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Road bike size/MTB size(6 posts)

Road bike size/MTB sizeMGS
Jan 20, 2002 5:05 PM
I've been investigating a Mountain bike for some additional riding experience. Although I know exactly what size bike works for me on a road bike, MTB's are a whole new world of fit and feel.

The seat posts are longer, suspensions move and handlebars don't have drops.

And to make matters worse, the sizes are typically in inches.

I ride a 57cm frame, 55cm top tube.

I would appreciate help in what size frame to consider for those of you who have crossed from road to MTB and back.


I'm guesstimatingjtolleson
Jan 20, 2002 6:08 PM
An 18" but even among MTBer's some like to ride a vastly undersized frame (easier to handle in aggressive terrain).
I think that's a good guess.Leisure
Jan 20, 2002 8:20 PM
Most of the time at least. Mtb geometries aren't as dialed as road geometries so look at an 18" first, being perfectly open to sizing anywhere from 16-19". My road size is 53cm while I ride an 18" frame by Rocky Mountain, which for most other companies would probably be a 17". I think sizing a mountainbike is much more difficult than sizing a roadbike. Some things I generally favor when you first put together an XC mtb: seat height above lower pedal the same as road bike, H-bar level to the seat, the flexibility to run a long stem while retaining lots of cockpit mobility and generous standover clearance. The latter two often mean it's better to err just a bit on the small side when choosing a mountain frame.
IMO, I think you'll benefit from knowing what stem length you want before even sizing a frame. Stem length has a big influence on handling in mountainbiking and test-rides in the parking lot can be deceptive. Handling that feels sporty on level pavement (which initially wows a lot of customers) will be twitchy on the trails when things get rough, fast, and tight. I prefer my bikes to have mellower handling than what a lot of companies have stock, which means a stem length of about 120-130mm as opposed to 100. If I'm running long stems then I don't want a frame with a long toptube that keeps me too stretched out or unable to move around when things get fast and steep. I've had a decent number of friends who listened to this and said, "Naw, I like the sporty feel of the short stem and why would I want to move my CG forward?" only to come around later to prefering longer stems. Most of them have lucked-out by having a frame a bit small to begin with, which is good.
re: Road bike size/MTB sizebiknben
Jan 21, 2002 6:58 AM
Colorado Cyclist offers some guidelines for bike fit. It's not Gospel but it's a starting point.
"For a mountain bike, we start by recommending a frame in the range of 10–12cm smaller than you take in a road frame. For example, if you ride a 55cm C-T road frame, look for a 43–45cm (17–18") C-T mountain frame.

In many ways, though, it is more important to fit a mountain frame by the top tube length needed, rather than by the seat tube length. For instance, you might be able to get to the proper frame clearance, saddle height and neutral knee position (see below) on either a 17" frame or a 19" frame. Yet the 19" frame will likely have a top tube 1" longer than the 17" frame, which changes your stem length accordingly. Or, one manufacturer’s 17" frame may give you a 22" top tube, while the next one’s 17" gives you a 22.8". More on this below… just make sure that you’ll be able to work out your top tube and stem length for a given frame."

Here's a link to the entire text:

I would recommend the smallest frame possible that still fits your torso. MTB Seat posts are a mile long to allow for this. Mt bikes take the sloping top tube idea to an extreme.

Spend some time comparing sizes of the different bikes you're considering and take them out for a test ride. Many shops have demo bikes you can take out for the day. Even if the demos doesn't fit great it will give you an idea of how different sizes feel while riding.
re: Road bike size/MTB sizepa rider
Jan 21, 2002 2:25 PM
I'm a MTB sport racer who started road riding ten years ago. I owned over 10 MTB in the past ten years. I see everybody is saying to start with a 18 inch bike or see if yor LBS has a demo bike. That's the best way to go.

But if your options are just to ride in a LBS parking lot then see if any of you friends would leave you test ride their bike or borrow.

I learned in the ten years that the bike fits the way you want to ride. If your going to ride fire trails, then you can get away with two inch clearance top tube. You can have a short reach. I ride ATB courses, so the guage is different.

I learned the smaller frame have three or more inches of top tube clearance. I usually get the bike seat adjusted correctly and look at the front hub. If my handle bars are over the hub (you see your hub first then the handlebar) this is the correct length.

I learned if the hub is right were your handle bar is located then you're ok for uphills and flats sections, but downhill riding is going to send you over the bars (you have too much body weight forward). I used this length for my commuter bikes. I could ride fast with this length, but knew if I road a technical downhill and it gets steep I could crash (I usually did).

I bought a Sugar and it has a "V" shape, which doesn't matter about the top tube height. I put some long 150 stems on some of my bike to give me a smaller frame (I'm 73 inches).

You being 67 inches should be able to find alot of LBS with your size of bike. Hope this helps. You just have to ride a few bikes to see how you feel comfortable. I hope your LBS has a demo bike. Mine usually have 18 inches because that size is common.

Are you getting a full suspension or hard tail? FS ride way different and you have to take the sag in play of your saddle height.

Good luck
~18", mediumcyclopathic
Jan 21, 2002 3:41 PM
go by the TT length and stand over

most of 17-19" would have TT 21-22" pretty much equv 55cm and would give you at least 3-4" of standover.

In terms of fit MTB gives you more upright position. It should feel as riding tops on road bike and riding barends should be like riding hoods.

Medium is usually what all shops stock you wouldn't have any trouble to test ride it good luck