Judging mtb frame size from photo?

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.htmlhastoomuch of a reach.

--
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"?)

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.

-pm

On 11/3/2008 12:03 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.htmlhas too much of a reach.

--
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.

Yep. Regarding the problem of a candidate bike scaling out too big in the
reach department because of a long stem is a fair criticism, however I
think that if I have a side view of the bike to look at I can certainly
judge how long that bike's stem is and estimate where the handlebars might
fall if the stem were shortened. On the sample photo, it looks like the
stem would have to point rearwards to bring it within comfortable reach.

It's also right-on to suggest that asking someone to measure the bike as I
request may be more of a hassle than it's worth, but there's no harm in
asking. I've had a couple folk do so.

Asking someone to put their tape measure on the top of the saddle at the
point where the C/L of the seat post intersects the top of the seat is
iffy. I figured that there might be some errors introduced there by not
have a glass seat to sight down through, but if the measurement the seller
provides is way off from my target then that bike can be removed from
consideration. If it looks to be pretty close then that's a bike to be
inspected in person.

Your suggestion of measuring seat tube and top tube lengths is somewhat
easier than my method because it doesn't require them to adjust the seat
height. So my next question is whether mtb frame geometry is sufficiently
standardized that knowing those two tube lengths will allow a fellow to
determine the reach?

--
Mike "Rocket J Squirrel"
Bend, Oregon

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.htmlhastoomuchof a reach.

--
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"?)

Good call on measuring parallel to the dimension you're after. Is
your 17 C-C? NVM, I see below it's C-T. That sounds about right, but
it's a custom frame, and not custom to me (although I'm the exact same
size as the guy it was custom for), so i'm not sure. In the interest
of satisfying curiosity, I'll measure it when I get home.


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.

You get 25.5 from the seat post to the end ot the stem on my orange
bike? Again, i'll measure it when I get home.

On Nov 3, 3:55 pm, Mike Rocket J Squirrel


Yep. Regarding the problem of a candidate bike scaling out too big in the
reach department because of a long stem is a fair criticism, however I
think that if I have a side view of the bike to look at I can certainly
judge how long that bike's stem is and estimate where the handlebars might
fall if the stem were shortened. On the sample photo, it looks like the
stem would have to point rearwards to bring it within comfortable reach.

I agree, and with that bike I’d agree the stem would have to come
behind the steerer to get your #. Thing is, the bike appears to be a
17”, or a medium. This leaves me wondering how you got your desired
reach #’s. It seems you’re looking for an awfully short frame.
They’re out there, but @ 6’6 it seems like you’re looking for
something smaller than I’d expect. This is just my opinion, however.
I’ve seen a woman about your height lower the saddle on my bike, ride
it and love it.


It's also right-on to suggest that asking someone to measure the bike as I
request may be more of a hassle than it's worth, but there's no harm in
asking. I've had a couple folk do so.

I agree, there’s no harm to ask. I just feel you may miss out on a
good bike that way, so if you could get the measurements you really
need (effective top tube, and arguably seat tube or even standover
clearance, which is really easy to measure) with less effort, more
people may do it, and therefore improve your selection. Standover is
extremely easy to measure, and if you’ve got a comfortable standover
(say 1-2, maybe 3” more than your floor to crotch measurement when
wearing your riding shoes) you should be ok heightwise. Then you just
need a top tube length, which should again be easy to measure, and
you’re in business.


Asking someone to put their tape measure on the top of the saddle at the
point where the C/L of the seat post intersects the top of the seat is
iffy. I figured that there might be some errors introduced there by not
have a glass seat to sight down through, but if the measurement the seller
provides is way off from my target then that bike can be removed from
consideration. If it looks to be pretty close then that's a bike to be
inspected in person.

I agree. That said, I think you’re thinking in terms of road bikes
when it comes to seat post height. If you’ve got a good standover,
you should be able to get the saddle height you want by setting the
post. If I were you I’d make sure I had a proper standover, worry
about top tube length and let that guide me in for the test-rides.


Your suggestion of measuring seat tube and top tube lengths is somewhat
easier than my method because it doesn't require them to adjust the seat
height. So my next question is whether mtb frame geometry is sufficiently
standardized that knowing those two tube lengths will allow a fellow to
determine the reach?

IME, yes. Some frames have special geometry (I was told my orange
bike is one of them, although I didn’t order the frame, and it
certainly feels that way, far more BMXish/aggressive than most, which
is what the original owner & I both wanted, being BMXers and members
of the same BMX race team), but your average, off-the-shelf MTBs are
pretty standardized in that respect. If you’ve got good standover,
you should be able to get the saddle height you want simply by raising
the saddle. If the top tube is close, stem swaps should cover any
needed adjustment. Seat tube angle tends to be pretty standard. Head
tube angle tends to be very standard.

You could always swing by an REI, a Dick’s, or even a *mart, and get a
feel for what top tube lengths seem to work for you. I think with
that and standover height you’d have enough to go on, at least to
warrant a drive out and a test ride.

On 11/3/2008 1:26 PM wrote:

On Nov 3, 3:55 pm, Mike Rocket J Squirrel


Yep. Regarding the problem of a candidate bike scaling out too big in the
reach department because of a long stem is a fair criticism, however I
think that if I have a side view of the bike to look at I can certainly
judge how long that bike's stem is and estimate where the handlebars might
fall if the stem were shortened. On the sample photo, it looks like the
stem would have to point rearwards to bring it within comfortable reach.

