xt m785 brakes! double 180 or 180/160 mm rotors?

i just bought a set of the new xt brakes. those ice tech rotors are pretty expensive so i held back and thought id ask first before i purchased them.

a brief back ground. ive been running juicy 3s for 2 years now. i like them, but after being given a set of elixirs, i find that i have more confidence to go faster with just a tad more modulation. used them a couple times more and found that this set im using, the rer brake lever will sink into its travel when it heats up. i decided to jump head first into an upgrade.

ive run 180 front and rear. i like 180 front and 160 rear better on my juicys. thats all ive ever run on the elixirs, and they seeem plenty powerful. my question is, with the modulation of the xts, what would size rotor would you buy for the them?

i am also going to try to adapt the xts to my existing 185/160 avid rotors and brake adapters. i know there may be fit problems, but im willing to give it a try. a test fit is a minor inconvenience compared to blowing 120 on hardware i may not need me thinks

 

I've been using the XTRs on my AM 29er with 160 mm rotors. At about 200 pounds, I've been quite impressed with their performance, but I can say the same for most all the newer Shimano disc brakes with the servo-wave function. Knowing your weight and wheel size can make a difference in a recommendation. In only one situation on a fast, technical trail did I cause the brakes to fade. I don't know your riding level, but this wasn't a situation for riders at a normal skill level, so I don't think it would apply to many. A 180 in the front would have helped.

You mentioned that the lever on your Elixiers sinks into the travel when things get hot. This is generally a characteristic if air or moisture is in the brake lines. Generally, when brakes fade, the braking performance is reduced, but the lever stays in the same position. But even if your Elixiers were 100% dialed, I think the Shimano's would still be a worthwhile upgrade.

The only downside for going with larger rotors than smaller rotors is weight. So long as you're not a weight weenie, opt for the larger size. Other than slight weight concerns, in this case, bigger is better.

Note that the midsize Avid rotor is 185 mm, whereas Shimano's is 180 mm. While I've used 160 and 203 mm Avid rotors with Shimano brakes, I've never used the Avid 185 with a Shimano caliper. The Avid rotors mostly work, but note that they are noticeably thicker than Shimano rotors. At the moment, I don't remember if there was any consequence.

Note that the new Shimano Ice-Tech rotors have a significant performance advantage over standard rotors by having a stainless braking surface sandwiching an aluminum inner layer. What this means is that you can get away with a slightly smaller rotor, in regards to heat displacement. The situation where I faded the brakes would have been much worse with the previous Shimano rotors or Avid rotors. But you can always upgrade to the Ice Tech rotors later, if you want/need better performance.

I don't remember if you can use the Avid adapters with Shimano calipers, so I can't comment on that. But like you said, it's easy to test.

It's crazy how expensive Shimano brake adapters cost here in the states. In Japan, they're about $8-10 each. Yes, I always keep some on hand for future builds.

Yeah, it's about 3:00 am, and I can't sleep.

 

My opinion, 160 front and rear is plenty for the new Shimano brakes. I have the XTR but run XT ice tech. I came off elixir CR and amazed at how much power the Shimano have. I ride aggressive XC in the SA mts.

 

@2wheel lee - the set was just completely bled by me. it worked great the first time i used it. but when i dialed it in for reach, the lever sank on the first descent. it did not fade. ive felt fade before a couple of times, this was not it. it felt more like i burped fluid.

i thought as much as you and rebled the rear. on closer inpection, the front is solid. the rear has an inch of lever travel between when it start to firm up and full lock. im almost sure there is no air in the system.

id do a rebuild on the lever and caliper but 35 for each side in parts seemed throwing good money after bad. i like modulation ah lot. i dont feather the brakes as much at first, trying to avoid getting thrown off the bike. i went ahead and bught a new brake set anyway

 

I'm running new XT with Avid rotors and adaptors.

I had to remove spacers on the adaptor that came with the Elixers.

Seems to run just fine

Sent from my SPH-D710 using Tapatalk

 

203's or go home

 

I have the new 2012 XT m785 Brakes w/ Ice Tech. They really work! Every other Disc Brake system I've tried faded with heat. First one to finish well. I never really liked Disc until these. Knowing what I know now, they are worth every penny of what I have experienced and I would buy them as an upgrade.

~Mikie

 

I have had bleeds on avid brakes like that a lot. I don't know what it is, I did everything by the book and thought they were good but nope. I haven't had an issue for a while now, it seems like you can do everything right but have it not work, but then one day have it work and from then on have success even though you can't figure what you are doing different. Getting the new pro bleed kits seem like it would be much easier, I was messing with them at the SRAM demo at the path and they are much better.

 

I tried a few test rides on my old Elixir Rs and observed the same. Note that the tests were not enough to heat up the system. I'm using Wagner DOT 5.1 Extra Heavy Duty fluid.

It all seems to boil down to setting reach.

I can get the rear lever NOT to sink to the bar by setting the lever reach at 3.25 inches from the bar. Not ideal for me, but manageable.

Enough clearance for the brakes not to hit my fingers before locking. 1+ inches of travel from actuation to lock. No sinking feeling.

In comparison, the front is set at 2.25 inches of reach. 0.25+ inches of travel from actuation to lock.

I think the length of the rear hose is expanding to the point that makes it unable to reach the same amount of hydraulic pressure to lock as the fronts.

Oh, well. I hope the XTs are better.

 

the xt's are better than any brake sram has ever made no contest

 

i bled the avid system a fourth time. i pulled the entire rear brake off the bike this time and hung it vertically.

what i think did the trick was pumping the lever aggressively to dislodge trapped air. i was able to get some bubbles in an otherwise air free system.

now only a trail ride will tell. will be putting the avid on my ss and the xt on my trail bike.

thanks!

 

The other trick is to use something like a rubber screwdriver handle to tap against the lever and caliper to dislodge the air. Keep in mind that it doesn't matter how many times you bleed the brakes, it's the one time that you're able to get all the air out is what matters. And Avids tend to be one of the more difficult brakes to get it right. Lots of brakes come from Avid with air in the system.

 

Shimanos are probably the easiest to bleed. We don't even have to bleed them when we cut down the lines if we're a little careful. Throw out everything you think you know, and just bleed them "top down" like motorcycle brakes. One of the last steps in procedures from Shimano IS to quickly squeeze and release the lever to dislodge a bubble that might get stuck behind the piston. On all brakes, I hang the caliper with the bleed port up, and tap it with a plastic screwdriver handle. Don't forget to use the bleed block, and get yerself the damn Ice Tech rotors!

 

bing, go back to the darker side. i have not had any fade or reach issues with my 26 inch "rotors"

xt v brakes ftw!