Road Cycling - Advantages & disadvantages of OS tubes

So what's the deal with oversized tubes on road bikes? I'm looking into getting a used frame but it saz it's a 1" headtube. I know almost all XC bikes are now 1 1/8" headtubes for rigidity. Are road bikes made that way for the same reason? Or like drop bars, some of them need larger stem sizes. Why?

So what's the deal with oversized tubes on road bikes? I'm looking into getting a used frame but it saz it's a 1" headtube. I know almost all XC bikes are now 1 1/8" headtubes for rigidity. Are road bikes made that way for the same reason? Or like drop bars, some of them need larger stem sizes. Why?

You want truth or do you want marketing mumbo-jumbo?

The original idea behind 1 1/8" headsets was to allow the frame builder to use a larger diameter head tube so that it would be easier to miter a large diameter down tube to fit. Large diameter down tubes are used to exploit the properties of aluminum.

Once you decide to do something for whatever reason, it's usually not too difficult to think up some noble purpose that doing it serves.

Over-sized head tubes are useful when they are short, eg on small bikes, which have a reputation for eating headset bearings.
Where fork steerer tubes are made of Al or carbon, they need to be wider than the steel equiv to be strong and stiff enough.
OS main tubes are useful on very big frames, where the extra stiffness of the tubing makes up for the longer tube length.
On med size bikes, OS main tubing makes for a very stiff ride, good for hard sprinting, a bit harsh for long rides.
On small sized frames, OS main tubes are positively brutal, add weight and are ugly to boot.

So what's the deal with oversized tubes on road bikes? I'm looking into getting a used frame but it saz it's a 1" headtube. I know almost all XC bikes are now 1 1/8" headtubes for rigidity. Are road bikes made that way for the same reason? Or like drop bars, some of them need larger stem sizes. Why?

oversize tubing only exist in material that need or can get away with it.

Generally - steel isn't made in oversized tubing, because steel is so much stiffer than if it was oversized it'll be a bone shattering experience... alloys like alum is made thin and large in diameter, because alum is actually less stiff as a material than steel. The consistent opinion that alum is stiff isn't because of the material - but rather the design of the tubing.

As with anything, there are no hard rules like people describe above.
There are OS steel, ti, carbon and aluminum tubes.

The 1 1/8 headset is good on a road bike for the strengthened steerer tube, especially with full carbon steerer forks.

What about those oversized drop bar clamp tubes? Why 26mm vs. 31.7mm?

What about those oversized drop bar clamp tubes? Why 26mm vs. 31.7mm?

To get you to buy new stems and handlebars... ;)

Some people claimed they were seeing give in the 26mm bars when torquing on those sprints. I guess I'm not strong enough to be able to do that as I've not experienced it myself on my standard handlebar setup.

Over-sized head tubes are useful when they are short, eg on small bikes, which have a reputation for eating headset bearings.

i agree with everything else you said, but can you explain what head tube length has to do with headset bearing life?

when i first started seeing oversized head tubes and forks i was i jr. high and riding BMX. they went hand-in-hand with threadless headsets and stems. i believe the reasoning then was that larger diameter tubing was stronger, and, with a clamp-on stem, manufacturers could make thicker, and thereby stronger fork steerer tubes. that's the only logical explanation/advantage that i can think of for making oversized headtubes and forks. IMO, oversized headtubes on road racing bikes are kinda superfluous, no one is taking their road bike out to the local dirt jumps, or riding it off ledges that exceed 6" (curbs).

while i like quill stems and threaded headsets, the alternative of threadless is beginning to make more and more sense to me. ever have to deal with a flared steerer tube on a used bike? it's not a dangerous thing, but annoying as all hell when you can't run your stem as low as you want it. two things solve this problem before it happens 1) don't overtighten your wedge bolt on a quill stem, or 2) go threadless. with the advent of full carbon forks, threadless makes even more sense. the only problem i really have with a threadless setup on a road bike (and this is purely personal aesthetic preference) is the ugly chunkiness of most threadless stems (salsa makes a nice, clean looking stem, and i think thompson does too).

this next part is more rant than useful info...that's not to say that there might be something useful tucked away in there, but just be warned...rant.

the oversized bar clamping diameter probably has something to do with increasing stiffness and strength, but when was the last time you saw anyone break their handlebars in half at the stem while they were JRA? i suspect the OS clamping areas have something to do with people putting their carbon bars in their 4-bolt stems and cranking down on the clamping bolts with the force of 10 frenzied gorillas because "the bolts didn't feel tight enough" only to discover later, while they're JRA, that they cracked their bars, of course, by the time they realised it, they're holding one half of their handlebars in one hand, and the rest of their bike is on the other side of the road. people, a 4 bolt stem has 4 bolts exerting pressure on the cap, not one, not two, but four. that spreads the load out, so the bolts don't have to be torqued quite as high as the one or two bolt stems of yesteryear...ESPECIALLY with carbon bars....the same thing can happen with over-tightening carbon seatposts too, and i imagine it happens a lot more frequently in that case.

speaking of seatposts, and oversized things, what's with 31.whatever diameter seatposts instead of 27.0 or 27.2? all the pegorettis use this new size, except maybe the luigino. why do we need thicker seatposts?

speaking of seatposts, and oversized things, what's with 31.whatever diameter seatposts instead of 27.0 or 27.2? all the pegorettis use this new size, except maybe the luigino. why do we need thicker seatposts?

To fit inside an oversize downtube. That's the only reason.

In fact, steerer tubes became larger because a few boffins were trying out Titanium steerer tubes and obviously the 1" size wasn't working. Apart from that, it's largely marketing, although a larger surface area on which to weld the downtube is a valid point.

Every material kind of has an optimal diameter to wall thickness ratio - one that provides similar stiffness regardless of material. Thats why Aluminium bikes have larger tubes, next comes Ti, then Steel.
In terms of individual frame members, the highest loaded is the downtube, followed by the seat tube, then the drive side chainstay. Each of these tubes experiences different types of loading, so thats why they're different sizes, shapes....kinda. ( /broad generalisations.)