bike geometry re: short and taller riders

This is in regards to bike geometry. I bought a bike last summer that happens to be considered a multi-sport tri bike. Let me add here that I am not a tri athlete (only in my dreams). I chose it for several reasons, mostly to accommodate my body. It does have a 76 degree seat angle, not terribly aggressive. I was looking at Running Mommy’s thread earlier about her new Giant bicycle. Being interested, I went to the Giant site and looked it over. Then I checked out the geometry and noticed the seat angle for me would be a 73 degree angle. The XS size is 75 degrees. Then I checked out Trek…the WSD XS was 75.5 degrees, for my size it was 73. It got me thinking--at the time I got my bike I had received remarks regarding my getting that bike because of the kind it was with the seat angle always brought up. It got me wondering. I realize that the length of top tube and head tube needs to be factored in. But, my wonder was, do short riders use muscles differently than taller riders? You hear a lot about how tri bikes save the athletes’ hamstrings for running… or something to that affect. Hmmm?

I don't know all the geometry reasoning behind it all, but my legs seem fresher after being on the tri bike after a long ride, than on the road bike. Totally different position, but maybe it's just because I'm lying down and relaxing like I'm in a barcalounger on the tri bike.;)

Tri bikes with the larger seat angles use a different set of muscles than a normal bike - You pedal more with your quads on a tri bike. Whereas a regular bike uses your quads and hamstrings.

So a tri bike saves your hamstrings for running.

I'm 5'1 - I like a 73 degree seat angle on my bikes... that seems to be where I'm comfortable & pedal efficiently. I've had 74 & 73.5 degree seat angle bikes and they always seem to make me hang my butt off the back of the seat to get comfortable.

my surly has like a 75 degree seat angle... and I'm getting used to it, but don't like it for long distances, I end up hanging my butt off the end of the seat.

They put larger seat angles on smaller bikes to shorten the top tube & reach for smaller riders...

Quote:

---

Originally Posted by Catriona

They put larger seat angles on smaller bikes to shorten the top tube & reach for smaller riders...

---

This answer wnyrider's wonder. The seat tube angle of my Fuji Finest RC XS is 76 degree. I'm all right with that.

And the design of tiathlon bike is different from road bike. Check this link.

Cervelo uses different approach to shorten the top tube length for small riders: reduces the head tune angle.

Here's an explanation to your question. This is from the Titus Bicycle website.
This information is for cyclists 5'5 and under.

"When it comes to fit, a true woman specific design will feature adjusted angles and geometry to fit a female’s body dimensions. Aside from a shorter top tube needed for a comfortable reach and increased standover, the seat angle should be steeper to accommodate a woman’s shorter femur length. The steeper seat angle position allows a woman to be positioned properly over the pedals. The average seat tube angle for both road and mountain non-female specific designs is typically between 72 and 73.5 degrees. The seat tube angle on female specific designs should be between 74 and 75 degrees. This steeper seat angle also contributes to better handling. A steeper seat angle results in a longer, more stable wheelbase. Anything that can be done to get the wheelbase a little more stretched out on a small frame will result in a more stable, better handling bike."

http://www.titusti.com/womensfit.html

I don't know if the short femur theory is true for every small woman but I'm
5'1" and all my bikes have the steep sta including my custom frame.
Without the sta there is no way I can get correct saddle setback or (KOPS). Even with a sta I require a zero degree seatpost and my saddle has to be set forward in order to achieve correct knee positioning.

I must just have weird femur leg lengths.

I'm 5'1, I use a set back seatpost with my seat all the way back and can get comfortable leg wise on a 73 degree seat angle. 73.5-75 degree seat angles, even with the setback & the seat all the way back, my legs are just not in the right position. I don't use WSD's because I find the top tubes too short - so my top tubes usually about 540 mm with a 100 mm 6 degree stem & standard reach handlebars. I usually use about a 48 cm frame.

Interesting reading and good sites to review...thanks. It still sounds like the smaller bikes have more of a tri frame design. Being taller I never paid much attention to the dimensions of the smaller frames. When the WSD became popular I started to pay more attention to geometry. I went to a Ladies Night at a bike shop recently and there was a Trek rep there. She explained the concept of the WSD and it was interesting. If I were to start all over again in my search of a new bike I may have made different choices. Next time I guess!

Here's an old discussion I had with Irulan about road bike fit vs men bike fit. I was trying to figure out why my mtn bike didn't feel as comfortable as the road bike. I found the Titus article and my mtn bike was designed as they said in the article, short tt but slack sta. We tried various things to get it to fit better but no luck. We just couldn't get my knees over the pedal. I still have the old mtn bike but rarely ride it.

http://forums.teamestrogen.com/showthread.php?t=585

I started riding in 1980 and went through many bikes trying to get a good fit. It wasn't until I bought the Titus and was fit by a qualified person that I realized what a good fit was all about.

Catriona, I don't fit the model for short women either. I have a long torso which makes up for short femurs.

The statements that women have shorter torso and longer femurs are nothing more than generalizations, we are all different. Knowing your body goes a long way in getting a well fitting bike.

BTW, here is an article that I found when I started to look for my first road bike:
Buying a bike that fits a woman (for MTB, road bike, including the touring bike)