SOURCE: The chain wants to jump off while trying to change gears
There are several things that could be wrong:
Shifter out of adjustment
Chain worn
Chain and gear(s) worn
Shifter out of adjustment:
Try adjusting the cable tension by turning the barrel (the part between the cable and the shifter). Count the number of turns and reset it to its original position if this doesn't solve it.
Chain worn:
Chains wear out. hold a ruler up to it, with one end centered on a pin. 12" away, another pin should like up very very very close to the 12" mark. If not, it's probably worn out and needs to be replaced. No way around it. Some say chains are good for 500 miles only. Your mileage may vary. (keep reading...)
Chain worn and gear(s) worn:
If the bike has been ridden witha worn chain for a while, it will make the gears in the back wear faster too, and a new chain alone will not work. If this is the case, you need a new chain and new gears in the back. Often, gears in the back are replaced all at once in a 'cassette'. You'll have to make sure your front gears aren't worn out too!
SOURCE: operator manual for huffy crosswind bike grip shift
Look for the manufacturers name and model number on the gripshift and check at www.parktool.com. Look under derailleurs for repair tips which will give you an idea how they work. A twelve speed has six gears on the rear sprocket and two on the crank giving you a combination of twelve speeds. sheldonbrown.com is another good site with good articles and pictures.
SOURCE: trying to reassemble rear wheel gear assembly for
This should help you:http://sheldonbrown.com/gearing/index.html. Also try here:http://www.parktool.com/repair/byregion.asp?catid=4 Hope these sites help. Good explanations and pictures.
Testimonial: "Thankyou, both sites were very helpful. Excellent pictures & directions both. Easy to follow. Another helpful site I found was bicycletutor.com. "
SOURCE: clueless
My $.02...
To expand and maybe simplify the great advice offered by hgpilot...
The smallest cog in the rear and the largest chainring will limit the highest speed the bike can be pedaled. Divide the chainring by the cog (11t). Give some thought to the other (climbing/high torque) end of the problems as rarely do we max out our bike's speed capacity out of necessity but when that monster hill looms we dive deep into the other end of the cassette and smaller chainring because we HAVE to.
All else being equal, when comparing the typical compact crank of 50/36 or with a typical road crank (53/39) there is less of a limitation on the high end (2/50 or -4%) but an appreciable increase in low end torque (3/39 or +7.6%) from the smaller chainrings. A triple chainring can widen that performance envelope at the bottom only (typical 28t).
Cranksets and chainrings are generally a long term commitment. Cassettes are a piece of cake to exchange, or you can stock different wheelsets for even faster adaptability.
You don't say what gear ratio and wheel size you're (presumably) spinning out in with your buds. If you're topping out a road crankset and a 12 cog you're amazingly strong for an apparent novice.
Even a modest but unlikely 48 x12 pushing normal 700c road wheels at 90 rpm cadence would be 4 x 90 x 2.19 meters = 791 meters/min = 47+ kph or 29+mph. If you could maintain THAT forever I want to be right behind you. Higher cadence and a typical large chainring gets you into pro speeds.
Having a closer-spaced cassette might make more sense if you're having trouble matching your cadence to your requirements and keeping up at high speeds. The 11-26 8sp might typically go 11-13-15-17-19-21-23-26. At the high end you have a 2-tooth jump from 13 to 11 for higher speed. That's a 15.3% increase in load for the same speed. Imagine if you got rid of the 26 and had a 12 instead. The jumps in load from 13 to 12 and 12 to 11 would be 7.7% and 8.3%, respectively. Much easier to adapt to when the boyz put the hammer down.
SOURCE: How can I raise handlebars on a 26 in. Mountain
You need an Allen wrench (a.k.a. hex key) to fit the bolt head right in the middle of the handle bars. Loosen this bolt just 2 or 3 turns then tap the head with a soft hammer or block of wood and a hammer. Then pull the handle bar stem up (and all of the way out so you can see how the wedge-shaped nut at the bottom of the stem works). Look for a mark on the stem telling you how high you can safely raise the bars (you have to leave enough of the stem inside the tube so that it will be strong.) Put it back in and tighten it up. If you found this helpful, please vote. Good luck
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