Judging mtb frame size from photo?

On 11/3/2008 4:39 PM wrote:

More bike measurements:

On the MTB, the seat tube is 17" C-T. The top tube is 22.5" C-T.
From the top of the seat tube to the saddle rail is 8.5", but that
varies with riding conditions. That's fire-road setup, it's never any
higher than that or I get a bit of side to side wobble at the bottom
of the pedal stroke, but it is often lower depending on riding
conditions.

On the road bike, the seat tube is 20.25 C-T. The top tube is 21.5 C-
C. From the top of the seat tube to the saddle rail is 7.25"

I should mention that going to the saddle rail is a tough call, as
it's angled. I picked where the saddle rail intersects the axis of
the seat tube on both measurements.

I should also mention that the MTB has a riser stem, while the stem on
the road bike drops down.


Mike,

I'm going to try to adjust my MTB per your sizing chart on your
blogspot. I find it a bit confusing though, as you show an angled
take running about parallel to the seat tube, from the top of the
pedal at the bottom of the pedal stroke to the back tip of the
saddle. The back of the saddle on the MTB rises a bit, where you
actually sit is a touch lower than the back of the saddle. What point
of the saddle are you intending these measurements to be taken from?
I'd expect it to be around the center of the saddle, where you'd be
sitting.

My arbitrary measuring point is where an imaginary line run up through the
center of the seat tube exits through the top surface of the saddle. Like
if an archer shot an arrow up through the seat tube.

Yeah, this is not how these things are normally measured but I figured
that your basic craigslist seller wouldn't be bothered too much by that.


--
Mike "Rocket J Squirrel"
Bend, Oregon

On 11/3/2008 4:20 PM wrote:

On Nov 3, 6:56 pm, Mike Rocket J Squirrel
wrote:
All good points. I just rode a rental 16'' mtb and found the reach to be
farther than I like. It could have been brought in an inch or so with a
shorter stem, but I'm frankly tired of having to ride bikes that are too
long and won't settle for it any more.

Fair enough.


I'm not 6'6'', I'm 5'6'', but you may have typo'd that.

That was indeed a typo, I had your right height in my head and my
fingers missed it.


It's true -- I
like a short reach. I came up with my target reach numbers after, oh,
about 40 years of riding and now that I'm old and fat I don't care to fold
over quite so much. I've got two bikes that feel right and I measured them
et viola! I have my numbers.

If I offended you, my apologies. I'm sure you know what you like for
fit when it comes to road bikes. You seem new to mountain bikes,
which are sometimes fit quite differently than road bikes, so I
thought it was worth an ask. If you measured your most comfortable
road bike, that may not be your most comfortable MTB position. I have
multiple road bikes, multiple mountain bikes, and have ridden tons
more than I own. I believe I have my perfect fit, after all these
bikes and years (although not 40) for both my road and mountain
bikes. The fits are quite different. That's all I was getting at.

Pshaw. No offense was taken! I'm in no danger of becoming a real mountain
biker. One of the side effects of the metal knee is that I must take
caution about falling as any twisting of the lower leg could cause the rod
that runs up my femur to rotate and shatter the femur. This because the
rod is hexagonal in cross-section. So I ride cautiously. My wife and I are
looking for simple, inexpensive little mtbs for riding the old people
trails. No extreme ups or downs, so we don't need to go for greatly
different geometries than what we use when riding our road bikes with flat
bars on our town bikes. The trails we want to ride are about as flat and
easy as road shoulders anyway. We're wusses.

--
Mike "Rocket J Squirrel"
Bend, Oregon

On Nov 3, 8:18*pm, pm wrote:
On Nov 3, 4:31*pm, " wrote:





On Nov 3, 3:46*pm, pm wrote:

On Nov 3, 12:10*pm, " wrote:

On Nov 3, 3:03*pm, " wrote:

On Nov 3, 2:15*pm, Mike Rocket J Squirrel

wrote:
On 11/3/2008 9:24 AM pm wrote:

On Nov 3, 7:51 am, Mike Rocket J Squirrel
wrote:
Mrs Squirrel and I are in the market for small mtb (13'' works for her,
15'' is kind of my size), but when folk advertise their mtbs on the local
craigslist, they rarely mention the size. I email them about it, but more
often than not they say that the size isn't on the frame anywhere.

