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Help, geometry question(4 posts)

Help, geometry questionnewrodie
Feb 7, 2002 7:13 AM
I want to get into road cycling and racing, comming from a MTBiking background and I absolutely don't understand the geometry issue.

I read a review that said the Specialized Allez has true racing geometry and another review said that the Jamis Quest does not have racing geometry.

According to Specialized the Allez has a 72.0 head angle and 76.0 seat angle on the 47cm frame. While according to Jamis the quest has 72 head and 74 seat on the same size frame.

What what is the angle cut off for racing geometry?

Are these the only two important factors (head and seat angle) or what other factors play a role?

What is slack head angle?


Totally confused
The racer guys will be all over this question....sprockets
Feb 7, 2002 8:00 AM
in a minute or two, but until then, let a former-racer from the toe strap and white cloth tape era have at it. Generally speaking, modern "race" geometry usually refers to a bike with a slightly more compact over-all frame design. This usually means a shorter wheelbase than non-racing style bikes. This comes about by using shorter chain stays, and a fork that tends to be more vertical (hence, not "slack" angled). From a racer's standpoint these latter two things are usually desirable in their own right, they are not done just because they shorten the bike. The shorter wheelbase is just a fortunate result of those design elements.

To get a long enough cockpit, designers balance how far back they can lean the seat tube (the more vertical, the less "slack"), how long they can make the top tube, and how long the stem can be. Some riders prefer a less vertical seat tube, but this can tend to make the chain stays a bit longer.

Your ideal geometry will depend on your own body, race type, and style. Some riders like to sit far back, others prefer to be a bit forward, while some have a long torso and need a bike with a longer cockpit so they must compromise somewhere else.

FWIW, some "classic" race designs had a less compact design. These bikes were in theory "all-around" style bikes, and they had short chainstays, a reasonably quick-steering front end (not too slack), but also a longish top tube which gave a longish wheelbase and a bit more high speed stability. Some considerable success can still be had on such designs, even on short, tight courses.
The racer guys will be all over this question....DINOSAUR
Feb 7, 2002 11:30 AM
Spockets did nail it real good. Also~ Most pro's ride bikes built to their spec's and underneath the paint and ht badge might be an entirely different frame made by a different manufacturer. Although Armstrong claims to ride whatever Trek throws at him, the difference being the saddle and pedals. A lot of it comes down to what you prefer, your pedaling style, and your anatomy. Usually the way you find out is by riding a certain bike for a couple of seasons and noting what you don't like about the geometry and going from there when you go to a new bike.

Pro's also ride different spec bikes depending on what type of race it is: Stage, TT, or Crit.

You might benefit by having someone size you, and discussing what type of riding you do and gathering input so you end up with a geometry you are happy with.

Most LBS's (local bike shops) just push bikes out the door and very few of them work with you for fitting.

Do a little research and make your purchase baised on fit and you won't end up riding a bike that doesn't fit you correctly (like me)...
re: Help, geometry questionTroyboy
Feb 7, 2002 9:10 AM
Sprockets nailed it pretty well. A TT frame is more likely to have one of those 76 STA. However, some in an effort to minimize ST to rear tire distance move the rear wheel up and slack that tube as well. Just remember you're talking about your example, you're looking at a 47cm frame overall. That's TINY! Generally speaking, most frames have more vertical STA's as they get smaller. That is only generally speaking. As Sprockets said, a tighter wheelbase with a fork with less rake and a smaller, stiffer, more upright STA frame is typically desired for a crit type racer. Only generally speaking, road racers are more slack in the STA and the fork rake and have a little longer wheelbase to make handling a little less quick (as some say sketchy). To figure out what type of geometry you like, you've simply got to experiment. It is virtually impossible to find high end bikes at shops that you can try and try and try. Typically, it's get fit, it's find one, ride it, ride it. If you like it, keep it. If not, sell it and move on. That's one reason why many of us have three times as many bikes as families have kids. My crit racers get smaller and smaller and I love them. I'm 5'8" and this season for crits I'm on a 51c-t and I love it. Good luck.