I purchased a new frame and it came with flat mounts. So I thought no problem and ordered a post mount to flat mount adapter. Went to fit said adapter today and upon pushing the bolt up and through the frame I realised that with only 2mm of the bolt sticking through it wasn't going to work.
I have now discovered that I have 30mm flat mounts and stock seems to be 25mm. Why can't things be bloody standardised!
I'm also not happy with flat mount rear placing inside triangle - making it near impossible to adjust caliper with wheel in... Ball ended hex, trapped fingers in spoke and lots of swearing as frame paint chips off..
Flat mount or frame design issue?
To be fair, using flat mount frames with post mount adapters is never going to be an optimal solution - just be thankful that you're not trying to do the opposite, as it can't be done at all (unless somebody knows different) or you've bought one of those frame sets with flat mount frame and post mount forks (you know who you are, you crazy bike companies)
And, for the benefit of anybody fitting flat mount calipers to a flat mount frame (not the fork), the length of the bolts on the Shimano tech docs refers to the thickness of the frame where the bolt goes through - failure to realize this may result in multiple trips to the LBS 🙁
Just strikes me as another example of a design aimed at making manufacturing simpler. No threaded bosses have.to be added to the frame.
Having to have different lengths bolts strikes me as ridiculous.
Yep. I've got a flat mount frame with post mount fork (Cannondale caad12). Although a bit of a pain with the brake department, the frame is terrific.
Having to have different lengths bolts strikes me as ridiculous.
Post mount forks have always had different length bolts though so it's nothing new
I’m also not happy with flat mount rear placing inside triangle
I'm confused. Is it not bolted through from underneath? Or is it a PM caliper on an adapter?
Plus you need to buy new flat mount facing tools, because some manufacturers just cant be arsed finishing the job.
I’m confused. Is it not bolted through from underneath?
Yes, or at least my Ridley is. Very easy to adjust and minimal faff. Nice design, I would say:
To be fair, using flat mount frames with post mount adapters is never going to be an optimal solution – just be thankful that you’re not trying to do the opposite, as it can’t be done at all (unless somebody knows different) or you’ve bought one of those frame sets with flat mount frame and post mount forks (you know who you are, you crazy bike companies)
Yup, that's my X-Trail - it has what looks to be a post-mount fork, with flat-mount caliper mounted on an adapter. That said, the end result is neat enough and I hadn't actually noticed it until reading this thread:
Actually that's a flat mount fork. The adapter is normal, and allows you to switch between 140mm and 160mm discs, and means that the fork, unlike the rear, doesn't bolt through from the other side.
...my X-Trail – it has what looks to be a post-mount fork, with flat-mount caliper mounted on an adapter
That's not post mount, it is very much a front flat mount. Here is a photo comparison of post-mount and flat-mount.
There are no flat caliper to post mount adapters on the market, but this doesn't stop anyone from making one.
(source)
So it's flat mount now then - not Hayes mount!? I really am out of touch with this cycling lark. 🙂
I’m confused. Is it not bolted through from underneath? Or is it a PM caliper on an adapter?
*blushes*
It is a PM on frame...
Actually that’s a flat mount fork. The adapter is normal, and allows you to switch between 140mm and 160mm discs, and means that the fork, unlike the rear, doesn’t bolt through from the other side.
TIL! Many thanks - I never knew this. What would be involved in switching to 160mm discs? A different adapter?
Edit: this is a good article and explains it. Yes, there is a slightly different adapter needed for 160mm discs, but it's much neater than the post-mount equivalent:
http://www.bikehugger.com/posts/road-disc-brake-tech-flat-mount-vs-post-mount
It is 160 on the front. To run a 140 up front you turn your existing adaptor around to face the other way. On the rear, you’d need a 160 FM adaptor.
What would be involved in switching to 160mm discs?
Undo all the bolts and turn the mounting plate round- there should be an up arrow on one side labelled '140' and the other side '160'.
Flat mount would be quite a neat standard if shimano hadn't decided to change the pad sizing from post, meaning my post mount rear, flat mount front bike has two different sizes of pads. Ah well, flat mount pads are expensive enough I raided the LBS spares and found a spare PM caliper, adapter and pads for slightly more than the price of a set of post mount pads. Ugly though.
Undo all the bolts and turn the mounting plate round- there should be an up arrow on one side labelled ‘140’ and the other side ‘160’.
Oh, that's even better then. Yes, it's currently 140mm on the front, but I got them really, really hot when descending Honister at half term and, as I'm not the most svelte rider in the world (85kg on a good day), I'd probably benefit from some bigger discs. I'd love Shimano's heat-dissipating rotors, but IIRC, they are centrelock only, and mine are 6-bolt.
