Disc caliper adaptor question

BG2000

Is there an adapator specifically for mounting an IS Shimano caliper onto forks with PM ?

I realise that most of the time people are going the other way round, i.e. mounting a PM caliper onto IS tabs.

I have a 160mm rotor.

nicklouse

yes KCNC do one to mount IS 160 calipers to 6"Post monts and keep a 160 rotor.

BG2000

Actually, could someone confirm something about the following adapator:

http://www.chainreactioncycles.com/Mode ... elID=13743

It states "74mm post mount caliper to a 51mm international standard fork mount with a 160mm disc"

Could it then also be used to mount a 51mm IS caliper to a 74mm PM fork with 160mm rotor ?

.blitz

I guess the caliper would bolt to the fork OK but would it line up correctly with the rotor hmmmmmmmmmmmmmmm

nicklouse

BG2000 wrote:

Actually, could someone confirm something about the following adapator:

http://www.chainreactioncycles.com/Mode ... elID=13743

It states "74mm post mount caliper to a 51mm international standard fork mount with a 160mm disc"

Could it then also be used to mount a 51mm IS caliper to a 74mm PM fork with 160mm rotor ?

no.

BG2000

I'm guessing it's a problem of alignment.

The KCNC adaptors Nick mentions have offset PM tabs. Problem is, I've not found one for 160mm rotors yet.

Is this because when you convert fork PM mounts to IS, you have to increase rotor diameter by 20mm ?

In which case, I'd have to change to a 180mm rotor to fit an IS caliper on my Revs....

nicklouse

looks like they have removed it from stock or it is out of stock. Call Clee Cycles.

BG2000

Cheers Nick,

I was ahead of you (for once !)

I phoned up Clee earlier and they found a 160mm version of the KCNC adapator, and added it to the website (it appeared when I refreshed the page) and I bought it straight away, and then they removed it again ! How's that for quick customer service !

They explained the reason why IS to PM 160mm adaptors aren't common - basically, there's no guarantee they will fit. The guy I spoke to at Clee was really good and helpful, hence they get my business.

I'll take the risk with it. My XTR caliper is fairly slimline, so may just fit against the adaptor. It's worth a try - otherwise I'll have to change to a 180mm rotor and use the more commonly stocked adaptors. I think Clee would just do an exchange for me.

Thanks for the help and advice...

allthegearnoidea

Andy at clee cycles is a top fella! tends to be my first port of call when looking for bits!

a2z did do one similar but is Very skinny/thin,

the shimano one as you posted the link to and as nick said wont fit, i have one of those in the shed after reading that it was PM-IS, but sadly its IS-PM, if you look at the picture you can see that where it Should bolt to the fork its Not flat and if you were to modify it to fit there would be Very little between the the post mount on the fork and the IS thread hole!

BG2000

My saga continues...



My KCNC 160mm PM Fork to IS caliper adaptor doesn't quite fit. Assuming I have it the correct way round, it touches the fork leg with the middle section. I could put some washers on the PM mounts to move it out a bit. The top bolt obstructs the caliper a bit which is why it isn't correctly aligned with the adaptor. I just need to file down the edge of the bolt head a bit.

Even with the above issues resolved, my caliper would be sticking out way too much for my 160mm rotor. I believe this is due the caliper being a rear mount only. Shimano used to do a front version of their XTR IS calipers (probably a BR-M965-F). I know people will say my problem is because you need to step up a rotor size when mounting on the front, but this KCNC adaptor is supposed to get round that issue, so I think the problem is with the caliper.

I'm assuming the front version of this caliper has much shorter lugs, but I can't find a photo of one on the web anywhere.

The only images I've seen of the front version appear in Shimano's tech docs for the BR-M965 series:

Front caliper: http://techdocs.shimano.com/media/techd ... 609096.pdf

Rear caliper: http://techdocs.shimano.com/media/techd ... 609097.pdf

Now my problem is trying to figure out if I can resolve this simply with a larger rotor. My photo suggests that my caliper is sitting more than 10mm out from the disc, so that would suggest that a 180mm rotor would still leave the caliper to far out. I could try a 203mm rotor and add spacers between the PM mounts and adaptor. That would at least resolve the first clearance issue I've mentioned.

Sorry for posting such a lengthy reply, and I really appreciate any time people spend reading all this. And I won't mind if someone simply says 'stop messing about and get a PM caliper !!

nicklouse

so it is a caliper from the rear with a 160 disc?

if so then yes it is a front 180.

all covered in the FAQs. the mounts are different front and rear.

BG2000

nicklouse wrote:

so it is a caliper from the rear with a 160 disc?

if so then yes it is a front 180.

all covered in the FAQs. the mounts are different front and rear.

Thanks for taking the time to read through my last reply - really appreciate your help.

