XTR discs going from 160 to 203

bazzer2

info: Front brake, lightweight XC (Iron horse Prodigy frame) full sus with 4" travel, on lumpy woodland single track stuff most of the time. XT and XTR mix. 160 XTR front and back.

My motivation for this is I have noticed on long descents the front fades and the lever comes back to the bar a fair way, even with new fluid and bleeding.

So I have a bracket for my brakes to space the caliper out, but not spent on the rotor yet (as they're not exactly cheap!) I wondered if anyone else has gone from 160 to 203? How does this affect the characteristics - is it that you can happliy use a single finger to scrub speed etc?

YeehaaMcgee

203mm rotors will offer substantially improved performance, but a few people don't like the increased power. I for one swear by them, but then I'm a big ol' unit.

What are the brakes, are they the XT 785, or XTR 985 versions? Finned pads? If so, you shouldn't be getting much, if any fade at all.
Maybe a good bleed is all they need (emphasis on the word "good")

The Rookie

If the lever comes back to the bar it's not brake fade, overheating the pads won't do that, that has to be overheating the fluid/trapped water or air in the system. A larger disc will not make a huge difference to that.

rockmonkeysc

Its not heat from the disc causing your problem. Sounds like they need a service.

YeehaaMcgee

The Beginner wrote:

If the lever comes back to the bar it's not brake fade, overheating the pads won't do that, that has to be overheating the fluid/trapped water or air

Which happens when the disc gets too hot (although admittedly, there has to be a contaminant for the lever to pull right back)

bazzer2

See, I could understand if there might have been a gibbon setting the brakes up in the first instance, but there wasn't. It's set up perfectly, new Shimano blood in there and when they're cold, they're ok. My line of thought is that the smallish disc can't dissipate enough heat to stop the caliper (and thus the fluid) getting hot to the point where it causes issues.
Bigger disc - more metal - cools off quicker etc. If the moment of the lever is further away it won't require as much force to turn (or in this case stop), no?

rockmonkeysc

That can't be right. My Deore brakes with 160 rotors have plenty of power and dont suffer fade, even on long fast descents.. XTR's should be even better.

The Rookie

Which model XT/R?

bazzer2

M975 XTR

njee20

If the lever comes back to the bar it's not brake fade, overheating the pads won't do that, that has to be overheating the fluid/trapped water or air in the system. A larger disc will not make a huge difference to that

But that heat is transferred to the fluid from the rotor...

That is a bit amiss, those brakes weren't all that, but assuming you're not either huge or riding Alpine descents they should be fine.

If you do it you'll have more power and less modulation.

YeehaaMcgee

bazzer2 wrote:

M975 XTR

Ah, yeah. Decent brakes, but not really in the same league as the historically awesome M985s, or the XT M785s - which I still maintain are so good, that we'll be looking back on them fondly for years to come, like us oldies look back on the old M636 stuff, and the DX range.

The Rookie

njee20 wrote:

But that heat is transferred to the fluid from the rotor...

From the pads surely, the disc takes heat from the friction interface the other way!

Bigger discs help with fade, improvement at the flluid is marginal (though not zero) as the same heat has to be generated at the friction interface for the same retardation.....

I still think bazzer needs to address root cause first.