Recumbent - fenders

can fenders add to speed? i build/ride/race gravity bikes and im wondering if i add fenders to my next build if i can gain any speed. ive been told that covering the wheel at "4 oclock and 11 oclock if looking at the profile" i can peel airflow away from the wheel reducing wind drag. is there anything to this? thanks, fast eddie outty

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wwwfreewebs.com/gravityracing/

Wat kinda speeds we talking? If you're travelling over 30kmh/18mph then it will have an effect, but 1st you gotta get the positions and shape right.
My suggestion is instead of fenders, why dont you make wheel covers? Wheel covers will stop the turbulance. Just make em out of cardboard for starters, stick em to the rim with double sided tape. Air passing through the wheel and then the turbulance thrown out by the wind passing ova the spokes is an issue that wheel covers take care of. Fenders of your design...I couldn't see it working frankly. A fender at the front aint needed- the leading edge of your tyres are much better then you think in terms of aero.

The concept of fenders cutting drag would depend on shielding the tire tread to prevent viscous drag along the contact strip. The problem is, if you run slicks there just ain't much viscous drag anyway. If I were to do something along those lines, I'd want to make them full wheel pods - aerodynamically shaped fenders with integral skirts on both sides, and covering at least the top two-thirds of the wheel. Otherwise, fenders would do nothing except introduce more turbulence by creating another uneven surface between the fender and tire.

I agree with wheelchairman - spoke covers will gain you almost everything a wheel pod would. The easiest way to make spoke covers is to get a plastic 'for sale' sign or two at the local hardware store and cut two disks out of it. Then zip tie the spoke covers to the spokes. The cardboard idea would be OK, except that it would probably interfere with your brakes.

aren't you only supposed to do that for the back wheel though (the covers)? I've always heard it was a safety thing because of cross winds and such.

Crosswinds will blow you around if you cover the front spokes, but on a 20" front wheel it isn't nearly as bad as it would be with a full size wheel. So it depends on if you've got a dual-bigwheel or a traditional bent configuration, and what your comfort threshhold is. If you go with cloth spoke covers, which are more involved to make, you can remove the covers from the front wheel on windy days.

makes sense.

this is the type of bike im wondering about putting fenders on. this is the bike im currently riding. the new bike im building is similar, it will have this same RST shock fork, a similar frame/seat set up, etc...
i have a plastic wheel disc for the rear wheel, and im thinking of putting fenders on the front and rear. i want to cover the wheels as much as possible, as close to the ground as i can get w/out interfering on the front of the wheel, and the same on the back. my thinking is that i can reduce wind drag on the rubber - from my understanding wind does not run smoothly over rubber - and it will keep other bikes/riders out of my wheels. we sometimes ride/race very close and there have been occasions that open wheel racing has caused crashes. weight is not an issue w/ gravity bikes, in fact heavier is better in our sport so i don have to worry about that, my fenders are smooth chrome so the air should go over pretty smoothly, but this is all theory. i am hoping to hear some knowledge from experience and testing, does anyone know who/where has done this? am i gonna have to do it myself? i hate testing! i just wanna go faster! i appreciate you guys help, keep posting if you have info i can use. fast eddie http://i77.photobucket.com/albums/j64/gravityracing/FEGB2.jpgoutty

I have to wonder if fenders would become a safety issue in your case. Fender mounting systems are usually pretty flimsy.

Hmm. I wonder if a good bent would out coast that? :) Ever think of going feet first?

The cardboard idea would be OK, except that it would probably interfere with your brakes.Opps my bad. Assumed it might've been a disc brake setup at least :o

Three things:
1. spoke covers. Space them out so they're flush with the braking surface on the rim.
2. get rid of the sissy bar! (Lower it to seat level.)The only thing saving you right now is that it's somewhat in the wind shadow of your body.
3. Get a long stem, to stretch you out more over the bike.

I've seen crashes caused by fenders going into wheels - I don't think you want them on a downhill bike.

3. Get a long stem, to stretch you out more over the bike.

Like superman! ;)

i appreciate the input guys, thank you. i have purchased a road bike stem with negative degree angle and a few inches of stretch for this bike, and a double crown suspension fork since that fork is gonna go on my next build. the new stem and double crown fork will help to "steady" the front end, bmx stems can get wobbly if ya dont stay on top of em.

good stuff, i never thought of fenders damaging another bike in a crash, and i hadnt thought of the flimsy mounting hardware. i wonder if i could do something to reinforce them.

i know the sissy bar really looks like a bad idea, but i drilled the holes to mount the seat lower than holes that were already drilled, i plan on using the higher/existing holes to mount a rear fairing peice to "close" the air behind me. just havent got to it yet-still doin my homework on how to do it best for my means/tools.

ive been asked about riding a recumbent style gravity bike. i was really excited about that idea a few years ago. but after riding for a few years now, i just dont think a recumbent mounting position would be maneuverable enough for the roads we ride/race. i steer the bike with my knees via the knee trays ive attached at the lower bracket. with very subtle shifts of my hips my weight is transferred to the trays which then act as levers to lean the frame, this makes it possible to take tight, very fast turns with little deviation from my "tuck" i build and ride recreational streetluges, but thats as close as i get to recumbent riding.

Recumbents cannot really be steered with "body english." This is because the rider's position is parallel to the direction of travel, rather than perpendicular. Many recumbents will become unstable when you let go with one hand at high speed, and some are quite dangerous (or impossible) with no hands. This is directly related to the length of the wheelbase, and there are a few exceptions.

If you wanted to build a recumbent gravity bike, it would probably have to be very low to the ground, with big wheels, and pretty long. It could only ride on paved roads. Look for pictures of lowracers, these should be your inspiration. Without any need for a drivetrain it would be a pretty simple build. Just be aware that the longer the bike, the wider the turning angle is.