Sloped Top Tube, Good , Bad, Ugly?

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Anonymous's picture

"In my research on purchasing a new road bike, I have notice that some manufacturers are offering road bikes with sloped top tube. I know that's very common on ATB bikes to protect your ""personal"" equipped in case you slide off your seat on uneven terrains, but that’s not likely to happen when riding on flat roads. So does anyone know of any practical/functional reasons for sloped top tube on road bike or is it just a stylish trend?"

Anonymous's picture
Evan Marks (not verified)

1) The main triangle of the frame is smaller, making it stiffer and lighter.

2) It's the latest fashion - goes well with threadless headsets and paired-spoke wheels.

Anonymous's picture
Art (not verified)
Fashion is Everything

">>It's the latest fashion - goes well with threadless headsets and paired-spoke wheels.<<

Yep, that's what all the ""cafe racers"" are using these days. Don't forget yer pink tires and goofy shades. Yuck!


Anonymous's picture
Robin (not verified)
Size matters

I think it also has something to do with economics. Many of these bikes, such as Giants, come in S, M, L instead of numerous incremental sizes.

Anonymous's picture
Evan Marks (not verified)
Thus, the continual evolution of the English language...

...a new oxymoron: Small Giant.

Anonymous's picture
Carol (not verified)
Compact Frames

The compact frame (with down-sloping top tube) is slightly lighter. It also can be advantageous for those of us with short legs, allowing good geometry on a frame with a comparatively long cockpit for the frame size. The downside, especially for heavier riders who tend to stay in the saddle while climbing, is that you're riding on more seat post and less seat tube, so you have more flex while climbing. For lighter riders or those who tend to stand alot while climbing, this is not a problem.

Anonymous's picture
John Z (not verified)
Right On

Keep in mind too that a length of seat post weighs more than a comparable length of downtube, so the net effect on the bike as a whole actually makes for a heavier bike, yes, with a lighter frame.

Anonymous's picture
Timothy McCarthy (not verified)
Interesting thread

"I ride a bicycle with a sloping top tube. I also have bicycles with level top tubes. I think the issue of sloping versus level of little consequence. Craftsmanship, frame material, angles of head tube and seat tube, top tube length, bottom bracket height, all have much greater impact on the ride of a bicycle.

Because sloping top tubes are relatively new on the block they seem to have to prove their worth. Yet we can turn this around and ask, ""why level top tubes?"" I view level top tubes simply as a long standing convention. What other tube on the bicycle can be kept so rigidly the same angle no matter what size of bicycle? The top tube can have any of a wide range of angles with little appreciable change to the ride quality. Contrast this to the significant effects of slight changes to head tube or seat tube angles .

On the plus side a level top tube provides the useful convention for sizing the length of a frame by measuring the top tube length. Slope the top tube and that convention goes away or at least becomes more difficult to figure. Level top tubes may rest better on the shoulder when carrying a bicycle.

Carol, I haven't noted any greater seat post flex with a longer seat post. John Z, I don't think I buy the idea that a sloping top tube leads to a heavier bicycle. With a sloping top tube frame the top tube is shorter, the seat tube is shorter, the seat stays are shorter. That can remove a significant amount of metal. Granted you put some back with a longer seatpost, but in most cases a sloping top tube frame offers the opportunity to lose some weight. This is probably most true with steel frames. However, I don't think a significant amount will be lost this way. In some cases it may be a wash.

As Robin notes, some bicycle manufacturers offer sloping top tubes for economic reasons as it allows them to offer fewer frame sizes. Pay close attention to achieving good fit--a much more important issue than how it looks or losing a bit of weight.

I prefer a sloping top tube because of the greater stand over height. I've grown to like the way it looks. Ostensibly the smaller main and rear triangles offer greater strength and stiffness, which makes sense to me, however I can't really tell.

Pay attention to craftsmanship, material, getting a frame that suits your riding style and objectives but most importantly get a good fit."

Anonymous's picture
Tom Laskey (not verified)
Compact is More (sometimes)

"Having recently purchased a Medium Giant after owning a pretty conventional steel bike (Pinarello) for some time, I can speak to the differences to some extent. Giant advertises that their ""Compact Geometry"" (the sloping top tube and shorter seat tube and chain stays) adds to the stiffness and responsiveness of their bikes. Comparing the Giant to the Pinarello, this is most assuredly true. Granted, some of this can be accounted for in the difference between Aluminum (Giant) and Steel (Pinarello) however, I think the geometry is also a large factor. I've also talked to others with experience with aluminum in a level top tube and compact geometry who have experienced a similar difference. On the other side of that equation, the compact geometry may also make for a rougher ride, I've found that to be true as well.

As to fit, after some tweaking, I find the fit of the Medium Giant totally comporable to the fit of my 54cm Pinarello. And, as one with short legs, it is nice to have the extra standover height the sloping top tube affords.

As for the weight issue, from most of what I've read, it's a wash between straight and sloping top tubes, the longer seat post probably adds back most of the weight that is saved by having less metal in the frame."

Anonymous's picture
John (not verified)
Sizing it up

Thanks for all the interesting feedbacks, my thoughts on the sloped top tube are (1) less clearance retrieving your water bottle mounted on the seat tube and (2) difficulty in mounting a frame pump under the top tube. I imagine the weight difference sloped versus traditional would be minimal with the small amount of metal saved on the frame going toward the seat post. What’s your opinion on downhill stability, which with a compact frame tends to wobble on fast descents. Also I now ride a 56cm traditional tube, on a sloped tube (M) @ 54cm, would I feel compressed and sit more upright or should get the next size up?

