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Old 01-31-08, 09:10 PM   #1
barth-karl
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touring with a MTB frame, how ought I size it.....

Not that I am operating out a modern assumptions of knowable truths, or a belief in a platonic form of bike size.

Just wondering what the popular theories are - do you use an MTB frame with measurements close to that of your road frame?

Many MTBs seem to have sloping DTs- would this mean finding a much larger than normal road sized frame?

Do you say 'screw it' and just use taller seat posts...?

Interested in your thoughts
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Old 01-31-08, 09:29 PM   #2
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Most people will ride a mountain bike which is sized smaller than their road bike. Such as in inches, my road bike is 22" and my mountain bike set up for touring is 19". The mountain bike is going to have you more upright. I have heard it suggested that if you are to use your mountain bike for touring consider going up one size in the mountain bike than you would normally be fit with, since the top tube is sloping there will still be plenty of room for stand over height but the larger size will give you a longer effective top tube and hence lay you out in a slightly more aerodynamic road position but probably still not as much as the road bike. The BEST thing to do is test ride and then test ride some more until you find what is most comfortable for you. No one here can tell you that
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Old 01-31-08, 09:48 PM   #3
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It probably wouldn't be easy looking for a MTB with 27" tires; maybe go for a MTB with 29s.
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Old 01-31-08, 09:57 PM   #4
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Get one with the distance from seat to bars close to that on your road bike. Distance seat to pedals can then be easily adjusted
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Old 02-01-08, 06:51 AM   #5
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Originally Posted by barth-karl View Post
Do you say 'screw it' and just use taller seat posts...?
Yes, but I do that on my road bikes too.
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Old 02-01-08, 07:50 AM   #6
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Originally Posted by robow View Post
Most people will ride a mountain bike which is sized smaller than their road bike. Such as in inches, my road bike is 22" and my mountain bike set up for touring is 19". The mountain bike is going to have you more upright. I have heard it suggested that if you are to use your mountain bike for touring consider going up one size in the mountain bike than you would normally be fit with, since the top tube is sloping there will still be plenty of room for stand over height but the larger size will give you a longer effective top tube and hence lay you out in a slightly more aerodynamic road position but probably still not as much as the road bike. The BEST thing to do is test ride and then test ride some more until you find what is most comfortable for you. No one here can tell you that
Good advice...my road frames run in the 25.5" range my most used MTB is 21" but for touring I would prefer a 23". From what I gather you want the MTB frame for MTB riding to be a few inches smaller so if you have to put a foot down....

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Old 02-01-08, 09:25 AM   #7
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Silly epistomologist. Try an empirical approach.

Translation: Go to the bike shop and get a bike fit, and try some bikes. The main things I would look for between regular mountain bike fitting and fitting one to tour on are steering not too fast/twitchy and chainstays long enough so your heels don't hit the panniers, if you are using panniers. If you put all the weight on the back (no front panniers) the steering becomes very light and twitchy on about any bike, so it might be good to be front-rack-enabled. Disc brakes can interfere with rack mounting, also.
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Old 02-01-08, 09:49 AM   #8
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Silly epistomologist. Try an empirical approach.

Translation: Go to the bike shop and get a bike fit, and try some bikes. The main things I would look for between regular mountain bike fitting and fitting one to tour on are steering not too fast/twitchy and chainstays long enough so your heels don't hit the panniers, if you are using panniers. If you put all the weight on the back (no front panniers) the steering becomes very light and twitchy on about any bike, so it might be good to be front-rack-enabled. Disc brakes can interfere with rack mounting, also.
Not too many of the current crop of MTB's would be suitable for touring IMHO. The most suitable seem to be the 80's to early 90's vintage, and not something you would typically find at your LBS. Also FWIW also IMHO the current fitting of bikes is a PITA compared to the older straight tube frames.

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Old 02-01-08, 09:51 AM   #9
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Get one with the distance from seat to bars close to that on your road bike. Distance seat to pedals can then be easily adjusted
+1

If you are looking at new bikes have a look at the manufacturer's specs. They should provide an effective top tube or horizontal top tube distance. Size it based on this value as you'll have bags of stand over on any MTB frame.

When I got my Thorn Sherpa frame I used the top tube length on my LHT to size it that way. I've got both bikes setup very similarly. The only difference is my Sherpa has 7" of exposed seat post and my LHT has 3.5"

If you are buying used just measure the horizontal top tube to compare bikes.
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Old 02-01-08, 12:04 PM   #10
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Well,

It's a interesting question - first comment retro mountain bikes have a different geometry than the current vintages, many have longer angeles less sloping top tube. That's why they can be good touring candidates. Did a mid 80's Miyata up build last year - it measured up identically to my road frame great fit, just got with a mid 80's Stowe which should of been huge at 20 inches it's to small - just got a early 90's Trek 750 which is a hybrid 700 and I am hoping at 21 inches it fits. I agree I am not sure the majority current mountain bikes will make good touring bikes
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Old 02-01-08, 04:41 PM   #11
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Effective top tube length is probably the best way to size a mountain bike, or hybrid bike. With the standover so low on those frames, you can go up a size without worrying too much, if that is what you want to do.

If you get a bike with a sloping top tube, you will be showing a bit of seatpost even when the bike fits correctly. 8 inches or more is not uncommon. There is nothing wrong with doing that.

In terms of whether or not they would make good touring bikes, I am not sure that the riding position would be so great. Also, the smaller frames might not be easy to mount a lot of racks or panniers to. And the smaller wheels are less efficient, which might be noticeable over long distances. I would get a road-style bike myself.

EDIT: If you do get a mountain frame, get a rigid one without suspension of any kind, and also a rigid fork. Suspension will make it very hard to mount panniers, especially in the back.
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Old 02-01-08, 05:19 PM   #12
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Originally Posted by barth-karl View Post
Not that I am operating out a modern assumptions of knowable truths, or a belief in a platonic form of bike size.

Just wondering what the popular theories are - do you use an MTB frame with measurements close to that of your road frame?

Many MTBs seem to have sloping DTs- would this mean finding a much larger than normal road sized frame?

Do you say 'screw it' and just use taller seat posts...?

Interested in your thoughts
Older MTBs/ATBs have features that make them more suitable as touring bikes.
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