Tech Talk - Why a Tri Bike?

Why a Tri Bike? Positioning for Non-Draft Racing

Hi all. I’ve been a mechanic for 4 years now, and have a keen interest in the gear associated with road and triathlon racing.  I’m here to offer what I deem to be more than just a casual interest in bicycle technologies. I wish I was sponsored so that I wouldn’t have to keep paying for "things to try", however I do get to work on and see enough new product to be able to evaluate what the goods are. If you’re reading Cliff’s blog, it may be because you’re a family member supporting him, but possibly you’re going to compete against him, and want to get into his psyche…  well, I’m going to offer some technical expertise: You can buy speed, but only up to a certain point. Unfortunately, I found this out the hard way as you can read in Cliff’s Bridgetown race report!

So. Over the next couple of chats, I’d like to talk about different equipment and how it can help you achieve your goals.

Let’s talk about a tri bike first.  

Fig.1

Fig 2.

FIG 1 Shows a typical tri bike. What is the importance of having one? Position.

Take a look at Line 1. Your butt and thus, leg power is directly over the crank. You are pushing directly down, or perpendicular, to the surface you are riding. This is achieved by a couple of things.

Line 2 shows the top tube of the bike. Quite close. Looks a little uncomfortable and youre mid-section to youre arms are quite close. But what this achieves is two-fold:

a) the aforementioned position relative to the crank, and

b) aerodynamics.

Line 3 shows the deflection of air around your body. Think of yourself as an arrow. The position of your hands form the tip of the arrow includingd a small area of your chest deflecting air around the upper part of the body. If you get into numbers a good tri bike should have a seat angle of 78^o - the angle of the seat tube (what you sit on) relative to the top tube.

Normal road bikes don’t have this seat angle as per FIG 2, even with aero bars.

Line 1 shows that seat angle, traditionally 73^o - between the top tube and seat tube. Again, it means that you are not directly over that crank (see line 1, compared to foot). Power transfer is not as complete. What it does help you do is climb hills. TimeTrial (TT)/Tri bikes suck at this.

Line 2 shows the longer top tube. Not as aerodynamic. Sitting more upright, chest is taking a lot more of the Ram air.

My personal results are as follow… same 10km TT course, with a true tri bike, 35 seconds were shaved off. Extrapolated over a 40km TT/Tri, and youre looking at 2 minutes saved. Nice? That’s the principal difference of a tri frame!

In future articles I’ll get into other bits of tri gear which can help you out.

Til next time, ride it like you stole it. ~ TJ

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