Road Crankset/MTB cassette, derailer
 

I'm in the process of replacing parts on my stiff fork/hardtail mtb commuter, and one of the important ones im replacing is the crankset; however, most mtb chainrings only have 42 teeth, I'm used to the current 52 my bike has, so would a road crankset be compatible with a mtb rear derailer, shifters and cassette? (These are going to be alivio 8speed when replaced)

It's going to be all MTB components in the rear right? You should be fine. You can usually mix road and MTB parts in the rear as long as you stay within the limits of the derailleur as far as max cog size goes and use the proper cage length.

Front dérailleurs are road or MTB specific with Shimano. You can't mix road shifters with MTB derailleurs. Derailleurs are also optimized for certain ring sizes and are designed specifically for doubles or triples. If your current derailleur was intended for a max ring size of 42, it may not work so good with a 52.

You could probably get away with a 48 tooth with a Front Derailleur that was shifting a 42 but it is touch and go much bigger as tjspeil pointed out. It may work but you will be havign a lot of issues with the chain dragging the FD with certain gear combination's.

I found that a 26/36/48 is a pretty usable crank set up on my bikes but I am running 700 wheels.

Honestly the best thing I ever did for my commute was quit trying to make a road bike out of my Mountain bike and got a touring bike.

What do you mean by that?

What I mean by that ^ is- I'm using an old Stumpjumper and/or an old High Sierra to make the ride in.

I've got Panaracer Paselas on the Stumpjumper- and I'm looking to get some "cruiser" type bars and something like a sprung B67 saddle for it.

I'm looking to get something similar to those tires on the High Sierra and a different saddle on there...

Are those bad ideas?

Boils down to the right tool for the job.

I have done what you are doing and ended up on a road bike like most commuters. The exception is if you do a lot of urban commuting on poor road surfaces. The Mountain makes a good winter bike I will give them that but summer if you have a moderately long commute (3+ miles of road) a road bike will leave you in the dust.


Let me ask you this:
Is your commute going to have you off pavement regularly or on rough roads? If so then go for it. It is a better option.

My comute is all street and as such I rapidly found that while I LOVE my M400 it had limitations. The 42/32/22 crank sets were great for the hills but I was always spinning out like you are finding.
Spinning 1.95 tires takes a LOT of extra effort even with a road biased tires. The difference between a 550gram tire and a 350 gram tire is a lot more then you would think.

Then we get into hand positions. I went from straight bars to riser bars to trekking bars trying to get my wrists to keep from hurting even after 5-6 miles. None of them could over come the gemotery of the bike.

A mountain bike starts by raising the bottom bracket for better ground clearance. That is a major Geometry change that is always a negative to street riding. I am a little over 6ft and my M400 is a XL (22inch) frame. To get the correct street riding postion to maximize my efficiency I ended up having a HUGE amount of seat post out. My Mountains seat height is close to three inches higher then my road bikes. because of the BB and seat tub angles.

Now I am at the extreme and if you are say around 5' 8-10" you may run into less problems then I did. Mountain bikes size smaller to give you stand over clearance on uneven terrain.
The older the Stump jumper the closer the geometry is to a Touring bike so this may become a mute point if you are running a early 90's model. So by ridding as tall as you can with a couple fingers of clearence between the top tube and your pubic bone you may not run into the same problems.

Here are the advantages of a road bike over a mountain when both used on the road.

Lower BB= lower Center of gravity.
Lower BB and drop bar= lower wind drag.
Drop bars= more hand positions to elevate wrist and hand discomfort.
Drop bars= Better aerodynamics.
Lighter thinner tires= less effort to sustain a given speed.

Here is what my M400 looked like after it got the Trekking bars. Notice how high the seat is?

http://www.bikeforums.net/attachment...4&d=1223229256