Post and IS mount Forks - dont understand

[jethro10]

Hi,
I broke something recently and while getting a replacement, decided to upgrade a little and got kinda lost. So I'm holding off 'till I understand

Front forks now, all seem to be Post Mount, my bike is I.S. mount

Q1. Not sure here, but all new Calipers seem to be post mount design, ie. they could bolt straight to a PM fork and take a standard 160mm rotor? Is this right, all PM calipers potentially fit any PM fork and take a 160 rotor? ie. all spacings/offsets are standard

my bike had an IS fork to PM caliper converter, so it caused no problem once I realised

Q2. by the number of adaptors about, it seems likely that until recently IS mount forks were the norm? but now PM ones are?

Q3. trying to understand the 'standard' here. So 160-180 PM to PM spacers all add the same spacer distance, although shape may differ to clear the particular brand caliper castings.

Can you follow what I say here?

Lets see how close I am?
thanks
Jeff

 

[Panter]

Hi,
I broke something recently and while getting a replacement, decided to upgrade a little and got kinda lost. So I'm holding off 'till I understand

Front forks now, all seem to be Post Mount, my bike is I.S. mount

Q1. Not sure here, but all new Calipers seem to be post mount design, ie. they could bolt straight to a PM fork and take a standard 160mm rotor? Is this right, all PM calipers potentially fit any PM fork and take a 160 rotor? ie. all spacings/offsets are standard

Yup

my bike had an IS fork to PM caliper converter, so it caused no problem once I realised

Q2. by the number of adaptors about, it seems likely that until recently IS mount forks were the norm? but now PM ones are?

Not sure, but I think so

Q3. trying to understand the 'standard' here. So 160-180 PM to PM spacers all add the same spacer distance, although shape may differ to clear the particular brand caliper castings.

Yup

Can you follow what I say here?

Lets see how close I am?
thanks
Jeff

What sort of upgrade are you looking at?

I've done similar myself recently, my Hardtail has IS mounts but the new full-susser build has post-mounts although, thinking about it, that fork is actually older than the fork on the HT so that's blown my answer to question 2 out of the water.

Basically, all the mounts and adaptors are available to fit pretty much what you want to whatever you want to fit them too.
It looks to me (although I'm probably wrong again) that the IS mounts double up as post mount extensions, i.e to fit a 185mm rotor, the mount looks very much like an IS mount but it also has holes drilled the other way to allow it to be used as a post mount spacer.....
I'm going to stop there because I'm just confusing myself now....

 

[Panter]

Actually, sorry, just ignore my answer completely. Someone who actually knows what they're talking about will offer some proper help soon I'm sure

 

[jethro10]

Actually, sorry, just ignore my answer completely. Someone who actually knows what they're talking about will offer some proper help soon I'm sure

lol.

I dropped a breezeblock and it's broke the caliper and bent the disk.

I'm happy to do ebay for used gear and probably what I'm getting at is how interchangeable things are.

Like if I have to buy a new rotor, mine is, er was 160mm so if I see a 180 for instance cheap enough, it looks like spacers are standard offsets.

Rest of it is just for curiosity, as I'm a curious guy. Well that's what my wife says

Jeff

 

[Panter]

ah I see, bad luck for that breakage
Wouldn't have been so bad if it had followed a heroic crash attempting a huge drop-off or something

If it helps, Wiggle have Avid Juicy Fives on sale at the moment, less than half price and you can specify whatever rotor you want (comes with the appropriate mount.)
They're really good brakes (I run them on my hardtail) so i've got a set for the new full-susser build.
Just wondering if replacing a caliper & rotor may not be much cheaper than a whole new system?

 

[Jonathan M]

Hi,
I broke something recently and while getting a replacement, decided to upgrade a little and got kinda lost. So I'm holding off 'till I understand

Front forks now, all seem to be Post Mount, my bike is I.S. mount

Q1. Not sure here, but all new Calipers seem to be post mount design, ie. they could bolt straight to a PM fork and take a standard 160mm rotor? Is this right, all PM calipers potentially fit any PM fork and take a 160 rotor? ie. all spacings/offsets are standard

my bike had an IS fork to PM caliper converter, so it caused no problem once I realised

Q2. by the number of adaptors about, it seems likely that until recently IS mount forks were the norm? but now PM ones are?

Q3. trying to understand the 'standard' here. So 160-180 PM to PM spacers all add the same spacer distance, although shape may differ to clear the particular brand caliper castings.

Can you follow what I say here?

Lets see how close I am?
thanks
Jeff

Rock shox forks are still IS aren't they?

You are right, IS was the favoured system, in the past only Manitou used the post mount, and this was backed up by Avid making post mount friendly disc brakes.

IS mount often need shims to get the caliper central over the disc, and unless the mount is 100% aligned then IS mounts often need shims just to be aligned. IMHO post mounts have always been easier to set up.

There were (are??) two sizes of post mount, although I think things have now standardised from that aspect, the difference being the spcing between the posts.

I'm in the opposite situation, running a Manitou fork of 2004 (ish) vintage with IS mount Formula B4 brakes, needing an adaptor from post to IS. Means I have a nice 185mm disc on the front though.


In terms of adaptors, if you disc brake manufacturer offers its own adaptor, use that, due to caliper casting you cannot be sure another make of adaptor or a supposed "universal" adaptor will do the job.

 

[jethro10]

Thanks folk, looks like I was right enough. This knowledge makes it so much easier to source parts, when you actually do have a clue what your on about.

Jeff

 

[jethro10]

ah I see, bad luck for that breakage
Wouldn't have been so bad if it had followed a heroic crash attempting a huge drop-off or something

Ah, no. I've been building a brick shed/outhouse to keep our bikes in. Basically complete and i was stacking up what was left. It slipped, hit the disk and bent it and that seemed to have cracked the casting of the caliper.

 

[Panter]

Doh!