aesmith

Hi,

Just wondering what the reason is for modern road bikes to have a sloping top tube, and when that evolved from the older horizontal top tube. Sort of related to that, I also wonder why the steering stem typically slopes up, again where a traditional (normal, in my eyes) bike would keep it horizontal.

Tony S

StanSeven

A sloping top tube can make for a more rigid bottom and less flex. While there's weight savings for the frame, most of that gets made up with a longer seatpost. It also provides more room.

rm -rf

The main reason: The bike store can fit more riders on fewer frame sizes, since the seat post has a large range of adjustment.
They probably also argue that the frame is stiffer, due to shorter stays and seat tube.

The stem sloping up is the shortest distance from the steerer to the bars, so it actually makes sense to do it that way.

I ride a modern Orbea, and love it. But, I rescued a 1970s Raleigh International from the trash. I do like it's look, with chrome lugs and skinny stays.

frameteam2003

What it does is lower the seat hight compaired to the same size standard frame.Lets a smaller rider ride a larger bike.This design is not new---many early safty frames had sloping top tubes.

Pepper Grinder

A road racing bicycle is designed for efficient power transfer at minimum weight and drag. Broadly speaking, the road bicycle geometry is categorized as either a traditional geometry with a horizontal top tube, or a compact geometry with a sloping top tube.

Traditional geometry road frames are often associated with more comfort and greater stability, and tend to have a longer wheelbase which contribute to these two aspects. Compact geometry road frames have a lower center of gravity and tend to have a shorter wheelbase and smaller rear triangle, which give the bike quicker handling. Compact geometry also allows the top of the head tube to be above the top of the seat tube, increasing standover clearance, and lowering the center of gravity. Opinion is divided on the riding merits of the compact frame, but several manufacturers claim that a reduced range of sizes can fit most riders, and that it is easier to build a frame without a perfectly level top tube.

THANKS WIKIPEDIA!

John E

True. In addition, the short seat tube / long seat post design permits most buyers to select a bicycle according to only one dimension, the seat-to-bars horizontal reach. Buyers of traditional diamond frames had to be mindful of both vertical "frame size" (seat tube length) and horizontal reach (top tube length) -- the conventional wisdom was to determine one's ideal frame size (generally 55cm C-T for me) and then to pick a make and model with roughly the right top tube length, making the final adjustment by swapping out the handlebar stem, if necessary.


As do I. The better traditional road bikes are beautiful.

Gary Fountain

Sounds like there are numerous good design reasons for a sloping top tube and stem that rises but I just can't convince myself to like the style. I must be old fashioned but I think the horizontal top bar and stem look is far more elegant.

CardiacKid

This is all about marketing. The sloping top tubes more resemble the mountain bikes the younger people grew up on. If you ask this question on the road forum, you will get much more support for sloping top tubes, which just kind of proves my point. I asked a similar question on the Framebuilders forum when I saw a custom road bike with a sloping top tube and a huge seat post. Richard Sachs provided the above answer. Unfortunately, being one of the greatest framebuilders in the world wasn't enough to prevent him being told he was full of it.

mrmw

Compact Frame
Traditional "road" frames have been built with level top tubes since the early 1900s. The influence of mountain and BMX bike design has led to the increasing popularity of frames with sloping top tubes, higher at the front.

"Compact" road frames have sloping top tubes, and are intended to be used with a long seatpost. Compact frames are a little bit lighter than traditional ones, but this is partially offset by the weight of the longer seatppost. Some riders believe they are stiffer.

Manufacturers like them because they are more versatile in terms of fit. Usually 3 or 4 sizes are enough to fit 98% of customers. This saves a lot of money for a manufacturer who doesn't need to deal with so many SKUs.

https://www.sheldonbrown.com/gloss_cn-z.html

stronglight

I don't happen to like compact frames. But I'm not a racer, so my preferred riding position is much different than what would be desired for a low aerodynamic profile - for which most modern road bikes are intended. And, the issue of optimizing power output is of little concern, so I don't mind the loss of maximized frame stiffness. Unfortunately (for ME) new frames tends to force me to accept a MUCH more tiny frame than I have been able to find on most older road bikes by making simple stem extension length adjustments to accommodate me.

