Why do people think 25km/h speed limitation is safe?

[amigafan2003]

Interestingly, I found that by simply replacing my cantilever brakes with Avid V-brakes, whilst still using the original bar lever, I suddenly had a system that would throw me over the bars if I wanted. Honestly, I've never had such brakes on a bike before. Then I found there's a small attachment which I should have bought to reduce the mechanical advantage - I didn't bother with that, as I've got quite used to them now.

Hehe - do you have a good dentist?

 

[peasjam]

Flecc, seriously... I gave you the mathematical proof that what you were saying was incorrect and you still nitpick on things that you know full well doesn't change the facts (or at least ought to know, if you are in fact a qualified engineer).

Your 18,500 odd posts doesn't make you an expert on everything not matter how much you think it does, nor does it justify your slightly irritating manner of self appointed authority.

Just grow up will you.

 

[flecc]

Oh dear, insulting again!

No Peasjam, you didn't give me any such proof for you did not complete the calculation.

You gave the approximately 3 times VR advantage of the disc hydraulic system against the cable rim brakes you were aware of and rightly acknowledged that is reduced somewhat by the greater grip of rim pads.

If you'd like to add to that the further reduction in advantage due to the hydraulic rim calipers you hadn't included, we are in the region of a 2 times advantage overall.

But to complete the calculation you need the factor I posted right at the outset, the rim wall radius. That is typically 3 or more times the radius of the operating band of the discs you mention.

The calculated answer is a clear advantage for the rim. It was after all you who said it's all about levers.

 

[Scottyf]

Most brakes are usually powerful enough on a bike to lock or at least throw the rider over the handle bars.
Theres only so much force you can apply using the brakes anyway before other forces come into play.

I always think you have to weigh up the advantages of each system before making a choice...

V Brakes
Advantages - Large Wheel circumfrance / Rim. Light weight, Cheaper pads. Cheaper to upgrade
Disadvantages - Affected by weather conditions, fiddly to setup correctly and require adjustment every now and then to get the best from them, cause's rim wear

Cable Disk Brakes
Advantages - Easy setup and adjustment, requires very little adjustment after inital setup. Not affected be the weather or mud
Disadvantages - Slight increase in weight over v brake, cheaper disc setups are generally weaker than the same price v-brake.

Hydro Disk Brakes
Advantages - Adjustment is automatic, very very powerful setup. not affected by the weather or road conditions
Disadvantages - Slight increase in weight over cable disk, expensive, Can bind and would require periodic maintenace to ensure pistons do not stick. Expensive if master cyclinder needs replacement



Disks are better on a bike application. If I was able to spec a bike I would choose a cable disk brake. Not so fussed on the rear being a disk would be happy with a v on the rear. However currently I have V brakes all round which do the job very well. Even though there a budget brake system.

 

[NRG]

There's another difference not mentioned yet between Rim and Disk (note: I'm not arguing for or against any type, I'm simply curious about the engineering differences) and thats how the braking forces affect the wheel. Rim brakes apply force at or as close as possible to the tyre / road interface meaning the torsional stress of braking is far less on the wheel spokes and hub.

With a disk brake the rotation stress or force of braking is felt on the calliper mounts on the forks and more importantly the stress is applied via the hub, spokes and rim to the tyre / road interface. Meaning not only is there some weight disadvantage with disk but also there is a need for a stronger wheel.


All in theory of course!

 

[Trevor Holloway]

Having stayed out of this thread so far, surely one major limiting factor would be the tyre grip on the road / gravel / mud / ice in which case it all gets academic (no pun intended) ?

 

[tillson]

Having stayed out of this thread so far, surely one major limiting factor would be the tyre grip on the road / gravel / mud / ice in which case it all gets academic (no pun intended) ?

Exactly Trevor, I made this point earlier in the thread. My hydraulic rim brakes are capable of throwing me over the handlebars in the dry or causing the front wheel to skid from under me in the wet. The only differnce that I can see is that the disc brake will achieve this with less pressure on the brake lever. Pointless discussion.

 

[flecc]

Agreed Trevor, I pointed out earlier that it was an academic argument as have some others on the same basis.

 

[Biged]

Wow peasjam sure has it in for you flecc. No matter what anyone says his brakes will throw him over the handlebars faster than rim brakes, so that makes them 'Better' ?????

 

[flecc]

Water under the bridge Biged, I'm always mildly amused when these attacks get personal.

It used to be my pedelec guru title on which attacks were centred, but with that out of the way it seems over 18000 posts makes me feel superior!

So it seems I'll have to get that zeroed and then I'll just be left with this latest accusation of having a "slightly irritating manner of self appointed authority".

Maybe that's a new way of describing good manners?

 

[NRG]

Good idea Flecc, get Russ to left shift your post count by two decimal posts then I'll have more posts than you

 

[flecc]

No doubt Russ will see this and I'd welcome resetting to zero. I do think the disparity of the present total influences others feelings, especially newcomers to the site.

 

[mike killay]

Seriously Flecc,
Have you thought of gathering your posts and publishing them?
I owe you a great deal for the knowledge that I have gained over the past few months.
Thank you.
Mike

 

[flecc]

Thanks Mike. In fact the posts belong to the pedelecs site and I could only use them with their permission.

I fear it would be too big an exercise though, well beyond the spare time I have. Also, because of their number, only a small proportion can be found via my website member entry, though earlier ones are still available when the link is known.