Bicycle Mechanics - Total newb riding 17.5" frame mountain bike - need some direction
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02-27-08, 10:52 AM
02-27-08, 11:19 AM
As for gearing, the rear derailleur is much smoother than the front, so if you start knocking off sprockets, I'd remove a couple front chainrings before downsizing to one rear cog. In your current setup, you'd only need a bigger chainring if you're consistently spinning out in your highest gear (largest front, smallest back). If your chainrings are removeable and there's adequate frame clearance you could put the largest one in the middle position and lose the rest (you'd need shorter bolts by the way).
02-27-08, 12:22 PM
Your gears may shift more easily if you relieve pressure on the pedals as the shifter mechanism is working. Another common newbie problem is using a gear that is too high and pushing the pedals really hard and slow. Experienced riders like to spin freely at about 80 revs/min at lower gears.
Your gears are quite low: in terms of Gear Inches (bikespeak for taking into account your small wheels) they range from 16" to 84".
A typical commuter bike may range from about 28" to 103"
If you want to alter the transmission, think about fitting a chainring with more teeth to make a bigger gear.
Note that there are several different types of 24" tyre for different sized rims, eg kids MTB, adults folding bike, recumbent style front wheel.
There is probably a more specific ETRO designation for the diameter on the tyre sidewall that looks something like:
507, 520, 540 or 547
This will help narrow down your tyre selection and avoid misfits.
The width (1.5 , 1.7 etc) can be varied without much harm, narrower will be lighter and a bit quicker, wider gives a smoother ride.
02-27-08, 02:48 PM
In one site: http://www.sheldonbrown.com
The late Sheldon Brown will be able to help you find most of the info you need. For gearing, check out this: http://sheldonbrown.com/gears/ I find "MPH @ 80 RPM" (or whatever RPM) to be the most useful. You have to input your tire size and the number of teeth of your sprockets. For the chainrings, you can just count them. For the cogs, I would count the biggest one and the smallest one, then try to find the correct freewheel/cassette based on the number of individual cogs and the sizes.
On my triple-chairing bikes, I find that I can keep the chain on the middle chainring most of the time and be able to use all of the rear cogs. The outer ring is only really for the last couple/few cogs and the inner ring is for the first couple/few. If you use that online gear calculator, you'll find that you don't really have "21" "24" gears or whatever, as the inner ring and outer ring practically duplicate what the middle ring could do with most of the cogs. Besides, you don't want to be cross-chaining anyway.
Oh and if you need definitions for any terms, Sheldon's site has a great glossary. Welcome back to biking.
Joshua A.C. New
02-27-08, 05:18 PM
Hi, Nathan! Welcome to a world of awesome.
A couple of comments:
Yes. Sheldon Brown knows everything. He died a couple of weeks ago, but he left us decades of distilled knowledge on his site.
Figuring out your gearing is easy, even without the calculator Jive Turkey sent you to (which is useful; don't get me wrong). All you have to do is count the teeth on your chain wheel (it'll probably be 46 or so on the big one, which is the one you want to use) and something like 13 on the small one in the back. The ratio of those will give you your top gear. Then count the teeth on the big gear in the back. The ratio of the big front ring to the big back ring will tell you your low gear. If you want to climb hills more easily, you probably need a lower (that is, larger) large rear sprocket. If you want to have a higher top speed, you probably want a higher (that is, smaller) small rear sprocket.
"Speed" can mean a lot of things. It could mean "acceleration", and the issue might be that you're shifting up too soon, which means you can't get pedaling very fast. Your only tachometer is your own nerve endings (unless you get a fairly fancy computer, and I wouldn't). It could also mean that you find yourself pedaling uncomfortably fast to get up to the speed you want. If the former is the case, you just need to pedal faster in lower gears, then shift when you redline your legs. "Speed" could also be a factor of efficiency. See "tires" below.
I usually (http://velospace.org/user/5834) run one big chain ring in the front and an appropriate but limited selection of gears in the back. I find that seven speeds gets me around very nicely where I live. Also, leaving three gears in the front means that you need something to take up the chain slack when you go to a smaller chainring, which means having a tensioner, and the easiest tensioner to get ahold of is your rear derailleur...
I'm glad you're thinking about tires. They make a huge difference. Unless you're hitting dirt and snow, you really don't need tread at all; it just slows you down. The whirring sound you hear when you ride is your lunch turning into sound instead of forward motion. A quick rummage around the Internet yielded these (http://www.konasports.com/index.asp?PageAction=VIEWPROD&ProdID=172775) tires. The grooves are fundamentally for looks. Somewhere on Sheldon's site is an article about hydroplaning, and if I recall, a road bike would have to be going 130 MPH to hydroplane. So that's not an issue.
As for where to get stuff, well, that's always a challenge. If you live near a university, there's almost certainly a good bike shop nearby. The question is if they're going to sneer you out the door. For some reason, a lot of bike shop guys think that their job is to show disdain for your bike. So ask around, find someone friendly and knowledgeable, and keep going there. Ordering stuff online is OK, but they can't give advice or give you used parts for ten bucks because it's what you needed. Plus, you don't pay for shipping and you'll get the stuff just as fast.
If you take some pictures of your bike, particularly the right (drive) side, we might be able to point out the stuff you need to pay attention to.
02-27-08, 09:45 PM
26" wheels with 1.25" tires on them are actually 24.5" dia, as the 26" size assumes that 2" high tires are mounted. These skinnier tires will roll easier. There are plenty of quality used 26" wheel bikes available from the early 90s with rigid forks. These will probably have more teeth on the biggest chainring, which will give you more top speed. The chain doesnt like running at an angle, so its best to use the biggest chainring with the smallest cogs, and the smallest chainring with the bigest cogs.
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