So I ask the seller to measure the bike per my blog entry he

http://socal2bend.blogspot.com/2008/...ain-bikes.html

But not all sellers are motivated to break out the old tape measure.

So before heading over to see the bike in person, it would be helpful for
me to eliminate those that are clearly too large.

While I've gotten pretty good at determining the size of a standard kind
of road frame by looking at a pictu the length of the seat stays are a
clue, as well as the length of the steering tube -- it's not foolproof but
I can generally see if the bike is a small one or not.

But I'm not clear whether one can make a call about mtb frames by looking
at the picture alone.

For example,

http://bend.craigslist.org/bik/903343909.html

--
Mike "Rocket J Squirrel"
Bend, Oregon

If you have a decently square-on side view, I've used a graphics
program that can tell the distance between two points, though you
could also just blow up the image and hold a ruler to your screen. You
know the rim is a standard size (559 mm), so you measure across the
rim, call it X, then measure the dimension you want, multiply by 559
mm and divide by X. This usually gets within an inch or so.

-pm

Very handy and obvious once explained. Since I know that my desired reach
should not exceed 24 inches (as measured per Dimension "B" the drawing athttp://socal2bend.blogspot.com/2008/10/seeking-used-mountain-bikes.html)

then the reach on the photo of a candidate bike should not be a whole lot
greater than the rim diameter of 559 mm, or 22 inches.

Using this method, I can see that the bike for sale athttp://bend.craigslist.org/bik/903343909.htmlhastoomuchofareach.

--
Mike "Rocket J Squirrel"
Bend, Oregon- Hide quoted text -

- Show quoted text -

That bike didn't look that big to me, but using the aforementioned
method in my CAD software, I got a B dimension of almost 32", or 8"
more than you're looking for. *Either that is a really big bike,
you're looking for a really small bike, or there's something off in
the measurement system somewhere.- Hide quoted text -

- Show quoted text -

Just tried the same method on my hardtail, although the bike is at a
bit of an angle to the cam so I expected skewed resutls. *Got a B
dimension of 28.86, wiht the saddle higher than you would want it, and
a stem of average length - not a monster but not short either. *I have
a feeling you're going to end up with a shorter stem. *Just fussing
around here trying to find how your equation works out with our new
sizing method, but so far i'm really leaning toward asking for top
tube and seat tube dimensions. *IMO top tube is more important, seat
heigth is easily adjusted.

If you want to be picky about it, you can minimize the effect of skew
by measuring the rear rim along a diameter that is parallel to the
dimension you're after. If I try that on your off-camber pic of the
orange bike it I come up with a 17" seat tube if I start by measuring
the rim parallel to the seat tube vs. a 19" estimate if I start by
measuring the rim horizontally. (is it actually a 17"?)

17" C-T. *It appears your method works quite nicely, even with a
skewed picture.

It worked pretty well for me sorting through the cheaper craigslist
mtbs -- the 21 was indeed a 21 when I got it home. Playing around with
it a while I've decided I'd be better on a 23" :-/



For the craigslist bike it's hard to see where the stem meets the
bars, and if you measure to the end of the bars it'll be inflating the
number. I got about 26" along a horizontal line from the seat post to
the end of the stem and about 17" seat tube length. On your orange
bike I get 25 1/2 " and a 17" c-t seat tube.

On a horizontal line from the center of the seat post to the forward
end of the stem (right where the front of the bars touch the stem, is
that how you were measuring?) it's 29.25".

I also took a more on-camber pic of the same bike.http://tinyurl.com/5a9nrp

On this pic I agree with your horizontal measurement pretty closely,
but I canted my measurement line a bit upward toward the back because
I noticed the rear wheel was higher in the image than the front. I
think my error in the earlier one is that it's hard to tell which line
is horizontal. Top tube length is probably easier to pick off with
photogrammetry.

-pm- Hide quoted text -

- Show quoted text -

Fair enough. The top tube of the bike does not sit horizontally, I
think that's part of the "agressive" stance the original owner was
going for. I find it's got a much more crotch-rocket position than
any stock bikes I've ridden. I almost feel like I'm going from crotch
rocket to cruiser when switching from that to one of my other MTBs. A
taller fork could change that, but that's the third fork that's been
on that bike. I believe that's the angle it was designed for. I find
it great for jumping, pulling around with my body, trials style stuff,
etc. When riding real calm stuff the stance is a bit agressive, but
I'm used to it, and if I know the whole ride will be like that I'll
just take another picture.

