Hey I am Nicholas Hardisty from CHS and I built a car last year along with my team, so this year I wanted to try something different. I was wondering if any one has tried doing a multi gearing system like a bicycle or an automatic car? If so what did you find that worked or did not work? If you havent I would still like to know what you think.
We have used internal hub gears with some success. These are use on bikes like Bike Friday brand and others. You can get them with spoke patterns to lace up with a 20" BMX rim and I'm sure a 16" as well. You just have to be sure never to shift under ANY power. The 3 speed ones were fairly useless as the three rear ratios were too far apart in ratio to be of much use. We had a couple of 7 speeds that some students got donated a few years back (~$250 each) and by using 3rd, 4th, and 5th as the low, normal and high speed they worked fairly well. There is a little loss of efficiency with them but on a course like Hood River, LCC, etc. where there is a large hill they can be helpful. 3rd up the hill, 5th down the hill and 4th for most of the flats. On most courses that are flat we found that you were better off with a single speed since most of the race was at about the same speed and the little gained getting up to speed at the beginning and again when getting around slow traffic was lost to less efficiency in the internal hub.
We have tried a couple of external shifting systems like a 10 speed and found them to not work. If you use a bike system, the ones we and any other team I have ever seen has had mechanical breakdowns before the end of the first race. The eTek motors put out about 2 to 3 hp during the race and our legs put out less than 1/4 hp and the extra force trashes the de-railers as well as the lighter bike chain. There may be a high end racing bike system that would work but not that I am aware of.
Kirk Swaney had a system he tried that had a friction cone directly on the eTek motor and the cone was pressed against the rear wheel and it transfered power by friction to the the back wheel. The whole motor was on a mounting system so that it was adjustable from inside the ****pit so he could change the 'gearing' as he traveled. Again he found there was a drop in efficiency over a single speed system. There was also problems when the track was wet and the tire got slick.
I built a car some years ago with a 6-speed derailleur in it. I actually used the entire rear half of a 20" 6-speed bicycle. I found three problems with it. First, I ended up using low (1st) gear over 90% of the time which made those other gears pretty useless. Second, I was using the pedal crank assembly (without the pedals) as a jackshaft. I drove the jackshaft with #35 chain and a huge sprocket to get the gear ratio low enough. Then the stock bicycle chain was used to connect the rear wheel and derailleur; the bicycle chain was only good for two races and then had to be replaced. They can't stand the strain and will stretch and then will not stay on the sprockets making the car unreliable. Also, the jackshaft arrangement costs a lot of power efficiency. Third, the whole conglomeration also added several pounds of unwanted weight to the car.
The folks I eventually sold it to cut all the bicycle frame out and rebuilt the car without all that extra junk. I build all my cars now with a single speed system - light weight and efficient.
