this without any research:

How does the 30g difference in rim weight compare to the difference in weight between a rim brake and a disc brake?
I hope that the disc brake including rotor is more than 30g heavier.


yes, on a touring(ish) bike, disc brakes are heavier than rim brakes by a lot more than 30g. By the time you have accounted for everything, ~300g would be not far from it. However it varies depending on what you start with and what kind of parts you use. BTW in some manufacturer's ranges the fork for rim brakes is made using the same fork blades as are used in the disc brake model; needless to say the rin brake fork is liable to be heavier and stiffer than it really needs to be.

cheers
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NUKe
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Re: Two sets of brakes?

Post by NUKe »

Vorpal wrote:There are already electric bikes with regenerative braking.

Do you have example of production machine with these, my understanding was that it was not possible in terms of bicycles as the power cost of the system would outweigh the charge produced. Quite happy to be proved wrong
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andrew_s
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Re: Two sets of brakes?

Post by andrew_s »

V/Canti bosses can also be useful for bolting things to - for example, there are quite a number of racks that use them.
Vorpal
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Re: Two sets of brakes?

Post by Vorpal »

NUKe wrote:
Vorpal wrote:There are already electric bikes with regenerative braking.

Do you have example of production machine with these, my understanding was that it was not possible in terms of bicycles as the power cost of the system would outweigh the charge produced. Quite happy to be proved wrong

They are still rare, and many of the bikes that have them are not legal to be used in the UK as bicycles.

https://www.electricbike.com/regenerative-brakes/ has a summary of bikes that have it and how to do it.

A number of companies have stated that it's not worth it, which is different from it's not possible.
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andrew_s
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Re: Two sets of brakes?

Post by andrew_s »

NUKe wrote:
Vorpal wrote:There are already electric bikes with regenerative braking.

Do you have example of production machine with these, my understanding was that it was not possible in terms of bicycles as the power cost of the system would outweigh the charge produced. Quite happy to be proved wrong

It wouldn't be so difficult with a wheel motor, but I think that it's more that the amount of energy available to be harvested is fairly trivial, since you can't get back what's been expended on air resistance (or rolling resistance), and then you've got to factor in harvesting and charging inefficiencies.
From what I've seen, you might get 1-5% on your range, depending on how hilly your route is and how often you have to stop.
Against that, there's added complications in the controller electrics, and brake lever switches, all of which is extra cost and extra things to fail.
Geoff.D
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Joined: 12 Mar 2010, 9:20pm

Re: Two sets of brakes?

Post by Geoff.D »

Many years ago (before disc brakes were commonly available) I had an adult/child back tandem frame built by Bob Jackson. I was keen to have at least 3 brakes, because I was also towing a second child on an Islabike tag-a-long. But I wasn't confident of the child stoker operating the traditional rear Arai drum brake, as a drag brake. I wanted all brakes under my control.

My solution was to ask Bob Jackson to build a wider front fork, enough to accept an Arai drum brake but to put cantilever stubs on as well. He did the same at the back. I could have had 4 brakes had I wanted, but never did use the rear cantis. I used a twin cable pull lever, and a single, up front.

It worked fine.
cycle tramp
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Re: Two sets of brakes?

Post by cycle tramp »

Yes... I once built a bike with three brakes, front and rear cantilever brakes were operated in the usual way, but i mounted a BMX caliper to the rear stay bridge and used an old friction gear lever to operate it. The idea being that i could set the third brake to scrub of speed on any long down hill road without tiring my hands.
...it worked well, but living in Sedgemoor, i wondered if the third brake was worth the weight and eventually took it off
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scottg
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Re: Two sets of brakes?

Post by scottg »

I have an E-bike sitting behind me with 4 levels of regen braking,
it works very well, feels like engine braking in a manual transmission car.

In theory it doesn't work as many vendors will tell you, the battery is rated
for 60 miles by manufacturer. Reality is you can ride 60 miles and still have
30+ percent battery left. Or ride it 40 miles and have 70% battery left.
Learning to ride it takes a while, a 3x9 mech drive train,
4 levels of assist, bike mode, 4 level of regen, +auto regen on brake lever
engagement and a throttle.
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Mike_Ayling
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Re: Two sets of brakes?

Post by Mike_Ayling »

Brucey wrote:
Mike_Ayling wrote:
Hey Brucey,

You can probably answer this without any research:

How does the 30g difference in rim weight compare to the difference in weight between a rim brake and a disc brake?
I hope that the disc brake including rotor is more than 30g heavier.


yes, on a touring(ish) bike, disc brakes are heavier than rim brakes by a lot more than 30g. By the time you have accounted for everything, ~300g would be not far from it. However it varies depending on what you start with and what kind of parts you use. BTW in some manufacturer's ranges the fork for rim brakes is made using the same fork blades as are used in the disc brake model; needless to say the rin brake fork is liable to be heavier and stiffer than it really needs to be.

cheers


Thanks Brucey

When I was selecting components for my Mercury about four years ago, Thorn who has reluctantly concluded that some customers do in fact want disc brakes, made much of the fact in their fork selection page that the disc capable fork would be a lot heavier than their whizz bank super lightweight Reynolds job. I eventually selected a mid range fork with braze ons for a front rack.

Mike
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John1054
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Re: Two sets of brakes?

Post by John1054 »

cycle tramp wrote:Yes... I once built a bike with three brakes, front and rear cantilever brakes were operated in the usual way, but i mounted a BMX caliper to the rear stay bridge and used an old friction gear lever to operate it. The idea being that i could set the third brake to scrub of speed on any long down hill road without tiring my hands.
...it worked well, but living in Sedgemoor, i wondered if the third brake was worth the weight and eventually took it off


I bought a tandem hub with screw thread to fit an Arai drum brake, in addition to the v brakes on my Thorn Sherpa - great for the Lakeland and North Yorkshire passes. Also useful as a parking brake for train assisted travel (gear friction operated). Downside is extra weight.
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