So I’m killing time at lunch and wonder into a bike shop. I see a line of Tri bikes including Treks and mention to the wrench behind the counter that ‘the curves on that Trek tri bike looks sweet,’ and he says, ‘that’s a TT bike, not a Tri bike. Trek makes great TT bikes but not Tri bikes.’
Set me straight brethren. What gives?
I’m guessing that by time trial bikes he means bikes that meet the UCI rules such as saddle nose x cm behind bottom bracket, double diamond design, etc. Bikes strictly used for time trials under UCI rules, such as those used in the tour de france.
Really, I think he’s just being overly strict on the definition. I would say any time trial bike could be used as a triathlon bike, but not every triathlon bike could be used for a time trial bike.
One has aerobars while the other has tri-bars 
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I’ll take a stab at the answer. A true TT bike may be set up a bit differently in consideration of the fact that a) it will only be raced for about an hour or maybe a little longer and b) the rider won’t get off and run 26 miles. As a result of those things, the seat angle will be a bit more slack to keep everything lower and more aero. This will not give the hamstrings quite the stretching they get on a tri bike with its more upright geometry.
But I could be wrong.
Bob C.
Time trial bikes are designed for flexible fast roadies for using in time trial races.
Triathlon bikes are designed for fat middle-class American triathletes who cruise at slow speeds to say I have done a triathlon. Slack position as on a time trial bike is more powerful and just as aero.
In contrast to these American triathlets who are gear obssesed, the really fast guys are Europeans who mostly ride road bikes. And man do they kick ass.
So in summary, it is all about UCI legal geometry for cyclists Vs UCI illegal geometries for those who have delusions of being able to buy free speed.
Trek makes their top of the line frame with a slack angle seat post and a steep angle post. One is called a TT bike, the other a Tri bike. Basically the same thing. I think the tri frame has a bladed post and the TT does not.
Any of you catch the little quote in triathlete this month about Trek Tri bikes? Tim DeBoom said they are trying to roll out a top end tri bike for Kona. I got the impression it is like the Team TT, but with a steeper angle. It was in the section that talked about Tim in the wind tunnel.
if tim deboom is talking about it, i’m sure trek is working something out with tri-dubai now.
A tt bike is generally less sexy than a tri-bike.
People who ride them are generally less sexy than triathletes, too.
'that’s a TT bike, not a Tri bike. Trek makes great TT bikes but not Tri bikes."
Is he saying Trek doesn’t make “tri” bikes or doesn’t make “great…tri bikes?” This was sort of mentioned, but what does Tim DeBoom ride? A modified TT bike with a steeper seat angle, so you can’t really call it a tri bike? Or does he ride a “Trek Tri Bike” that “isn’t great.”?
A tri bike is ridden during a trathlon…a Time Trial bike is ridden during a time trial…
easy enough…
Triathlon bikes are urine-resistant…TT bikes aren’t so much.
M
Not only that but they have ugly bento boxes, between the bar drink holders and dangerous bottle rocket launchers on the back of the saddle. Sometimes they are even festooned with melting globs of disgusting powerbars and gels. These otherwise light “tri” bikes are then heavy as a tank and handle like one as well.
No one has touched on the actual difference that the shop guy was referring to (even though he was being a bit arrogant). A TT bike has a traditional seat angle, maybe slightly more than a road bike. A triathlon bike has a steep seat angle, around 78+ degrees. In UCI racing, the nose of the saddle must be no less than 5cm BEHIND the bottom bracket. In triathlon the nose of the saddle must be no more than 5 cm IN FRONT of the bottom bracket. So to sum up, TT bike = slack angle, Tri bike = steep angle. It sounds like the guy was being a jerk, but this is the difference he was referring to.
Most of the CSC team seem to ride in a fairly Triathlon style position even though their saddle postion conforms to UCI rules.
Plus I am European and I am not that quick
"Most of the CSC team "
Another wonderful thing about owning a Cervelo. With one quick flip of the seat post you can have a TT or a tri bike.
CSC is just one team. And we have seen how their handling skills were tested on a P3.
You might be slowish for a Euro, but in comparison with a typical American triathlete (90kg middle-aged executive or a lawyer on a Lightspeed Blade or a P3) you are a gossamer – I am sure.
I see the Euros in the races loading their bikes from whatever car they have – a small Fiat, an old van, a sporty BMW whatever. But Americans need a Honda Element or a Hummer to carry a delicate race bike for that one Half Ironman race they are doing in the end of the summer.
Oh boy…here it goes again. 
M