A separate but related issue is the the typical threadless stem. This adds to the problem because many are only available in just a few lengths or angles of rise. The "effective" top tube lengths of typical sloping tube frames essentially makes a frame longer than was common on many older horizontal tube bikes. This means that for someone like me (with long legs and a short trunk) you need to find a smaller frame to get a reasonable top tube length. So, for me, I might need a foot of seat post sticking out above the frame. Then the short head tube will require finding a steeply up-sloping threadless stem to raise the equally reduced head tube.

You can perhaps visualize this by imagining a rider normally seated on a 60cm traditional frame. Your object is to get the saddle and bars level. Now, place that rider on a 53cm similar frame. You raise the seatpost up an additional 3 inches for a good leg length. But, now you have a VERY low headset. On a traditional frame you might jack up the bars of the too small frame with a monstrously long Technomic stem, chosen in a suitable extension length.

Not so simple on a non-raise-able threadless stem. So you'd need to find one with a just the right (very steep) angle, long enough to get your height good, yet not too long so it would increase your forward reach too much. So, the most common shop "remedy" would be to find a modern adjustable angle stem, in a suitable length - and there are very few length options. And, ultimately, it's going to still look as goofy with your near vertical threadless stem and BMX bike looking seatpost as would the tiny traditional frame. So, what seems simpler, actually has become more complicated for everyone - except for the bike manufacturers.

Trust me, I've driven bike shop employees nuts experimenting... just for fun, because they insisted they could easily fit anyone on a certain model... and I actually know what best fits ME well, rather than what I can be approximated to sort-of-kind-of-maybe fit onto.

One shop actually had a PC program which could graphically fit a rider's dimensions in with the frame geometries of a few different manufacturers, and you could enter in different components to achieve your goal fit. The results were just graphically as awkward as they were looking at a modified bike. The shop guys kept saying "No, this can't be right... something must have been entered wrong" - as each of them tried options one after another and came up with the same oddities graphically displayed.

Now, if I were to have a custom frame made for me, I would have no problem with either a sloping top tube or a threadless stem, but that's a lot more than I would want to spend...

Especially since I still just don't happen like the look of non-horizontal top tubes on a bike.

cyclotoine

My opinion, they do offer a bit of a weight savings and on a big frame should theoretical offer a stiffer ride. As someone said they lower the center of gravity and alloy people to ride a frame with a higher stear tube. This is good as it means less saddle to bar drop. As stated earlier the rising stem makes a lot of sense too... I am tall so I can appreciate every extra half cm that I can get the bars up without looking dorky. Lets face it, nitto technomics are dorky. If you put on on a vintage racing bike it's like putting mud flaps on a Ferrari.

edit: I guess buying used is a problem as people will have already cut the stear tube but I see threadless systems as offering more stem adjustment options.

solveg

I like* how they look! But sometimes I am a dork.

John E

Many of us concur.

aesmith

Not convinced by the rising stem. On my bike I have a horizontal stem, and the stem is almost at the lowest possible position. That's on a traditional threaded fork, with quill stem, of course. If the stem sloped upwards, I'd need a smaller frame and therefore a shorter steering head.

Tony S

cyclotoine

Well the look a lot better on touring bikes, and certainly better than my threaded to threadless set-up... yuck... but it gives me better fit options... and I don't think a 65cm touring bike is going to turn up on the cheep anytime soon for me.... I need a custom 26" with threadless 1 1/8" stearer.

SweetLou

I have the opposite problem, I am short with short legs and a long torso for my size. Though I prefer the horizontal top bar look more, I find compact frames easier to get a good fit. Actually I can usually get a range of frames to fit me well, with the older style, I often have a hard time finding a bike that fits.

When sloping top tubes first started to be common, I did not like them at all. Now that they have been out for a long time, I like them. But I am like that with everything. When a new car model comes out, I don't like the new styling, a few years later, I come around and like it.

Kommisar89

I'm not sure I understand how the sloping top tubes make the frame stiffer or noticeably lighter - didn't the old mixte frames have sloping top tubes? I don't recall them being stiffer. Picture a standard diamond frame. Now in your mind unbraze the top tube from the seat tube and move it down 8" and braze it in place. I would say you probably had to add some length to the tube but since seat tubes are angled it probably about the right length. Now you can do the same with the seat stays. They might get a little shorter. Maybe. And then cut the seat post shorter. Let's just say I'm skeptical that you measurably increased stiffness. And weight? Well the frame might be lighter but as already pointed out you have to use a significantly longer seat post so that offsets the shorter seat tube. A new high-end road bike can weigh 13.5-lbs with the sloping top tube. So who cares if it weighs 13.6-lbs with a straight top tube even assuming that's true. Now a short rider with unique sizing concerns might well appreciate the additional standover clearance of a sloping top tube but not everyone will benefit. I'm included to believe it's just a cost saving feature for the manufacturers. I think I'll take some measurements on my bike when I get home just to see.

