Why go for 31.8mm bars instead of 26.0mm ?

Ezy Rider

what are the main reasons for selecting the oversized type ?

MrChuck

Oversized usually means stiffer.

Ezy Rider

MrChuck wrote:

Oversized usually means stiffer.

any benefits in comfort ?

MattC59

It's been a while since my degree, but.......... here goes (in very simplistic terms !!)

Basically, as you increase the diameter of a tube, for a given wall thickness, it's stiffness increases. So, if the wall thickness is the same, a 31.8mm tube will be stiffer than a 26mm tube.

Or, if you increase the diameter, but reduce the wall thickness, then you can maintain the stiffness but lose weight.

Cannondale were doing this on their round tube mountain bike frames back in the early 90s.

There's an optimum ration of wall thickness to tube diameter, for a given material, but I can't remember what it is.

MattC59

Ezy Rider wrote:

MrChuck wrote:

Oversized usually means stiffer.

any benefits in comfort ?

That generally depends on the material it's made from and the tubing profiles.

P_Tucker

MattC59 wrote:

It's been a while since my degree, but.......... here goes (in very simplistic terms !!)

Basically, as you increase the diameter of a tube, for a given wall thickness, it's stiffness increases. So, if the wall thickness is the same, a 31.8mm tube will be stiffer than a 26mm tube.

Or, if you increase the diameter, but reduce the wall thickness, then you can maintain the stiffness but lose weight.

Cannondale were doing this on their round tube mountain bike frames back in the early 90s.

There's an optimum ration of wall thickness to tube diameter, for a given material, but I can't remember what it is.

And does this make any difference that could be measured outside a lab?

nmcgann

Availability of good drop shapes is the only real reason I can think of. I wanted some nice-shaped compact bend bars and there just weren't any in 26.0mm.

The problem then is finding OS bars that don't have stupid tapers or flat bits preventing lights and other accessories being attached :roll:

top_bhoy

Having been looking recently for a shorter stem, while 26mm stems are available, in my opinion the 26mm choice is limited in comparison to what is available in 31.8mm. From a practical stance, I'd go 31.8mm bars if only because the major manufacturers main focus and support now seems to be there.

Berk Bonebonce

It is not so much that people choose 31.8; that is where the industry has taken them. And the industry is fast moving to 35mm - see Deda TrentaCinque stem and M35 bars.

cougie

Marketing.

I've never noticed any flex in my bars before.

I have noticed that you can pick up tri bars to fit the older diameter bars for bargain prices compared to the new standard size.

MattC59

P_Tucker wrote:

MattC59 wrote:

It's been a while since my degree, but.......... here goes (in very simplistic terms !!)

Basically, as you increase the diameter of a tube, for a given wall thickness, it's stiffness increases. So, if the wall thickness is the same, a 31.8mm tube will be stiffer than a 26mm tube.

Or, if you increase the diameter, but reduce the wall thickness, then you can maintain the stiffness but lose weight.

Cannondale were doing this on their round tube mountain bike frames back in the early 90s.

There's an optimum ration of wall thickness to tube diameter, for a given material, but I can't remember what it is.

And does this make any difference that could be measured outside a lab?

Yes, considerably, certainly in the case of Aluminium.

what brakes

The 31.8 are larger and therefore spread the pressure over a greater area of your hands. Lessening the pressure points making for a more comfortable hands.

Monty Dog

FWIW the diameter of the bar than you grip remains the same at 22mm - it's only the centre bulge that's got bigger. Anyone proposing a larger diameter grip has got to address things like lever clamps / grips etc. which I can't see the component industry rushing to create product proliferation.

cougie

I did think that. Otherwise you'd need 'oversize' and 'standard' bar tape !

crankycrank

As mentioned the main advantage of 31.8 is availability, far more stem choices. Also I think there may be an advantage if you're using a carbon stem or bars as the larger clamp area requires less torque to hold the bars in place reducing the chance of cracking the CF. I don't see any real advantage to the 31.8 over the 26 as far as strength. As Monty Dog mentioned it's just the center and the rest of the bar is the same size. I've got some old Cinelli 26.0 bars that are nothing exotic but seem to be stiffer than many other 31 bars I've tried that are in the same price range or more expensive. It's more down to design and material choice than clamp size. Seems more marketing than function. Save your money, the one piece bar/stem is now gaining momentum and will soon make your new 300 quid 31.8 CF bars and stem obsolete. :P

sheffsimon

crankycrank wrote:

As mentioned the main advantage of 31.8 is availability, far more stem choices. Also I think there may be an advantage if you're using a carbon stem or bars as the larger clamp area requires less torque to hold the bars in place reducing the chance of cracking the CF. I don't see any real advantage to the 31.8 over the 26 as far as strength. As Monty Dog mentioned it's just the center and the rest of the bar is the same size. I've got some old Cinelli 26.0 bars that are nothing exotic but seem to be stiffer than many other 31 bars I've tried that are in the same price range or more expensive. It's more down to design and material choice than clamp size. Seems more marketing than function. Save your money, the one piece bar/stem is now gaining momentum and will soon make your new 300 quid 31.8 CF bars and stem obsolete. :P

Get your old Cinelli's on eBay, I sold an old pair of CInelli 66-42's for almost £50 on there

MattC59

crankycrank wrote:

As mentioned the main advantage of 31.8 is availability, far more stem choices. Also I think there may be an advantage if you're using a carbon stem or bars as the larger clamp area requires less torque to hold the bars in place reducing the chance of cracking the CF. I don't see any real advantage to the 31.8 over the 26 as far as strength. As Monty Dog mentioned it's just the center and the rest of the bar is the same size. I've got some old Cinelli 26.0 bars that are nothing exotic but seem to be stiffer than many other 31 bars I've tried that are in the same price range or more expensive. It's more down to design and material choice than clamp size. Seems more marketing than function. Save your money, the one piece bar/stem is now gaining momentum and will soon make your new 300 quid 31.8 CF bars and stem obsolete. :P

Good point about clamping force. Technically, I guess you're right, as a 31.8mm bar will have more surface area, therefore more friction than a 16mm bar of the sme material.

The strength (stiffness) component to this is fact. A 31.8mm clamping arera will be stiffer than a 26mm clamping area, for a given wall thickness. As mentioned, if you thin out the wall, you get the same strength (stiffness) but lower weight. Assuming that you keep to the optimal ratio.

These days, with varying tubing profiles as well as composite and alloying technology, you're right, design and material will have a larger factor over stiffness.

Back to the OP's point though, as we've digressed into engineering detail
If you had two bars, of plain gauge tubing, one with a 26mm clamping area, one with a 31.5mm clamping area, but otherwise identical; the bar with the 31.8mm clamping area would be stiffer.

In the real world though, the benefit is most likely that you'll get more choice of bar / stem combo if you go for 31.8mm.