Hope rx4 rear 140/160 adapter?

I’m installing a set of hope rx4 brakes with hope Rx 160 rotors.

Do I need an adapter for a frame designed for a 140 rotor?

With the caliper flat to the frame mount, the rotor cannot rotate, 2nd photo shows the extra spacing that’s required for the pads to line up with the rotor.

I made the assumption that there was a standard location for rear flat mounts… Stupid right?

20mm flat mount rear adapter. I’m using a sram one I think, moves it along and up a bit.

I made the assumption that there was a standard location for rear flat mounts

There is and it’s for 140mm rotors.

(although Hope state 160mm rotors only for that caliper so I presumed they’d effectively built an adaptor into it but clearly not)

Grr. Just about to go fit a post mount RX4. I hope I’ve not bought a pair of 160mm rotors I didn’t need (though older designs of Avid rotors can be picked up very cheaply on eBay and I’m really doubtful that the newer Centreline rotors offer any noticeable benefit over the older HS1s)

although Hope state 160mm rotors only for that caliper so I presumed they’d effectively built an adaptor into it but clearly not

Yeah it looks like the caliper is designed to compensate for the larger rotor, but it’s just a little bit off.

Post mount one needs adaptors to work with a 160mm disc on my frame as well. I wonder if the length of the pad on a four pot disc means they don’t play nicely with the sweep of a 140mm disc? (although back in the day the XC4 brakes worked with 140s I think)

Are all post mount +20 adaptors the same? A lot are marked 180mm but don’t they just take it out on a radius?

Considering I was running 140mm rotors with Ultegra calipers previously, and if the adapter is effectively built into the RX4 flat mount, so that it’s only compatible with 160mm rotors, I don’t understand why it doesn’t fit. It’s a custom frame, maybe the mount wasn’t positioned correctly?

I’m thinking if I add an adapter, it might take it too far in the opposite direction.

Trying to work out what adaptors I need for post mount came across this –
https://www.bikehugger.com/posts/road-disc-brake-tech-flat-mount-vs-post-mount/
which suggest you always use the adaptor for post mount, but a diffent way around depending on whether it’s 140 or 160mm discs (at least that’s how I read it)

Thanks @b33k34, but I don’t think there’s any post mount involved here, unless I’m missing something.

I found these black metal 5mm spacers that came with the frame, that my frame builder assured me are for the forks, but seem to be the perfect size. Just need to hack saw hope’s bolts down now!

Are these spacers a bit janky?

My rear RX4 works fine with a 140mm Swissstop rotor. Post mount, no adaptor.

This is flat mount, 160 only

140 to 160 flat mount looks like its a Y mount according to Hope

https://www.hopetech.com/product-documents/brakes/#!brake-mounts

Interesting @carlos, just concerned moving further away from the axle, the pads may not make full contact with the rotor. I’ve emailed hope about it I’ll see what they say and update here.

It looks like it just lifts the calliper a few mm as per your last pic and you’ll use the standard Hope bolts to bolt direct through the calliper, mount and then into the frame

Thanks @b33k34, but I don’t think there’s any post mount involved here, unless I’m missing something.

I misspoke – that link covers flat mount as well.

Interesting – Hope make an X2 flat mount now https://www.hopetech.com/product-documents/brakes/#!tech-3-x2-flatmount

I’d not seen any MTB’s using flatmount yet (not that I’ve been looking). wonderful thing standards….so many of them.

Cheers @b33k34 that’s a good read. I completely agree with it that to use 160mm rotors with Shimano calipers you should use an adapter since the Shimano calipers are for 140mm rotors. However, the Hope flat-mount calipers are 160 only, and it appears the offset required for standard rear mounts is built into the caliper.

I could be completely wrong about this.