Getting a new gear cassette
 

Hi, is it a structurally sound thing to do to replace my bicycle's rear gear cassette with a physically smaller one so I can pedal faster? Or would I risk collapsing some structures on the bicycle? If this is ok, what tools would I need and how do I go about picking a cassette from the myriad of brands?

thanks for your help!

garcon, If you use a cassette that is compatible with your brand and number of gears, then possibly. It may depend on how great the difference is between the new and old cassettes (which can effect other parts).

Let us know what you presently have, both front and rear and what you want to use.

Brad

A bike with smaller cogs will not help you pedal faster, probably just the opposite.

Well, there are a bunch of things that has to be compatible, but apart from that, switching cassettes are done all the time.

If you want to pump your legs faster, you'll want a bigger cassette(more teeth on each sprocket), not a smaller one. If you want to go faster, look at the engine and the rest of the set up first.(tires, riding position...)
Most bikes will happily let a decently fit rider hit 25 MPH / 40 KMH without any tweaks to the gearing. Are you really going that fast? for extended times? frequently?

if it's a compatible part, and you do the job right - no.

No way to tell w/o knowing a lot more about what's on the bike today.

I have one of those generic "Bolt" Walmart bicycles; I don't really know what choices I have as far as gear cassettes?


- The tires are inflated to 35 PSI; they are both kevlar banded tires
- it is a mountain bike
- the seat is a slight bit higher than my waist level when I stand up next to the bicycle
- the chain is well oiled
- I think the derailleur is a lower end Shimano brand

PS I always thought it was the ratio between the front gear and the rear gear that determined the revolutions per minute you can pedal?

I know the buses on my campus have a speed limit of 20-25 MPH; even if I pedal with all my might I cannot catch up to them (there comes a point where I am feeling the gears turn as fast as possible and even if I pedal faster the bike doesn't go much faster)

the only time where I know I can go up to 30 MPH is going down a steep hill; at this point even if I pedal really really fast there is not too much change to the bicycle speed.

thanks for your help

Google don't seem to be able to locate a "Bolt wal mart bicycle" so it's pretty much guesswork from here. Odds are that you have a something called a freewheel on the back. These are pretty much all interchangeable, so you should be able to pick just about anyone with the same number of speeds.
Question is, why?
I repeat:Most bikes will happily let a decently fit rider hit 25 MPH / 40 KMH without any tweaks to the gearing. Are you really going that fast? for extended times? frequently?

Your fitness and physiology determine how fast you can pedal and how much force you can exert on them. The gearing then allows the bike to go as fast as you can apply that rotational speed and force.

@ dabac: my bike is similar to the one here http://www.walmart.com/ip/Power-X-Me...cycle/11089998

I have never properly measured my speed but I would say it's usually around 15 mph? The reason I want to go faster is that I am disappointed that my 3 mile commute in the morning takes 15 mins by bicycle, where I have to stop at red lights, slow down for car drivers who don't watch when they take right turns (i.e. stop before every intersection), and generally be hypervigilant. I can take an alternate route that has less intersections but the commute still takes 15 minutes. I don't think I can make 25 MPH for any reasonable stretch of time before meeting an intersection where cars need to turn against my direction of travel.

To do what you want to do you really need a road bike with skinny high pressure tires. On a mountain bike with 35 psi tires you're doing well to make 15 mph. Leave the bike the way it is and start your commute earlier. On pavement keep the tire pressure at the maximum recommended on the side of the tire.

And the sad little thing they post as "specification" isn't much help either. Whyh not try counting the teeth, and we'll know what we are up against?
Meantime let's guess at 22-32-42 front and a 14-28 on the rear.

Wide? knobbly?

Smooth, narrow and pumped harder can help.

Nothing wrong with that, but a cheap MTB is by definition a heavy MTB. Makes a difference when you've got to get it moving.

Doesn't really say a lot. Bikes can be built farther or closer to the ground, and the key measurement is how straight/bent your leg is when you're in the saddle and the pedal at the bottom.

Good start.

From a functionality perspective those are usually perfectly fine.

Again, you have to differ between bike speed over ground, and what the rider is doing.

There's a word for it -cadence - that's how fast the rider is turning the pedals. These days the stock recommendation is that you should aim between 80-100 turns/ minute. If you can't crank at that pace, you're probably using a too heavy gear, which increase the risk of knee troubles.

So first you find out "how hard can I crank and still keep up the 80-100 turns?" Then you see how much speed that effort will buy you on a certain bike.

Hitting a cadence of 100 is well within reach for most of us, maybe with a little training. Even if you can only make 90, that should still have you going 20+ MPH

That's called spinning out, but unless you have something very special going on with your body, that shouldn't happen until well past 20MPH

Have a look at Sheldon's gear calculator Enter your tooth counts, set it to display MPH at cadence and see what you get.

Most MTB-based bikes would have you spinning out at 30 MPH, you need serious road gearing to keep inputting power at that speed. But outside a race setting, who needs it? I'm quite happy to coast those few seconds out instead.

That's almost running pace. First off - how long have you been riding? If you're brand new to it, you can expect to pick up some speed eventually. But if you're trying to stay below the sweat level there's only so much you can do.

Then there is that bike. A full-sus, probably heavy as you wouldn't believe, with knobbly tires and an upright position. Running pace isn't too bad considering. You should have a rigid bike with skinnier tires and a more hunched over riding position.

Why so low?
This is a bike, not a car.
A 2" wide mtn tire normally has a max pressure rating of ~65PSI.
Check the sidewall for the max pressure of the tire, and just don't exceed it.
If you want to improve road speed, get a slick, semi-slick, or a mtn tire with a continuous center rib.
Examples of the latter are Performance Versatrac, or Nashbar Elevator.