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Tuesday, September 8, 2009

Whiny Wheels

Right at the moment, CrazyBike2 is undergoing a mutation with the 26" rear wheel tests. This is going much better using a wider steel rim with a regular 7-ring freewheel cassette than it did with the narrow aluminum one that bent.

Speaking of that, here's some pics of that rim. It's more obvious that it's bent without the tire on it.

I have it stacked on top of the rim I am going to use to replace it, once I get the freehub relaced into it.

Yeah, it's pretty bad. I'm surprised I couldn't really feel it that much while riding--it looks like I ought've been going THUMPETY THUMP down the road, but it didn't.

A side by side shot shows the rim i will be using is not quite twice as wide as the one that bent:

I'm hoping the extra width will also allow the tire to better support the bike, giving it more room for air inside the tube, and better side-loading resistance during turns, against the weight of the bike. Also when it's parked, since it rests on the bottom edge of one cargo pod, tilted to one side, plus the tires, it side-loads the wheel then, too, though it's static rather than dynamic.

I don't have it laced up yet, so I'm using one of the rims off the old Kensington "spare" upright bike, which I've been kind of parting out for some of my experiments and repairs to both this bike and the Columbia upright, my main "spare" bike (which is still short a rear wheel till I lace one up for it, since the bent one was from that, though I can in a pinch put the original first wheel it had back on, which has some truing problems I need to fix).

It's not as wide a rim as the one above, but it's close, and it's also steel. It has a regular thread-on freewheel hub, so I put the 7-ring cluster from the 24" wheel on to it, and back on the CrazyBike2. You can see it a little in the pics below (about the derailer). I've ridden about 10 miles on it now, and it works as well or better than the aluminum one that bent, and the current draw (and road speed per ring) is lower than it was with the freehub with the lower tooth count on each ring.

The tire I used is narrower and rounder than the Kenda Kross road tire I had been using on the bent rim, mostly because the chainstays are not far enough apart for that tire to not rub a little, even on a non-bent rim. I used the only other road tire I have, which is the "spare" for the upright DayGlo Avenger's front tire, a Cheng-Shin with a more car-like tread, which appears designed around a wet road environment (but is still smoother by far than any of the 24" tires I have).

I can still reach 20MPH on the next to highest gear, and haven't tried to see what the max is on the very highest, but I suspect around 22MPH, on motor alone. I don't intend to use that speed for anything other than emergency "passing gear" in case of a situation in which going faster is a better solution than braking, which does not happen very often, but on occasion has been something I would like to have had (would have saved me lots of panic).

Plus it would probably suck about 25-30A doing that, and kill the 17Ah batteries in only a few minutes.

The point of the bike is not speed, but rather range and ease of riding, as well as comfort and cargo capacity, all in roughly equal parts.

Now, I mentiond that the Cheng Shin tire is narrower than the Kenda Kross, but since I put it on the wider rim, it "balloons" out more because the bead is spread wider. Effectively, it is almost as wide as the Kenda, but not in the same place, so it's not as bad a problem.

So, until I get the chainstays spread a tiny bit more where the tire passes between them at the front, the little ridges (where whitewall would be on some tires) around it's sidewall rub ever so slightly on the chainstay tubes, just enough to cause a really interesting "robotic motor" whine while I'm at speed going down the road. It's such a high pitch it gets dogs looking around, but people can hear it too, for at least a couple hundred yards.

It sounds so strange, it grabs their attention. Not loud, but definitely an ear-catcher. Wish I had a quick way to record it, but it isn't picked up right by my camera. Gotta dig out the old recording studio stuff for the computer and set it up, before I fix the problem, because it is such an odd sound.

Funny that it would sound so much like a really high speed servo motor/gearbox, because the actual motor/gearbox is nearly silent!

Since I forgot to take pics of the "new" derailer, here's the one I'm using now:

You can see the gap between the top and bottom derailer wheel cages that lets one simply drop the chain right in there. I don't understand why they're not *all* made like that, because it is MUCH easier to deal with, and makes even pulling the wheel off to change a tire easy. Just lift the chain out, and now you don't have to deal with the derailer's spring tension pulling the chain taut while you're trying to pull the wheel out or put it in!

A clearer but more distant shot, above.

Another pic I forgot to take before, of the battery strapping:

It looks stupid, but it works fine until I get something better. Maybe someone will submit it to "ThereIFixedIt". ;-)

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