Pedaling in Rear Wheel design

Question

I had built a bike similar to this one before. I think many would have this idea, too.

However, for some reason, not many of these designed are commercially marketed.

https://sites.google.com/site/pendalbike/pendalbike

There are several advantages on this design:

• More aerodynamic posture
• Better up-hill climb efficiency (personal experience)
• Less maintenance for the drive train
• Less Frame materials (weight are transfer directly through the pedal to rear wheel, and through fork to Front wheel)

There are disadvantages:

• Fewer gears (I doubt this, technology in this Information age should be more than enough to design a robust Internal Hub gear that support a pedal axle in the middle)
• Cost: Obviously it is not in the stage of mass-production, so the cost would be high. But I do not see why it should be more expensive (if not to say cheaper) than a normal bike.

Unless I missed many unforeseen disadvantages, what else could prevent this design from becoming popular in the last 10 years? What are other disadvantages in comparison with a normal bike that can level the advantages I have stated?

Answer 1

One problem is that the design would not be appropriate for technical riding requiring speed. Getting behind the seat to push against the pedals would put you out over nothing, instead of out over the back wheel. The design would be less stable because of that and consequently unsuitable for technical riding. The puts it out for mountain styles of riding.

On the road side, the UCI has been fairly quick to ban anything as non-traditional as this. While materials improvements and the like are generally the norm, major changes to the geometry of a bike is combed over closely and often thrown out.

New designs take sometime to take hold (Fat bikes are a good example from recent years). The fat bike market lingered for years because very few companies were producing the tyres, bottom brackets, cranksets, hubs and rims it needed to grow. Although most of the other parts were standard road and mountain bike parts, key components can be a hold back. Once these bikes started getting raced regularly, the market and manufacture of the specialty parts took off.

For the design you are talking about, I don't see enough appreciable advantages for the commuter market to champion it. Since it's not appropriate for the other markets, I can't see such a radially departing design gaining any traction.

Answer 2

There are a few designs that could involve rear wheel pedalling, and none of them seems to be particularly advantageous when compared to today's standards. Here are two major ideas:

1. The design which is shown in the picture i.e. saddle somewhere around rear wheel axle - when using a standard frame your position will be very hunched. Yes, this may give an advantage in terms of drag coefficient and frontal area, but it is proven that your muscle efficiency falls with decreasing trunk angle (about 1% per 1 degree of smaller angle). Therefore the consensus is for TT bikes for this angle to be not lower than 30°, while in this design the angle would be way less than this.

   Hence the frame must be designed to be much shorter. This will make a bike be less stable, especially at high speeds. Body-balancing is also an issue because your weight is put around the rear wheel level, meaning you would have less control over the front.

   There is also another problem with weight distribution. In order to achieve the same pedalling efficiency, the sadle needs to be behind the rear wheel axle (to work like an inclined seat tube). This puts your CoG (centre of gravity) more than less over your rear wheel axle. This in turn means that during accelerationyour front wheel will be pulled upwards unless handlebars are much below the saddle, which as mentioned above decreases trunk angle. This can get even worse on the uphil when your CoG moves virtually behind the rear wheel additionally decreasing wheel grip (although this change would be barely noticeable on tarmac).

2. Another thing you can do is leave saddle where it is in a normal frame and just put entire drivetrain at the back. In this case you would be practically lying on the frame, so both frame and saddle would need to be redesigned. Also since the rear wheel axle is further than bottom bracket, the range of leg motion will be smaller thus producing less power (although it may result in fewer injuries). Also your technique would be impaired as body balancing could turn out to be virtually impossible.

   Plus obviously it would be less comfortable and standing on the pedals would require almost superhuman agility. (well, maybe not, but still it would do more harm than good)

So as you can see there are quite a few issues which are hard to overcome, and definitely hardly worth the effort. A more reasonable way to reduce drag and improve muscle efficiency is to use a recumbent or semi-recumbent bike, where it's easier to incorporate direct drive. In such a concept pedals are attached to the front wheel and you can see this employed in designs by Thomas Kretschmer.

Answer 3

Do not worry about riding stability in pedaling-in-rear-wheel-designs! ¤ as long the hands are placed on the front - so do that as a rule.

And my "pedal-gear-crank-hub in-rear-wheel bicycle" offers several riding positions: on the same cycle; from the upright "uni-cycle" to the low racing posture; even on a very short bike - as shown below, enjoy

So, the rider decides how much weight to put on the rear. In mud or heavy snow you would like load on the driving wheel !

I have years of good experience from riding on several of my Pendal Bike designs. Please commend and comment. Enjoy your ride, Jens Mindegaard