a couple of questions about mudguards

davek said:

Just fitted some SKS "chromoplastic" mudguards to my bike after being
fed up with the amount of muck it has been gathering on recent rides (a
bit after the horse has bolted, but better late than never). Anyway,
two questions...

1. What is the optimum spacing between mudguard and tyre, both from a
performance point of view and with regard to aerodynamics? I've guessed
the mudguard should be as close as possible but I don't know better.

It depends on your definition of "performance" :-)

Fitting it close leads to rubbing when your wheel goes out of true, and
also means that it captures less of the upthrown muddy water that's
aligned with the plane of the wheel but is thrown off between contact
patch and mudguard. If you go anywhere *really* muddy it can clog up,
too.

Aerodynamically, I dunno. I can't imagine it'd be significant in any
practical setup.

Quoted message said:

2. The rear mudguard came fitted with both a reflector and a light,
presumably meant to be connected to a dynamo. If I fit a dynamo, where
would I connect the wires to make the light work? I have a hunch that I
should wire it up to the mudguard bracket that clips to the chainstay
bridge, and that the metal in the mudguard will act as a conductor.
Unfortunately, the instructions that came with the mudguards were
unenlightening.

Using the mudguard and/or frame as a conducting path is fraught with
difficulties. In theory it should be fine, but in practice... you'd
be much better off fixing a pair of wires 'twixt dynamo and light.

R.

davek said:

Just fitted some SKS "chromoplastic" mudguards to my bike after being
fed up with the amount of muck it has been gathering on recent rides (a
bit after the horse has bolted, but better late than never). Anyway,
two questions...

1. What is the optimum spacing between mudguard and tyre, both from a
performance point of view and with regard to aerodynamics? I've guessed
the mudguard should be as close as possible but I don't know better.

2. The rear mudguard came fitted with both a reflector and a light,
presumably meant to be connected to a dynamo. If I fit a dynamo, where
would I connect the wires to make the light work? I have a hunch that I
should wire it up to the mudguard bracket that clips to the chainstay
bridge, and that the metal in the mudguard will act as a conductor.
Unfortunately, the instructions that came with the mudguards were
unenlightening.

tia,

d.

My SKS/Bluemels guard has said light/reflector (Both BS6102 actually).
One terminal is connected to the muguard stay and hence frame. The other
runs through the mudguard to a spigot on the other end of the guard so
its between the chainstays when fitted. Like the other response I would
wire it with two wires to the lamp though if I ever come to get my dynamo..

in message <[email hidden]>, davek

(') said:

Just fitted some SKS "chromoplastic" mudguards to my bike after being
fed up with the amount of muck it has been gathering on recent rides
(a bit after the horse has bolted, but better late than never).
Anyway, two questions...

1. What is the optimum spacing between mudguard and tyre, both from a
performance point of view and with regard to aerodynamics? I've
guessed the mudguard should be as close as possible but I don't know
better.

Mud, grit and other obnoxiousness will accumulate on the inside of the
mudguard. The gap needs to be larger than the largest particle of crud
that might so accumulate, so bigger in sticky gravelly conditions and
very muddy conditions. On normal road surfaces, as close as possible
*without* touching is good.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; all in all you're just another click in the call
;; -- Minke Bouyed

davek said:

Just fitted some SKS "chromoplastic" mudguards to my bike after being
fed up with the amount of muck it has been gathering on recent rides (a
bit after the horse has bolted, but better late than never). Anyway,
two questions...

1. What is the optimum spacing between mudguard and tyre, both from a
performance point of view and with regard to aerodynamics? I've guessed
the mudguard should be as close as possible but I don't know better.

No! You need some mud clearance. Half an inch is good.

Richard said:

also means that it captures less of the upthrown muddy water that's
aligned with the plane of the wheel but is thrown off between contact
patch and mudguard.

Having a full-length front guard with flap should protect my bottom
bracket, though, right?

Quoted message said:

Aerodynamically, I dunno. I can't imagine it'd be significant in any
practical setup.

I thought aerodynamics was one of the reasons road bikes didn't come
with mudguards, but would I be right in guessing that it's a secondary
reason after weight and frame clearance issues?

Quoted message said:

Using the mudguard and/or frame as a conducting path is fraught with
difficulties. In theory it should be fine, but in practice... you'd
be much better off fixing a pair of wires 'twixt dynamo and light.

Wilco.

d.

davek said:

Richard said:

Aerodynamically, I dunno. I can't imagine it'd be significant in
any practical setup.

It may be a small factor but mudguards would spoil the effect of aero
wheels. Even wide tyres can.

Quoted message said:

I thought aerodynamics was one of the reasons road bikes didn't come
with mudguards, but would I be right in guessing that it's a secondary
reason after weight and frame clearance issues?

That's right. Also it's one less potential cause of problems, plus it's
easier to change a wheel and maintain the bike without mudguards.

~PB

davek said:

Richard said:

also means that it captures less of the upthrown muddy water that's
aligned with the plane of the wheel but is thrown off between contact
patch and mudguard.

Having a full-length front guard with flap should protect my bottom
bracket, though, right?

Quoted message said:

Aerodynamically, I dunno. I can't imagine it'd be significant in any
practical setup.

I thought aerodynamics was one of the reasons road bikes didn't come
with mudguards, but would I be right in guessing that it's a secondary
reason after weight and frame clearance issues?

Quoted message said:

Using the mudguard and/or frame as a conducting path is fraught with
difficulties. In theory it should be fine, but in practice... you'd
be much better off fixing a pair of wires 'twixt dynamo and light.

Wilco.

d.

I read in one of Ed Burkes books that mudguards increase drag by 20-30% IIRC

On Wed, 16 Feb 2005 13:41:18 +0000, MSeries <[email hidden]>

Quoted message said:

I read in one of Ed Burkes books that mudguards increase drag by 20-30% IIRC

Possibly for the bike alone, but for a bike + rider I would be
surprised if the effect is that great.

Richard <[email hidden]> wrote:

: Aerodynamically, I dunno. I can't imagine it'd be significant in any
: practical setup.

It's surprisingly noticable once you get above 20mph IME.

Arthur

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It is better to light a candle than to curse the darkness