frame size

[McLovin]

Hi,
I bought a Caad3 Cannondale from 2001. The size on the frame is 58 but when I measure it it's 61. How is this possible?
I'm 185 cm and I'm affraid it's going to be too big for me. I can't try it now because of the weather.

 

[Bustedknuckle]

Hi,
I bought a Caad3 Cannondale from 2001. The size on the frame is 58 but when I measure it it's 61. How is this possible?
I'm 185 cm and I'm affraid it's going to be too big for me. I can't try it now because of the weather.

2 most importtant measurements are seat tube ANGLE and top tube LENGTH..not really 'size.

The first is related to your femur length and where your knee is when seat height proper and the cranks are forward, parallel to the ground.

The second to torso/arm length, flexibility.

Other things related, like head tube length, but

You are probably measuring center of BB to top of seat tube? Actually means little as it relates to 'size'.

I am 6 ft(183cm), ride a 58cm frame, center to center..with a 57cm top tube and 73 degree seat tube.

Got a decent bike shop handy that can do a fitting on you and the C-dale?

 

[JayKosta]

Do you have adequate 'stand-over' clearance from the top tube?
If not, then frame is too large.

Can the seat height be adjusted to your 'BB to top of seat' measurement?
If not, then frame is too large.

Can the stem/bars be set to a good height for you?

With seat at proper height, place elbow on front of seat, do your fingers reach the bars? Or compare to a bike that does fit you.
This is a rough initial fitting test.

Jay Kosta
Endwell NY USA

 

[McLovin]

Thanks to both of you. I managed to make a short ride uphill, some 4 km at 4%. IT was ok, just a little pain on the exterior of my knee (I had some problems last year). Yes, I can reach the bars with my fingers, quite easy actually. I probably should go to a local store and hope somebody could help me. But I still don't understand why it's that difference between what it's written on the frame and what I measured.

 

[avanti]

You can double check your measurements using this chart
http://web.archive.org/web/20060513070151/http://www.cannondale.com/bikes/01/geo-20.html
Note where Cannondale takes their measurements.

 

[fatsprintking]

I have a 58 caad4 and can confirm that the top tub c-to-c is 57.5 - don't take the manufactures word on sizes, you need to have the actual measurements. As Bustedknuckle has told you, the really important measurements are the top tube and seat tube angle. Dales of this size have a 73.5 degree seat tube. If you are in the 185cm range, unless you have an unusual body type a 58 is your starting point. I would have ridden a 56 in the dales back in the day with a longer headstem, but I prefer the room of the 58 now in my late 40's.

 

[Bustedknuckle]

Thanks to both of you. I managed to make a short ride uphill, some 4 km at 4%. IT was ok, just a little pain on the exterior of my knee (I had some problems last year). Yes, I can reach the bars with my fingers, quite easy actually. I probably should go to a local store and hope somebody could help me. But I still don't understand why it's that difference between what it's written on the frame and what I measured.

They gotta call it something. Most bike shops have riders stand over the bike and announce, 'Good to Go' if the top tube isn't snugged against their nether regions.

So they size it by the seat tube length, which really means little. If the seat tube angle and top tube length are proper, standover generally takes care of itself.

 

[ustabe]

The two most important frame dimensions are stack height, the height of the top of the head tube relative to the bottom bracket (y-coordinate), and reach, the horizontal span between the bottom bracket and that point (x-coordinate).

Lacking that info, most riders can work with horizontal top tube length and head tube length, given that seat tube angles usually vary a degree or less, and bottom bracket drop a millimeter or two or three, for the range of sizes that might work for you.

My personal sizing triage goes like this. First, can you straddle the bike comfortably? Second, without sliding the saddle all the way forward, can you reach the brake hoods comfortably? Finally, manipulating stem and spacers, can you position the handlebar at a height that works for you?

Nominal size is a fleeting thing with bikes. In the days of horizontal top tubes, you had to ask whether it was center-to-top (of seat lug) or center-to-center. On bikes of standard steel tubes, the c-t number was about 1.5 cm larger than c-c.

Nowadays, with short "compact" seat tubes and extended "endurance" head tubes, the source of the numbers could be anyone's guess.