Sloping vs Horizontal Top Tube

[Vikeonabike]

I know one slopes and the other doesn't. But what is the difference..is it just to do with stand over hight? Does one handle better than the other? Or is it purely for looks?

 

[rusky]

I may be wrong here but the sloping tube is usually found on compact frames.

i.e. where the length of the top tube is the same as a horizontal one but the seat tube is shorter & the seat post longer to accomodate this.

The low end Carerra bikes are like this, the set tube is 51cm but equates to a 58(ish) one.

Of course I may have understood this & someone will put me right!

 

[GrasB]

Best answer/explination I've seen so far:

The differences are actually very easy to measure and understand, unfortunately few people in the industry are interested in the actual differences or in testing and rather just make up stuff for their brochure.

The differences between sloping and horizontal are small, but if you use the same tubeset for both frames, the following differences will occur:

1) slightly higher bottom bracker stiffness for the sloping frame
2) slightly higher torsional stiffness for the horizontal toptube frame
3) slightly lighter frame with the sloping toptube
4) slightly lighter seatpost wit the horizontal toptube frame
5) slightly more seatpost compliance with the sloping frame.

issues 3 and 4 are a wash, and for us at Cervelo the choice between sloping and horizontal depends on whatcombination we are looking for out of 1, 2 and 5. For our Alu bikes, which have plenty of bb and torsional stiffness anyway, we go with a sloping toptube (or a dropped toptube on the tri bikes which has the same effect) to get a bit more seatpost compliance.

For the steel frames, this is not necessary and so we can increase the torsional stiffness by keeping the toptube horizontal, especially nice for the twisting and turning on rough roads.

For the new carbon frame, the seatpost compliance wasn't an issue but we did want to get the highest possible bb stiffness, so we opted for a sloping frame.

 

[PpPete]

Interesting .... I even understand most of it but what the <bleep> is "seat post compliance" ????

 

[fossyant]

Fashion............


Can't get it now,,,,my 56 old skool is now a 54 top tube, could be a 54 seat tube or even a 51 or lower....FFS.............

 

[longers]

Interesting .... I even understand most of it but what the <bleep> is "seat post compliance" ????

That's what I thought, is it to do with being comfortable?

 

[GrasB]

'seat post compliance' is the amount of 'give' in the seat post. The more give the more compliant, thus comfortable, the seat post is.

Fashion............

Certainly on very stiff & harsh aluminium frames the extra give you get from a sloping seat tube is noticeable & for someone like me who can generate a lot of force at the pedal does that by making the BB area stiffer (though this I don't notice)

 

[Moodyman]

Though bike makers don't admit it, I'm sure there's some development savings for them also - use the same frames for hybrids & commuters as they do for mountain bikes.

 

[michaelrmgreen]

It's all to do with economy of scale vs traditional appearance. Sloping top tubes reduce the number of sizes required to service a specific size range. BUT some consumer groups (roadies mostly) are resistant to non-traditional frame geometries.

 

[Grasen]

all the above is a load of bollocks.
the sloping top tube is to better reflect the suns rays on hot sunny days in the american desert.
that is why all mtb bikes have sloping top tubes and traditional european racing frames don't (the sun is lower in the sky in europe)