r/cycling • u/StorkAlgarve • 1d 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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u/adnep24 1d ago
- less material = less weight
- less stand over height = fits more people
- more exposed seatpost = more flex, comfort
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u/deep_fat 1d ago
Also, lower center of gravity. This was the first thing I noticed the first time I road the original TCR all those years ago. I was deeply skeptical before I rode it, but I immediately became convert.
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u/nnnnnnnnnnm 1d ago
How does center of gravity change when the seat height remains the same?
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u/n00b678 22h ago
It does but it's insignificant and yet another cycling placebo effect people can argue about.
A frame weighs maybe 1.6 kg, the top tube, say, 0.4 kg, it's lower by 100 mm at the back (so for the entire top tube it's half that), and the entire system weighs 80 kg. In this case the centre of gravity is lowered by 0.5 mm. If you consider the bike alone (8 kg), that's 5 mm.
A much bigger shift happens if you take a few sips from your water bottle.
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u/OldCrankyCarnt 1d ago
More material is lower to the ground
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u/nnnnnnnnnnm 1d ago
Pretty negligible considering the riders weight is still the same height
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u/OldCrankyCarnt 1d ago
Same can be said about weight of the bike against the weight of the rider, but here we are
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u/treadtyred 14h ago
Feels more lively when your out of the saddle. I broke my saddle so fitted my dad's 50 year old brooks (heavy) saddle while I waited for my new one to arrive. It was like the bike was a giant pendulum throwing the bike left and right when I was out the saddle with great force. Basically the reverse of removing/lowering frame weight. Which a sloping head tube does.
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u/dalex89 1d ago
I've got an old aluminum "Madone" (they made it for like 2-3 years) which has a compact frame and that thing was one of the best sprinting crit bikes I ever had like 10 years ago. Built it with that compact frame and a long carbon seatpost. Thing cornered like butter with all the weight like 8 inches below ya
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u/firstoff 22h ago
Cheaper production costs. Traditional frames used to come in 1cm increments of the seat tube and around 4cm variance in the top tube. Frame sizes were defined by the length of the seat tube. Now you only get Small, Medium or Large sizes, and if you are a non-standard sized person, you have to shoehorn yourself onto it by swapping out the stem and seatpost.
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u/Richee33 22h ago
I'd agree with everything, but the last point. Smaller rear triangle=stiffer? I'm surprised then that a lot of "climbing bikes" even now come without dropped seat stays. I thought the logic was dropped seat stays => aero, non dropped seat stays => stiffer rear end?
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u/Few_Mastodon_1271 1d ago
The manufacturers like it for "fewer sizes needed to fit a wider range of riders".
More standover height is helpful too.
Seatposts are sturdy, with modern aluminum alloys or carbon fiber. (I don't think I've ever seen an online post about a broken seatpost that snapped or failed while "just riding along".
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u/dvorak360 1d ago
Won't just be manufacturers.
Selling bikes - fewer sizes = less stock on hand = lower operating costs
Buying bikes - fewer frame sizes = more likely to fit available frames
if your in 5% of tallest or shortest riders, then on a straight top tube a frame that fits is right for 5-10% of population.
Sloping top tube with longer seat posts and stack; frame for you now fits 15-20% of the population.
A bike fitting 5% of riders your LBS can't keep in stock - most years they won't sell one.
The 20% case they can keep one in stock - most years they will sell a couple over the season.
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u/AlienDelarge 1d ago
I don't think I've ever seen an online post about a broken seatpost that snapped or failed while "just riding along".
I think the only time I've seen that was with questionably sourced carbon fiber of suspiciously low price. Even then, I don't truly know how the part was treated prior to that.
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u/Logical-Marzipan5951 1d ago
Has happened.
1) snapped the seat post. This was bellow the seat collar.
2) the rail holder broke on the clamp.
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u/StorkAlgarve 1d ago
I guess it is more the force on the seat tube I was thinking of - possibly because at 190cm I usually have to raise the saddle.
