sloping toptube?

Question

Other than asthetics, does a sloping toptube affect the ride quality on a roadbike in comparision to a horizontal toptube?

Answer 1

Excellent question.

I have been designing bikes and frames for most of my life and now do it for a living.

In the mid-70s, Bicycling! magazine had a framebuilding contest to try and coax out some ideas that garage builders had, to perhaps improve the product. The winner was a person that developed a frame with a sloping top tube with the seat tube extending far beyond the top of the top tube.

For some reason this became the norm for mountain bikes when they were finally introduced as their own species and I think this is the primary reason for the technology "bleeding" into road bikes.

I far prefer horizontal top tubes, but end up having to design what sells, so I go along with the flow of compact (full sloping, 11º top tube) and semi compact (5º top tube) geometry.

Regarding ride quality I think that the horizontal top tube is more responsive but work with other people that absolutely insist that the sloping tube is... then again, their experience is primarily in sloping models. I don't like the "wobbling" frame flex at the seat tube/top tube/seat stay joint, nor do I like the look of a hyperlong seat post.

So, if it were me, I'd make every effort to get a horizontal TT frame but unfortunately this is something that is primarily the forte of custom builders now.

Answer 2

That is indeed a great question. I have tried some of the newer road bikes with the sloping toptube and I really like how they fit me as opposed to the old style. I suspect that the resulting frame geometry plays a big part in this. But ,then again, someone else may feel very differently about this.

Answer 3

A sloping top tube should make a frame that is a little stiffer than one with a horizontal top tube. But the change to the overall stiffness of the bike, with all the other components added, is unknown because you generally have to build the bike with a longer seatpost and higher stem extensions in order to move the control points out to where they fit the rider. The rear triangle should be a bit stiffer because the seat stays (between the rear wheel and the top of the seat tube) are shorter. In general, frames with sloping top tubes came about because the components to make them fit more riders became more available as a result of the popularity of mountain bikes. Since there were so many long seatposts and other components available to fit the sloping top tube of a mountain bike, the manufacturers started looking at road bike frames with sloping top tubes, with the advantage for them being they can build fewer sizes of road bike (Small, Medium, Large, XL versus 50, 52, 54, 56, 58, 69, 62) and fit most everyone. I guess they ride OK and if you can get the fit dialed in they work OK too. I'd still rather have a horizontal top tube because I like the look of it better, but each to his own.

Answer 4

Sloping tubes offer a lower standover. All good frames can be very stiff for performance. I think if you could ride 'em blindfolded you wouldn't know what your riding.

I have and always had horizonal TT frames. But if I had a nice Giant TCR I'd ride the hell out of it! Manufacturer's claim's one way or the other is marketing. It's probably true about the reduced inventory idea someone brought up. Get it if you like it.

Answer 5

Great answers to a very good question. I´d just like to add that a slopped top tube makes for a more compact, hence lighter frame. The big question would be: Does this small amount of weight difference make a big deal or is it an inventory thing?

Answer 6

Mirage has a great answer. I would only add / clarify that "ride quality" is totally subjective and there's plenty of hype and voodoo about it. There's so many variables like tires, wheels, handlebar height/reach, etc that's it's nrealy impossible to make a definite claim.

Bottom line, it you "think" a compact frame will ride better, it will. Buy the bike you want to buy and be happy.

Answer 7

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Answer 8

Not so much the ride as the standover. It's bound to affect the ride minimally, but if you had identical frames otherwise, I don't think you'd notice.

Answer 9

I suspect the main reason for this 'innovation' was to let manufacturer's get away with making fewer sizes.

Fewer sizes = lower inventory

Answer 10

No. A sloping tube is for girls.