Yes, it's a rear caliper and I'm running a 160mm rotor at the front. It's identical to the caliper I'm already using at the rear which bolts directly onto my frame's IS tabs and is using a 160mm rotor.

I did think that it should then follow the usual '+20mm rotor if used on the front' rule.

It's just that from the photo I've shown, the caliper piston centre seems to be more than 10mm away from the rotor edge.

Hopefully then, I can assume that using my 160mm KCNC adaptor, the front end now has an IS mount at exactly the same distance from the rotor than at the rear, as it's the caliper's shape that needs a 20mm larger rotor. I guess I need to measure my IS mount positions and confirm this.

Thanks again... :?

nicklouse

yes rear and front calipers that run 160 and 180 rotors are identical. (just like the IS to post adaptors)

but in this case i would replace the caliper with a post one if you want a 160mm disc.

seems that like Clee said they dont always fit.

BG2000

nicklouse wrote:

yes rear and front calipers that run 160 and 180 rotors are identical. (just like the IS to post adaptors)

but in this case i would replace the caliper with a post one if you want a 160mm disc.

seems that like Clee said they dont always fit.

I am willling to buy a 180mm rotor if it allows me to use my rear caliper on the front.

I took a couple more photos this morning to try and compare the alignment of my IS mounts (front via adaptor) with their respective rotors:

Rear IS mount - image rotated about 90°


Front IS mount (via 160mm adaptor)

Should the alignments of the front and rear IS mounts not be the same, with respect to the rotor ?

The only reason I would need a 180mm rotor is that I'm trying to fit a rear IS caliper on the front, right ?

On the first image, the upper IS drilling is in line with the edge of the rotor. With the second image, it's about an inch too high. So I can't see how a rear caliper will fit with a +20mm rotor.

It doesn't even look like a dedicated front IS caliper would fit.

allthegearnoidea

here's mine with a hope +20,
manitou forks with 180mm post mounts,



much like how you described exoecting it to be,
could be that whilst you have the adaptor to run a 160mm caliper, if the fork is 180mm then it wont work as it'll effectively mean you can run a 180mm IS caliper on as std. almost seems if you need an adaptor ti run a 140mm caliper from a 160mm PM fork to allow you to run the caliper how you want, if that makes sense???

nicklouse

allthegearnoidea


but Revs dont have 8" post mounts..

if the adaptor fitted it would all be fine.

BG2000

nicklouse wrote:

allthegearnoidea


but Revs dont have 8" post mounts..

Quite right, and it's currently fine running a 160mm rotor with a knackered old post mount caliper - hence the reason I'm trying to replace the caliper with a 'spare' IS caliper I have.

But thanks to allthegearnoidea for the info. It's comforting to see a photo of what I assume is a brake that works OK !

Well, I now have a brand new SM-RT75MA (180mm XT rotor) in my bag that I bought at lunch time. I'll try fitting it all tonight.

My last question (for now) is what are the risks of filing down my adaptor so it doesn't hit the fork leg ? I'm guessing it acts as a structural bridge between the two PM studs on the fork, helping to prevent them flexing upwards when breaking hard ?

nicklouse

I was about to suggest this.

how much spacer would be needed to be fitted for the adaptor to clear the fork.

I WOULD NOT BE FILING THE ADAPTOR as it is thin enough.

if you can get away with 2.5-3mm on between the mounts and the adaptor see if you can find a 185mm disc. (Hope/avid....)

BG2000

Thanks again Nick.

There's just enough flexibility in the adaptor such that it can be tightened in place without any spacers, though it does press against the fork lower.

With the caliper installed, the pads are a couple of mm over the edge of the rotor :


So I think your idea about getting a 185mm rotor is a good one.

Will an Avid Clean Sweep G3 rotor work fine with my caliper ? That seems to be nicest 185mm rotor I can get.

nicklouse

rotors are mainly very interchangeable as long as they are spaced correctly.

some have a small variation in thickness so a piston reset is needed.

allthegearnoidea

have a nose at the superstar rotors, something like a tenner??

BG2000

nicklouse wrote:

rotors are mainly very interchangeable as long as they are spaced correctly.

some have a small variation in thickness so a piston reset is needed.

Great. I might even get this done ready for the weekend !

What do you mean by a piston reset ? This is a new unused caliper, so I was just going to use the Shimano yellow plastic piston spacer when purging the lines with mineral oil.

Are you saying I should use an Avid spacer for this ?

nicklouse

resetting the brakes. push pistons home and then apply the brake a few times to set the pads against the rotor.

as this is a "new" build you will be setting the pistons after the bleed anyway.

BG2000

Thanks again for the advice Nick.

Finally got it all running yesterday, using a 185mm G3 rotor. Gave it a thorough test at Lee Quarry in the evening:



The pads are still slightly too deep - there's just under 1mm sticking out above the rotor. I won't worry about that - they work very well.