It seems a bit silly now virtually every aftermarket stem/handlebar comes exclusively in 31.8 .. I believe it's all Easton does now ..

Yet 25.4 is still referred to as 'standard' – when it really isn't.. and 31.8 is still 'oversize'.

It used to be the same way with 1" and 1"1/8th steerers I recall .. but we got past that.

What is the benefit. I never figured

stiffer innit

As bad as Post Mount and IS…..

whilst I don't like standards changing all the time, I do prefer 31.8 bars and post mount brakes

That's the great thing about standards; there's so many to choose from.

nixon_fiend – Member
It used to be the same way with 1" and 1"1/8th steerers I recall .. but we got past that.

Yes, we got over it…..now we have 1", 1 1/8", 1 1/2" and tapered…….really sorted that one out 😉

stiffer? really? as the bar tapers down very quickly to the standard diameter I doubt its significant. anyway has anyone ever thought the bars were too flexy?

Its all about planned obsolescence and encouraging people to buy more. IE its for marketing

well if 31.8 became standard then 25.4 would be "undersize" and wouldn't sell because no one would want an undersized product.

I don't see the point in calling anything "standard" just use the size in MM or Inch

Why are most rear brake mounts still I.S when the majority of forks and brakes Post Mount?

Who cares what they call it – its stiffer and lighter, what more do you want?

Why are most rear brake mounts still I.S when the majority of forks and brakes Post Mount?

I think it's because its a PITA to construct post-mount rear stays without adding extra weight, but I could be wrong.

stiffer and lighter? Really?

IS is a far superior system to post mount. Post mount is easier for duff mechanics to set up but most importantly is better for production engineering. Much easier to assemble bikes on the production line with post mount.

Its a dreadful bodge using slotted mounts on a brake and is heavier and more flexible

That makes sense…fair enough.

stiffer and lighter? Really?

Yes

i've got WIDE bars on my singlespeed – the width helps with all the heaving and hauling that's sometimes needed.

i've tried 25.4 and 31.8mm bars, and i'm sure i can tell the difference – it might just be placebo of course…

(i can feel an experiment coming on)

i can't say whether the stiffness/flex is a good or bad thing, but the idea of snapping my bars is easier to ignore when i'm on the big bars.

TandemJeremy – Member

stiffer and lighter? Really? – yes, definitely do-able. s'just engineering innit.

M/I = s/y = E/R etc.

Having used both IS and post mount I find it best, to have post mount fixings with IS adaptors. There are few worse jobs than sitting undoing IS bolts putting another washer just to get the disc centered.

TJ,

stiffer? really? as the bar tapers down very quickly to the standard diameter I doubt its significant.

You appear to have completely missded the fact that even 'standard' bars are tapered (25.4->22.2 IIRC). Increacing the cross section increaces stiffness and strength (upto a point, the failiure mode for a tube in compression is related to the modulous of the material).

Pretty much any structure you want to be strong light and stiff is generaly tapered, even the tubes on your bike are butted (which achieves the same effect).

I understand that completely. I just doubt that making the central section larger diameter is going to be able to increase stiffness without increasing weight. The wall thickness of the wider section would have to be so thin so as not to add extra weight………..

For sure it is possible that it is stiffer and lighter in theory. In practice? I doubt it How thin would the wall thickness have to be?

*briefly resists*…

TandemJeremy – Member
stiffer? really? as the bar tapers down very quickly to the standard diameter I doubt its significant. anyway has anyone ever thought the bars were too flexy?

Its all about planned obsolescence and encouraging people to buy more. IE its for marketing

It is noticeably stiffer TJ, in spite of your doubts, guess you should have tried some eh? Fair point re planned obsolescence, this is one area where it does make a difference though.

TandemJeremy – Member
stiffer and lighter? Really?

Its a dreadful bodge using slotted mounts on a brake and is heavier and more flexible

Potentially stiffer and lighter, yes.

Your comments on post mount are laughable, they are running happily on thousands of bikes.

IS is a far superior system to post mount. Post mount is easier for duff mechanics to set up but most importantly is better for production engineering. Much easier to assemble bikes on the production line with post mount.

Its a dreadful bodge using slotted mounts on a brake and is heavier and more flexible

Not so sure about this. If the brakes were on a car the bolts wouldn't even be done up tight and the calliper would float/self centre themselves. Not sure why it's heavier either, but can't see why it would be inherently lighter either?

With PM when you brake, you load the mounts along the line of bolts and the push/pull is against the thread, with the force being transmitted directly into the fork leg in it's strongest plane. With IS you have a shear force across the bolts and this load is transferred sideways as well, so the mount itself is under greater stress.

