Tell me more ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.
up vote 1 down vote favorite

MTB's cranks usually have a 42 or 44T where as Road bikes range up to 53T.

So far I am under a impression that more tooth, means more speed. Same goes for cassettes, lesser the tooth more the speed.

But, nothing is as it seems, I want to know what are bad things I expect when I take this move? Is it that bad, that it would be simply better to forget about it and move on?

My main intention is to create a super fast MTB, where possible.

Please Note: I am not a expert on crank & cassette

share|improve this question
1  
The higher the gear ratio, the more speed you have. It's the combo between front and rear sprocket -- the larger the tooth ratio between the two, the faster (for a given cadence and wheel diameter). – Daniel R Hicks Apr 24 '12 at 10:57
@DanielRHicks, I am certain... I was trying to mean that, but didn't know the how to put them into sentence like yours :P – Starx Apr 24 '12 at 11:00

1 Answer

up vote 3 down vote

There are several things to consider:

  1. Chain ring clearance to the frame, because a larger tooth count has a larger diameter. Since the chain stay is at an angle, and designed for a certain diameter, too large a ring will come too close to the frame. Anything closer than 5 mm, is not a good idea, since a larger chain ring will also flex more.
  2. Maximum tooth count for front derailleur. A front derailleur is designed to work and shift well with a certain size of ring. There is usually a small range above that which can be used. (i.e. Shimano's 3x XT FD-M785 is designed for a 44t, but can accept up to 48t.)
  3. Cable pull ratio for front shifter/Chainring spacing

There are special shifters designed to allow a road bike drive train to run with a flat bar brake and shifter. But there is no easy and guaranteed way to run a road crank set with a mountain bike drive train, unless you replace all of the drive train parts, and buy road touring flat bar shifters.

It is usually more cost effective to buy a road bike.

share|improve this answer
1  
Can you explain the point no 1? – Starx Apr 24 '12 at 6:35
Also, please review my update, My intention is to create a super fast MTB, where possible – Starx Apr 24 '12 at 6:42
Answer updated. Where possible will be key. Are you riding it off road? It doesn't appear so from the questions you ask. – zenbike♦ Apr 24 '12 at 9:04
Not neccessarily off road, but whenever I approach a smoother terrain, where I could pump for extra speed. I want the extra speed on these cases. – Starx Apr 24 '12 at 9:09
1  
If you must have a moutain bike frame, then Point 1 is the most relivent. You may be able to change the bottom bracket if the frame interfares with the larger chainring, however that will upset the chain alignment to the cluster - defeating the purpose of the exercise. Remember that 53 Road chainrings typically were used with 12 (smallest) on the rear, so a 48/11 combo is, to all practical purposes the same. As far as "more tooth, more speed" (on the chainring) - that assumes you have the brute strength to push it and that you want to regardless of issues like damage to your knees. – mattnz Apr 25 '12 at 6:10
show 3 more comments

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.