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Last year I, after cracking an sks chromoplastic, I decided to get some stainless steel fenders. I noticed at the time that the fender (700x45) was almost identical to the diameter of the tire (700x35). This seemed odd to me and I took this picture.

enter image description here

You can see the problem - if I lift the fender up about 1/2" to clear the tire, the two ends of the fender are still very close to the tire. The solution is to bend the fender during installation, to stretch those ends away from the tire, which I did. I installed this fender about a year ago. It cracked at the seat stay bridge today.

I have steel fenders on my 26er, which is strictly a snow commuter, and they did not need to be stretched and forced to fit. They've held tight for two winters.

I feel like I need either a flexy fender which won't crack, or a perfectly fit steel fender. Or maybe there is a way to modify steel fenders so that they are not under tension when forced to fit?

EDIT: The crack: enter image description here

  • Guessing - perhaps the design is weak because it only has one support strut, and the free length between the brake bridge and the end can flex. Separately, could you post a close up of the damage? We may be able to suggest some patch repairs, if they're out of warranty. – Criggie Nov 29 '16 at 4:50
  • I added a photo. As for a repair - the hole in the fender at the chain stay bridge is long and vertical and I had mounted the fender with the bolt at the top of this hole. This means that I am able to slide the bottom broken piece up. So I drilled a hole in it near the break, then drilled a hole in the other broken piece and overlapped them at the seat stay bridge. So now the repair is holding but the fender is not sufficiently rigid for my taste. I hate it when stuff comes loose when it's -10 F and I think that's what I'm in for. – jqning Nov 29 '16 at 5:37
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    That fender was obviously designed for a skinnier tire. 45 mm is pretty wide. Bending it may have weakened it, or maybe it was weak to start with - no way to be sure. – Mike Baranczak Nov 29 '16 at 6:20
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    Did you use a leather washer between the fender and a hard mount (e.g., frame). Metal fenders can crack from vibrations, a leather washer helps to dampen road vibrations. – Rider_X Nov 29 '16 at 7:18
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    You need to find a fender that fits. – Daniel R Hicks Nov 29 '16 at 12:29
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I think your fender failed because of the stress that you introduced by attaching it without having it properly reshaped. Metal fenders must be mounted stress-free, otherwise they will be prone to fail and crack. This means that before installation the fender has to follow the tire without being supported by the frame and fender struts attachments.

Mounting metal fenders properly

Start with reshaping the fender so that it follows your tire at a constant distance of 15-20mm.

To enlarge the radius, squeeze the fender edges towards each other (as if you would try to make the fender narrower) and it will open up. Work all the way along the fender in order to obtain a constant radius/curvature. With stainless steel fenders this is a bit more difficult than with aluminium ones, but it is possible. If you want to decrease the radius, bend the edges apart instead.

When the fender has got a nice shape following the tire with constant distance (about 15-20mm), drill a hole at the brake bridge, so that the lower end of the fender extends some centimeters below the chain stays (this keeps drip water off the chain). Deburr the hole carefully (this is where cracks start!) and attach it at the brake bridge. A leather washer goes between fender and frame, and a large diameter but rather thin stainless washer between fender and bolt head (the washer on your picture is far too little).

Measure where the chain stay bridge attachment is, and drill the hole there. When deburring it, you can ovalize it a bit with a file if it is not exactly in the correct position. It is very important that you don't put any stress or strain on the fender when attaching it at the two frame mounting points.

Now it is time to attach the fender stay(s) 10-15cm above the back end of the fender. Once again, bend the stays before installing them so that they have the right shape/angles to be mounted stress-free.

Well-mounted stainless steel fenders can hold a long time (many 10000 kilometers).

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    +1 and good answer, with one caveat: on all the many frames where the chainstay and seatstay bridge attachment points aren't anywhere close to equidistant from the axle, which is the ideal with metal fenders, you often have to space them out there to prevent the fender from having built-in stresses. I always do it with leftover aluminum tubular spacers from Planet Bike Cascadias. – Nathan Knutson Sep 11 '17 at 19:31
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    +1 - this is the correct answer. Unfortunately the OP's error lead to the early failure. Here is a good step-by-step tutorial from velo-orange describing how to re-radius fenders. Re-radiusing will work best with fenders with a round profile, your mileage may vary with some the new square profile metal fenders (e.g., PDW and Specialized) - although in theory it should work here too as you will be changing from a square to slightly round profile. – Rider_X Sep 11 '17 at 22:10
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You may find the addition of leather washers (as mentioned) or some thin rubber (as might be used for mud flaps) helps prevent this cracking.

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