Author Topic: Mudguard skills  (Read 194 times)

Ben T

  • What you saying, then?
Mudguard skills
« on: January 14, 2019, 05:35:56 pm »
Would like to increase skills in mudguard maintenance/fitting.

My rear SKS bluemels cracked in two places. Shop has agreed to replace so will only cost a couple of quid in postage to replace.
One crack was midway between the (plastic, non-riveted) brake bridge mount, and went right through (but the tape used to fasten the light wire on held it together) and the other was just below the upper (riveted) stay mount, and hadn't quite gone right through.

I would ideally like to acquire the ability to (a) prevent them cracking in future, but also (b) scope out if there is any better semi-permanent way of attaching the dynamo light.
I guess as far (a) goes, make sure the stays aren't bending it / holding it under tension, but anything else?
I previously thought rivets were a source of cracks, but here, one crack has occurred near the rivet but another one away from it. I guess it could be that the one near the rivet occurred first, and that put increased pressure on the rest of the guard that caused the other one. Hmm...

As far as (b_ goes, previously I used this tape: which has stuck, very well - in that it has remained completely in place and has actually held the guard together when it cracked - but slightly too well - in that it has peeled off little patches of the lacquer of the mudguard, leaving the silver inside showing.#
I would like to be able to remove and re-fit the guard ideally with minimal damage in order to be able to fly with the bike. I guess it's better than tape that comes off when it's wet, as if it peels any lacquer off in future I can just stick new tape over it, but if anybody knows any that doesn't do this, but still sticks well, would like to know. Does the lacquer contribute to the robustness of the mudguard or is it just for looks?
Unless you put on overalls, boots, and a helmet with a high tech pre fitted lamp - and you dig coal - nope, you don't know me.


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Re: Mudguard skills
« Reply #1 on: January 14, 2019, 06:03:05 pm »
Pics of the mudguard fitting would be helpful. Can't ever say I've had any SKS mudguards snap in half. My rear dyno light is on the rear of my pannier rack...

Re: Mudguard skills
« Reply #2 on: January 14, 2019, 06:15:29 pm »
IME the #1 cause of cracked chromoplastic mudguards is that they were not fitted correctly. Some top tips;

1) make sure the stays are secure and that they are not strained sideways when fitted; in other words they should be 'set' so that they sit in the correct place naturally, even when not attached to the mudguard

2) avoid straining the mudguard curvature esp near the brake bridge.  If necessary space the mudguard away from the chainstay bridge so that there isn't permanent strain on the mudguard.

3) chamfer/trim the mudguard if necessary so that it fits between the chainstays without being strained.

4)  if some strain is unavoidable, you can locally heat the mudguard (eg using a hairdryer) so that it takes a 'set'. It is less likely to crack vs being strained when fitted.

5) fit the (stainless steel, the plastic ones are crap) brake bridge mount so that the bottom of the slot is not exposed, if necessary by using washers either side of it, 

6) crimp the bridge support so that the mudguard doesn't rattle there

7) avoid having the stays differently bent one side of the bike to the other; this is commonly the case on disc brake bikes but it encourages the mudguard to flap from side to side more than it should.

8) make absolutely sure that your bike is in track; if it is slightly lopsided (eg a pannier on one side is enough) then again the mudguard will vibrate from side to side more and this (other than massive strain) is what destroys them most quickly.

9) use nylocks etc so that the mudguards are not likely to work loose

Basically if you slacken any one mounting bolt and the mudguard immediately moves under its own steam, there is some strain in it somewhere, and probably this can be reduced or eliminated, thus giving the mudguard an easier time of it.

I agree that the rear light is best put somewhere else; a lightweight reflector is much less likely to strain the mudguard.  Having broken a couple of mudguards with the light on (they seem to crack at the middle stay mounts when the light is attached, and strain all the other mountings more too ) I have my light on the seat stays.

I think that these mudguards are polycarbonate and therefore eventually embrittle and become likely to crack. Some solvents and UV light will speed this process up.  But I have had a set of chromoplastic mudguards last about 30 years (mostly outdoors) before I broke them; however when they broke they were as brittle as glass.

I'd also note that skinny mudguards and skinny high pressure tyres are a bit of a double-whammy; the mudguards see a lot more vibration damage with this kind of setup.


Ben T

  • What you saying, then?
Re: Mudguard skills
« Reply #3 on: January 14, 2019, 06:35:34 pm »
Thanks for the pointers on making sure they're not strained.

Agree the seat stay is better maintenance wise for the rear light, but can you counter my suspicion that there is a "blind point" where a road user (e.g. a car) could be in a position such that they can't see my rear light due to the mudguard or wheel being between them and the light source?

Is it worth bothering moving the light to the left seat stay when riding abroad?
Unless you put on overalls, boots, and a helmet with a high tech pre fitted lamp - and you dig coal - nope, you don't know me.

Re: Mudguard skills
« Reply #4 on: January 14, 2019, 07:01:21 pm »
I use lights mounted on the seatstays but above the wheel. They might be obscured by flappy clothing and/or might be obscured side-on by your legs as you pedal. In the latter case the light becomes a flashing one, so no big deal. [the extent to which this happens depends on frame design; an old fashioned frame with a horizontal top tube and long seat stays is better here without doubt]. The seat stays are not far apart and the light is offset anyway; I wouldn't bother to move it when I'm riding on the other side of the road but I might angle it differently.

FWIW I think rear lights are of most use at long distance when vehicles are coming up behind; you might well be outside of their (dipped beam) headlight range.  From other angles/distances the driver of  any vehicle with working headlights is more likely to see you because of reflectors etc rather than lights.  Many modern rear lights don't cast a lot of light sideways anyway, but a few do.