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Friday, September 4, 2009

26" wheel experiment

I've been planning to move the cargo boxes up to be level with the top of the tire, and get rid of the slanted rack, for a while now. Partly it would have been to make the top of it one single level surface I could put cargo all the way across, and part of it to raise up the boxes so that tight turns doesn't scrape them on the pavement, or high curbs catch the bottom panel when I have to get in the gutter from agressive traffic and/or poor road edge conditions. Kept putting it off because something was nagging me about it.

Turns out it's because the cargo pod with the lockable top would then either have to be moved back about 8", putting *all* of it behind the rear axle, or else I'd have to rebuild the top of it so it's hinged at the inside edge (nearer the tire) and locked at the outside. That'd require adding a lip reinforcement to the top edge of the current hinge side panel, so the lock would have something to hold against. Since it works the way it is now, and I have a lot of other things on my mind at the moment, I decided to leave it the way it is, since I'm also doing another experiment that will affect the most important problem, of the scraping.


I had to take them off anyway, to do this other experiment, so I took a few pics in the process.

Currently they just bolt on with four 1/4" bolts, two thru the top square-tube rail, and two thru the old rackmount rail on the bottom. On the left side it bolts right up to the face of the rails, and the right box has about 1" of spacers at the bottom so it will clear the derailer's full swing during shifting.

I did also remove the twisted remains of the fender support, which you can see just above the bottom rail in this pic. I had not done so in the months up to now because it required taking the pods off, and I had no other reason to do that yet. It's very light, and wasn't in the way, so I didn't bother.


The other experiment was to try a 26" wheel on the back instead of the 24", for several reasons.

First, because I only have road style tires for 26". All the 24" are MTB knobby types, though the gray wheelchair ones are less so in the center than most of them, and the Schwinn tire you see in the pics above is continuous all around the center band for 1/8" wide--not the full surface, but it's better than the knobbies. Still, with any of them I can feel the vibration from the tires even on smooth pavement.

Second, because I would like to see how much difference the extra diameter makes to the ride quality over dips and bumps, because on the 24" they're pretty bad, and it's not quite that bad on my 26" upright, even without the spring-seatpost. Also the extra air in the tire from it's larger circumference may make some difference; I'm not really sure.

Third, if I use the rear wheel off my upright bike, it's got a freehub instead of freewheel, and that means it's a LOT quieter, and based on test-stand spindown tests, it's also less friction than any of the freewheels I had then (one of them same as the one that's on the bike now). Still 7 rings, but slightly smaller numbers of teeth on each one, ranging from 27T down to 11T.

(BTW, on a previous post I'd said my current rear cassette was 28T down to 11T; it's actually 28T down to 14T--I was apparently remembering the freehub's cassette's smallest ring).

Due to the larger diameter of the wheel, I don't think it'll end up any faster because of the smaller rings, but it should essentially compensate for the larger diameter, if I am thinking correctly. (no, I didn't do the math; I'm going to test it anyway....)

I could lace the freehub into a 24" rim to test it, but I'd rather do all the things at once because it's a very simple wheel changeout this way, and it's already trued and whatnot, with the tire, tube, etc., all already on it.

The one big drawback is it's an aluminum rim, and about 1/4" narrower rim than the current steel 24" one I'm using. Long term that might not be good for it with the load this bike must carry.


Actually changing it was more difficult than planned, because this freehub uses a hollow axle and quickrelease spar. The lower cargo rails bolt to the dropout in such a way that while there's plenty of room for the solid axle ends and nuts/washers, there isn't enough room for the flip-handle end of the quick release. I had to notch the cargo rail to clear it, and unless I take a big chunk out, there is not enough room to fully open the release, so I can't take the wheel off without taking the rightside cargo pod off, then unbolting the rail, too.

I also changed out the derailer from the heavy steel old and heavily-used-in-testing SIS unit for the aluminum Suntour unit from Mark's old bike, which already donated it's smaller front chainring to the pedal freewheel (once that's completed). It's a nice design, allowing one to remove the chain from between the idler/jockey wheels without unbolting anything. Each half of the outer cage is independent on the right side, with a gap for the chain to go thru.

Since it had come from a non-indexed 10-speed, with only 5 chainrings to shift between, I wasn't sure it would work with a 7-ring unit and indexed shifter, but it does, once adjusted for high/low gear positions and tension adjusted.


I'd like to change the front wheel, too, but I'd have to pull the shock fork off my upright bike to do it, since this one is only 24" max, and the 26" would not even fit under the brakemount crossbar.


I took the rear rack off too, which forced me to finally bolt it to the back of the cargo pods.

Makes for a slightly less wiggly rear end, too, since it's bolted across the tops of them, keeping them from wiggling independently laterally for any reason, and much less likely to wiggle together (more damping).

While I was at it, I bolted the turn signals as far out as they'll go without sticking out past the edges or tops of the pods.

Another bit I did since I didn't need it to hold the front of the rack anymore was to move the seat top crossbar up and forward, so it becomes my shoulder rest. I have a tubular snap on pad from the top tube of a kid's BMX bike to put on there to actually rest my shoulders on, but hadn't run across it yet when I took the pics.

I also noted that while I still have the seat held on with radiator hose clamps, it's still as tightly affixed as the day I did it, and I had totally forgotten that I had intended to go back and drill bolt holes in the rails and seat bottom crossbars to bolt them together, once I'd worked out the ideal position for the seat. I guess the seat must already be ideal for me, since I didn't notice and forgot about ever adjusting anything. ;-)


Here's another great vid, nice and long with only about 5 seconds of relevant info, about 15 seconds in or so. :-)
video
You can stop it after that, or watch if you're really bored.

This time I was smart enough to start on the street, rather than leap off the driveway again like last time. It's testing the acceleration from dead stop using the 27T ring on the new rear cassette, plus the 42T ring on the front cassette, at full throttle. Normally I would change gears as it speeds up, but here I just let it go to see how it reacted, partly because at the instant I started, a car decided to come around the corner I'm facing, much closer to my side of the street than the one it should have been on. You see it parking later in the video.

Acceleration is pretty good, for the gear it's in with no shifting up, and no pedalling.

2 comments:

  1. I've ordered some USB speakers which might make video watching more feasible, so long as my DSL lite service works out.

    ReplyDelete
  2. There's usually not much of interest sound-wise n my vids. I try to do a voiceover of what's happening, but I can't do that for the ones that show me riding.

    ReplyDelete

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