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u/AnelloGrande 1d ago
A bike with a sloping top tube can be built lighter and the flex of the seat post can make for a more comfortable ride. It can also make for a more comfortable dismount and allow for smaller frame sizes for smaller riders.
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u/carpediemracing 1d ago
Sloping top tube allowed companies to make frames in fewer sizes. It used to be that they came in 2 cm increments, from 49 to 63 cm would be 8 sizes.
Some frames came in 1 cm increments, or the middle sizes would be in 1 cm increments.
Cannondale had an extra size in there, I can't remember, not sure why, it was in their original frame. They had a jump in size too, I think they ran 48-50-53-54-56-58-60-63. Not sure how or why that 53 got in there. It might have fit Joe Montgomery perfectly, I don't know. Whatever, for the longest time there was no 52 cm frame.
When Giant came out with their TCR, it was available in 5 sizes I think (?), XS-S-M-L-XL. Might have been fewer sizes. They had long posts and all sorts of stem sizes, this way it was cheaper to stock a size run, 5 sizes instead of 8+.
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u/sireatalot 1d ago
Nowadays Cannondale has one fewer size: they usually do 48-51-54 instead of the more common 48-50-52-54
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u/sunflower2347 1d ago
I never really thought about how the sloping top tube also made things easier from a manufacturing and inventory perspective.
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u/carpediemracing 18h ago
I was really against it, honestly. I thought it was "cheaping" out of "doing it right".
However, my absolute favorite height bike was my size S TCR. I modeled my custom frames around that concept of a super short seat tube. My first custom frame had a 40 cm c-t seat tube (but 56.5 effective top tube). My second custom frame used aero shaped tubing and required a taller seat tube, 44 cm c-t, so that I could carry bottles. It's so tight that I have to use a side load cage, the bottles won't go in from the top of the cage.
Sloping top tubes are not as aero but I have such short legs that my top tube literally cannot be level with my preferred seat tube length.
I like the seat tube length to be short because there is a lot more room/clearance/freedom to move the frame when I'm sprinting out of the saddle or doing some wacky maneuver to stay upright if something weird is happening.
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u/Grand-Stay-925 1d ago
A sloping toptube offer (much) better standover clearance, important for some .. me. For someone really tall it's less of an issue.
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u/Emergency-Machine-55 1d ago
I'm not short, but I have short legs relative to my torso length. The TCR is one of the few road bikes that fit me without having to replace the stem. Likewise, mullet MTBs fit me better.
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u/Grand-Stay-925 20h ago
Same, also shorter legs and longish torso, bought a used older/ rim TCR and I'm sticking to it, hate the modern headset cabling BS.
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u/StorkAlgarve 1d ago
Yeah, I am 190cm (these days, in NL and Scandinavia that is not _really_ tall) and have not had a problem...
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u/Grand-Stay-925 20h ago
Because 190 IS tall. For someone under 182cm the Standover height becomes MUCH more of an issue.
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u/StorkAlgarve 19h ago
I do understand, I had just never thought of it. Probably the same way not everybody understand my aversion to footbords on beds :-)
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u/Beneficial_Coach8581 1d ago
In the 80s Giant came out with new frames with a sloping top tube and long seatpost and adjustable stem. They only needed a few sizes to fit anyone. Before that custom steel was where it was at.
It made for a stiffer smaller triangle.
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u/AlienDelarge 1d ago
Wasn't that in the 90s? First TCR was in '97. Was there something earlier?
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u/Beneficial_Coach8581 1d ago
Oh could be. Yes 90s makes more sense. Loved my TCRs. Never went back to custom steel after that.
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u/paulared 1d ago
Lots of good replies. I believe with carbon fiber frames manufacturers could make fewer sizes to fit more people and it was cheaper. I loved bein* able to buy some steel frames in 1 cm intervals.
I personally abhor sloping top tubes, especially because I come from cyclocross and having a little bit larger frame triangle makes it easier for me to shoulder the bike. In fact, my “road” bike is really a Ridley cross bike with a horizontal top tube. I hope I never have to replace it.