Anyway, it seems you've got figuring measurements from a picture down
pretty well. I understand your method and have access to CAD
software, so it should be helpful to me in the future. It should help
Mike in his search as well.

Mike, it seems you've got this down yourself, but if you find yourself
in a pickle post up, and I'll see if I can't import the pic into a CAD
program and use PMs method to get you some measurements.

On Nov 3, 9:21*pm, Mike Rocket J Squirrel
wrote:
On 11/3/2008 4:39 PM wrote:





More bike measurements:

On the MTB, the seat tube is 17" C-T. *The top tube is 22.5" C-T.
From the top of the seat tube to the saddle rail is 8.5", but that
varies with riding conditions. *That's fire-road setup, it's never any
higher than that or I get a bit of side to side wobble at the bottom
of the pedal stroke, but it is often lower depending on riding
conditions.

On the road bike, the seat tube is 20.25 C-T. *The top tube is 21.5 C-
C. *From the top of the seat tube to the saddle rail is 7.25"

I should mention that going to the saddle rail is a tough call, as
it's angled. *I picked where the saddle rail intersects the axis of
the seat tube on both measurements.

I should also mention that the MTB has a riser stem, while the stem on
the road bike drops down.

Mike,

I'm going to try to adjust my MTB per your sizing chart on your
blogspot. *I find it a bit confusing though, as you show an angled
take running about parallel to the seat tube, from the top of the
pedal at the bottom of the pedal stroke to the back tip of the
saddle. *The back of the saddle on the MTB rises a bit, where you
actually sit is a touch lower than the back of the saddle. *What point
of the saddle are you intending these measurements to be taken from?
I'd expect it to be around the center of the saddle, where you'd be
sitting.

My arbitrary measuring point is where an imaginary line run up through the
center of the seat tube exits through the top surface of the saddle. Like
if an archer shot an arrow up through the seat tube.

That's basically how I was figuring it when I took the measurements
listed. That said, you're looking for a very small frame.


Yeah, this is not how these things are normally measured but I figured
that your basic craigslist seller wouldn't be bothered too much by that.

Probably not, but if it's faster and easier for them to just take a
tape measure to the top tube, you may get more input that way, and
hence have more to choose from. Of course, thanks to PM you may not
need all that, you may be able to get most of what you need just from
a picture. I know this thread will change how I look at used bike
pics in the future.

On Nov 3, 9:30*pm, Mike Rocket J Squirrel
wrote:
On 11/3/2008 4:20 PM wrote:





On Nov 3, 6:56 pm, Mike Rocket J Squirrel
wrote:
All good points. I just rode a rental 16'' mtb and found the reach to be
farther than I like. It could have been brought in an inch or so with a
shorter stem, but I'm frankly tired of having to ride bikes that are too
long and won't settle for it any more.

Fair enough.

I'm not 6'6'', I'm 5'6'', but you may have typo'd that.

That was indeed a typo, I had your right height in my head and my
fingers missed it.

It's true -- I
like a short reach. I came up with my target reach numbers after, oh,
about 40 years of riding and now that I'm old and fat I don't care to fold
over quite so much. I've got two bikes that feel right and I measured them
et viola! I have my numbers.

If I offended you, my apologies. *I'm sure you know what you like for
fit when it comes to road bikes. *You seem new to mountain bikes,
which are sometimes fit quite differently than road bikes, so I
thought it was worth an ask. *If you measured your most comfortable
road bike, that may not be your most comfortable MTB position. *I have
multiple road bikes, multiple mountain bikes, and have ridden tons
more than I own. *I believe I have my perfect fit, after all these
bikes and years (although not 40) for both my road and mountain
bikes. *The fits are quite different. *That's all I was getting at.

Pshaw. No offense was taken!

Glad to hear it.


I'm in no danger of becoming a real mountain
biker. One of the side effects of the metal knee is that I must take
caution about falling as any twisting of the lower leg could cause the rod
that runs up my femur to rotate and shatter the femur. This because the
rod is hexagonal in cross-section. So I ride cautiously. My wife and I are
looking for simple, inexpensive little mtbs for riding the old people
trails. No extreme ups or downs, so we don't need to go for greatly
different geometries than what we use when riding our road bikes with flat
bars on our town bikes. The trails we want to ride are about as flat and
easy as road shoulders anyway. We're wusses.

