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Discussion Starter · #1 ·
So.

I'm looking at a Motobecane Fantom Trail, with near certainty that I'm gonna get it--but in comes the question, what size?

I'm around 5'9"-5'10" (I can never remember to be honest), 160lbs., and I've been rockin' out a 20" on my Cannonade for the past couple years and I've never found a problem with it. Stepping down to my brother's 18" was actually less comfortable (but I guess part of that might have been due to what I'm used to). However, it's only been recently brought to my attention that maybe an 18" would fit better given my stats.

I'd normally pose the question to some friends in the biz of riding bikes, but most of my friends ride roadies, so here's my question to the lovely MTBR community:

I'm pretty sure I'm gonna check out a couple LBS' and feel out the frame size, but what benefits am I really gaining by having an 18" vs. 20"? I can still touch the ground without my frame getting in my crotch, and I personally don't think I notice any differences in pedal power, etc. What do you guys think?
 

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A lot of people say that standover height isn't important. I'm gonna go on the other side and say that it is a pretty crucial stat.

Given the geometry, you should have a good 2 or so inches of clearance.

But again, because some bike geometries are so different these days, standover isn't the only thing you should look at.

Given your stats, it does seem like an 18 or 19 would be more suitable, but if you just don't feel comfortable, then forget about it. Ride what is comfortable for you first and foremost!

Btw, I almost exactly match your stats and I ride an 18". Sometimes I think I should even be riding a 17" and I can ride a 19" without too much complaint. Again, it comes down to what is personally comfortable.

Give your LBS a shot. See what they think too.
 

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A 20" frame from one company is not going to have the same fit as another make's 20". Comparing different bikes by seat tube length is not very useful. The measurement you should be looking at is effective top tube length. If you're truly comfortable on the 20" 'dale (which btw does sound big for someone 5'9" or 5'10"), make sure your next bike has the same ETT.
 

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Discussion Starter · #5 ·
True story, I'm just finished up my finals and am yet to get a chance to get all the specs and fun stuff in order. I appreciate the helpful advice; it's nice to see that I know more than I thought I did.

Bummer I didn't find Mtbr forums sooner than I did!
 

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holycrikey said:
A lot of people say that standover height isn't important. I'm gonna go on the other side and say that it is a pretty crucial stat.

Given the geometry, you should have a good 2 or so inches of clearance.

But again, because some bike geometries are so different these days, standover isn't the only thing you should look at.

Given your stats, it does seem like an 18 or 19 would be more suitable, but if you just don't feel comfortable, then forget about it. Ride what is comfortable for you first and foremost!

Btw, I almost exactly match your stats and I ride an 18". Sometimes I think I should even be riding a 17" and I can ride a 19" without too much complaint. Again, it comes down to what is personally comfortable.

Give your LBS a shot. See what they think too.
Seat tube length has nothing to do with stand over height, and how do you know your stats match the op? He only gave his height, he could have a long torso and a long wingspan or long legs and no torso.

But lyndonchen hit it right on the head compare geo on different frames with your current one and it will give you a good idea where to start. Just remember seat tube height (i.e. 17,18,or 20" sizes) and stand over doesn't always go hand and hand so research effective top tube is very important just make sure you have clearance for your small appliances if you know what I mean!:D
 

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Find out the effective top tube length of what you already own, and factor that into any choice. This will give you some idea of the actual reach on a frame as opposed to the whole 18" / 20" thing or the S/M/L thing.

Sizing a bike only by standover height is not the right way to go about it.
 

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Discussion Starter · #8 ·
No, I understand what you are saying.

The size seemed right for me, but the only thing that would have help it back would have been the stand-over.

Just got the bike today, and everything looks great, there's a minor derailer detail that's easily fixable. Other than that, the bike looks great, everything seems to be in working order, and the sizing is just right!

Thanks for the help everyone!
 

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tduro said:
Looking at the diagram, for a given reach and stack the seat, front wheel, and rear wheel could be just about anywhere. What does this measurement accomplish?
As far as the front and rear wheel, this measurement is not intended to replace chainstay length, head angle, or wheelbase length.

As far as the seat, however, you are correct, the seat can be put just about anywhere on any given bike, which is the point of this measurement. Effective top tube does not always relate to the saddle-head tube distance, and the seat tube angle does not always relate directly to the fore-aft position of the saddle. Think about it. You are generally going to adjust the seat in relation to the bb location. If you have a bike with a slacker seat angle, that means you are going to slide the seat forward. Slide the seat forward on the rails and you just accomplished the same thing as a steepened seat tube angle and shortened effective top tube of any bike.

Take two bikes with the same effective top tube. Bike A has a steeper seat tube than bike B. Since you are going to need to slide the seat more forward on B than on A, A will end up having a longer distance from the saddle to the head tube. This "reach" measurement is meant to take top tube length - seat tube angle interaction into account, or rather work around it. Like you say, it does not tell you where the top of the seat tube ends up, but you can slide the saddle forwards, backwards, up, down, or whatever, to get it where you want it, anyways.

Besides, I assume most companies would still give you the seat tube angle and effective tt measurement, anyway. But I think this "reach" measurement is more useful than either one.
 
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