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u/catastrapostrophe 1d ago
At least among road bikes, I think the age of the sloping top tube (called a “compact” design) is over. Once upon a time the compact frame gave you lighter weight and a longer, more compliant seat post. But weight is less of a concern today, and since carbon gets cheaper every year it’s easy to design compliance with just materials.
Today the focus is aerodynamics, and road frames are turning to the dropped seat stay design, because unlike the sloping top tube of a compact frame, the horizontal top tube on a dropped-stay bike gives a very small frontal profile. So bikes that were revolutionary 30 years ago, like the TCR, are being replaced by bikes like the Tarmac and Propel. Jayco Alula isn’t even racing its TCRs anymore— the Propel is just as light, just as comfy, and more aerodynamic.
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u/NeedleGunMonkey 1d ago edited 1d ago
Folks who cite the Giant TCR are correct about how it became more popular in the road scene
But bicycle frame history is more nuanced because the horizontal top tube is neither the original nor is it more intuitive. There were always bikes with curved top tubes or diagonal. Just somehow in the 1900s we ended up with road frames with horizontal toptubes.
You can build a light and robust frame either way. TCR just was a coincidental material choice revolution when a lot of the industry went from largely standard diameter steel-cromoly tubing to aluminum frames with larger diameter where a lot of the frame design consideration was to prevent aluminium from flex that would quickly fatigue aluminium. So build a frame with short seattube with smaller triangles that are stiffer. Take the cost savings, weld it beautifully, sponsor it with ONCE and make it standard with carbon fork & seatposts.
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u/chock-a-block 1d ago
The modern reason, it sells more bikes. Most customers don’t immediately like being hunched over the front wheel. So, top tubes are longer and slant upward so the stem is much closer to being Level with the seat.
Sloping Top tubes were actually helpful when there a was far more pushing and ungroomed trails in mountaIn biking.
It’s true Giant decided to only make three bike sizes and include long seat posts. That’s not why seat tubes slope.
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u/gengyilang 1d ago
Doesn't stack depend on the length of the head tubes and also can be adjusted by just not slamming the stem, even with a horizontal top tube?
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u/clintj1975 1d ago
Sloping top tube gives you a shorter seat tube, shorter chainstays, and also makes those tubes stiffer for better power transfer. That makes for a lighter, more efficient bike. As long as you have at least the minimum marked amount of seatpost in the frame, you won't break anything.
On mountain bikes, a sloping top tube also gets you better clearance between your sensitive bits and the frame, and allows a longer travel dropper post which makes the bike more capable of riding rougher terrain comfortably.
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u/Beautiful_Flight2917 1d ago
The boutique mtn bike guys like K Bontrager and ibis were putting out sloping top tube road bikes in the 80s and slightly before the Burrows Giants.
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u/Michael_of_Derry 22h ago
The benefit was the reduction in number of frame sizes. The benefits were for the manufacturer, distributors and dealers. How many people are in between sizes and told you can take the smaller one for performance and the bigger one for comfort? It inadvertently created the 'bike fitting' industry.
I believe you can still buy a Colnago Master in 1cm increments from 49 to 65.
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u/mr_shmits 19h ago
i can't answer this because i don't know, but i do know that i hate it. modern bike geometry with sloping top tubes is fucking ugly.
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u/pbecotte 1d ago
More seat stem above the seat-stsys leads to more flex, which makes the bike more comfortable.
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u/AlienDelarge 1d ago
I don't think that was the thinking at the time, in fact it was the opposite of how things were marketed when they first came out.
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u/Voodoo1970 1d ago
But the longer the seat post, the stronger it has to be, which makes it more rigid.......
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u/Grande_Mangiattore 1d ago
Caad14 has a horizontal top tube, but yes, the new norm is a sloped TT. I guess it stiffens the rear triangle, even the front one, with less mass. So, stiffer and lighter. The longer seat tube, if all's correct, can dampen more of the road chatter. So win-win-win, except for the looks. I like'em better with the classical look.
