azitiz

[there was some talk of this burried on another thread, but thought
I should make it its own thread so others could perhaps share their
wisdom -az]

MTB Frame Sizing for Touring?

Okay, I’ve been getting conflicting information from places and need
some help sorting this out. I know that the real answer is, “it depends”
and that I should obviously try each bike out to see how it fits, but
because I am trying to find a used bike online (craigslist, classifieds, etc),
I have to be able to narrow it down to bikes within an acceptable
range. So here’s the deal:

I fit well on around a 56cm road bike (average body/weight, 5’10.5ish).
I am looking to use a MTB as a long distance, fully loaded, touring
bike. Do I want to find a MTB frame around the same size as I would
a road bike?

People often talk about getting a MTB smaller than they would a RB,
but this is if it’s being used as a MTB. Some have mentioned to me
that since I’d be using it as a Touring bike (long days, after days,
in the saddle) I’d want a frame as large as I could take. Others
have said that because MTB seat posts and stems can be adjusted
fairly high, and they often have longer toptubes, that I could go
with a smaller frame.

If I understand correctly, the frame being as large as possible mostly
makes it easier for the handlebars and saddle height to be correct for
your body (which MTBs seem to be able to accommodate over a large range
of sizes). Is there another reason a bike for touring would want the
frame as large as possible?

This also becomes a question because most of the MTBs I see for sale
are in the 17-19 inch range…could I make one of those work and still
be comfortable over long distances?

Alexander, confused, in Providence

Cyclist0094

A larger frame in general will have a bit more flex which is not a bad thing, as you have already surmised the big issue is comfort. I rode a 19" MTB frame for years with the bars 5" below the saddle( I am 6'1, 34" inseam). It was fine for 2-3 hour MTB rides and it looked cool. But riding it all day put me on an advil diet for the next two days. These days a 22" MTB is the better fit , putting the bars just below the saddle while still allowing adequate standover. For touring I built a 23" MTB based touring frame which allows me to keep the bars at or just above the saddle height. I have ridden several 100+ mile days on this bike.
You also have to pay attention to top tube length which can vary greatly on MTB frames.

roadfix

Nothing wrong upsizing mtb frames for touring or commuting purposes but watch that top tube length.....it can get long...

azitiz

Many people have been telling me to go by Top Tube length...is there a way to get a good range of what thay might be myself. The local shops will only do a fitting if you're buying a bike there. Or else charge you a huge amount of money.

Cyclist0094

IMO There is no unimportant measurement in frame sizing. Problem comparing a road bike to an MTB is that MTB handle bars are straight at the stem clamp with a slight sweep to the rear which is normaly where you ride on a MTB. On a roadbike with roadbars,most people ride on the hoods which can be 6 cm or more forward of the stem clamp , so MTB top tubes tend to be longer. The good news is unless you have unusally short or long arms/ torso there usually is enough variation is stem lengths (65mm- 160mm) and handle bar reaches to make up for most top tube differences if the seattube length is close to your size.

What I do when I look at bikes is bring a record of my saddle and handle bar position with me along with a cloth measuring tape.
I record the measuement from my crank center to the top of the saddle and then from the top of the saddle level to the handlebars and record the diffrence in height between saddle and handle bars. I use that same measurement to locate the center of the stem clamp where the center line of the seatpost passes through to the center of the stem clamp. This list isn't doesn't include saddle offset from the crank, crank length or other factors, but it gets you close enough to determine if a frame can fit.

sivat

Try this. It should give you a pretty good idea of a top tube length to get.

azitiz

Interesting...I took those measurments best I could (by myself) and came out with top tube length between 53.7 - 55.3 - a pretty small range (less than an inch!).

So, what folks are saying is that if I find an 18" frame or a 22" frame, as long as i have a top tube close to that range i should be able to make it work??

Cyclist0094

CC's calculator is a very good one and my favorite but it is for road bikes. MTB's have higher bottom brackets and I already talked about the difference in handle bars and top tubes. Frame size between 18 and 22 " ? where do you want the handlebar height to be? Do you want to use an extension stem or a riser bar? on an 18" frame. Will a 22" frame put the bar too high? are you going to use drop bars, flat bars or butterfly bars?

azitiz

I'm not sure on the bars...though probably not flats...want something with multi hand positions
for long days....sorry for being thick here....I always thought i was good with geometry/spacial
things....but i just can't wrap my head around this. feeling stupid. I guess I'm going after something
that will be comfortable over long days of riding (over speed). I guess I'm not sure how
it matters if I have an 18" frame with a long stem made so i can sit more upright, or a 22"
frame with the a shorter stem? As long as I'm in a similar position, which it seems like stems and seat posts can adjust to, does it matter so much what size frame it is as long as the top tube is
in range.

NoReg

The best place to start is with known rides. Have you ever owned an MTB, and what size did you ride etc...

Anyway. Back when MTBs were first available I always bought them about 2 inches shorter than the road bikes, which was the regular advice of the day. I tended to ride a 23 inch road bike and a 21 inch MTB. That was in the early 80s when the bikes were more similar to touring bikes in their general proportions than they later became.

I think if you go for the smaller frame it is possible to get your position in the same place, but it means both wheels are tucked in more under that position. This means a harsher ride, changed stearing, and shorter stays for your bag/heel clearance.

Another small point to consider is your wheels. If you are riding big MTB tires then the bike would fit normally as regards that, if you ride smaller tires then the whole ride will drop a little which will affect your fit slightly, mostly for the OK.

If you live in a big place you should be able to find second hand MTB frames for the cheap in second hand stores (not just bike places) or on the garbage run.