[NapalmCheese]

Out of curiousity spurred by the 'wide handlebars' thread in the downhill section I started looking around the internets. So most mountain bike bars come in either a 25.4 mm clamp diameter or a 31.8 mm clamp diameter. I had always assumed that the 31.8 mm clamp diameter was simply stronger, and that's why it's offered. However, it would seem that dirt bike handlebars have much smaller clamp diameters. So, if dirt bikes can get away with having skinny bars why can't bicycles?

 

[sanjuro]

I believe the industry wanted to go away from the different widths (25.4 for mountain, 26.0 for road) and standardize on one, the oversized 31.8.

As for strength and stiffness of the o/s, I use 25.4 on my bikes simply because I have a bunch of bars and stems in that width. I can't tell the difference between that width and the 31.8 I use on my road bike.

 

[Matrimony]

I think they use a different material for motox bars because weight isnt an issue as much, im guessing if you pick up some motox bars theyll be a crapload heavier than bike bars, not just because of the length difference, but because of the material difference...i could be wrong though...and on top of that, motox bars have the extra support bar in the center, and when i used to dirtbike, i wasnt pounding on my handlebars on my dirtbike like i was on my bike....all of those factors could contribute to the motox bars staying thin

 

[A.P]

Its because mega-companies like trek or specialized can spec the same 31.8 stem on road and mountain bikes, particularly low and mid end road and mountain bikes which are produced in the many thousands.

Simply a cost saving manuver by companies...then the "hype" and marketing BS was invented afterwards. Its crap- 25.4 absorbs vibrations better, and you need to make a 31.8 bar significantly heavier to be just as strong. So at the same weight, the 31.8 bar will always be weaker.

 

[El Caballo]

AJP: motocross handlebars are clamped in two places, not just one. This is about a million times stronger than one clamp in the center, so going oversize isn't necessary.

If motocross bars had a mountain-bike style stem, both the stem and bars would have to be massively heavy and oversized. But since all motocross forks have always been dual crown, they can use the stronger and lighter dual clamp system.

I know it's fashionable to be a retro-grouch and complain every time a standard changes. Lots of times it's done gratuitously, just to make you upgrade. But in this case, the result is actually stronger.

Also the flex argument is BS. You can make OS bars flex as much as you want by changing the taper and the wall thickness.

 

[binary visions]

A little old but what the hell, I didn't see it the first time around.

I believe MX steerers are 1" as well. Comparing MX equipment with mountain bike equipment is a simple exercise in futility. The physics completely change when you have a human pedaling instead of an engine pushing. The importance of certain suspension characteristics, the materials used and the dimensions involved are all completely different.

The strength-to-weight ratio is of paramount importance in mountain biking. Larger diameters can have more strength for a given weight. That's all there is to it.

A.P. is way off.

 

[Transcend]

The strength-to-weight ratio is of paramount importance in mountain biking. Larger diameters can have more strength for a given weight. That's all there is to it.

Actually, for bars this is incorrect. The 31.8 bars are weaker at the same weight due to thinner walls and more butting. They also transmit much more vibration into the hands.

 

[binary visions]

Actually, for bars this is incorrect. The 31.8 bars are weaker at the same weight due to thinner walls and more butting.

Hunh?

Why are bars exempt from this basic law of physics?

As a general rule, thinner walled, larger diameter tubes are stronger for the same weight than thicker walled, smaller diameter tubes. I don't understand where bars will differentiate from this formula. 1.5 headtubes are a prime example of this.

 

[sanjuro]

Its because mega-companies like trek or specialized can spec the same 31.8 stem on road and mountain bikes, particularly low and mid end road and mountain bikes which are produced in the many thousands.

Simply a cost saving manuver by companies...then the "hype" and marketing BS was invented afterwards. Its crap- 25.4 absorbs vibrations better, and you need to make a 31.8 bar significantly heavier to be just as strong. So at the same weight, the 31.8 bar will always be weaker.

I don't know if narrower or wider diameter bars absorb vibrations better, but I do pay attention to one company's bar information, Easton, and they list the 31.8 version of the EC70 as 15 grams heavier.

Keep in mind that O/S bars are wider in only one place, the clamp area. I wonder if that requires more engineering and material to ensure strength. In comparison to pipe spindles and steerers, the diameter is uniform.

 

[Trench Goat]

Simply put, a larger clamp means there is more surface area for the bar to clamp the stem. Maybe not so important for aluminum bars, but carbon bars don't take to clamping forces so well and when you can distribute that force over a larger area you can (effectively) tighten down more without damaging the material.
The comparison to motorcycles is interesting, although I believe not valid. A ten-gram weight savings on a motorcycle is not a big deal, but on a bicycle you can bet people will notice...at least before the sale, if not on the bike. I suspect most motorcycle handlebars are quite a bit thicker than bicycle handlebars anyway.

 

[dirtygirlmagnet]

Hunh?

Why are bars exempt from this basic law of physics?

As a general rule, thinner walled, larger diameter tubes are stronger for the same weight than thicker walled, smaller diameter tubes. I don't understand where bars will differentiate from this formula. 1.5 headtubes are a prime example of this.

you speaketh the truth