top tube sizing ???

Yes, top tube sizing is about all I pay attention to these days. But bikes are still generally marketed by seat tube sizes so you have to look at the geometry tables to choose the 'right' size based on (effective) TT length.

-Dave

nfeht said:

im currently riding a 52cm (measured C-T) 30lbs old raleigh road bike with 27x1 1/4 wheels and am looking to upgrade.

my inseam is approximatly 30in (im 5'9"😉 but i feel that standing over the bike itself is the best way of determining whether the bike fits hieght wise.

however wouldnt the top tube length be more important since it cant be addusted by a taller/shorter seatpost. and where should your shoulders be positioned relative to the handle bars when riding (in order to determine the about what i need).

i'd want to buy a used bike because of my budget. i've gone to dealers but they have never realy been that helpful, but show they will be if i proceed to buy the bike (which hasnt worked out since i cant quite afford a new bike of the quality and level i want)

Two most important measurements on a bicycle are seat tube ANGLE and top tube LENGTH. The first is determined by your femur length(not inseam) and the second by your torso/arm length. Standover, particularly in this era of sloping top tube frames, means about nothing. If the ST angle and top tube length are proper, standover almost always takes care of itself.

Peter@vecchios said:

Two most important measurements on a bicycle are seat tube ANGLE and top tube LENGTH.

Maybe I should pay more attention to seat tube angle, but these days, for any given size in stock frames, seat tube angles are pretty close. Head tube length is important though.

My basic fitting algorithm goes like this:

Standover--can you safely and comfortably straddle the bike?
Top tube--using a stem of reasonable length, can you dial in the right amount of reach?
Head tube--given your saddle height and the stem of your choice, can you dial in your preferred height for the handlebar?

all I know is that on my current bike my shoulders are well past the handle bars when im in the drops sitting down.

If your shoulders are, in fact, past the tops of your handlebars when you're in the drops, then your top tube is way too short. Way too short. As Peter said, if you've got the TT measurement correct, then stand over will likely be fine, unless your body has some unusual dimensions. Having your body shoulders past the bar tops indicates that you've likely got a too short top tube (assuming your saddle is positioned correctly) and that your seat angle might be too steep. With your body positioned as such, I can't see your knees being anywhere near where they should be with respect to the bottom bracket.

You need to get thee to a fitter.

i have always considered seat tube angle as adjustable by moving your saddle... or perhaps in some cases installing a different seat post. on a 60cm frame I think a 1 degree difference in seat angle works out to 1cm more or less setback.

its hard to find a stock frame that differs greatly in top tube length these days... of course looking at 2nd hand you might find a custom frame with significantly longer top tube, but its more likely that the frame with be 1cm short of 'square' 54cm frame with a 53cm top tube. although Gios comes to mind as a short top tube exception.

as another poster mentioned i would also be concerned about the length of the head tube, if your current setup is comfortable AND you've been on it a long time I would try to reproduce that position with your next frame. some sloping top tube frames that i can straddle would seem like they fit me but the size of the head tube makes the bar height too high for me...

has anyone mentioned online bike fit calculators? i have foud some of them to be very good for estimating top tube length.

good luck

yea the bike im riding is my mom or dads old bike so its prob about 25-30 yrs old.
I also have a much shorter legs than other people my height.

alienator said:

If your shoulders are, in fact, past the tops of your handlebars when you're in the drops, then your top tube is way too short. Way too short. ...
You need to get thee to a fitter.

Or some friends who can ride with you and give some tips. My rule of thumb is that after dialing in saddle height and set back, and handlebar height, the humerus should be at about a right angle with the torso when your hands are on the hoods. For the kind of riding you're doing, that should be close enough. On a road bike.

oldbobcat said:

Or some friends who can ride with you and give some tips. My rule of thumb is that after dialing in saddle height and set back, and handlebar height, the humerus should be at about a right angle with the torso when your hands are on the hoods. For the kind of riding you're doing, that should be close enough. On a road bike.

looked at my seat... its all the way back. this is why im looking for a new bike.
i ride with people who race collegically when i can and am at there level w/ my heavy steel frame

nfeht said:

looked at my seat... its all the way back. this is why im looking for a new bike.
i ride with people who race collegically when i can and am at there level w/ my heavy steel frame

I hope they teach spelling at that college.

Regardless, most 52s are too small for guys who are 5'9". Try something in 53-55cm, if you can straddle them, with long-ish top tubes and fairly normal head tubes--Giant TCR, Specialized Allez and Tarmac, Felt F, and Cervelo come to mind, but there are others. Don't be cheap and insist that a bike fit you right out of the box--with your atypical proportions you'll need to do some stem and possibly handlebar swapping.

I recently put a customer on a 53cm Bianchi with a 13cm stem. With stock stems his upper body wanted something between 55 and 57, but his legs were too short for the 55.

FWIW, I'm 5'8.5" with a 29" inseam (pants size, not crotch to floor) and 33" sleeve length (shirt size). I ride a 54 Aegis Aro Svelte and a 52 Van Dessel Flahute (both road bikes), each of which has a 110mm stem. I also ride a 52 Bianchi Cross Concept (cyclocross bike), which is probably a bit too big for me. All three bikes were bought on eBay for far less than a comparable bike would cost at your LBS. Both the Aegis (paid $1275) and the Biachi (paid $750) came full Dura Ace, except for the full carbon FSA crank and Pauls brakes on the Bianchi. The Van Dessel I built up myself with 105 and better components for less than $1000 total.

My bet is that your "ideal" road bike frame size is probably either 53 or--more likely--54, with a top tube no longer than 53.5. My 54 Aegis has a 53.5cm top tube (c-c), a 54cm seat tube (c-t), and a 72-degree seat angle. My 52 Van Dessel has a 53cm top tube (c-c), a 50cm seat tube (c-t) and a 74-degree seat angle. Interestingly, the "smaller" Van Dessel actually has a longer wheelbase (97.3 vs 96.6cm), a fact attributable to the Aegis's "bent" seat tube and greater fork rake. Here are links to my bikes' geometry, if you're interested:

Van Dessel Geometry
Aegis Aro Svelte Geometry
Bianchi Cross Concept Geometry

You need to be aware that reach to the bars is easily altered by shortening or lengthening the stem. Seat height and fore/aft placement should be determined based on positioning of leg/knee/ass relative to the pedal; reach to the bars should have no bearing on seat placement. Reach to the bars should be determined after appropriate seat placement, with any necessary adjustment made by shortening or lengthening the stem, with stem height being adjusted either with spacers or by flipping the stem over.