NoWhammies

I think the disc rotors on my bike are 140mm. The braking system (I believe) is Shimano Ultegra hydraulic.

If I wanted to upgrade the front disc rotor to Ultegra 160mm, is it just a simple matter of swapping the rotor? Or do I need to adjust something on the bike/wheel?

And finally, what's the best/easiest way to know when you're rotor thickness is done and needs to be replaced? Are there wear bars or something I need to keeping an eye out for?

Thank you.

Elvo

Shimano specs the minimum rotor thickness in their installation manual. Measure it with some digital calipers.

To swap you probably will need new bolts (if 6 bolt) and rotate the flat mount adapter to the 160mm position or buy a 160mm adapter if not using flat mount.

WhyFi

Didn't you just get the bike? I'd ride it for a bit, first. Braking will continue to improve as the pads/rotors bed in. You'll prolly have plenty of stopping power.

Otherwise, what Elvo said ^^^ (except those Shimano rotors will be CenterLock/AFS, so no 6-bolt. If your wheels are 6-bolt, you're out of luck as far as any of the snazzy Shimano rotors are concerned).

firebird854

It's up to your weight, if you're on the larger side, 160mm is the way to go (especially for the front). I personally weigh around 135lbs and have opted for 140mm Dura-Ace rotors front and back and have had 0 issues whatsoever.

Also, it's far more typical for stores to sell bikes specced with 160mm rather than 140mm, so there's a good chance yours is 160mm. Out of curiosity, are you having issues stopping?

Cyclist0108

Shimano XT Icetech rotors are 6-bolt. These go down to 160mm, but not 140mm.

I would not want anything smaller than 160mm on my front. If the frame allows it (as mine does), 160mm on the rear, too.

You might need a different adaptor, or might need to remove the adaptor, depending on your fork. Apart from that, it is a very straightforward process.

To measure wear, get a good caliper, and measure the thickness in several places, using one of the several notches in the disc. The edges don't wear down, so you will get a false measurement if you don't go in where the notch is. Shimano's specs (1.5 mm) are very conservative. You can probably wear them down to 1.25mm. I measure and order rotors when I am at 1.5 mm, and then change them out when I next feel the need. Also keep an eye on the pads. When they wear down, they will destroy your rotors fairly quickly.

160mm rotors will last longer than 140 mm.

NoWhammies

@Elvo thanks for the info re flat mount. My rotors are centre lock, BTW.

@WhyFi I've had the bike for just over a year, with approx 8,000km on the bike/rotors. I ride a lot of hills and do a lot of fast descents. I'm on my third (maybe fourth?) set of front brake pads and second (maybe third?) set of rear pads. The front and rear rotors are likely still in a safe thickness range, I'm just doing a bit of advance research for when it comes time to replace them. Plus if I see a good price on a set of rotors, I want to know what to pick up.

@firebird8545 no, I am not having any stopping issues I'll have to take a closer look at the rotors to know what size they are.

@wgscott I bought a quality caliper last week for this very reason - to check the thickness of the rotors. Thanks info on the specs. I have to go to the LBS today, and it is the store I bought my bike from. I'll ask them some questions about the rotors on the bike when I'm there too.

WhyFi

Ah, cool - I thought this was the new bike that you've been posting about.

Yeah, if there's still life in them, no reason not to take advantage of it, but when they do need to be replaced, might as well bump up (though my rear wheel will lock up with little effort, so I don't know how much you'll gain there).