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Surely a post mount fork/frame with post mount brake is lighter than IS fork/brake. You're also more likely to get away with using aluminium bolts if that's your bag, as there's no shear forces on the front brake particularly, as you well know.
Post mount is far easier to install and adjust, I really do struggle to see how IS is simpler or stiffer, particularly considering the surface area contact is far far less.
njee - look at the angle of the bolts - of course there is shear forces. However the bolts in both set ups do not take shear loads unless they are loose - what happens is they clamp the faces together and the friction between the faces takes the sheer load.
Contact surface area is greater on IS as there is no slot.
IS is simpler and stiffer as there is one less bolted joint ( 160 front / 140 rear excepted) and in all sizes the joint is better supported as the mount is not slotted. Similarly IS is lighter as you have two bolts not 4
IS mount is a fiddle to set up the first time then never need be done again.
Also check the post above about the hope method of centring pistons.
go an have a real good look at both
TandemJeremy - Member
so you think a slotted mount is a better idea than a shimmed mount? Using an extra adaptor and two extra bolts?
You fail to grasp basic engineering.
IS mount is lighter, stiffer, simpler and stronger.
give it up tj ffs.
Thousands use both quite happily. What you define as basic engineering is irrelevant.
Are we not using 7/8" bars anymore?
Aah, I use 160/140 on my bikes, so was thinking in that perspective. I can see a 180mm IS is simpler than a post mount with adapter, although personally I would use post mount every time, despite the 'complexity'.
fair enough Njee. I sold brand new shimano post mount to fit secondhand hope IS mount to my bike
Al - just because people use it happily does not mean its a superior system. a slotted mount is never as good as a shimmed one. whether you care about this or not is up to you but it simply is not as strong. As lotted mount only has around half the area of mating surfaces in contact.
Tj my point is whether you think post mount Is inferior is irrelevant as it's clearly good enough.
If you knew anything about engineering you'd know this was more
important.
I'll accept its good enough as it works. It just upsets me because its such an inelegant solution and IS is so much more elegant.
yes PM does not fail - except in being heavier than it need be
I think it's a more elegant solution but there you go.
think about this pragmatically, rather arguing semantics with the ether
1) have you ever had or seen a caliper or a brake mount break? or flex in such a way as to be detrimental to the performance of the brake?
2) is the greater weight of post mount (if it is greater) noticeable to the rider?
3) is it far easier to set up post mount? or adjust trail-side?
.
to me the only disadvantage to post mount is the risk of damaging the thread in the fork/ frame
bakes - thats the point al makes and I accept it
Al - have a look at a post mount and IS mount side by side - the IS mount is much neater and smaller and 2 bolts instead of 4 for the bigger sizes.
IS is so much more elegant.
shims are not elegant, they are a bodge
compared to using a separate mount and slots? I don't think so. Still if you think it better to have an extra mount and two extra bolts using slots then your choice. I get to buy up IS calipers cheap
so your final argument is that they're cheaper? nothing to do with design or engineering elegance?
the truth is out!
Tj lots of is mounts need adaptors.
I really don't know why you bang about this. Truly trivial.
triviality breeds contempt
2 bolts instead of 4 for the bigger sizes.
Really?
Take a look at Magura forks. PM and take a 180mm disc without adapter on the Thors, and 203mm without adapter on a Wotan.
If the inelegance of PM disturbs you so much, then you probably have too much time on your hands 😀
Al - IS mount do not need adaptors if you have the right caliper for your disc size. I have 7 sets in varying sizes from 140 - 203mm and none have mounts.
Thats one of the key things with IS. The caliper is sized to the disc so no mount is needed. You can bodge a caliper meant for a 160 disc to a 180 disc witha mount if you want
[i]2 bolts instead of 4 for the bigger sizes. [/i]
GavinB beat me to it, My Thors are direct mount 180mm rotors. Shims are the work of the devil as far as I'm concerned
My skinny tubed steel HT has skinny bars.
My fat carbon FS has OS bars.
Both seem to suit the bike in question, that is all.
Just as an aside - the skinny bars on the HT are held in place with an OS stem and shims. No reason apart from I had a stem available in the shed when I needed one. I tend not to get worked up about it.
I also couldn't really give a shiny shit how my brakes fix to the forks either, as long as they are in the right place and don't move.
Tj is that true for every is brake caliper?
Skinny bars for rigid, fat ones for bounce. Simples!
Just to dig up this old chestnut again
nickegg - MemberWhy are most rear brake mounts still I.S when the majority of forks and brakes Post Mount?
My understanding of this is because in terms of mass production it's near impossible to fix a post mount frame that has been manufactured with any misalignment of the posts. Frames are mostly made using processes where this is a real possibility whereas fork lowers are cast so this isn't a possibility, or at least shouldn't be. Which is why you'll generally only find post mount rear brakes on the most expensive & CF bikes as the standard of quality control in manufacture & the alignment of the post mounts is much easier to control. My €0.02
I've used both and cant feel a difference, but haven't been running identical versions of the stem/bar. I prefer 25.4 or whatever it is - looks nicer and cleaner to me. Oversize bars look chunky and stupid.
I hate 31.8 bars/stems. if I used 28"+ wide bars I could see the point otherwise it's just more weight.
I guess all those who think 31.8 is stiffer ride rigid bikes with solid tyres to notice. Fair play to em.
Congratulations on apparently not understanding why tyre stiffness and bar rigidity wouldn't give the same response.
I think part of the reason for larger diam bars is the larger interface area and larger diameter makes for smaller leverage forces in the stem clamp and better grip of the bar.
31.8 will become standard as soon as someone dreams up some other damn fool new standard to replace it.
I've got three bikes with Easton EC70 25.4 Monkeylites and one with 31.8 Monkeylites, the 25.4's are more flexy, more comfy and easier to fit lights to due to the shallower taper.
Northwind - Member
31.8 will become standard as soon as someone dreams up some other damn fool new standard to replace it.
I heard 29.8 is on the cards 😉