What are the positives and negatives of a Sloping Top Tube for a tri-bike?
Thanks!
positive: you think it looks cool.
negative: you do not think it looks cool.
the wisdom behind the sloping top tube is suposed to be that it makes the triangles of the frame smaller and therefore stronger. It also helps keep frame weight down (a little).
Thse are the only two arguments that I think hold water, although there are those that will argue there are several other advantages.
The main purpose I see for sloping top tubes are to reduce standover height and to increase head tube length without increasing seat tube length. These haven’t been issues for me on my tri bikes.
A compact frame to me always looks like you’re riding your little brother’s bike. I’ve got one and although I’m not crazy about the amount of round seatpost I have showing I can’t complain about what it cost me for the frame and fork ($105) or how it actually rides.
I believe the basic idea behind the compact frame is that a frame manufacturer can get away with making fewer frame sizes and that it’ll be lighter than a traditional frame.
History lesson:
The current trend of top tubes that slope from the head tube down to the seat lug area were popularized by Giant Bicycles’ designer Mike Burrows who was predominantly a mountain bike designer. This design concept started during the height of the mountain bike craze when road bikes simply were not selling. This was the pre-Armstrong era.
Burrows idea for Giant was two fold: Firstly, since road bikes werent selling then perhaps making them look more like mountain bikes may make the MTB buying public more inclined to buy a road bike for, ahh, “training” for their off road riding. Secondly, also since road bikes were not selling Giant and everyone else had to reduce their overall SKU’s of road bike models. That means redusing the numbers of colors and sizes in a given model.
Burrows introduced compact geometry with “T-Shirt” sizing; frame sizes were no lonmger referred to as “54 cm, 56, cm, etc.” they now became “Small, Medium and Large”. This served the dual purpose of reducing the number of frame sizes a company had to carry and it also sounded familiar to MTB buyers who were already accustomed to that vernacular for frame sizing.
Then some kid from Texas won this race in France. Seven times.
Giant originally claimed that their three sizes of compact frames would fit 80% of the customers to come through your door. I think it was more like 15% since the top tubes were hopelessly long even for a road frame. Giant soon discovered the more fit-oriented dealers were not getting good fit results as road bike popularity began to re-emerge in the late '90’s. They added additional sizes to the three size “T-Shirt” sizing stable. It still didn’t address the needs of everyone’s fit- hardly any bike company’s geometry chart does except for maybe Guru, Colnago and Serotta to name three.
Now, as all this spun around some utility for the “compact”, rearward sloping top tube design did manifest itself.
The sloping top tube design did seem to work for those with shortish inseams and very long torsos (me…). Us guys and gals were previously restricted to buying a slightly “larger” frame to get the correct top tube length (long enough) and then stuck with very little stand over height and a dorky looking bike with that always looked like the seat was too low. The standover height actually does have a functional element when it comes to climbing out of the saddle- a lowered top tube gives you more room to rock the bike back and forth between your legs for additional climbing leverage out of the saddle.
Now, from th perspective of a triathlon bike: Remember that across the board most well-designed tri bikes trend toward shorter top tube lengths than does a road bike. The top tube on my tri bike is about 3 cenitemeters shorter than it is on my road bike and my reach is about 5 centimeters shorter on my tri bike than it is on my road bike.
Also, Tri bikes seem to have addressed the stand-over height issue by featuring a lowered top tube with some type of seat extension. This also enables the rider to have a low-ish head tube providing the optinon of fitting the additional height of aerobar elbow pads in there and still having reasonable rise to the rider’s torso.
So, ultimately, the number of people who probably need a rearward sloping top tube triathlon bike is very small. I have two bikes right now with a very gradually downward/rearward sloping top tube: A Guru Crono (new) and the Kuota Kalibur in small. The Guru fits better than the Kuota (it’s custom) and has a less significantly rearward/downward sloping top tube and seat tube extension.
I would suggest the sloping top tube thing for most tri bikes is largely fashion, not function. You would need a very long torso and very short legs for this to be a necessity.
the key word in tom’s history is " popularized".
sloping top tubes on road bikes existed long before the burrows/giant bikes - and they carried none of the burrows/giant baggage with them. they still do. it is a mistake to equate a sloping top tube with giant’s/burrow’s interpretation of them. the two are NOT one-and-the-same. the giant/burrows interpratation was a marketing issue, primarily.
a sloping top tube is simply a tube which slopes. the rest of the bike, how it fits, need not be any different from that of a horizontal top-tube bike. indeed, numerous bikes have top tubes that slope upwards. it is just a design element, nothing more. take any well fit frame in the world, make a diagram of it - erase the horizontal top tube and pencil in a sloping one - presto you just made a sloping top tube frame fit anybody. generalizations about which type rider is “best served by a sloping top tube” speak more to the giant/burrows sizing concept, than they actually do to the sloping top tube. again, they are not the same thing.
Exactly.
So how about the C4 carbon frames (see www.c4carbon.com) where the bottom bracket is behind the join of the seat tube with the down tube? The idea works with both sloping and non-sloping top tubes to give a different effective top tube length depending on the height of the seatpost. Their chrono frame uses a slopping top tube, not quite sure why though.
SteveMc
that chrono is the strangest frame design I’ve ever seen. it look moe like a 29er than a tri bike
And it’s a “one size fits all”!!
They used to make it with a custom aero seatpost but have opted for a more straightforward design now.
The rear brake is nicely positioned though and the seatstays are close to the wheel before turning outwards for the derailure holder.
SteveMc
ALSO, in larger frames, made of some of the more flexible round tubing, the compact frame can enhance stiffness of seattube and remove some bottom bracket sway. Of course, with the advent of carbon, shaped tubing (Ti), large diameter aluminium, this purpose has largely become style. Also, there is also the production cost issue. While the difference is small on one bike, it is huge in the long run for mass production companies.
The question is: Trek is producing one! Does this mean the disapperance of the traditional horizontal top tube?
steve, not sure what you are asking - as you note their idea works independant of any slope ( or lack therof ) to the top tube.
print off a copy of each of those frames. erase the sloping tt, and pencil in a straight one. vice versa. makes no difference.
by the by, the basic concept being used there is also used by mtn bike manufacturers, or was. ibis had the same basic thing goin on with their old szazbo bike, back in the early 90’s, for one.
steve, not sure what you are asking - as you note their idea works independant of any slope
( or lack therof ) to the top tube.
Agreed, I’m just making a small point of information that one needs to look beyond the “triangle” and into the lengths and angles of any given frame. The C4 carbon frames illustrate this nicely as they managed (but I’m not sure how well) to get rid of even the t-shirt sizes…
As a side note, Burroughs claimed aerodynamic benefits of a sloping top tube and aero seatpost combo. I think this came out of testing on a track so I’m not sure how that holds up to modern windtunnel data.
SteveMc
Great explanation. Thanks!
Tom
I was on Litespeed’s web site today. Then I read this thread. It looks like all there road bikes for 07 have sloping top tubes.
PS: Thanks for the info.