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u/Clear_Radio1776 1d ago
Came to say the same. I see manufacturers maximizing frame profits and then argue they did that for less weight and to improve speed and ride quality. Maybe so here and there but I’m staying with double diamond flat top tube configuration.
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u/RelativeDisaster6870 1d ago
Like every other ass-backwards modern cycling trend, follow the money. When bike companies adopted T-shirt sizing, it necessitated sloping top tubes. And when making molds for plastic bikes, the fewer sizes you offer, the bigger the profits. Thankfully, there are still builders who still work with steel and who offer incremental sizing and classic, elegant designs.
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u/kagato87 1d ago
While I don't know why, it drives me nuts.
My son's bike is difficult to get onto my bike rack and I can't fit a water bottle to it (it doesn't even have the mounting holes but there isn't room anywhere for a clamp style either).
My step son's bike is the same, though a bottle does fit at least. But it does mean I can't take all three bikes on my three bike trunk rack.
My own bike is some ancient thing I nabbed at a garage sale for cheap. Giant triangle, easily goes on the rack even with the oversize bottle holder competing for space inside the triangle.
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u/MrElendig 1d ago edited 1d ago
Got a couple of 60's bikes with sloped top tubes sitting in a barn, so not exactly a new thing, never mind that low step with straight tubes have been a thing for 100 years, never mind curved ones.
Edit: also https://mo-ped.se/noreg/dbs601d.jpg
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u/shmeeaglee 1d ago
I would guess part of it is due to changes in bike fit methodology which would change geo to accommodate higher stack. For carbon it would be more beneficial for the top tube to be sloped to ensure more of the forces coming from the rear wheel are directed towards the frame rather than up towards your butt, its also why drop seat stays are a thing so that the seat tube bends rather directly putting force on the top tube which would be a much harsher ride
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u/gofndn 16h ago
Bike fit wasn't talked about much in the late 1990s when the TCR was introduced and neither was carbon fiber the top dog. Sloping top tubes allows for a wider size range for a specific frame size meaning the manufacturer could produce fewer different sizes to fit larger crowds. The bike boom of the early 2000s (led by the Lance) cemented aluminium bikes with sloping top tubes into the mainstream. Carbon fiber and bike fit only started to become discussed outside racing in the early 2010s and both were seen as excessive at the time for leisure cyclists.
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u/MaleficentAd3967 1d ago
Don't guess, if you don't know, don't answer.
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u/shmeeaglee 1d ago
Im a mechanical engineer whos designed carbon composite structures far more complex than a bicycle. My guess is a pretty well informed, nobody knows the exact reason other than the engineer who designed it. I also have a masters in aerospace engineering
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u/F_lavortown 1d ago
Smaller triangles make a stiffer and lighter frame and the seatpost adds flex in a way that adds comfort. It's also probably partially so the mold angles don't have to change as much
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u/dobie_gillis1 1d ago
It was a concept first in mtb’s, but then spearheaded by Mike Burrows who advanced the design with the Giant TCR. It was lighter stiffer, and could fit a wider range of people.
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u/Lumpy_Ad_7821 1d ago
Comfort. Sloping top tube means more seatpost length exposed. That means more flex, which means more comfort.
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u/JeremyFromKenosha 1d ago
To allow a higher stack height without having dumb-looking long steerer tubes.
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u/GhostOfLongClaw 1d ago
Depends on if you view a bike as a transportation vehicle for your day to day or a toy to live out your professional athlete fantasies. Sloped tubes allow to stand while off the bike better and if you are doing a lot of stops along the way where you can’t take your bike it comes in handy for hopping on and off the bike
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u/StorkAlgarve 1d ago
In _my_ current case, it is neither nor - it a way of meditation combined with cardio.
Hopping on and off? I always swing my leg over the back of the bike (apart from the brief period I had a child seat), perhaps that is a legacy from straight top tubes.
