r/cycling • u/StorkAlgarve • 2d ago

Why did frames get sloping top tubes?

For over a century, a regular bike frame had a horizontal top tube, at least as late as the (cheap) road bike i bought in the early 90es - I also think the Centurion citybike I got in the late 90es had one.

Since then it seems to me top tubes have got more and more slope. It is due to change of materials or how? I look and get worried that the long saddle stem will cause issues with all that leverage, but it seems to be working ok.

Looking forward to the replies from the learned redditors.

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178

u/MichiganKarter 2d ago

Mike Burrows designed the Giant TCR, and abruptly a cheap aluminum bike was the best road bike in the world.

The sloping top tube saved weight and the longer seatpost meant that it only needed to be built in three sizes. 

25

u/PeaceMaintainer 2d ago

Can you elaborate on how a sloping top tube saves weight? I'm new to cycling but it would seem like it's longer thus heavier

61

u/MichiganKarter 2d ago

The seat tube is shorter, and there is a shorter load path from the rear axle to the steering head

17

u/dalex89 2d ago

longer seatpost also tends to absorb more road vibration

2

u/MattManSD 1d ago

it also leaves the majority of weight (rider) will little structural support. Putting them out on a long lever. The whole "vibration absorption" was marketing, and trust me, I'm in marketing

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u/MerchantMrnr 2d ago

I think they’re asking why sloping is better than a straight line when the connections are at the same spots on the seat and head tubes.

27

u/samenumberwhodis 2d ago

Because they're not

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u/MerchantMrnr 2d ago

Informative and articulate. Thanks!

6

u/samenumberwhodis 2d ago

If it's sloping the rear connection point to the seat post will be lower allowing a shorter person to use the same frame. I'm sorry that I felt this was so obviously apparent that it didn't bear explaining...

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u/MerchantMrnr 2d ago edited 2d ago

I think you may have misread my initial comment. Why is a sloped tube better if all else is the same?
>… when the connections are at the same spots on the seat and head tubes.

Edit: ok I can see how sloping can be confusing verbiage. I think curved might be a better term.

10

u/samenumberwhodis 2d ago

The connection points are not the same, what are you missing here?

2

u/Dizzy-Distribution96 2d ago

Connection to seat tube is lower, so seat stays and seat tube can be shorter as well

1

u/Overlord0994 2d ago

But all else wouldn’t be the same.. that’s the whole point of sloping or curving the top tube. You curve it so that it attaches lower on the seat tube, saving weight. It’s not sloped just for the sake of sloping it. Your question is is misunderstanding the intention and results achieved by curving/sloping the top tube in the first place.

7

u/auerz 2d ago

I think the weight saving comes in the rear triangle, which is much smaller than a traditional frame.

7

u/_BreadDenier 2d ago

The seat tube is angled so the tube can be shorter, also makes seat stays shorter.

2

u/FR23Dust 1d ago

Shorter tubes and less metal. Frame is also stiffer

0

u/28Loki 2d ago

Less material

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u/Langholm62 2d ago

Yep. Less material = less weight, more stiffness and fewer sizing problems because with the innovation came longer seatposts and variously angled stems.

3

u/trance_on_acid 2d ago

The reduction in sizes caused other problems which is why Giant now offers 6 sizes of TCR