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Due to the rainy weather and my daily commute, I've decided to invest in some SKS Raceblade fenders. The fenders extend only just past vertical of the axle, and so I wonder about how wet I/my drivetrain can expect to get from the remaining exposed tire.

Has anyone looked at this carefully/experimented with the amount of water coming off the tire at different angles/speeds? I would assume that most of the water stays near the ground, and incrementally less water goes around the frame.

What I'm trying to understand is whether I need to buy another fender to block water that will hit my drive train, or if so little will be present by the time it gets past the fender that it won't really matter.

I've uploaded a photo to illustrate my question.

my understanding of water flying off the tire.

Nate
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    From what I can see of the photo you've posted, the spray of water from the front wheel is going to soak your drivetrain thoroughly - along with your feet and lower legs. Assuming there's nothing sitting on that rack, the only thing that rear fender is really going to do is prevent you from getting a racing stripe on your back. If there is something on that rear rack, the fender will stop if from getting soaked in water that's likely muddy and/or oily. If you want to stop your feet from getting soaked, you need fenders with a spray flap on the front that goes almost to the ground. – Andrew Henle Jan 21 '20 at 22:13
  • Is that complete? Some mudguards come in two pieces, with a junction or brief gap at the brake caliper. Perhaps the front piece was not installed. – Criggie Jan 21 '20 at 23:40
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    @Criggie, there was only once piece for the front, and one for the rear :( – Nate Jan 22 '20 at 00:00
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    So, clearly Nate has one of those clip on fenders for use on bikes without eyelets. Those are inherently partial fenders. – Weiwen Ng Jan 22 '20 at 01:00
  • @AndrewHenle There is quite clearly a fender with a spray flap in the front. It may be slightly short, but not by a lot, and it will intercept at least 80% of the spray from the front. – DavidW Jan 22 '20 at 15:56
  • @DavidW That "spray flap" looks extremely narrow and is about as high off the ground as the crankset axle. It's effectively useless for doing anything other than stopping the spray that would hit upper half of the downtube. It sure isn't going to keep any spray off the drivetrain or the rider's feet and lower legs. – Andrew Henle Jan 22 '20 at 16:00
  • Thanks to all that gave their advice. I adjusted the fender in front (which is wider than it looks in these pictures), and I rode in the wet yesterday. My shoes ended up a bit wet, but less than before, and my drivetrain stayed much drier than I expected. I don't know the exact relief the front fender affords though, because I was riding among friends, and spray coming off their tires drenched me. My backpack was completely dry, which was a relief. – Nate Jan 24 '20 at 00:53

2 Answers2

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That rear mudguard/fender is definitely better than nothing, but its not a good full-coverage guard. As you note, water will fly off the tyre and hit the frame and underside of your legs while riding.

A good rear guard will start low at the back, perhaps even with a mudflap. Then will go over the whole outside circumference, with its lowest point below the BB/chainstays.

If your roads have any dirt on them it will be picked up an ddeposited on the rear of your seat tube, and possibly on the top of the kickstand bracket if your bike has one between the chainstays.

Most-all full guards have stays that support and brace the rear of the guard. I can't see any in your pic, but I bet the guard's a bit floppy and perhaps even buzzes on the tyre while riding.

Related - the tread on your tyre has a lot to do with how much water is carried around the wheel. A blocky MTB knobbly will throw road water like a rooster tail, but a road bike in the same conditions and at the same speed will throw far less water.

Separately, that front mudguard is okay but not great. It could go down further, again with a mudflap to protect the BB and chainrings and your feet from road water.

Criggie
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The same rear fender/mudguard would be more effective if you installed it to run from the BB to just behind the brake bridge. I am familiar with removable guards that install that way, reference "Flinger". I agree with others' advice about your front guard not going low enough too.

Henry S
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