If that blue fork above is yours it's 160 at the moment. You can read it on the mounting plate.
You can get aluminium core rotors in 6 bolt, just not the crazy finned ones. RT76 IIRC. How much benefit they are I don't know. Alternatively I think superstar do their own finned rotors.
Or fit the (horrifically expensive) finned pads.
If that blue fork above is yours it’s 160 at the moment. You can read it on the mounting plate.
FFS, I'm not doing very well today. You are, of course, quite correct.
You can get aluminium core rotors in 6 bolt, just not the crazy finned ones. RT76 IIRC. How much benefit they are I don’t know. Alternatively I think superstar do their own finned rotors.
Or fit the (horrifically expensive) finned pads.
I really don't know how much difference any of this makes anyway. I'm pretty sure than me weighing 5kg less would probably be a much more effective way to improve thermal dissipation on descents! Thanks for the tips though.
I really don’t know how much difference any of this makes anyway.
Never bothered me. But then we don't have many hills down south that go on long enough. Although a camping load coming round Dartmoor and through West Dorset last week had me thinking about it again on some of the downs. I've got some finned pads in a spares box, if I ever go road riding to the alps they'll get fitted, otherwise they're just emergency pads.
There's got to be a kickstarter in mounting a C02 cartridge to cool your rotors in an emergency, surely?
I'd actually be less worried about alpine descents than some of the stuff you can find in the UK. The alps descents that I've ridden are generally fairly fast, open roads, punctuated by hairpin bends. Fast means lots of cooling on the brakes, and also losing more of your potential energy to wind resistance.
In the UK (Wales, Lake District) we have some very narrow, twisty and steep roads, with often awful surfaces. It can be very hard to get off the brakes for more than a moment or two, or get enough speed to get any useful cooling.
Owing to a maintenance fail, I ended up on a road ride in Wales in the winter trying to use just the front brake. I was surprised at how quickly it could fade, and also how quickly it escalates: one moment you've noticed the braking isn't great, the next you're pulling harder and harder and barely slowing down. It really doesn't take a lot of altitude: it's the gradient and the (lack of) speed.
This was a 160mm non-finned rotor, finned pads and I'm under 70kg.
Now obviously I should have had a rear brake too, but assuming say, 65/35 front rear brake distribution, it's not a huge margin for error. I'll be sticking with finned pads, which are cheap enough from Rose if you're buying other stuff to spread the postage.
Flat mount would be quite a neat standard if shimano hadn’t decided to change the pad sizing from post, meaning my post mount rear, flat mount front bike has two different sizes of pads. Ah well, flat mount pads are expensive enough I raided the LBS spares and found a spare PM caliper, adapter and pads for slightly more than the price of a set of post mount pads. Ugly though.
That's not really the fault of Shimano - it's more down to those crazy bike manufacturers that I mentioned earlier
You can get Shimano flat mount pads without the cooling fins that are cheaper. But can’t remember the number
Not to try and derail the thread, but the 2 issues above (PM VS FM etc and brake fade) are the exact reason I don't want discs anywhere near my road bike.
Not to try and derail the thread, but the 2 issues above (PM VS FM etc and brake fade) are the exact reason I don’t want discs anywhere near my road bike.
PM vs FM isn't an issue if you buy a frameset that only has FM.
Not sure about brake fade, as I haven't encountered this yet.
Not to try and derail the thread, but the 2 issues above (PM VS FM etc and brake fade) are the exact reason I don’t want discs anywhere near my road bike.
I took mine down Honister Pass as I thought it unlikely I'd find anything substantially harder on the brakes in the UK. I'm no waif (85kg-ish) and had no problems with braking. I certainly got the back brake a bit noisy on the way down, but at no point did the brakes feel like they were going to let me down or I wouldn't be riding it now!
I know of people who have blown inner tubes on the lakeland descents purely due to excessive heat from rim brakes too and a blown front tyre on a 25% descent is no fun either...!
I ride Honister fairly regularly, and like you no issues. The Welsh hill that I had trouble was probably harder on brakes because due to crap surface and poor visibility, you just couldn't get off the brakes to let them cool. The gap between "not feeling like they were going to let me down" and "too faded to stop" was alarmingly short. I'm sure if I'd had both brakes working properly it'd have been fine, but it reinforced my view that skimping on non-finned pads isn't worth it. I know from tinkering with home made bike lights how much effect a heatsink can have.
