Astoundingly cheap commuters

[Plodder]

"Dave" <[email protected]> wrote in message
news:[email protected]...
> On Fri, 01 Jun 2007 11:24:04 +0000, Zebee Johnstone wrote:
>
>> But then I suppose I can pick up a front disk and brake for $150 if I
>> look hard enough.
>
> Probably even less, if you stick with cables. For hydro it's a touch more,
> but the Shimano Deore offerings are both pretty good, and I've also heard
> good things about Avid's cable brakes.
>
> --
> Dave Hughes | [email protected]
> "Contrary to popular belief, Unix is user friendly. It just happens to
> be very selective about who its friends are" -- Kyle Hearn

Good point about the hydros. I got so fed up of my Hayes hydros playing up I
changed them to Avid BB7s. Bloody good move IMO. Far less trouble and they
feel much better - more modulation.

Me

 

[TimC]

On 2007-06-03, TimC (aka Bruce)
was almost, but not quite, entirely unlike tea:
> On 2007-06-02, Zebee Johnstone (aka Bruce)
> was almost, but not quite, entirely unlike tea:
>> In aus.bicycle on Sat, 02 Jun 2007 13:25:23 GMT
>> PeteSig <[email protected]> wrote:
>>> Incidentally, does your recumbent have a smaller front wheel (eg 20") I'm
>>> not sure about the physics of it but I do believe discs should be more
>>> effective on a small wheel than a 26" as they are proportionally bigger
>>> compared to the rim. Thus greater braking leverage. Someone here will tell
>>> me if I'm wrong or not.
>>
>> It's a 20" front. No idea about the physics but it does seem
>> intuitively likely.

Whoops, forgot to look at the disk brake situation. Anyway, rim
brakes:

> Torque is decreased at the hub because of the smaller radius, but
> that's irrelevant because that torque has to be converted back to a
> linear force at the bottom of the wheel. Think of the brake as being
> some kind of linear brake that is sitting some distance off the
> ground. It makes no difference if it is 20" or 26" off the ground,
> the same lateral force is being applied.
>
> I think.

So no change for small vs large.

And disk brakes:

For a given force on the disks, you get a given torque. Torque is
force multiplied by radius, so the linear force is going to increase
because of the smaller radius.

Damn, your intuition is better than mine. I blame the lack of coffee.
Damn weekends, I don't get to drink coffee for 2 days in a row.

--
TimC
Just keep in mind that when you are using TRANSFER, you are not
programming, but hacking. All else follows logically from this
premise, Grasshopper. -- James Van Buskirk in comp.lang.fortran

 

[PeteSig]

"TimC" wrote:
>
> Torque is decreased at the hub because of the smaller radius, but
> that's irrelevant because that torque has to be converted back to a
> linear force at the bottom of the wheel. Think of the brake as being
> some kind of linear brake that is sitting some distance off the
> ground. It makes no difference if it is 20" or 26" off the ground,
> the same lateral force is being applied.
>
> I think.

Surely the torque from a wheel radius of 13" acting against a 3" radius disc
is going to be a lot greater than that from a 10" radius wheel acting agaist
the same 3" radius disc?? Hence the braking power of the disc on the smaller
wheel is greater.

Caveat: I am no engineer nor mathematician

Cheers
Pete

 

[Zebee Johnstone]

In aus.bicycle on Sun, 3 Jun 2007 12:21:48 +1000
TimC <[email protected]> wrote:
>
> For a given force on the disks, you get a given torque. Torque is
> force multiplied by radius, so the linear force is going to increase
> because of the smaller radius.
>
> Damn, your intuition is better than mine. I blame the lack of coffee.
> Damn weekends, I don't get to drink coffee for 2 days in a row.

I just figured that swept area of disk as a proportion of size of
wheel was greater for the smaller wheel.

Zebee

 

[BT Humble]

M Bison wrote:
> On Fri, 01 Jun 2007 02:06:20 -0700,BTHumble wrote:
>
> <snip>
>
> > I reckon a penniless uni student could fully equip themselves with
> > bike & gear for under $200, which is only about 10 weeks' commuting at
> > Canberra bus ticket prices. Back when I was at uni you couldn't buy a
> > bottom-of-the-range K-mart MTB for that...
>
> Which makes the bus half the price if the bike only lasts 5 weeks!

Oh ye of little faith!


BTH