Have you given any thought to a CX bikes? May be more suited to your
style and what you're used to. Either way, it sounds like you're on
the way to finding what you want, and PMs methods sure should help. I
just hope you are able to find a frame that will give you the short
top tube you want without requiring too much seat tube extension, it
seems like you might be almost into custom geometry territory here. I
don't know, and there's a good chance I'm wrong. I hope I am, for
your sake. Good luck, and let us know how it turns out for you.

BTW, have any local pawn shops? You seem to know your bikes. I got a
killer deal on a Marin a couple years back at a pawn shop, just needed
a little love, a spoke and some wheel trueing.

If you do, and you call them, be sure to specify you're asking if they
have any bikes for sale. I called one asking if they dealt in bikes
and they said no. The next day I drove by and saw the Marin. After
the haggle & buying it, I told him I was the one that called and asked
why he told me they didn't deal in bikes. He said they try not to as
they prefer to stick with gold, jewelery & instruments, but
occasionally get stuck with one. He thought I was trying to sell one,
not buy one.

On 11/3/2008 7:18 PM wrote:

On Nov 3, 9:30 pm, Mike Rocket J Squirrel
wrote:
On 11/3/2008 4:20 PM wrote:





On Nov 3, 6:56 pm, Mike Rocket J Squirrel
wrote:
All good points. I just rode a rental 16'' mtb and found the reach to be
farther than I like. It could have been brought in an inch or so with a
shorter stem, but I'm frankly tired of having to ride bikes that are too
long and won't settle for it any more.
Fair enough.
I'm not 6'6'', I'm 5'6'', but you may have typo'd that.
That was indeed a typo, I had your right height in my head and my
fingers missed it.
It's true -- I
like a short reach. I came up with my target reach numbers after, oh,
about 40 years of riding and now that I'm old and fat I don't care to fold
over quite so much. I've got two bikes that feel right and I measured them
et viola! I have my numbers.
If I offended you, my apologies. I'm sure you know what you like for
fit when it comes to road bikes. You seem new to mountain bikes,
which are sometimes fit quite differently than road bikes, so I
thought it was worth an ask. If you measured your most comfortable
road bike, that may not be your most comfortable MTB position. I have
multiple road bikes, multiple mountain bikes, and have ridden tons
more than I own. I believe I have my perfect fit, after all these
bikes and years (although not 40) for both my road and mountain
bikes. The fits are quite different. That's all I was getting at.
Pshaw. No offense was taken!

Glad to hear it.


I'm in no danger of becoming a real mountain
biker. One of the side effects of the metal knee is that I must take
caution about falling as any twisting of the lower leg could cause the rod
that runs up my femur to rotate and shatter the femur. This because the
rod is hexagonal in cross-section. So I ride cautiously. My wife and I are
looking for simple, inexpensive little mtbs for riding the old people
trails. No extreme ups or downs, so we don't need to go for greatly
different geometries than what we use when riding our road bikes with flat
bars on our town bikes. The trails we want to ride are about as flat and
easy as road shoulders anyway. We're wusses.

Have you given any thought to a CX bikes? May be more suited to your
style and what you're used to. Either way, it sounds like you're on
the way to finding what you want, and PMs methods sure should help. I
just hope you are able to find a frame that will give you the short
top tube you want without requiring too much seat tube extension, it
seems like you might be almost into custom geometry territory here. I
don't know, and there's a good chance I'm wrong. I hope I am, for
your sake. Good luck, and let us know how it turns out for you.

BTW, have any local pawn shops? You seem to know your bikes. I got a
killer deal on a Marin a couple years back at a pawn shop, just needed
a little love, a spoke and some wheel trueing.

If you do, and you call them, be sure to specify you're asking if they
have any bikes for sale. I called one asking if they dealt in bikes
and they said no. The next day I drove by and saw the Marin. After
the haggle & buying it, I told him I was the one that called and asked
why he told me they didn't deal in bikes. He said they try not to as
they prefer to stick with gold, jewelery & instruments, but
occasionally get stuck with one. He thought I was trying to sell one,
not buy one.

We were just in Spokane, WA. Sat down at a table in a cafe next to
Auntie's bookstore, just as I spied two pawn shops across the street each
with many bikes. And just as they were locking the pantograph gates across
the storefronts.

--
Mike "Rocket J Squirrel"
Bend, Oregon