Flat mount calipers on an IS frame?

Hi all,

I’m running an old disc road bike from 2014 (trek crossrip, from the time before “gravel”) that I’ve been pondering banging a cheap, new groupset on.

Some of these Chinese (ltwoo, sensah etc) fit the bill, and could then I could even go full hydraulic on the brakes.

BUT all current road brakes seem to be flat mount, whereas my old frame is IS mount. I think these adaptors would work but mean I’d have to run 180f/160r rotors, right??

Damn the world for moving away from the clearly superior IS standard, which for the cost of a £5 bracket meant you could replace a stripped thread or alter rotor size.

Thanks!

You could probably pick up some cheap second hand Shimano IS calipers, and just run those instead of the provided ones. Or IS/PM is a known quantity.

Thanks, but honestly I was hoping for minimal faff of installation, and a bolt on bracket seemed the simplest solution!

One of these, I was thinking.

https://www.aliexpress.com/item/1005006159561275.html

Or one of the others, that I can mount to my pm/is adaptors already in situ…  Feels like a bad idea though, with adaptors bolted to adaptors… May come to that!

I don’t think the PM-Flat adapter would play with is a IS-PM adapter, looks like it’d be too deep to sit in properly.

What brakes are you currently running on the frameset?

https://www.ebay.co.uk/itm/384328028710?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=gkz_h6vyrzk&sssrc=4429486&ssuid=kQvGtg5dTuC&var=652512729902&widget_ver=artemis&media=COPY

Just eyeballing it, but even the +20 adapter doesn’t look like you’d get the PM-Flat adapter on top of it.

Thanks folks.

Currently running some Shimano r515 mechanicals which are ok, but if I were to change the groupset, I may as well go the whole hog and get hydraulic brakes too…

I may just have to buy one of the IS/flat mount adaptors and see if it fitts, front and rear!

Cheers

Keith

I may just have to buy one of the IS/flat mount adaptors and see if it fitts, front and rear!

In case it helps, there’s a compatibility checking template for an equivalent adapter. I bet they’re all basically the same shape.

https://www.assolutions.ca/shop/adapters/flat-mount-adapter-for-is-frame/

I had a similar problem putting rival on an old bike, and just bought some sram mtb calipers, bolted straight on. Does the Chinese company you’re looking at offer mtb brakes as well?

There is one option that works with many brakes, and I have actually used this to install brakes for a customer – GRX flatmounts to an old steel IS frame. It is from a small Canadian shop.

Flat Mount Adapter (IS-FM)

It is the only properly made one I have seen, and you do need to make sure they will fit your frame – they have an image you can print and cut out to check your frame clearances before ordering.

Disc size is also set in stone – 160mm rear and 180mm front.

Edit: Oh someone mentioned this already above!