Anonymous's picture
Tom Laskey (not verified)

1) Less clearance for water bottle
Takes some getting used to but ultimately, not a problem.

2)Difficulty in mounting a frame pump
No difficulty for me whatsoever.

I also don't find it wobbly on descents in fact, just the opposite, handles better on descents.

For the top tube length you can try a shorter top tube and a longer stem to compensate or the reverse,longer top tube and shorter stem. Your seat position fore and aft may have some effect also. This is definitely in the area of try before you buy.

Anonymous's picture
Christian Edstrom (not verified)
Perceived stiffness of compact frames

While compact frames may well have their place in the pantheon of bikes, any arguments about their stiffness are based more on marketing and hype than any appreciable empirical evidence.

Some people refer to stiffness as the vertical complicance of a frame. I think most people will stipulate that the vertical compliance of a bike frame approximates 0. Simply put, the distance between the seatcluster and the bb or dropouts doesn't vary sufficiently in response to load to be measured. If you want a more vertically compliant bike, buy one that fits 700x28's.

The second discussion about stiffness addresses, correctly, the torsional load on the bottom bracket shell. As you pedal, the load from the pedals acts to turn the cranks about the bottom bracket, and also to torque the bottom bracket shell sideways. However, the claim that compact geometry will allay this is specious. The way to reduce bottom bracket torsion is to make the downtube more torsionally resistant. This is generally done by increasing the diameter of the entire dt (eg Cannondale) or increasing the diameter of the dt near the bb shell (eg Serotta).

However, if bb torsion were a real problem for riders, the simplest solution would be to both increase the dt diameter and build a spar from the seat tube to the dt, seated about 5 inches from the bb shell on both tubes. This would have a vast effect in reducing bb torsion. Thus far, I've not seen a single bike with this solution.

The idea that a compact frame would more effectively resist bb shell torsion because of a smaller main triangle, somehow affecting the bb shell like the above suggested spar, makes for appealing marketing, but I've not seen _any_ evidence that this is actually true. Not even the manufacturers who make such a frame have done a public study to verify the conjecture. Given the number of joints and the size of the triangle, even on a compact frame, I find it hard to believe that any improvement in torsional stiffness can be measured.

Lastly, if bb torsion were a problem, it should affect sprinters and big riders most. Yet the marketing of compact bikes does not take this into account.

Now, Tom is likely a more experienced cyclist than I, and if he perceives his new bike to be better than his old one, I have no beef with that. But I think there are other explanations than compact geometry.

As far as how compact bikes look; De gustibus non disputandum est. But bikes with integrated headsets look terrible.

Oh yeah, if a compact frame fits you well, then it fits well. And a bike that fits well is always a good purchase.

Warm regards,
- Christian

Anonymous's picture
Charles Lam (not verified)
useful info

Thanks for the interesting viewpoints Tim and Tom. As someone who is gifted in torso length, I’ve considered getting a compact frame for my next bike (whenever that is). If one is to get a comparable fit, are there any other downsides to a frame w/ sloping TT other than a slightly longer seat post? (All other things being equal)

Has anybody ever seen or owned a custom frame w/ sloping TT? And why not? Is it convention and looks alone?

Anonymous's picture
Evan Marks (not verified)
>custom frame w/ sloping TT
Anonymous's picture
Carol (not verified)
Custom Compact Frame

"I own a custom Independent Fabrication steel touring frame with sloping top tube. I happen to have very short legs, so even with the compact frame I only need a standard length seat post. (I only have about 5"" of seatpost above the top tube.) The compact frame allows me more standover room and easier mounting and dismounting of a loaded bike. I have no trouble mounting a frame pump under the top tube. I do have tight clearance for water bottles, but that's because the frame is so small in general. I'm very pleased with the bike - it fits me like a glove and is extremely comfortable to ride. (My upper body is relatively long compared to my legs, but with a custom frame I have no problem.)"

Anonymous's picture
Art (not verified)
Sloping Top Tube Saves $$$ for Manufacturer

The sloping top tube allows the manufacturer to design/build/stock only three frame sizes instead of 6 or 7. Would you buy a suit or pair of shoes that only came in S, M, L?

To compensate for the slope, an extra long seatpost is required, offsetting any weight savings.

Effective Top Tube length is perhaps the most important fit parameter for a frame. Having only three different TT sizes to choose from compromises fit.

Riders with short legs may benefit from the sloping top tube in that they can get adequate standover clearance.


Anonymous's picture
Mordecai Silver (not verified)
Sloping top tubes

I can think of several advantages of compact frames:
1) Production expenses are reduced: fewer frame sizes saves a lot in the cost of jigs, fixtures, and tubing.
2) Fewer sizes (three sizes fit all) means that the distributor and retailer need to order and store less inventory, so there's less risk, and storage costs are reduced.
3) The manufacturer can advertise a slightly lower frame weight.
4) To entice the bmx and mtb crowd, who are used to the sloping top tube look.
5) To perk up the flat road bike market with a new fad. The industry has been doing this quite a bit in the last few years.

Anonymous's picture
richard rosenthal (not verified)
2 unlikely reasons against getting a sloping top tube

If you carry your bike on your shoulder.

If you have a bike rack with a horizontal holder for the top tube.

-Richard Rosenthal

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