The above is a marginal benefit, but PM is easier to setup and adjust for pad wear, or a bent rotor and it's also much easier to change rotor sizes too. Only disadvantage vs IS that I can see is that if you wreck one of the threads, it's the fork lower you've ruined not a half caliper.

Anyone remember how you hcanged otor sizes with Hope brakes? you bought a new half caliper. PM is progress.

Actually the bars are heavier, but the stems generally lighter, so it roughly evens out. I'm not aware of any bars that are lighter in 31.8 than 25.4, Easton being the obvious example as they do directly comparable bars.

I use OS bars, as that's what everything is these days, no reason to complain!

The Cannondale Flash uses post mount rear disc, which I can imagine was solely done for weight saving given the rest of the bike. You can't use a 140mm rotor, but you don't need an adapter. Post mount is far better than IS, for all sort of reasons, Paul sums it up really!

I'm sure i've seen handlebars for sale where the 25.4 version is lighter than the 31.8. Not sure I can be bothered to check though.

Actually I can (sort of). A quick scan through weight-weenies suggests that where two otherwise identical bars have different diameters, the 31.8mm bar is either the same weight or slightly heavier than the 25.4mm equivalent.

There aren't many to compare between though.

Could this be because although the bar gets stiffer when the diamter is increased, you still need to have a minimum wall thickness for fatigue/impact damage or something?

Anyway, I think that saying out of hand that OS bars are all lighter is a bit misleading. Better stiffness to weight ratio might be more appropriate, plus it probably facilitates wider handlebars as is the trend now.

I guess all those who think 31.8 is stiffer ride rigid bikes with solid tyres to notice. Fair play to em.

TJ, have you ever cut open a set of bars, the aluminium is pretty thick, particularly in standard diameter bars, the ones on my old bike were almost solid in the middle!

DezB – Member
I guess all those who think 31.8 is stiffer ride rigid bikes with solid tyres to notice. Fair play to em.

🙄

tinas

yes. The bars I have are variable but the quality ones have a very thin wall.

The diameter is 25% more – so for a lighter weight the wall thickness must be more than 25% thinner.

I have weighed a few bars that I have – of varying quality. The OS ones were all heavier

When I had a Ritchey 4Axis carbon stem and WCS Carbon bars (OS) you could grab the bar ends and watch the stem twisting, I can't say I ever really noticed it when riding, but it was a bit disconcerting. I now use an New Ultimate aluminium stem with Race Face Next SL risers, but don't have the same problem. Ergo, it's not the size so much as the individual components. Common sense really!

Easton EC90 flat bars are about 20g heavier in 31.8 than 25.4.

the stem is larger as well – so the clamping bits must be heavier.

TandemJeremy – Member
I have weighed a few bars that I have – of varying quality. The OS ones were all heavier

LOL. Can I quote this when you next flame someone for coming out with non-peer-reviewed articles?

the stem is larger as well – so the clamping bits must be heavier.

Do you think before you type?

Actually most stems are lighter or virtually identical, Thomson being the most notable example of the former. Very few stems are significantly heavier, and a lot of the lightest, like the Extralite UL3, Rotor SL etc are 31.8.

31.8mm bars and stem in my experience are stiffer – presume it's the bigger interface area for bar and stem, pretty much eliminated creaking too. Mind you my switch to OS also included newer bar and stem so maybe bar/stem production in general have gotten better too.

Pretty sure thats a trolling comment dezb.

Not a big fan of post mount myself heavier (if you use >160mm rotor), a bugger to setup straight and if you have to remove the calliper for whatever reason you have to go through the whole setup again, with IS you only have to do setup once to figure out which spacers you need.

Changing rotor size is useful tho I guess and never thought about shearing forces before – good point Paul.

al – which is why I said what my data source was – so people understood the data was of poor quality

On hope you could change the calliper half and keep things neat, everyone else just put a 20mm mount in just like post mount brakes.

PM brakes, to set them up I would normally just do the bolts up almost tight, lock the brakes on, then tighten the bolts before releasing the brakes. If you think IS is easier to setup, it sounds like you're not doing it right!

Thomson being the most notable example of the former.

Isn't it a totally different design though?

[img]http://www.lhthomson.com/images/x4.jpg[/img]

TandemJeremy – Member
stiffer and lighter? Really?

Do you really struggle with this?

Hamfisted over tightening of is mount needs a caliper repair or replacement do it on a post mount and your in bother

al – I understand the theory that it could be so. I simply doubt that the mtb bars are that well made to take advantage of the theoretical advantages. ( as I stated above)

IS mount caliper is simple to set up – and is stronger and lighter.

Post mount you should centre the caliper using the slots and then centre the pads using the hope method to get the best result. IS mount centring the caliper is more of a fiddle – but it is a lighter and stronger assembly.