sloping tt vs horiz

[shankldu]

I know that pros have won on both ,Lance for ex on a madone, and say others on cervelo's etc , but it seems to me that shorter seat stays even outside of the top tube would be stiffer and put power to the ground . It feels that way to me when climbing , acelerating etc ,although by the same token the sloping frames ride more firmly as well .

[rain dogs]

You're talking about two different frame design decisions

1. Sloping top tube vs Horizontal Top Tube

2. Shorter seat stays vs Longer seat stays

You don't have to have a sloping top tube to have shorter seat stays. Look at many older GT's, Lemond Maillot Juane, which have horizontal top tubes and short seat stays.

Many Time trial bikes like Orbea, Ridley, and Kestrel have this design as well... to name but a few.

[Chance]

I know that pros have won on both ,Lance for ex on a madone, and say others on cervelo's etc , but it seems to me that shorter seat stays even outside of the top tube would be stiffer and put power to the ground . It feels that way to me when climbing , acelerating etc ,although by the same token the sloping frames ride more firmly as well .
What do you mean by outside of top tube?

[palincss]

I suspect he means something like "short stays alone, even without taking the top tube into consideration."

[tannhauser]

Do you have a question?

[eddief]

but i'd wager if you put on a blindfold you'd never ever be able to tell the differences. on the other hand, aesthetics can cause one to lose a lotta sleep. i get a bigger kick out of talking myself into how much i appreciate good tires. currently loving my ultremos x25. they seem really nicely bouncy.

[Fixed]

polarizing topic

i have had both
i liked both
cheers

[Kontact]

Why would shortening the stays and making the seat post longer make for a stiffer system? If you want the bike, as a whole, to be stiffer for riding, slope the top tube up to the saddle and extend the stays up to, like the old TT funny bikes.

But if you want the frame to be stiffer and lighter, without any reference to a completely bike or with a rider, compacts are great for advertising.

[oldpotatoe]

I know that pros have won on both ,Lance for ex on a madone, and say others on cervelo's etc , but it seems to me that shorter seat stays even outside of the top tube would be stiffer and put power to the ground . It feels that way to me when climbing , acelerating etc ,although by the same token the sloping frames ride more firmly as well .

There is really only one reason to have a sloping top tube. On frames where the headtube length is dictated for bike fit/handlebar height and the top tube needs to be sloped for standover. Slope or not in the real world is a fit issue, not a performance issue. Altho marketeers will say otherwise(stiffer, lighter, more comfy, fit better..blah, blah, blah)

Some bike makers like it cuz it means fewer sizes, particularly on monocouque frames, where molds cost a bundle. But there is no performance gains or losses for either design.

[gearguywb]

Purely asthetics.

'Tis all about the engine.

[Chance]

I suspect he means something like "short stays alone, even without taking the top tube into consideration."
If that is what he means then Kontact is probably correct. The longer seat post of a compact will contribute to more flex than longer seat stays compared to short ones.

[EDS]

If that is what he means then Kontact is probably correct. The longer seat post of a compact will contribute to more flex than longer seat stays compared to short ones.

What if you are standing?

[veloduffer]

From Tom Kellogg/Spectrum on the subject:

In designing the our first compact prototype back in mid '98, we wanted to discover what if any the real world differences there would be between traditional and compact frame designs. Our first compact frame (still my favorite frame) was an exact replica of my then current titanium frame in materials and geometry save for the sloping top tube. I designed it with a severe (17 degree) slope to ensure that any differences would be as obvious as possible. We had assumed that the new frame would be somewhat stiffer and lighter. It was lighter (about 4 ounces) but it was not appreciatively stiffer. Although we were able to measure a slight increase in stiffness, it was too slight to feel. The big change came when I stood to accelerate or climb. As I stood up, the bike appeared to loose three pounds. The inertia of the bike as I rocked it back and fourth was reduced so much that I felt as though I was on a twelve-pound bike. Interestingly, when seated, a compact frame feels exactly like a traditional design. The compact design has no effect on handling beyond the increases responsiveness during climbing and accelerating.

FWIW, I like (and own) both horizontal (Ottrott, Sachs) and sloping (Parlee, Kish, Giant). I can't tell the difference. I like the Parlee best for climbing, but it is probably due more to the light weight (15 lbs with pedals for size Large) than its compact geo. None of my bikes have 17 deg slope - I think the Giant has the most with some 10 degrees.

[Chance]

What if you are standing?
Then seat post won't flex much. ;)

If you ask engineers they'll probably tell you that compacts should provide a slightly softer ride while seated due to added vertical flex of seat post. Additionally the frame should be slightly stiffer in torsion when standing so it should be slightly better for climbing or sprinting out of the saddle. That's provided you think stiffer is good and apparently not everyone does as demostrated in "myth" thread.

Differences are very slight and probably insignificant in the real world so it's not worth worrying about.

[tannhauser]

There is really only one reason to have a sloping top tube. On frames where the headtube length is dictated for bike fit/handlebar height and the top tube needs to be sloped for standover. Slope or not in the real world is a fit issue, not a performance issue. Altho marketeers will say otherwise(stiffer, lighter, more comfy, fit better..blah, blah, blah)

Some bike makers like it cuz it means fewer sizes, particularly on monocouque frames, where molds cost a bundle. But there is no performance gains or losses for either design.

