mtb geometry- trails v. road- Mtbr.com
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  1. #1
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    mtb geometry- trails v. road

    I am thinking about building up an old mtb as a commuter with slick tires. I ride a 17" Monocog with 26" wheels and I am comfortable on that. should i be looking for a mtb about the same size for commuting, or would a larger frame suit me better? i know i ride a 52-54cm road frame, although i don't have a roadie at the moment, and that tt is a lot taller than my mtb size. how different is the geo on an old road bike from a mtb with a similar TT size?

    another question: (probably opening a new can of worms here) would an old roadie with 700c wheels better suit me for pavement only riding? how about a 20" mtb frame with 700c wheels on it? (i can deal with hub spacing issues just fine.)

  2. #2
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    What you are most comfortable with is probably your best choice for commuting. I have learned that the number one priority is reliability. 700c tires make a big difference to make your ride quicker. But the MTB geo makes feels more in control since it is a heads up ride.

  3. #3
    weirdo
    Reputation: rodar y rodar's Avatar
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    When it comes to angles, I`m quite a dunce, but the obvious difference in mtb VS road geometry is in the tube lengths. For the most part, road bikes will have shorter top tubes (look how far ahead of the stem the hand positions are on most peoples` drop bars) and mtbs will have shorter seat tubes (standover is much more important). So a road bike that fits you well will almost always have a lot shorter seat tube than an mtb that fits you.

    As far as the wheel diameter goes, my opinion is that it makes very little difference by itself. Granted, that`s the subject of much debate and plenty of people see that one differently.
    Recalculating....

  4. #4
    Fat-tired Roadie
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    Big can of worms.

    Road bikes are better on the road. That's not quite the same as better on the street, though - I think in a city, it doesn't make as much difference. I use an older road bike as my commuter, but I get a lot of road miles anyway, so I'm pretty comfortable on drop bars. I feel I get quicker handling and a higher cruising speed than I would with a mountain bike. But I still spend a lot of time at stop lights, following slower cyclists, stuck in traffic, etc. So I don't think that the advantages I get from choosing a road bike are very significant over a mountain bike with slicks. A mountain bike has better low-speed stability and is easier to set up with a more upright riding position, both of which can be an advantage in the city despite being irrelevant and/or annoying on a longer road ride.

    Most 26" mountain bikes can clear up to about a 700x28 with no particular problem. It looks a little funky, but whatever. You need to be using disc brakes to make it work without a weird adapter. See the Cannondale Bad Boy as a commercially-available example.

    If I used a mountain bike as my commuter, I wouldn't upsize. I might end up using a longer stem or putting it lower, but it wouldn't be by very much.

    If a frame fits you well with flat bars, it's too big to use with drop bars unless you use a very short stem and/or are a masochist. And vice versa, except with a long stem.

    If you get a mountain bike frame with the same top tube length as your typical road frame, you'll need either a very long stem and a flat bar or a lot of spacers and a drop bar to make it work. It won't handle quite like a road bike - it'll be a little sluggish in turns, and might be a little harder to keep on a good line on a climb. But I don't think it would be particularly bothersome on city streets. Controls are also designed to fit either road or mountain handlebars, which have different diameters, and a road lever pulls a different amount of cable than what a V-brake or disc brake needs to work. People have described varying results with these setups - I think CommuterBoy has standard mountain disc brakes on his drop bar build, and says it works fine.

    You could also get a hybrid. I think they suck, but at least they come out of the box as an upright, flat-bar frame with 700C wheels. Supposedly, there are a few out there with decent frames. There's also the whole flat-bar road bike thing. I think maybe it's the bike companies trying to build hybrids but distance themselves from their crappy reputation. They do seem to have nicer frames and a higher grade of components. (They're still not road bikes, IMO.)
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  5. #5
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    I've done a lot of commuting on mountain bikes, including the 700c Bad Boy, as well as road bikes.

    I don't think wheel diameter matters that much. I would ride the correct frame size, 17" mountain and 54cm road for you, even if you started to switch wheels around.

    What I think does matter is tire width. I ride 23c's on my road bike, and I almost lost the bars when I hit a pothole hard. But my 2.2 inch urban FR tires are a little too much for daily commuting.

    In adequate conditions, I would use a 28c or a 1.5 tire. Smoother road, go narrower; worse roads, go wider.

    Otherwise, while every bike is slightly different, I believe with all my bikes, the secret geometry measurement, front-center, is identical, regardless of tire size.

  6. #6
    Ovaries on the Outside
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    I think that geometry is what you're asking about. There are small differences beyond tt length- wheelbase, HA, fork rake, chaingstay length, just to name a few, that make bikes different.

    I don't think there is a better option- just go with what your needs are. Fenders, fat tires, better stability when loaded? Maybe a mountain bike. Sharper handling, faster... road bike?

  7. #7
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    Road bikes have steeper head tube angle and twitcher handling. A road bike could have a headtube angle of 73 degrees or more. Mountain bikes are slacker as little as 69 on some of the antique stuff and more like 71 or so now.

  8. #8
    LCI #1853
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    Having commuted on a mountain bike for about a year before going to a dedicated commuterm the biggest difference I made on the MTB was raising the saddle an inch or two for more efficient pedaling on the pavement.
    Ride a mountain bike... you will not regret it if you live.
    (with apologies to Mark Twain & The Taming of the Bicycle)

  9. #9
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    Quote Originally Posted by PscyclePath
    Having commuted on a mountain bike for about a year before going to a dedicated commuterm the biggest difference I made on the MTB was raising the saddle an inch or two for more efficient pedaling on the pavement.

    Yup that is the big one to watch....

    Also a set of slicks on a second set of wheels is nice if you are doing a lot of commuting.

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