So I’m building up my new Ibis Mojo HD and it has a post mount for the disc caliper at the rear…

I have post mount Magura Louise BAT caliper and a 180 rotor. Should be easy?

So I need a PM to PM 180 adapter. However I don’t seem to be able to find one? For some reason I vaguely remember that a front PM to PM 203 mm adapter will actually do what I want when used on the rear? Is this so or is my memory shot?

my 180 rear louise came with a pm to 180mm pm adapter.

I thinkt he standard spacing for rear on frames is for a 160mm so you need soemthign that, effectively, is PM to PM+20.

[edit] I’d link to crc but it appears to be down but this seems to be what you need;

http://www.winstanleysbikes.co.uk/product/24788/A2Z_Post_Mount_to_Post_Mount_Adapter_160mm_to_180mm

Yeah but I don’t want the A2Z one as if you read on wiggle for the same: http://www.wiggle.co.uk/a2z-adapter-pm-to-pm-160mm-to-180mm/. It’s actually just a couple of big washers!

I also think the rear works different to the front for some reason – that’s what I wanted to check?

PM to PM is the same front and rear. So you could use this –

http://www.starbike.com/php/product_info.php?lang=en&pid=8658

It’s actually just a couple of big washers!

Probably because that with some slightly longer bolts is all you need 🙂

What’s going on with the quote thingy??

Probably because that with some slightly longer bolts is all you need

No it’s not. Because of the angles involved it’s a bit more complex. Check the link Mister P posted. If what you say were the case then both ends of that adapter would be the same length.

and by the way you missed a / in your end quote.

I’ve found a photo here http://forums.mtbr.com/showpost.php?p=7730016&postcount=14 Which I think partly answers my question: The rear is different to the front! And I need an adapter like in the photo contained in that link.

angles don’t matter as its all relative to the axle. 2 long bolts and spacers, either seperate or as a complete bracket is a much tidier solution than 2 pairs of bolts on an offset bracket.

Can’t see the pics in that link unless you are a logged in member.

There’s no difference between adaptors front and rear in order to fit the same size disc.

Mine has the same pm-pm ‘H’ Hope adaptors at both ends, in order to fit 183mm discs.

The difference in adaptors in the pics you’ve linked to (I can’t see a close up of the front, so assume it look different else you wouldn’t be posting it) is because the rotors are different sizes.

her’es the Magura doc listing all of them and their uses;

http://www.magura.com/uploads/media/downloads/Adapter2009_02.pdf

The Magura doc doesn’t specifically list a Post Mount rear 180.

I already have a PM to PM 180 on the front so I’ll try it when I get home…. If my memory is right though it won’t work?

I bet you a jammie dodger it works.

I owe you a jammy dodger 😉

160 on for now and I’ll order the right adapter… (Magura QM6 or equivalent).

I’ve also remembered why I thought the 203 front = 180 rear. That was IS mount adapters for my older Maguras that did that….

yeah the IS adapters are different lengths front and back as the rear can actually go down to 140mm using IS frame. If your frame is PM and 160mm without any adapter then it is the same as PM forks which are 160mm without adapter so you just need a +20mm PM adapter which is not +20mm at each bolt hole as the caliper does not move on a radial path away from the axle.

Using a front 160mm IS to PM on the rear can let you use 140mm discs but you need to space the caliper in by about 1mm as the caliper holes on the rear adapters (shimano anyway) are slightly off-set from centre. Geometrically the rear 160mm is the same as a front 180mm but due to the offset holes if you use a R160 on the front then the caliper will be too far in towards the wheel and the pad will rub.