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My local bicycle mechanic advised me to get mudguards (such as the ones in Image 1) to extend the life of my drivetrain and protect it from spray in the winter. If I have £20 to spend on either a chainguard (see image 2) or a front fender, would I be better off with a chainguard? Would this be lighter and provide better protection for the drivetrain vs front-wheel-spray? Image 2 shows how a chainguard on a bike (3-9 derailleur) could block both spray which would be stopped by a front fender (green lines) and spray which would slip past underneath a front fender (blue lines).

Are there any chainguards which would divert mud flowing along the underside of the down tube, so it drips to the ground before it can flow onwards and build up around the axle for the pedals? (Otherwise I guess I could accomplish this by DIY-fixing a mudflap to hang down from the down tube.)

NB, I would still use a rear mudguard regardless.

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    Even if you had the 1x drivetrain to make the chain guard feasible, I'd still recommend sticking with the fender for simplicity's sake – Paul H Feb 12 at 17:11
  • Note that the chainguard you've pictured (and a lot of the classic ones) will only work on a 1x bike; if you have a front derailleur (i.e. you have a 2x or 3x configuration) it won't work. – DavidW Feb 12 at 17:13
  • @DavidW I do have a 2x front derailleur, good point – novice Feb 12 at 17:15
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    Why not both? You're already using a rear mudguard. – Criggie Feb 12 at 23:24
  • @Criggie for the same reason that I will only be getting a gravity axle for the front wheel and but the back wheel as well: on grounds of cost (I lock my back wheel with a mini D lock anyway along with the frame, so it's not necessary for both wheels). I want to avoid buying items which could be made redundant or semi-redundant by better items, and I want to minimise redundancy in my setup on grounds of cost. – novice Feb 14 at 19:14
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Chainguard is not there to protect chain from dirt spray from tires, unless it is a completely enclosed chainguard (which is not feasible on derailleur bicycles). A chainguard is there to protect your pants from chain oil.

Should you install a chainguard, then? Yes! It protects your pants from chain oil.

But to protect your chain from dirt spray, you'll need fenders, too.

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  • See above: I edited the question to show a bike (3-9 derailleur) with a chainguard which appears to form a barrier between the front wheel and the spray. – novice Feb 14 at 19:06
  • *or the front wheel and the chain rather – novice Feb 14 at 19:18
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The rear fender will act mostly to keep spray off of you, as opposed to the drivetrain; the spray hitting the bottom bracket and chainrings will be coming off the front wheel. I would argue that it's more important to have a front fender than a rear one.

Sheldon Brown has a pretty good page on fenders; it explain how full fenders are much better than anything else. Your front fender should definitely have a mudflap on it.

Note that while the bike's frame itself (downtube or seat tube) will catch a fair bit of the spray from the wheels (in the absence of fenders), the rounded shape of the tube means that this basically just spreads the spray out in a wider pattern. :) Also, since you steer with the front, it won't line up with the tube all the time, which is a problem with "fenders" that clip onto the frame. And from personal experience, in a rain heavy enough to leave standing water on the road if your front tire has any tread to speak of (like a touring tire, not a slick) it can move an amazing amount of water into your shoes in a very short time! :)

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  • I appreciate your point about the front fender. Is it still important to have a rear fender which can divert spray downwards, away from the seat tube? Because I have had an issue with lots of dirt getting into the rear axle, which I suspect comes from lots of dirty water being channeled there along the seat tube (and the downtube). – novice Feb 12 at 17:56
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    @novice Sorry, I didn't mean to suggest you don't need the rear fender. But since you said you'd still use a rear mudguard anyway, I concentrated on the arguments in favour of a front fender. A rear fender will also be very useful in dirty conditions; at the very least it will keep you cleaner, unless you like having a stripe down your back. :) – DavidW Feb 12 at 18:06
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    No fender is a substitute for regular cleaning and lubrication of the drivetrain. At least weekly for bike operated full time in all weather conditions. – Jeff Feb 13 at 10:20
  • @novice A good mud flap on the front fender is the most important thing you can use to keep spray off both your bike - and you. Your bike appears to have clipless pedals, and unless you're wearing something like "winter cycling boots", your shoes will have holes for the cleats - and the spray from the front wheel will hit those holes and rapidly soak your feet (and your drive train...) with dirty, debris-laden water. And even if you have "winter cycling boots" that don't allow water in through cleat holes. that spray will hit your shins and then run down into your shoes anyway... – Andrew Henle Feb 13 at 14:09
  • (and if you ride long enough in the wet, you'll be totally soaked no matter what you do...) – Andrew Henle Feb 13 at 14:11

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