That, and a sloper uses less material and a low seat cluster feels lighter out of the saddle.

[jr59]

Some bike makers like it cuz it means fewer sizes, particularly on monocouque frames, where molds cost a bundle. But there is no performance gains or losses for either design.

^^THIS^^

I have a 1.5% slope in my custom. It was for fit only!

[MadRocketSci]

the op was talking about shorter seat stays being stiffer than longer ones...however...

1) as pointed out, you can still have short seat stays with a level top tube

2) straight seat stays are mainly in compression, which is much easier for tubing to handle than bending, and thus can be made almost spaghetti #9 thin...well, almost, as they have to be strong enough not to buckle under seated loads. See the past cervelo models for examples of ridiculously thin seat stays.

[rain dogs]

Some bike makers like it cuz it means fewer sizes, particularly on monocouque frames, where molds cost a bundle. But there is no performance gains or losses for either design.

Agreed. This is why you'll start seeing tons of -17degree stems.

So that makers can build molds with giant headtubes and allow aggressive riders to still get the same lower hand positions through stem selection, and not through frame design/sizing.

Tom Kellogs words were interesting, but again, that equal to the function of using a smaller frame (super tall seatpost and super long stem)... or in otherwords.... the "pro" fit.

If you can handle the seat-bar drop, it's all equal. But normal riders cannot... so sloping frames, tall headtubes and -17 stems evolve to be the norm, with no noticeable difference in performance other than a tiny frame.

Sammy Sanchez (5'11") tall...rides a 54cm equiv. frame (with tall headtube and about a 140mm stem).... odd but true.

[Chance]

the op was talking about shorter seat stays being stiffer than longer ones...however...

1) as pointed out, you can still have short seat stays with a level top tube

2) straight seat stays are mainly in compression, which is much easier for tubing to handle than bending, and thus can be made almost spaghetti #9 thin...well, almost, as they have to be strong enough not to buckle under seated loads. See the past cervelo models for examples of ridiculously thin seat stays.
That and also brake loads which places seat stays in bending. A hard rear wheel impact during hard braking could easily buckle seat stays if too thin.

[shankldu]

when accerating you not sitting in the sadde , seat post has nothing to do with it.

[Ken Robb]

when accerating you not sitting in the sadde , seat post has nothing to do with it.
I don't stand every time I accelerate and I have never been found myself "a :beer: ccerating" at all.

[CunegoFan]

Agreed. This is why you'll start seeing tons of -17degree stems.

So that makers can build molds with giant headtubes and allow aggressive riders to still get the same lower hand positions through stem selection, and not through frame design/sizing.

Tom Kellogs words were interesting, but again, that equal to the function of using a smaller frame (super tall seatpost and super long stem)... or in otherwords.... the "pro" fit.

If you can handle the seat-bar drop, it's all equal. But normal riders cannot... so sloping frames, tall headtubes and -17 stems evolve to be the norm, with no noticeable difference in performance other than a tiny frame.

Sammy Sanchez (5'11") tall...rides a 54cm equiv. frame (with tall headtube and about a 140mm stem).... odd but true.
I think the only reason we are seeing more -17 degree stems is fashion. Originally the plan was to make fewer frame sizes and use seatpost and angled stems to force a frame to fit, but stems angled up are associated with freds. People make fun of bikes with "erect" stems. Since the saddle to bar drop is too much for many casual and new riders that want their bikes to look like the pros' bikes with horizontal stems, the makers have "solved" the problem by using giant head tubes. The riders who needed a lot of saddle to bar drop are now screwed.

[Bob Loblaw]

This is true for certain brands, especially the high-volume makers like Trek and Specialized. Boutique bikes like Parlee are the exception, and there's always the custom bike route. For those (like myself) with limited capital resources to spend on bikes, the used market is a good option.

All else being equal, I don't think there's a perceptible difference between a horizontal top tube and a sloped one. I agree the sloping top tube came about as a way to save money by making fewer frame sizes. The rationalizations for why it is "better" came from the various marketing departments after the cost-saving decision had been made.

Manufacturers will make what sells. If they can convince consumers that what they have this year is better than what came last year, they will keep making it.

BL



I think the only reason we are seeing more -17 degree stems in fashion. Originally the plan was to make fewer frame sizes and use seatpost and angled stems to force a frame to fit, but stems angled up are associated with freds. People make fun of bikes with "erect" stems. Since the saddle to bar drop is too much for many casual and new riders that want their bikes to look like the pros' bikes with horizontal stems, the makers have "solved" the problem by using giant head tubes. The riders who needed a lot of saddle to bar drop are now screwed.

[Kontact]

You can certainly make the stays shorter and use a level TT, but there are lots of engineering reasons not to do this - the seat cluster is stronger than mid tube, and forces are better dealt with by having the TT and SS oppose each other.

Ideally, frames would be designed to have a certain amount of seat post exposed per rider weight, and the TT would slope to whatever was needed to have that much post out. Too little and you don't get the suspension of a good post, too much and you are losing stiffness between saddle and pedals.

No one has formalized this, just as no one has done any real research on seat post ride qualities.

TKs ideas about lightening up the top of the bike for sprinting are interesting, though. But we spend 90% of our time in the saddle, and I tend to think that's what is the most important. IMHO, and all that.