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Bike Geometries - Are they really that different?(5 posts)

Bike Geometries - Are they really that different?Berm
Feb 19, 2002 10:31 AM
In smaller size bikes are geometries really that different? Not understanding angles very well in terms of how they affect the bike, what is the opinion as to these four bikes and how they would handle/fit putting aside material differences? These geometries are from a Lemond, Colnago, Pinerello and a Moots.

SEAT TUBE 49 (C-C)
TOP TUBE MM 520
HEAD ANGLE ºº 72.5
SEAT ANGLE ºº 74
FORK RAKE MM 47

SEAT TUBE 49 (C-C)
TOP TUBE 527
HEAD ANGLE ºº 71
SETBACK 12.7
FORK RAKE 4.3
SEAT ANGLE ºº 75

SEAT TUBE 49 (C-C)
TOP TUBE 525
HEAD ANGLE ºº 72
SETBACK 13.5
FORK RAKE 5.0
SEAT ANGLE ºº 74.15

SEAT TUBE 50 (C-T)
TOP TUBE 526
HEAD ANGLE ºº 72.75
SEAT ANGLE ºº 74.25
re: Bike Geometries - Are they really that different?tarwheel
Feb 19, 2002 11:21 AM
These all look pretty close to me. I'm no expert on the handling characteristics of different geometries, but I can tell you a few things related to fit. The seat angle can effectly lengthen or shorten the top tube. A steep angle "lengthens" the top tube, while a slacker angle "shortens" it. That is, a frame with a 74 seat angle effectively will fit about 1 cm shorter across the top than a frame with a 75 seat angle, all things else being equal. That's because, with the steeper angle, you have to move the seat further back to achieve the proper knee-over-pedal (KOPS) position. I am not certain what effect head tube angle has on this, but I would assume that a slacker angle would effectively shorten the top tube by bringing the handlebar closer to the saddle. Putting this all together, it looks like frame #1 would have the shortest effective top tube, #2 and #3 would be marginally longer, and #4 would be have the longest effective top tube (about 1 cm longer than #1).

In my personal experience, I sold a 57 C-T Bianchi that was too long across the top for me (56 C-C). I replaced it with a 57 C-T Gios with a 55 C-C top tube. Both frames had 74 seat angles. The Gios fits me much better because it is shorter across the top. The chain stays are about 1 cm shorter on the Gios than the Bianch, but the Gios stays can be lengthened about 1 cm (which I've done). The Gios is a much more comfortable frame -- less road buzz and vibration -- which I attribute to the frame material. The Gios is steel, and the Bianchi was aluminum w/ carbon fork.
re: Bike Geometries - Are they really that different?Berm
Feb 19, 2002 12:46 PM
Thanks for the response. If you are correct, so much for the generalization that Lemond bikes have long top tubes and Colnagos have short tob tubes. The Lemond is No.1 and the Colnago is No. 2 on my list.
Check out Mountain Bike Actionhikerryank
Feb 19, 2002 11:40 AM
This month's mountain bike action has a section devoted to how geometries affect the ride of a bike. Though this is based on the Land Rovers of the bike world, I'd imagine the information would cross over to our sports cars. The info is pretty basic but enough to give a general idea as to how an angle will change the ride of a bike. Can't help you with the specifics as I wouldn't want to prove how bike dumb I am. Well, too late for that based upon some of my previous posts, but no reason the reinforce it.
HRK
you mean Mountain Bike FICTIONnm
Feb 19, 2002 12:32 PM