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#11
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MTB speed increase ideas
Leo Lichtman wrote: "bill" wrote: Any sprocket less that 13 teeth is stupid. It wears too fast, and the percentage change in gearing from one to the next is too great for fine-tuning your cadence. The only reason it is acceptable on a road bike is that you are working with a 53 or 54 tooth chainring and so the relative change in ratios are still almost acceptable. (clip) ^^^^^^^^^^^^^^^ Sorry, but the relative change in ratios is not affected by the size of the chainrings. The change from 12 T to 10 T would be 17%. You are right...brain fart. I meant to say that the relative change per tooth is less severe, the larger the number of teeth you have to start with, so 53 vs 52 is lless change than 43 vs 42 etc. |
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#12
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MTB speed increase ideas
3.5 * 26" *3.14*90*60/12/5280 *3600 = 24.35 MPH sorry about the omission. |
#13
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MTB speed increase ideas
Bill Sornson wrote: bill wrote: ... "Spinning out" is not a problem for someone who can spin. I can spin 150 RPM at a road speed of 25 MPH and keep at it for 20 minutes. Clark Kent Baka! LOL Bill, I'd pay money to see you spin 150 RPM for /half/ a minute! (This on the purple girl's Huffy or another marvel of rolling efficiency?) Pay me real money and I'll spin 200RPM for you for 30 seconds. |
#14
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MTB speed increase ideas
Hope you liked the song, at least Yep. |
#15
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#16
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MTB speed increase ideas
bill wrote:
Bill Sornson wrote: bill wrote: ... "Spinning out" is not a problem for someone who can spin. I can spin 150 RPM at a road speed of 25 MPH and keep at it for 20 minutes. Clark Kent Baka! LOL Bill, I'd pay money to see you spin 150 RPM for /half/ a minute! (This on the purple girl's Huffy or another marvel of rolling efficiency?) Pay me real money and I'll spin 200RPM for you for 30 seconds. That rusty hamster wheel in your head doesn't count! eg |
#17
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MTB speed increase ideas
I'm confused then. This "beginner" runs out of gearing doing 25 MPH Something does not compute: The landscape here slopes gently down to sea level, with 15 MPH average tailwinds. When travelling east, you can pick up appreciable speed...and higher gearing is definitely appreciated by the average commuter...why not travel faster if you can? Going in the other direction is a totally different story...staying in the largest chainring can be quite challenging at 90 RPM. One other thing I should have mentioned (and this is changing as of today), my friend is using platform pedals. This probably limits his ability to efficiently spin at a high rate. He was trying 'em out tonight, so we'll see if he reports any improvement. |
#18
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MTB speed increase ideas
Your friend doesn't need new gears. 42/12 is good for 24 mph (39 kph) at your basic 90 rpm cadence. If he can sustain that for any length of time on level ground riding a cheap MTB with knobbies, he should quit his day job and get serious about going pro. Problem is, there's very little in the way of flats around here, and the prevailing winds are in the downhill direction....I personally do about 40-50 km/h on worn knobbies, until I turn around and travel in the opposite direction. Then I'm sure I average under 20 km/h. However, semi-slicks will help a little and there are a variety to choose from. I used Michelin Jet-S for a while, but they are out of production, not to mention pricey and prone to punctures. If he doesn't do any off-road, get a full slick and a narrow one. After the slick tires, getting faster will depend almost entirely on his level of fitness. I'll check with my LBS...but they do tend to charge quite a bit more than mail-order. Cheers, Dave |
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#20
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Bill Sornson wrote:
Sorni, I think this is a different "Bill." Rats. You're right, of course. The "road racing tubulars" should have tipped me off, but that spinning 150 RPM for 20 minutes is just so...BAKA! My apologies, Iron Bill. Hope you liked the song, at least I didn't say I got any useful power at 150 RPM but I can do that cadence for about that time and then I have had it, even at 12 MPH. The cadence itself wears me out. Bill Baka |
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