UKC

Hi all, my full sus has SRAM centerline 200mm disc on the front and the pads make 100% contact - the rear is a centreline 180mm and the pads make around 90% contact (there’s an obvious rim to the pad where it’s not in contact with the disc)

This ‘normal?’ - I’m no bike tech but I’m thinking not. Brakes have been bedded in proper but would explain why the rear never felt like it was breaking true.

Thanks 

Sounds weird. I'm not a bike tech either though. 

How big is the lip on the pads? Are you maybe using a 183mm caliper with a 180mm rotor?

Sounds odd

Do the original specs specify 200 front 180 back?

Wrong caliper?

You don't say which calipers you're using and what attachment they are - PM or IS/IS with adapter?

I used to have some Giant MPH brakes which used a 163mm disc - perhaps you've got the reverse issue?

Full day just now but will whip the wheel off later and get the pads/calliper out 

I’ll have a better look later, but if this was the case is it a ‘big’ issue, plainly wrong or not too consequential? It’s how the bike came/set up btw 

Unfortunately if the rotor is too small you'd have to replace it with a bigger one, or if the caliper is mounted on an adaptor then you might be able to swap the adaptor. If they're SRAM brakes with the spherical washers you could possibly ditch these and replace with a selection of appropriately sized shims, though you'd risk alignment issues. If it was me and it is a mismatch in rotor and caliper size I'd probably sort it but I'm quite anal about these sorts of things.

Was the bike brand new? If so and the difference between rotor and caliper is small it might just be a tolerance issue which would be awkward, but not impossible to solve and possibly easier just to live with. If it's a small enough mismatch, a very good bike shop would have a brake mount facing tool and would be able to cut the mounts down to get a better fit, but obviously this is a bit extreme and not reversible so I'd be cautious about going down that route.

If you can take some pictures it might help to suggest what the best options are. Particularly of the caliper and how it's mounted to the frame, the worn pads and if possible the rotor in the caliper (might be difficult to get a photo at an angle to really see what's going on though)

This isn't unusual in my experience, you don't need such a big brake on the rear as most of your braking is done by the front.

I may have pictured this wrong in my head, but if your pads are developing a lip (where they are not touching the rotor) then don't you risk the pads wearing and then the lips meeting in the middle, then no back brake...?

Hard to say without any photos or knowing what the calipers and frame are, but if there's an adaptor, check it isn't upside down or anything like that. Or if it's SRAM, as mentioned earlier, check the washers are in the right place.

In reply to 'is this a big issue' - it can be. If the pads sit higher than the rotor and a big enough lip is being worn on them, the pads can contact each other before they contact the rotor, potentially meaning no brakes until you replace the pads. (Edit - like Dave Todd said above.)

The issue could be an imperial/metric issue between a 7 inch and a 180 mm rotor. I recently did a bit of a botch job taking a old Shimano (metric) brake from an old bike and putting it on a SRAM (imperial) rotor on my newer bike. I had to shim out the calliper mount a little to get correct alignment.

The difference you've felt could be a variety of issues ranging from the extra length of the hose on the rear giving a more spongy feel or just the smaller disc giving less braking power.

I wouldn't be too worried about it although I have low standards as you can tell from my note above, I would however keep an eye on the pad wear at a disc is only about 2 mm thick and you could easily build up a lip of 1 mm on each pad and bridge the disc at the one side.

Just to add it’s a new bike, delivered assembled and just shy of 2k. I sent a pic and details to the builder and they say ‘take it along to a local bike shop, might need a tweak’ - though i’m thinking it’s more of an issue with the pads/callipers really?

bit of an underwhelming response (or am I expecting too much?) 

I can ‘sort of’ live with it but had expected the spec/build to be 100% spot on for that price and rep of build

If it's a big brand that has high street presence you could take it to one of their shops, if it's a third party brand or bespoke build then I'd tell them to pick up the bill for any work the bike mechanic thinks is necessary.

Any washers between the mount and the caliper?

Sometimes SRAM come with a double washer that aren't always needed.