Sean on top and seat tube length.

Steve sent us this article from Sheldon Brown at Harris Cyclery

Top Tube Length: More Important Than Seat Tube Length!

Sean, from B&L Bikes in Pullman, as well as current vice-president and former PResident of the club, has fitted many of us for bikes over the years. Here is Sean’s response.

Steve,

A few quick thoughts on what you wrote. Seat tube length is something we hardly talk about anymore. One of the reasons is the new bikes have the sloping top tubes, making it much easier to stand over them. I can sometimes have a person stand over a bike that is two and sometimes 3 sizes too big for them and they still have standover clearance.

Top tube length is the most important thing as Steve learned with 19 inch Big Sur. However there are a number of factors that determine proper top tube length that as smart as Sheldon Leonard is, he does not take into consideration. First off is of course torso length. Steve has learned this. I’m about 2-3 inches taller than Steve but we have the same length legs, which means he has a shorter torso than I do, hence he probably needs a bike with a shorter top tube than I do. (I’ll come back to the probably).

Another factor affecting top tube length is the person’s flexibility and injury history. Corrie (sorry Corrie) would be a case in point. Corrie is very inflexible in his back and hamstrings. If Corrie were more flexible than he is. I think he would probably ride a bike a size larger than he does.

Thirdly Seat tube angle is hugely important. Both of you guys have been fitted in our store and we’ve used the plumb bob in fitting. We drop the plum bob from the bony protrusion (tibial tuberosity) just below your knee cap. We adjust the saddle for and aft to have the plum bob be above the pedal axle or a tad bit behind. Seat tube angle affects this. If a bike has a relatively steep seat tube angle this effectively makes your top tube longer. We would have to move the saddle further back on it’s rails for your knee to be in the proper place. A bike with a slack seat tube angle effectively makes your top tube shorter because the saddle has to be moved further forward.

Related to seat tube angle is the individual’s femur length. One’s femur length also determines how your knee will fall over the pedal axle. A person with a longer femur will need to move their saddle further back, again lengthening the top tube. I’m a good example in another way. I have very, very short femurs, ask Brice, he’ll tell you. I have to take a seatpost and switch it around, with the clamp in front of the seat post. Most clamps are behind the post. Then I have to run the saddle most of the way forward on it’s rails. This really shortens my top tube by several centimeters. So for me because I have such short femurs I have to ride a bike that is technically a size or two too big for me so that I can have a long enough top tube. I’ve only recently really discovered this. What I had been doing for several years is riding with really long stems like 130-150 mm long. This helped but I was still a bit scrunched on my bike. As I’ve sold my bikes I’ve been buying larger ones. Ten years ago I would have had a harder time because of the flat top tubes back then. I would have had a hard time standing over a larger bike but nowadays it’s not a problem, so I’m thankful for sloping top tube bikes. My other option would be to get a custom bike that has a really steep seat tube angle. The reason why I earlier said that Steve probably needs a shorter tube than I do is because of femur length. If I had really long femurs and Steve really short ones, even with our height difference we could ride a similar sized top tubed bike.

I hope I’ve explained myself clearly enough let me know if you guys have any questions. Corrie feel free to use this on the website though maybe it’s overly technical for some.

Steve, get your butt up here so we can ride.

Sean

If you are interested in bike fit you might want to take a look of the youTube videos that Doug found. http://www.youtube.com/results?search_query=John+Howard+Bike+Fit&search=Search

After listening to these I think my seat is to low and I need to tilt the nose down a hair…I think I have the nose slightly raised now…..interesting to try anyway.  I also pedal to much heal first and not enough toe first.

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