ekrekeler

Hi, I'm fairly new to mountain biking, but I just got my second mountain bike and I am eager to try it out. However, I noticed that the largest sprocket by the pedals on my old bike is larger than the largest sprocket on my new bike. So I would like to change out just the sprockets by the pedals, preferably without the cranks, to give my new bike a little more speed. I've already taken measurements and I have decided that the old sprockets will still work with the shifter on the new bike, if I raise it half an inch up.

The only problem is that I can't figure out how to get the sprockets off either bike, let alone the cranks. Both of the bikes have a bolt fastened to the shaft of the cranks that are hidden by a cap, so I figured that the configuration of these cranks and sprockets are common in mountain bikes. I removed the bolts from both sides of the shaft, but I still couldn't get the cranks off. Am I missing something here? Do I need some special tool to remove the sprockets?

Here is an image of my old bike:


The new bike is no different, except that the largest sprocket is an inch smaller in diameter.
Please ask if any more information is needed to help.

HillRider

Once the bolts or nuts are removed you need a specific puller to remove the crank arms from the spindle. However, the crank you show has the chainrings (aka the "sprockets") riveted to the spider arms and they can't be removed or replaced.

Bill Kapaun

One bike may have smaller rings, but did you compare the cogs in back? They may be smaller also, resulting in a similar gear ratio.

FBinNY 

On the crank in the photo, the chainrings (sprockets) seem to be riveted to the crank arm. So the only option is to remove the entire crank which is easy enough with a crank remover. (search for a tutorial "removing cotterless cranks" and find one relating to square taper cranks).

You'll have to do the same with the old bike, but unfortunately have no assurance that the cranks will swap over and fit right. OTOH you have very little to lose trying. Good luck.

dsbrantjr

"give my new bike a little more speed" As Bill K mentions, the gearing may or may not be higher on your old bike, it is the product of both the front chain ring size and the rear cogs.

Higher gearing does not equate to "more speed" unless you have the power to accomplish this. Having a bike which is geared unnecessarily high can be hard on your knees. Unless you are "spinning out" in the highest gears of your new bike you likely won't be able to go any faster with bigger gears.

Learning to spin faster will cause less wear and tear on your legs and be better for your cardiovascular fitness.

onespeedbiker

There is the possibility that the two cranks might be similar enough that you could switch them; the only way know for sure is to do the switch and see if it works.

dabac

+1

Unless you can give evidence that you actually are limited by the equipment, which for a standard configured MTB would be doing considerable riding around / above 25 MPH/40 KMH there's little to nothing to be gained by higher gears.

Kimmo 

+1 waste of time.

Learn to spin like a pro instead of mashing like a noob, and you won't have a lot of use for the big ring.

It's way more efficient around 90rpm. One gearing change worth making to most MTBs (that don't get ridden up mountains) is a road cassette; eliminating the huge gaps between gears allows you to stay in your powerband.

But even more important than that is riding position; if the seat is too low and the bars too high you're throwing away speed by the bucketload.

Slick tyres help too. But it'll still be slower than a proper road bike.

If you want to go fast and you're under 90kg, you shouldn't be riding a MTB.

ekrekeler

Thanks for all the feedback given, everyone. I have ridden both bikes and compared the speeds that I can achieve on both, and found that I am able to travel faster with my old bike (over the distance of five miles). The only reason I bought a mountain bike is because I like to ride some dirt trails nearby my residence, otherwise I would have gotten a road bike for all the city commuting that I do. Also, the cogs on the rear of the bikes are the same sizes. I'm going to miss the extra speed on the old bike, but many of you have advised against changing out the sprockets, and I don't have the tools necessary for removing the cranks. So I will just have to deal. Other than all that, I really dig my new bike!!!

fietsbob

Shown, fixing crank on, looks like a nut fixed onto a solid spindle. part of the lowest price point component choices,
to make a bike sell at a pretty low cost.

Yea just ride it as is and have a good time in the woods.
next bike can be different , by then you will know more about your needs ..

cny-bikeman

If the first bike is a road bike and the 2nd a mountain bike that is likely the difference, rather than the gearing. A mountain bike typically has heavier wheels with lugged tread that is much slower on pavement than the higher pressure smooth road tires. It it simply not possible for higher gears alone to produce more speed.

sreten

Hi,

Just put road tyres on your old MTB and you are good to go.

You can't just swap the chain rings and with the above you
wouldn't want to, the road / commuter wants the bigger ring.

(Nevermind issues like the FD's not matching the rings.)

Your old "hybrid" will be lot faster on the roads than your new
MTB which with different tyres will dust the old bike off road.

(And with good road tyres a lot faster than it ever was.)

rgds, sreten.

Two bikes is good, share the wear, each one less compromised.

Kimmo 

I'd be amazed if the reason you can't go as fast on the new bike is really gearing.

Are you hitting 45-50km/h?

Try searching google for "pedalling technique".