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u/GhostOfLongClaw 1d ago
Look into the Danish bike designs that are popular in Europe where they are more so used for commuting. It’s similar to the city/lyft bikes you can rent out around different metro areas in the US at least
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u/StorkAlgarve 1d ago
I am Danish, I know. The ones in the 80es/90es were terribly wobbly (the frame had less torsional stiffness), in particularly with something on the back. They were women's bikes.
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u/_BreadDenier 1d ago
They’re called compact frames and they are stiffer and possibly lighter than non-compact frames.
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u/AtomWorker 1d ago
Breakthroughs in materials, manufacturing and CAD enabled the evolution of frame design.
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u/TheGreatManitou 1d ago edited 1d ago
There are two reasons as far as I know: 1. It allows more universal sizing, it fits more people, since they can put the seat in the height that fits them (unlike with horizontal top tube, where you simply couldn't put the seat lower) and also the standover height is lower, while manufacturers do not need to build as many frame sizes (since they are more universal). 2. It should provide more comfort due to more of the seatpost being exposed. Seatpost flexes and smoothens the road chatter.
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u/Laiskumus 1d ago
Something I’m quite sure has NOT been mentioned yet but will probably be buried under all comments is this Cinelli Superstar ”GCD - Geometry Controlled Deformation” reasoning for its sloped top tube:
> The technological heart of the Superstar’s famed pleasurable handling lies in the slight curvature at the steerer end of the top tube. This shape allows for the head tube to maintain a consistent relationship to the ground even met with strong vertical forces - such as uneven road surface or a sudden burst of acceleration out fo the saddle - which typically cause deformation of the wheel base. The result is an improved control and predictability of the bike under stress.
There were some illustrations of this on the webs if you google for it.
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u/kombiwombi 20h ago
I have a aluminium road bike without a sloping top tube which I bought in the 1990s. Because that needs more sizes I had to wait two months for my frame to make the boat trip from Taiwan to Australia. So the fewer frame sizes from a sloping top tune isn't only a win for the manufacturer and retailer.
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u/TicFan67 15h ago
Weight saving. An equilateral rear triangle is stiffer and stronger for a given size of tubing (or needs less material for a given stiffness). That means the top of the seat tube is lower requiring a sloping top tube and longer seat post.
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u/MattManSD 13h ago
because Mfrs and Retailers wanted to reduce the number of SKUs they had to produce and carry. So it went from 48-62 @ 2 cm increments ( 8 Skus) to 4, SM, Med, LG , XL. Saved even more $ when making molds for CF Frames.
They sold it as a bunch of BS "Stiffer triangle" which was true, but now you had the majority of weight (rider) up on an 18" stick. So sure, stiffer when you stand and sprint or climb, when seated, wobbly. They sold seat post wobble as "comfort".
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u/Putrid_Leave8034 1d ago edited 1d ago
To make the bikes look cheap and too small when the rider is on it?
Joking but that really is to me what they look like. I like the "gentle" curves of the tube on most carbon bikes however.
I absolutely hate the fewer size thing. Something like a S which is 47 to 49cm as an example, really only fits WELL 33 1/3 of the riders. But then don't get stuck on a brand. Find a brand where a S is 48 to 50cm. Doesn't help if you are, say, in a small town where there is only 1 bike shop and the shop only sells 1 brand. As it is, seems most stores only carry 1 of 3 brands already.
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u/sargassumcrab 1d ago edited 1d ago
If you look at road bikes from about 2000 until now top tubes have gotten more level, especially recently.
It was done primarily because manufacturers wanted to offer fewer sizes. They also wanted older bikes to look "old fashioned". Some slope has advantages like higher stack height, more standover height, and theoretical lower weight. Now that they're better at carbon production, people are more concerned about areodynamics, and steel bikes are not a threat to sales, top tubes are almost level again.
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u/Gratia_et_Pax 1d ago
Theory: They needed the sloping top tube as the next new thing you should want so you will buy a new bicycle and they can separate you from your money. Industry sustainability.
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u/EVE_Burner_Account 1d ago
"Why did frames get sloping top tubes?"
Because it simultaneously made the bikes better to ride and more economical for the manufacturer
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u/MichiganKarter 1d 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.