Do Fenders really perform / work ????

[Ken M]

I've got some Topeak M1 Defender Fenders on my Polaris eBike (Court did a review video of these on his own bike a while back). They are good fenders (especially if you like the more motorcycle fender appearance) but I really question if there is such a thing as a truly effective bike fender when riding at any speed over about 15mph.

The wheel speed tends to literally pump most of the water that collects on the underside of the front fender forward and then it streams up and into your body and face. I know there is a fender on a Specialized bike with channels that move the water to the outside edges of the fender but I have no first hand experience with them so would like to hear if that works. The other problem with every front fender that I can think of (mainly if you ride on on a road with any standing water) is the splashing of the tire. You can simply take a yard stick and take it from the contact point of the tire back to where your feet and lower legs are going to be while pedaling and it's obvious that this is not blocked by a fender. The few times I've ridden in significant rain (had Gortex protection on except for my feet and I was just wearing 100% leather sneakers) my feet go soaking wet in about 10 minutes. If you want to arrive with dry feet when it's raining I think a set of waterproof shoe covers is a must.

Fenders to reduces the water that is released by the tire that end up on the rider but it's time dependent. If you are riding for say more than 10 minutes in the rain fenders result in no difference to how wet you are going to get. If the road is just wet and it's not raining, I think you'll still end up pretty wet.

I do think a rear fender can prevent a lot of the flinging of water up onto your back as that is a total different performance issue for fenders and they do a decent job of solving that (the front tire is just much more difficult because of splashing and the movement of water to the front edge of the fender when it just releases into your path.

I think the best that can be said about fenders based on experience is that they reduce some of the water that may be picked-up and tossed onto you when you come across occasional wet spots on your urban commute. If riding on very wet roads or while raining, fenders really won't do much to keep you dry or clean.

I would like to hear if others that urban commute on an eBike have experienced this.

 

[JRA]

I have to disagree. My fender system(s) that see lots of wet use here in OR do a lot to keep me dry, especially my lower back and feet which are the two most vulnerable areas of discomfort I find using a bike with little or no fender coverage. The trick is you have to get as full a coverage as possible. Those little "mudguards" that you see on bikes are worthless IMHO.

This illustrates how effective fenders are with more regards to those following you:

Otherwise it really helps to have the proper riding apparel for the conditions as no fender is going to defend you against direct rain contact. That is where it gets tricky because truly effective rain gear is probably not going to be very breathable and so you will get wet from the inside out.

 

[Ken M]

As I stated, a rear fender can be effective at keeping water off your back side (your fender zone chart simply shows the effectiveness of keeping those behind you from getting splashed higher up which is out of context with my question if fenders really work). There is a short segment rear fender that is actually designed to be pretty effective at preventing rear water flinging that other riders would appreciate but I'm interested in something that will keep me full body (feet to head) dry and that mainly involves performance of the front fender.

The front zone graphic does represents the problem I have experienced - water coming off from under the front edge of fender and spraying up and out. I think that coverage past the apex of the tire could ensure that water doesn't go up at higher speeds but there is nothing in that graphic that represents the problem of your lower legs and feet getting soaked by the lower tire splashing (and the added spray of an extension on the top that will still result in some water hitting your legs and feet even if it keeps your body and head from getting wet).

There are some Youtube video reviews of fenders but they all seem to address a short stretch of riding thru puddles and how much less water actually collects in the riders clothing. But if you do the math, even if 95% effective for those few puddles you are still going to be soaked if you are riding continuously on a wet road which is real world (I can slow down for an occasional puddle and not really impact my commute times).

What no one really talks much about is that usually if the road is wet it's usually raining so you are going to be hit by water and the only real protection (if you want to have dry street cloths when you arrive at your destination) is to have waterproof coverage (even over your shoes). I pretty much keep as light/thin waterproof (usually with a breathable membrane such as Goretex) jacket and pants in a back pack or seat pack that I can toss on. For my feet I just ended up with cheap plastic film booties with rubber bottoms that are good for a few dozen uses (only a few $s so then you just toss em and buy another pair).

When I started commuting on an eBike I thought fenders would be effective but I just feel they all fall short in reality if your ride is more than a few minutes.

I've seen some new ideas that have a very bristle brush that touches the tire surface such that water surface tension is broken and most of the water on the front tire is released before it can get to the front of the fender. Conceptually that sounds like a good idea if something simple could be designed that you only use when it's wet/raining. Still will not keep your feet from getting splashed but maybe it works to keep your upper body from being sprayed by water released by the front edge of the fender.

 

[Ken M]

Hey JRA....is that one of the new Grin Technologies hub motors on your bike?

