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Monday, September 21, 2009

Road Tires and Rolling Resistance.

A friend found All Electronics in California had some salvage NOS 24" road slick tires (ex-Currie Izip chopper front tires) for only $5...but couldn't take them on the plane. However, I checked with AE and they will ship them for a reasonable cost, so I skimped on a bunch of things on my last grocery run and ordered four, since it's unlikely I'll run across this kind of deal anytime soon, and I do need better rolling resistance tires, with a smoother tread. Of course, now I'll have a dozen comments from blog readers telling me about much better deals. ;-)

I figured four since then I have one pair plus two spares, or if I later use all three on a trike I have one spare. I can't afford any more than that.

Hopefully they'll ship them Monday, and be here within the week, if I'm lucky. Then I can test speed vs current compared to the tires I already have, as well as a coastdown test to see what difference they make in just plain rolling resistance.

I'll test first the already-mounted rear 26" with road-type tire, and front 24" MTB-style wheelchair tire. Next, the same front tire with the old 24" Schwinn-marked tire that is a cross between MTB and road; still knobbly but not nearly so much as the front one is. Then I'll pull both tires off and replace with the new smoother ones.

The coastdown test will be done hopefully somewhere with no traffic at the time, so I can concentrate on a stopwatch and the spedometer and the start point on the road, without worrying much about anyone suddenly being in my path or they in mine. Basically I'd just mark a point on the road at which to turn off the motor and coast down to a stop (or actually, down to a known speed, around 9mph in my case being the slowest it's really stable at), from a specific known speed (20mph, giving me the longest coast test, if I can).

I can't do the traditional coast to a stop because the bike is not self-stable at lower speeds than that, and I'd have to keep either wobbling and weaving to stay up, and then at some point start touching the ground with my feet to balance, which will all be significantly different each time I do it, and affect the run's results too much. So I just have to make a cutoff point in speed, and stop the timer there.

Repeat the test a few times with each tire set, and average the times, to help account for changing wind conditions.

This will also tell me something about the bike's aerodynamics (which are pretty awful, I'm sure), for later comparisons as I add fairing bits.

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