luker

I'm in the process of putting together a new bike for spring, if it ever gets here. The frame has a seat tube and a head tube that would be okay on a 55 cm traditional bike, but the top tube has been lowered to make the frame stiffer(?) and to yield more standover height. I uncovered a hidden (at least to me) problem with the danged threadless steerer tubes. The original owner of this bike was about three inches shorter than me, and so he cut the steerer tube nearly all of the way down. In order to get myself properly fitted, I had to switch to a slightly shorter stem with a 6 degree rise (instead of the road normal 17 degree negative stem). A much better fix, of course, would be for me to buy a new fork and cut the steerer to my correct height.

Aren't forks a lot more expensive than a quill stem?

Lamplight

I would think the biggest advantage to a compact frame design (concerning the ride itself) would be a small increase in stiffness. Since I despise overly stiff bikes, this is of no concern to me. Actually it's the opposite of what I prefer! I also think that a sloping top tube looks pretty bad on most road bikes, although I have seen exceptions. Of course I also don't like the way fat tubes look, so I guess most modern mass-produced road bikes don't offer me much.

P.S. I don't mind Technomic stems as I have them on most of my bikes. I simply can't get comfortable when the handlebars are much lower than the saddle. I admit it probably looks a little weird on my Bertoni, but oh well:

https://img.photobucket.com/albums/v2...CN0048_WEB.jpg

A friend rode it with me on a ride and couldn't believe how comfortable it was compared to another friend's modern Trek. (He was considering getting a road bike)

Ex Pres 

Sloping top tube is made so boys can ride a girls bike without feeling feminine.

kmart

Felt makes some of their frames (for example, the Felt F55) with *slightly* sloping top tubes.

Their frames are still sized in cm instead of S, M, L. Compare that to what is usually referred to as compact geometry (as patented by Giant):

I love the traditional flat top tube look, but I think on the Felts that bit of slope gives them a slightly "aggro" racy look, like a Toyota pickup truck with the front suspension slightly jacked up

Mooo

I can't help it, every time I see one I see Homer and a low, sloping forehead.
But from the manufacturer's point of view it's brilliant: Fewer sizes, less material cost, better markup if you can convince enough people they're the hot item.

Kommisar89

Ok, here my results (admittedly gathered with nothing more scientific that a tape measure and my eyeballs):

Current measurements of my Bianchi (in cm):
TT: 55.5
ST: 55.0
WB: 99.5
CS: 41.0
SS: 52.0

Now if you lopped 6" (15cm or so) off the seat tube, without changing the geometry, here's what you would get:
TT: 53.5 actual length
ST: 40.0
WB: 99.5
CS: 41.0
SS: 43.5

Abraham Lincoln is purported to have once been asked how long a man's legs should be and he is purported to have answered, "Long enough to reach from his body to the ground". I suspect it works the same way with bicycle frames. Now I see no reason to suspect that seat posts are any stiffer or lighter than frame tubes so the 15cm you took off the seat tube does nothing. The only other significant change would be the 8.5cm you took out of the seat stays. So somebody explain to me please how this would make a frame either significantly stiffer or lighter.

lofter

didnt girls bikes used to have sloping top tubes too?

repechage

If I read this correctly, you are stating that a more direct route from your headset to the bar center is not as good? From a STYLING view, yes reads "comfort" bike, aka $340. hybrid. Now the length is another story, if you cannot get the correct length with the rise, thats a supply problem.

Do note, I can ride a 2cm smaller frame with the same top tube on a 40's to 50's bike than a 70's frame as the saddle has a different dimension from rail to contact surface, but I like 8cm of drop from saddle to bars...old racers have a hard time doing otherwise. But I will admit, I ride on the hoods mostly, then get into the drops when the going gets Serious.

A distributor loves this compact geometry stuff, as noted makes the SKU's easier to manage, now there is a possible chance that a short top tube (effective horizontal length) MIGHT when mated to a long stem to get a good position will yield a better handling machine. I felt that way on an old criterium bike in the 70's, but NOT when going down hill, just around 90 degree turns.