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| Photo From Here |
I stumbled across this photo and was surprised to see the little train. Regular readers may recall I came across one similar to this at the Hunnert Car Pileup back in 2009 and decided I should make one for the grandson.
Here it is just before the finish paint job and final assembly.
And here it is all done up sitting next to the pond sailer I made for the other grandson. I might not be the best at any one thing, but you have to admit I'm versatile.
Now for some math. Please keep in mind I learned math before Common Core so I'm at a big disadvantage here.
The Sportster has a 23 tooth countershaft sprocket and a 51 tooth rear sprocket now. Depending on the year, stock is either a 20T or 21T. The 23T will give less acceleration but lower RPMs at cruising speed and a higher top speed.
For a 20T@ 6200rpm: MPH = rpm x effective real wheel radius / overall drive ratio x 168 = 107.7mph
For a 23T@6200rpm: MPH = 123mph
For a 20T: RPM@60mph = 3454rpm
For a 23T: RPM@60mph = 3005rpm
With only about 2 useable gallons in the little peanut tank, if I ride this thing to work I'll have to fill up pert near every time I leave the house. Definitely not going to be the touring rig. None of the roads on the way to work have a speed limit above 55 and I see no reason to concern myself with a difference in top speed between 107 and 123. The difference in revs at 60 miles per hour can be substantial, however, depending on where that falls on the power curve. With a motor known for lots of torque, probably won't be an issue here. Need to pass a car? Just twist it up and drive around. The old drag racer in me likes the idea of quicker acceleration, however. In fact, you can go as low as a 19 tooth sprocket.
Alright then, what's the point of all this you ask? Just wondering if it would be worth the expense to swap out to a smaller sprocket or just get it running with what I've got and see how I like it. By doing the math I'm at least able to make an informed decision. And that's why you pay attention in high school.
3 comments:
I would ride it first to see how it torques out, but I'm betting you'll end up with at least a 21.
That current setup seems to me pretty luggy on the low end. But again, that first ride will tell the tale.
For what it's worth, I never felt safe on any Sportster over 80-85 mph.
HEY BOB, RICH IS RIGHT AS FAR AS MY EXPERIENCE ON SPORTSTERS AS WELL. AFTER 80 THEY JUST DON'T FEEL SAFE. TO LIGHT OR SOMETHING?
TALK TO YOU SOON,
TVI
A sprocket is only about $25.00 and with a barn full of crap to work on, I think I should just swap it out and be done with it. If I have to order anything else, I'll get a sprocket too.
As far as going over eighty, I'll take the word of both of you guys. I've slowed down a bit over the years and my riding habits are much more conservative than they used to be. Probably best if it stays that way. Besides, it's the 0 - 60 that's the most fun anyway.
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