I'm taking with them to do some beta testing of their new hub motor as conceptually they have dramatically improved the design to address some of the shortfalls like heat dissipation and weight.

 

[Ken M]

I also ave a Haibike Trekking RC with full coverage fenders and the front fender releases water up at higher speeds just like the Topeak Defenders so this performance issue is not just limited to aftermarket add-on fenders.

I know rear fenders can keep your backside from getting wet, but is there any assessment of front fenders that really proves they perform....not just reduce how fast you get wet but are effective for longer and faster rides. Sure if I ride at 5mph on wet sidewalks the full coverage fenders perform great, but at 20mph and faster the water is just spraying and splashing everywhere.

I think some riders are claiming their fenders work because they ride so slow the water isn't even splashing or flying off the front tire. I don't want to ride at a walking speed when I'm commuting.

 

[JRA]

I did mention that the picture was more to do with those following you but it also illustrates spray pattern in general and I included it to help others visualize that.

My feet and face are fine with the fenders as shown on my bike. I don't slow down for that effect either.

I picked up this idea online and made a few samples to try but got sidetracked with my e mtb.

As well as adding length to my existing fenders/flaps the idea is that the string, I used some Spectra fishing line, as well as creating the curvature will cause the spray to turn to mist before it hits the flap. I really need to get back to this.

Yes it is a Grin Any Axle motor run @ 25A/52v. I have about 3000 miles on it now. I also have a similar bike with a 9c that I use as a comparison. Although both motors are similar in power output the weight loss of the AA and the option to use on a thru axle fork tips the scales in its favor for me. Also I have it set up so that it is a tool less removal due to their integrated torque arm.

As mentioned it is lighter but as far as heat dissipation goes the 9c controls that better due to its additional mass. The Statorade product Grin uses helps control the temps but it does dissipate over time I have found and needs to be recharged. I figured this out because I was getting higher temp readings through my CA climbing the same hills than earlier and after adding more they came back down again. I am overall very pleased with it and would use it again or recommend it to anyone that sees the benefits in using a front hub motor as I do.

 

[Ken M]

Wow. I really want to extend our conversation but more directly than thru this forum. Are we allowed to exchange emails on EBR. Want to maybe discuss a possible win-win arrangement with you.

I'm just thinking you have a parallel interest in fast pedelecs if you are testing/running the Grin AA hub motor and using a CA. I like that you are running it at 25A/52V as that is a power level that should result in some good performance numbers. Is the Kv high enough on your AA to provide assist to 30mph or higher? Do you have any idea what the max stall torque is on the motor with that much power - I'm guessing in the range of 75-100NM such that even gear-less it's got some appreciable assistance thru all speeds.

Would like to work with you on improving fender performance on fast pedelecs as well. Looks like you were also thinking of breaking the surface tension of the water early enough to prevent the front fender spraying. I've been trying a few ideas myself (mainly just trying to channel the water to the edges near the front which does reduce the upward spray but my legs and feet still get pretty wet.

 

[Trail Cruiser]

vs

https://janheine.wordpress.com/2012/11/19/why-we-dont-need-rain-bikes-any-longer/

https://janheine.wordpress.com/2013/02/16/no-mudflap-what-a-mess/

https://electricbikereview.com/forums/threads/full-cover-fenders.9029/

 

[J.R.]

A good visual of what can work at speed. 20 mph, with a 20 mph headwind.

 

[Ken M]

Those are definitely full coverage fenders. I need to install a front fender like one of these on my commute bike and get a subjective feel for how well they perform. My two priorities is the lower splashing of the feet and legs and the front edge release of water pumped up under the fender at higher speeds that just seems to always be coming into me when the roads are wet. Maybe that is eliminated with a front fender going a bit past the apex of the front wheel so the air then pushes the released water down instead of up.

Have to give it a try but also want to see how effective breaking the surface tension of the water on the tires is as well.

Let's keep our ideas flowing.....

 

[JRA]

This is what I did to my mtb to plug the gaps. A combination of some store bought parts and .04 ABS and zip ties. It doesn't see speeds much above 20 so I don't have a front fender extension past the shock linkage. Other than the rear fender needs a bit more length to come back with a totally clean lower back it seems to be working ok. Especially in regards to keeping the motor/battery areas clean even under the worst conditions.

Kind of ugly up close but not as bad from 15' away!

 

[Dunbar]

The other thing to consider with fenders is the width. Ideally you want them to be at least 10mm wider than the tires. You can have the fullest coverage fenders available but, if they’re not wide enough to prevent water spraying out the sides, they won’t be very effective. I’ve lost count of how many bikes I see with fenders that are barely any wider than the tires (if not narrower than them...) I use 60mm fenders on ~45mm wide tires and they work very well.