newbie question

[Hbw]

I raced a few triathlons 15 years ago and am trying to get back into it. I was wondering why I see
triathlon bikes with 650 c wheels instead of 700's. Is there an advantage to this?

Thanks

 

[MJuric]

On Thu, 12 Jun 2003 14:59:46 -0400, "HBW" <[email protected]> wrote:

>I raced a few triathlons 15 years ago and am trying to get back into it. I was wondering why I see
>triathlon bikes with 650 c wheels instead of 700's. Is there an advantage to this?
>
>Thanks
>
My understanding is they are lighter and therefore accelerate quicker. Not being a bike guy
however I often wondered about the advantages here myself as the equition for calculating
rolling resistance is directly related to wheel size. Larger bing better. Thus I can see teh
advantages of a 650C on uphills, less weight to carry up, and in a sprinting or cornering
based course. But aren't most of the courses mostly flat? Are there aotehr advantages to
650CC wheels?

~Matt

~Matt

 

[Topdog]

"HBW" <[email protected]> wrote in message
news:<[email protected]>...
> I raced a few triathlons 15 years ago and am trying to get back into it. I was wondering why I see
> triathlon bikes with 650 c wheels instead of 700's. Is there an advantage to this?
>
> Thanks

It's not the wheel size, it's the seat tube angle. A tri bike has a more foward position, and a tri
frame will have different geometry to help you do this. What this means is that the rear stays are
shorter. As a result, the small to mid-sized frames cannot accomodate 700c wheels, so they use 650c
wheels instead. A larger sized tri bike will use 700c. This set up DOES tend to help in that you are
in a more aero position, and able to do better sprints. I've heard that it also uses slightly
different muscles so that you will have more strength for the run, but I've also heard that that is
hokum. I CAN say that I can average at least 1-2 MPH faster with my tri set up (including aero bars)
than my road set up, at least over shorter, not so hilly distances.

Bottom line - using 650c wheels will not help you in the slightest, but a tri frame (which may
necessarily have 650 wheels) may well be a big help.

 

[Topdog]

> My understanding is they are lighter and therefore accelerate quicker. Not being a bike guy
> however I often wondered about the advantages here myself as the equition for calculating
> rolling resistance is directly related to wheel size. Larger bing better. Thus I can see teh
> advantages of a 650C on uphills, less weight to carry up, and in a sprinting or cornering
> based course. But aren't most of the courses mostly flat? Are there aotehr advantages to
> 650CC wheels?

The differences between 700c and 650c wheels in terms of both drag and rolling resistance is
negligible. The reason for the 650c wheels on many tri bikes is not due to any advantages that they
give, but rather that the tri bikes have shorter rear stays, and 700c wheels do not fit on small-med
frames. Larger tri frames will have 700c wheels, since the stays are long enough to accomodate them.

Tri frames are made to provide both a more forward and aerodynamic position on the bike. They also
allow you to steer better with aero bars (which can be dicey on a road bike). The foward position
gives more speed, allowing for faster sprints and time trials, while a set-back position (such as
that on a road bike) allows for more power.

 

[Mark Hickey]

MJuric wrote:

>On Thu, 12 Jun 2003 14:59:46 -0400, "HBW" <[email protected]> wrote:
>
>>I raced a few triathlons 15 years ago and am trying to get back into it. I was wondering why I see
>>triathlon bikes with 650 c wheels instead of 700's. Is there an advantage to this?
>>
> My understanding is they are lighter and therefore accelerate quicker. Not being a bike guy
> however I often wondered about the advantages here myself as the equition for calculating
> rolling resistance is directly related to wheel size. Larger bing better. Thus I can see teh
> advantages of a 650C on uphills, less weight to carry up, and in a sprinting or cornering
> based course. But aren't most of the courses mostly flat? Are there aotehr advantages to
> 650CC wheels?

The "lightness" of the wheels isn't really a huge issue when accelerating, since you have to spin
the smaller wheel up to a higher RPM to reach the same speed (essentially negating any "advantage").

Others think there's an aerodyamic advantage, but in the end since the rider has to end up in the
same position no matter what the size of the wheel, the frame has to be taller, again, pretty much
cancelling any advantage.

The one advantage of the small tires is that the front end can be lower if you need that to achieve
proper positioning. But if you look at most of the 650c tri bikes out there, you'll see them set up
with a riser stem and numerous spacers to get the bars up where they would have been with a 700c
wheel. It's a potentially great thing for some shorter triathletes, or those who can tolerate a VERY
low position.

The down side is the availability of tires. If I were going to build myself a "small wheeled tri
bike", I'd probably design it around the 26" MTB rims instead. There are many more choices for rims
and tires.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame