MTB Sizing ???

[Louis]

How in the world do I figure out what MTB size will work for me?

(Off the shelf road for me is 60 c-c ST, 58.5 TT, and custom is a bit taller ST (61) and a bit shorter TT)

The MTB sizes are numbers like 15.5", 17", 19", 21", and 23" and I'm not ever sure what that's measuring. They also talk about effective TT, but that doesn't seem to correspond to road bike TT.

TIA

Louis

(I'm thinking of getting a cheapo SS 29er to ride around my subdivision when the weather is not conducive to longer road rides)

[echelon_john]

what's your saddle height on your road bike--bb ctr to saddle top?
what's your saddle tip to near-edge of handlebar measurement on your road bike?
what's your bar drop on your road bike?

[crownjewelwl]

your position on mtb is totally different (read: more upright)

I got sized and it wasnt close to what i expected...also since riding for the last year ive changed the fit with stem length and angle quite a bit

But sounds like youre not actually riding off road??

[Louis]

Hi John,

I don't know - I'll have to measure them when I get home later tonight.

[Louis]

But sounds like youre not actually riding off road??

Correct - this would not be for "real" MTB riding.

[Ken Robb]

Go try some demos and err toward a larger size. In mtn. bike sales like road bike sales most shop folks tend to fit people like they were going to be racers. For the riding you are considering I would want a rather erect position. Not only is it comfy but you can wear a hat with a brim to keep rain/snow out of you eyes and neck.

You may want the biggest sizes that most companies offer since their road bike sizes top out near your ideal fit too.

[Louis]

The MTB sizes are numbers like 15.5", 17", 19", 21", and 23"

Physically on the bike, what do these numbers measure?

[echelon_john]

not much. that's why the other measurements are helpful.

[cat6]

Sometime near present day a mysterious plague sweeps the world, killing almost every adult and leaving behind "a world of orphans". Some fortunate few are raised by the surviving adults, including Lee (John Stockwell), who is taken in and raised by Albert (James Earl Jones) on his remote farm. Fifteen years later, Lee decides to set out for the nearby ruins of Los Angeles in the hopes of joining the Clippers, a famous motorcycle gang. Lee arrives in the city only to find it seemingly empty, but spots a convoy of cargo trucks heading through the streets. He follows them into a well-lit, fenced off building, where he is quickly noticed by Bolo (Norbert Weisser), who is overseeing operations. When various workers begin to converge on Lee he flees on his motorcycle.

[Louis]

I do have an old non-suspension GT MTB that kind of fits me (but I don't want to convert it to SS) so if I know what the "Size" measurements mean, I can measure the GT then figure out what size I should get on the proposed frame. However, since I don't know what the MTB size numbers mean, I have no idea what to measure on the GT.

[cat6]

Sometime near present day a mysterious plague sweeps the world, killing almost every adult and leaving behind "a world of orphans". Some fortunate few are raised by the surviving adults, including Lee (John Stockwell), who is taken in and raised by Albert (James Earl Jones) on his remote farm. Fifteen years later, Lee decides to set out for the nearby ruins of Los Angeles in the hopes of joining the Clippers, a famous motorcycle gang. Lee arrives in the city only to find it seemingly empty, but spots a convoy of cargo trucks heading through the streets. He follows them into a well-lit, fenced off building, where he is quickly noticed by Bolo (Norbert Weisser), who is overseeing operations. When various workers begin to converge on Lee he flees on his motorcycle.

[rice rocket]

Physically on the bike, what do these numbers measure?

It's seat tube length, like how road bikes are. So basically it means nothing.

[oliver1850]

The size in inches is usually the seat tube c to t. I'd be careful about going too large, as seat tubes have gotten much shorter recently and TTs seem to be longer. If you look at Specialized's and Cannondale's SS 29ers, even the 2nd largest sizes have ETTs of 64 cm. When I bought my last new Cannondale MTB (26" wheels) the 2nd largest size (20") had an ETT under 60 cm. Geo chart for Stumpjumper SS29 below.

http://www.specialized.com/us/en/bikes/archive/2011/stumpjumper/sjht29erss#geometry

[EnginCycle]

There is nothing similar from a mtb fit to a road fit short of a similar saddle height. The TT length is using the assumption that flat bars with a single position is being used. Road bikes are a long reach from the stem to the shifters and that makes a big difference. Just about all bikes are using the effective top tube. Unless your frame has a dead level top tube measuring the tube itself tells you nothing. It is a virtual measurement from the intersection of the head tube/top tube then making a level line til you hit the seat post. That is the "effective" top tube length. That is the main number that matters but you need to consider the seat tube angle as it will effect the number if you are looking for a specific length.

With all that said if you are riding a 60+ cm road frame then there is not a stock mtb bike that will be too big for you. Just get the extra large/20+" or whatever they call it. Some tweaks will be done but it will work IMO. Just a guess but probably a good one.

-Drew

[Lovetoclimb]

I used the competitive cyclist online fit calculator to size myself for a 29er. I thought for sure I would be an XL (21") but turns out I am closer to the L (19") given all those measurements. Very helpful stuff.

[ofcounsel]

In road, I'm a standard 54cm, running a slight setback post and 100mm stem.

I'm a 17.5"-18" in MTB with a setback seatpost,and usually running 85-90cm stem.

You're probably about 20-21" I'm guessing, but you can probably run a 19" if you run a setback post and a longer stem.

[Ken Robb]

It is EASY in my area to get all the demo rides one could wish for on mtn. bikes. It may be the same where you live so forget about the measurements, ride the demos and buy the one you like best.