I agree, and with that bike I’d agree the stem would have to come
behind the steerer to get your #. Thing is, the bike appears to be a
17”, or a medium. This leaves me wondering how you got your desired
reach #’s. It seems you’re looking for an awfully short frame.
They’re out there, but @ 6’6 it seems like you’re looking for
something smaller than I’d expect. This is just my opinion, however.
I’ve seen a woman about your height lower the saddle on my bike, ride
it and love it.


It's also right-on to suggest that asking someone to measure the bike as I
request may be more of a hassle than it's worth, but there's no harm in
asking. I've had a couple folk do so.

I agree, there’s no harm to ask. I just feel you may miss out on a
good bike that way, so if you could get the measurements you really
need (effective top tube, and arguably seat tube or even standover
clearance, which is really easy to measure) with less effort, more
people may do it, and therefore improve your selection. Standover is
extremely easy to measure, and if you’ve got a comfortable standover
(say 1-2, maybe 3” more than your floor to crotch measurement when
wearing your riding shoes) you should be ok heightwise. Then you just
need a top tube length, which should again be easy to measure, and
you’re in business.


Asking someone to put their tape measure on the top of the saddle at the
point where the C/L of the seat post intersects the top of the seat is
iffy. I figured that there might be some errors introduced there by not
have a glass seat to sight down through, but if the measurement the seller
provides is way off from my target then that bike can be removed from
consideration. If it looks to be pretty close then that's a bike to be
inspected in person.

I agree. That said, I think you’re thinking in terms of road bikes
when it comes to seat post height. If you’ve got a good standover,
you should be able to get the saddle height you want by setting the
post. If I were you I’d make sure I had a proper standover, worry
about top tube length and let that guide me in for the test-rides.


Your suggestion of measuring seat tube and top tube lengths is somewhat
easier than my method because it doesn't require them to adjust the seat
height. So my next question is whether mtb frame geometry is sufficiently
standardized that knowing those two tube lengths will allow a fellow to
determine the reach?

IME, yes. Some frames have special geometry (I was told my orange
bike is one of them, although I didn’t order the frame, and it
certainly feels that way, far more BMXish/aggressive than most, which
is what the original owner & I both wanted, being BMXers and members
of the same BMX race team), but your average, off-the-shelf MTBs are
pretty standardized in that respect. If you’ve got good standover,
you should be able to get the saddle height you want simply by raising
the saddle. If the top tube is close, stem swaps should cover any
needed adjustment. Seat tube angle tends to be pretty standard. Head
tube angle tends to be very standard.

You could always swing by an REI, a Dick’s, or even a *mart, and get a
feel for what top tube lengths seem to work for you. I think with
that and standover height you’d have enough to go on, at least to
warrant a drive out and a test ride.

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.

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

Also, I have this metal knee. It has a limited range of motion and can't
fold much more than about 100 degrees from straight. This limits how far
down I can set a seat before the knee reached its folding limit on top of
a stroke and shoves my entire thigh and butt up. A useful thing if one
needs to fart and requires an assist to achieve the necessary lean to
provide egress for the noxious fumes, but otherwise mighty uncomfortable.
33 inches from the saddle top to the top of a pedal at the bottom of its
rotation is comfortable. + or - depending on shoe type and crank arm
length. It's a start, anyway.

That's good news to know that mtb frames are sorta kinda standardized.
You're right -- all I really need to look at is the top tube length. My
bet is that with such a short top tube, most mtb's will have sufficient
standover. Or close enough to warrant a closer look.

--
Mike "Rocket J Squirrel"
Bend, Oregon

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.


Also, I have this metal knee. It has a limited range of motion and can't
fold much more than about 100 degrees from straight. This limits how far
down I can set a seat before the knee reached its folding limit on top of
a stroke and shoves my entire thigh and butt up. A useful thing if one
needs to fart and requires an assist to achieve the necessary lean to
provide egress for the noxious fumes, but otherwise mighty uncomfortable.
33 inches from the saddle top to the top of a pedal at the bottom of its
rotation is comfortable. + or - depending on shoe type and crank arm
length. It's a start, anyway.

I can relate there. I have a bad knee the docs want to make metal,
but I've been holding out. I guarantee I'll have a metal knee well
before I get 40 years of riding under my belt though.


That's good news to know that mtb frames are sorta kinda standardized.
You're right -- all I really need to look at is the top tube length. My
bet is that with such a short top tube, most mtb's will have sufficient
standover. Or close enough to warrant a closer look.

I agree.

Just for fun & comparisons sake, I'm going to measure and compare my
most comfortable MTB & road bikes right now, just too see how
different the fit is. I know it's different, because my position on
them is different. I've never measured the difference, but I did go
through countless hours and bikes to get these perfect fits, and I'm
pretty damn sure that each is right for me, for the respective
disipline. I was going to grab those measurements off my MTB anyway,
so i'll grab similar measurements off my road bike while I'm at it.
If there are any in particular you'd like to know, to help you figure
sizing or just out of curiosity, just ask.

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.htmlhastoomuchof a reach.

--
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.


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

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.

On Nov 3, 7:39*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.

Here's another pic of the MTB with the saddle adjusted per Mike's
page. It actually wasn't much lower than my "fire road" setting,
which is surprising considering the 4" of height difference between
us. http://tinyurl.com/59vanl

With that saddle height, using your method, I got a "B" measurement of
30". I must admit, though, that this type of measurement is far more
complicated to take than a C-C top tube, even if you take adjusting
the saddle height out of the equation. I think you are probably on to
something just looking for top tube lengths. It should give you the
info you need, and will certainly be easier, faster, and less prone to
error on the sellers end.

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.htmlhastoomuchofa reach.

--
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