Bike Frame Geometry – what happens when you ride a Time Trial Bike.

The design of a time trial bike is quite different to the design of a road bike. The time trial bike is specifically designed to help you get through the challenges of a triathlon.

Triathlons within themselves place unique stresses on the body.  Swimming places strain on both upper and lower body, cycling works the lower body in a seated position, whilse running works mainly the lower body but in a standing position.

Over the last number of years the concept of a bike designed specifically for the sport of triathlon has evolved. The two major changes on the bike are the steeper seat tube angle and tri-bars.

The purpose of this article is to look at what a steeper seat tube does to the riding experience.

A little bit about seat tube angles:

A typical road bike has a seat tube angle of between 70 – 76 .  You sit in a similar position to sitting on a chair with your feet a bit forward from your hips. A Time Trial bike has a steeper seat angle normally greater than 76 .

Some observations with regard to the different effects caused by the seat tube angles.

  1. Your cardio and respiratory loads are slightly lower on a Time Trial Bike thus making a TT bike a more efficient bike to ride.
  2. Road bikes with a less steep seat angle are easier to handle in typical road riding situations.  You have a better weight ratio between front and back wheel on a road bike – that makes the bike easier to handle.
  3. Road bikes are safer, in that you generally have quicker access to your brakes.
  4. A Time Trial bike allows the hips to be extended, the spine to be more flattened and the rider to create less drag than on a road bike.
  5. You are able to run faster after climbing off  a Time Trial bike.
    Garside and Doran (2000) found that cyclists were able to run the first 5km of a 10km run significantly faster after a 40km time trial, when using a bike with a seat angle of 81  as opposed to a bike with a seat angle of 73 .
    They also found that stride length was greater after transitioning from a TT bike indicating that the hamstring group shorten in the traditional bike position.
  6. Under intensive testing (Richard et al – 2005) analysed Electromyography (EMGresults of various leg muscles. EMG is a technique for evaluating and recording the electrical activity produced by skeletal muscles. The most profound result of the test was that the Biceps Femoris and Semimenbranous muscles worked a lot less in when placed in a bike with a steeper seat tube. The fresher the hamstrings, the better your run afterwards.
  7. Tight Biceps Femoris muscles explain why some triathlon runners appear to run in a squat like position after climbing off the bike. One of the benefits of a TT bike is that the Biceps Femoris muscle is forced into a stretched position thus enabling the runner to run in a more efficient position.

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Regards
Mike
Mike Roscoe

About sbrsport

SBR Sport specialises in Swimming, Biking and Running. On the medical side we are able to do intensive bike setups, leg assessments and soft tissue release. Follow us on twitter - www.twitter.com/swimbikerunshop and/or facebook - www.facebook.com/sbrsport.
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8 Responses to Bike Frame Geometry – what happens when you ride a Time Trial Bike.

  1. Wow interesting, didn’t know that! Now I wish I had a TT bike!

  2. SBR Sport says:

    Reblogged this on .

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  4. Awsome website! I am loving it!! Will come back again.
    I am bookmarking your feeds also.

  5. mrzona says:

    Awesome, very informative. Thank you very much for all the posts. I’ve learnt a lot from the ones I’ve read.

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