MTB Conversion For Lighter Commuting

Question

Just want some opinion. I have a MTB bike, but I want to make it lighter. So here are some of my thoughts currently on what I think I should change:

• 700c rims and tires
• Cantilever brakes
• Rigid fork

The details of the bike are as below:

• Disc brakes
• 26er wheels with road slick
• Suspension fork

Additional details:

• Bike frame weighs 11kg with suspension fork without wheels
• Current wheel set (rim and tire) weigh 2kg
• 7x3 speed
• Flat handlebar

Other related questions:

• Should I change the gearing of the bike into that of a road (7x2 speed)?
• Should the 700c rims able to withstand 10-11kg of frame? (note that the rider is 75kg)
• The rear end of the bike does not seem to have a place to mount cantilever brakes, but has two small holes that can somewhat screw in something on each side the frame. What is it actually for?

Thanks for sharing your opinion and information.

Answer 1

Its not a light bike, even by MTB standards, and will never be a great road bike as it will always be heavy.

Start with the easy and relatively cheap stuff - tires and tubes. Dump excess rolling weight by getting light tires an even going tubeless. The next biggest bang for your $$$ will be replacing the fork. You should be able to pick up a second hand fork for next to nothing - just watch the geometry. If you do this, canti brakes on the front is likely worth doing.

Replacing wheels is probably not worth the effort, you will shave off a few hundred grams (admit-ably rolling weight), but it will cost big money.

Look very hard at the costs of any proposals. My guess is that for what you are proposing, a cheaper option that will give you a better outcome would be to buy a second hand bike that does what you want, rather than trying to make your current bike into something it is not. You may have access to cheap parts, but in that case you probably have access t cheap bikes.

Answer 2

The two holes are probably rack mounts (two silver bolts in the frame right below the arrow for the noodle):

(image from http://sheldonbrown.com/canti-direct.html)

If they're the posts to which the v-brake is actually mounted, chances are a rim brake won't be able to be lined up with a 700c rim anyway (however, if you get a 700c disc wheel, you may able to line up the rotor with the disc). This isn't worth the expense. You'll also probably lose some comfort as well. It is also unlikely a 700c wheel will even fit in the frame anyway, so the swap probably isn't even possible.

Rim brakes are generally lighter than discs, but you require rim brake compatible rims (some rims are disc only), which may be an additional expense. If you do want to cut some weight for this and you have the mounting posts, you can do this with some cheap v brakes (e.g. Avid Single Digit 5's) and your existing levers if your brakes are mechanical discs or new levers if your brakes are hydraulic. You may also like the disc brakes better if your rims are prone to messes (such as road grime in rain, snow, mud, etc.). You will also need new cables as well probably. This is probably more effort than its worth, so I'd stick with discs.

Presumably you have a 3x7 (3 chainrings on the front, and a 7 speed set in the back (probably freewheel in the back)). Swapping in a double or single in the front wont save you much, and you probably cant fit a bigger front chainring anyway like a road double due to chain+derailleur issues. You might be able to get a smaller cog freewheel /cassette (there is an important difference) for the back, but this isn't necessarily useful (see next point).

Replacing with a rigid fork can cut out weight, but even keeping the fork locked out should be fine for commuting on the road. If you want to go faster, chances are you should increase your cadence and use gears more efficiently.

Slick tires are the way to go, but you already have those. Keeping your bike in good condition on slicks is probably the best thing to do along with a rigid fork swap if you have the cash. You can combine this with a v-brake swap to the front at little additional cost (the v-brake and cabling) if you have mechanical discs and the front rim is rim brake compatible.

If you want something faster/lighter, you may want to look at purchasing a hybrid or road bike instead, such as the Trek 7.2 FX. But gains for this sort of stuff should probably come from increasing your fitness and technique. A 11kg hardtail (i.e. no rear suspension) frame is heavy, but should be fine for commuting if you're reasonably in shape.

Answer 3

Don't worry too much about weight. Yes you can buy lighter components but sometimes they're less durable. You'll eventually get fit enough that the weight will be less of an issue.

Regarding the gearing, on my MTB I fitted larger chainrings on the front, 46t, 36t, and 26t (the number of teeth on the large, medium, and small rings respectively). Unfortunately chainrings can be a little pricey and it may work out the same price to just get a whole new crankset. For example the Shimano M590 triple chainset comes with external bottom bracket, hollow crank, and 48.36.26t chainrings, so it saves some weight as well as increased higher gear ratios. If you have a square-taper bottom bracket currently, then the external (or alternatively ISIS or Octalink bottom brackets) will be stiffer and more responsive.

In my experience commuting (on and off over the past year or so) by MTB, the wide gear range of an MTB rear cassette means I can never quite find the right gear and frequently find myself shifting down on the rear and up on the front (or vice-versa). So I have bought a road-cassette with greatly reduced number of teeth on the low gears (ie 26t-11t as opposed to 34t-11t) meaning I am more likely to find the right gear (at least I hope that to be the case as I am yet to fit it).

Lighter components, especially for the drivetrain, either cost more or are less durable.