Noob question: Numeri Uno (#1)

The rear hub for road bikes is designed around a 130mm OLD (over locknut dimension). Mountain bikes are designed around 135mm. That means that a mountain bike wheel doesn't have to be dished quite so much and is consequently stronger. It also means that an unmodified mountain bike hub won't fit easily onto a road bike.

Many mountain bike front hubs have larger diameter axles.

Mountain bike gearing is much lower than road bike gearing.

At the present time, the upper end road bikes use 10-speed rear cassettes. Mountain bike cassettes have only 9-cogs. This makes it possible for mountain bikes to use a wider chain which some riders claim is stronger and/or longer wearing.

Shimano mountain bike rear derailleurs are offered in "Rapid Rise" (low normal) design. this causes them to shift opposite from road bike derailleurs. Some riders find the rapid rise design works better in certain hilly conditions.

All road bike front derailleurs are actuated by a cable that pulls from beneath the bottom bracket. While down pull mountain bike derailleurs are available, most mountain bikes frames are designed for top pull front derailleurs. Mountain bike front derailleurs are also offered in a top swing design in which the derailleur cage is located above the parallogram mechanism.

Thank you very much for your response, it was a big help. But there's one thing I'm still confused about; what do you mean mountain bike deraileurs shift "opposite" of road deraileurs?

Mr. Freeman said:

But there's one thing I'm still confused about; what do you mean mountain bike deraileurs shift "opposite" of road deraileurs?

RD cable pulls you into higher gears, rather than into lower gears as has been the norm for decades. Expressed another way, it means that the big shifter lever will change you to a higher gear rather than a lower gear.

Brakes are different, too. MTB brake calipers tend to have greater leverage and force, as brakes tend to get used a lot more. Leverage on the brake levers is different, too. Mixing MTB calipers and road brake levers can result in overly sensitive brakes.

Same with disc brakes - not really necessary on a road bike, but nice to have on the mtb where mud on them isn't nearly as detrimental as mud on a rim style brake. Disc brakes are becoming popular on road tandems, as they tend to place greater demands on braking than does a single.

Hey, Artemidorus - is that a Trek Y you have? I still have my old Y22. I put on a locking shock with remote lever, and it makes a great combination. Lock it for climbs, unlock for rough downhills and I can leave hardtails behind. There's something about that frame turned out in natural CF that just grabs my eye.

JohnO said:

Hey, Artemidorus - is that a Trek Y you have? I still have my old Y22. I put on a locking shock with remote lever, and it makes a great combination. Lock it for climbs, unlock for rough downhills and I can leave hardtails behind. There's something about that frame turned out in natural CF that just grabs my eye.

JohnO, that's a '96 Y22. Was in worse shape than I had hoped when bought on ebay. Had to replace most components, but still ended up much cheaper than an equivalently spec'ed modern full sus. bike. I use a stable platform rear shock (a Swinger 3-way), which works really well, rather than a lock-out shock. It's a very pretty bike with the unpainted carbon. Draws many more admiring comments than my friends' Fuels/Trances/whatever, much to their chagrin.
(My avatar is actually the ebay photo, as I haven't any other pictures of it!)