Massive brake fade

[mitchy_]

...many XC MTB forks also have rotor size limits.

I've heard about this, and the only explanation I've read that makes some sense is that the longer bolts can place more stress on the caliper mounting points.
I would argue if the fork caliper mounts were moveable to accommodate different disc sizes, there probably wouldn't be a limit.

they somewhat are movable. most 203mm mounts will move the caliper up instead of out from the mounts... yet plenty of carbon forks will have a 160/180 limit, despite 180 mounts using either longer bolts, or a similar setup to the 203mm mount.

[MichaelB]

No way I'd go 180m on a front rotor with roadie slicks. Massive overkill that will likely result in a busted collarbone. I've done it before with 32mm slicks and it was scary - especially in the wet. Much too sudden.

.....

I've run a 180 front disc for last 5 years now, and have not ever had an issue. And I've braked HARD on many opportunities, dry and wet.

Maybe I'm special ???

[m@]

Depends on so many things... at just shy of 80kg I couldn't imagine needing over 180mm on the roadie, even with my crappy Avid BB7 roads... but then when upgrading the MTB from Elixirs to XTs I downsized the front rotor to 160mm on the LBS's recommendation.

[Nate]

Ran some "semi-metallic organic" pads today, with the HS1 rotor.

MUCH better - no issues/fade like the previous pads.
Just a slight amount of fade on the 3rd small descent, massively improved.
(Malga Rd --> Babbage Rd --> Two Creeks Track = 12% --> 5% --> 24%)


Not as good as the old sintered...
Got an Ice Tec rotor on its way, more metal on the rotor & sintered pads the way forward.
Will throw in some stock BB7 sintered pads to confirm.

[baabaa]

Malga Rd --> Babbage Rd --> Two Creeks Track

So you commute using two creeks track? Wow bit rough is it not, wish I had that sort of option to start the morning off .
Re the your brakes, dunno have been using Avid bb7 Metal Sintered pads on both bb7 road and mtn since 2007 and find they just work. Could be all the lousy Sydney weather with mega road junk on the roads over the past 3 weeks that have had some influence on pads and rotors.
I still think that the people who design the bikes know just what is the best in terms of rotor size for the frame and fork. If it comes with xyz mm rotors, just use xyz. I doubt anyone would be able to say “Well that extra 20 mm really prevented me from that dooring”. 160 mm front and rear offers more than enough power for me but I also use my rear quite a bit on long hills to take off speed. Again, could be just me but re heat and rotors I have found that heavy weight phil wood kiss hubs (f&r) works very well in sucking heat from the rotors.
Someone should do some rotor heat testing in fly weight vs. solid hubs. Would also be worth doing some spot tests on loose vs sealed bearing life as I found anything with loose just ends up heating out the grease and ends up with a constant need for maintenance, repair, and overhaul; maintenance, repair, and overhaul;....

[MichaelB]

....Someone should do some rotor heat testing in fly weight vs. solid hubs. Would also be worth doing some spot tests on loose vs sealed bearing life as I found anything with loose just ends up heating out the grease and ends up with a constant need for maintenance, repair, and overhaul; maintenance, repair, and overhaul;....

I've found that when checking the system components after some solid stops when the rotor is DAMN hot, the only really hot bits are the disc (friction surface - REALLY ...) and the pads themselves. The rotor stator arms are warm, as is the caliper itself.

This has been noted on RT-86 Ice-Tec rotorsm, and solid SS rotors like G2 Cleansweeep and my current Hayes V7 & V5.

I tend to agree with baabaa re the difference in the 180 vs 160, but my take is that it has more thermal mass, and therefore can take more heat input (more & harder stops), so it's added safety factor.


Is the end result that pad compounds need to be different for road use vs MTB ? As the typical braking profile can be quite different.

[Nate]

Malga Rd --> Babbage Rd --> Two Creeks Track

So you commute using two creeks track? Wow bit rough is it not, wish I had that sort of option to start the morning off .
Re the your brakes, dunno have been using Avid bb7 Metal Sintered pads on both bb7 road and mtn since 2007 and find they just work. Could be all the lousy Sydney weather with mega road junk on the roads over the past 3 weeks that have had some influence on pads and rotors.

not the whole track, just the paved bit under the Roseville bridge (assumed it was called that).

+1 on Avid sintered pads as above.
EBC were slightly better, but they're the baseline for sure.

As for "what came with the bike" (previous poster) this was pretty sub optimal & wouldnt stop my new lighter bike on the 25% slope.
unlike the previous setup on a much heavier bike! OK for road use - but not for my commute

[barefoot]

As for "what came with the bike" (previous poster) this was pretty sub optimal & wouldnt stop my new lighter bike on the 25% slope.
unlike the previous setup on a much heavier bike! OK for road use - but not for my commute

I think you put too much consideration on the weight of the bike.

What's the difference between a light and a heavy bike? 3kg? 5kg? About 5% of the total bike+rider weight?

6 months ago, I weighed as much without my bike as I weigh now on my bike. I haven't noticed any difference in the performance of my disc brakes.

[Dragster1]

As for "what came with the bike" (previous poster) this was pretty sub optimal & wouldnt stop my new lighter bike on the 25% slope.
unlike the previous setup on a much heavier bike! OK for road use - but not for my commute

I think you put too much consideration on the weight of the bike.

What's the difference between a light and a heavy bike? 3kg? 5kg? About 5% of the total bike+rider weight?

6 months ago, I weighed as much without my bike as I weigh now on my bike. I haven't noticed any difference in the performance of my disc brakes.

Your a brake man aren't you from memory what are your findings with heat concerning lining materials of brake pads

[barefoot]

Your a brake man aren't you from memory what are your findings with heat concerning lining materials of brake pads

Yep, but I'm not going to profess much knowledge in areas way outside my own niche.

We don't deal in sintered metal friction materials at all, and all I know about stainless steel rotors is that their friction behaviour is different to cast iron [1].

I think that the three broad families of friction materials used on cars all fall into the category known as "organic" on push bike disc brakes. I'd say that the three families (non-asbestos organic, semi-metallic and low-metal) are vastly different to one another, but it would seem they're alike enough - by comparison with sintered pads - to be lumped in as a single type.

About a decade ago, when I first got disc brakes on my MTB, I had a try at DIY pads by bonding slivers of automotive NAO friction material to a set of backplates. They seemed to work quite nicely until the bonding let go. That was a fun descent . Obviously, I have no idea how they'd go for wear.

tim

[1] One of our overseas sales departments wanted to start buying and on-selling motorcycle pads, and had a few options to choose from. I figured out a dodgy test, cutting and welding the pads to fit in a car caliper that I could test on dyno. They found some tame moto riders to test them. My car brake test - on a cast iron rotor - showed one material had wildly unstable friction and the other was low but stable. The test riders reported the exact opposite - the one I said was stable, they found grabby when cold and useless when hot, but the other one was rock solid under all conditions.

[Dragster1]

Your a brake man aren't you from memory what are your findings with heat concerning lining materials of brake pads

Yep, but I'm not going to profess much knowledge in areas way outside my own niche.

We don't deal in sintered metal friction materials at all, and all I know about stainless steel rotors is that their friction behaviour is different to cast iron [1].

I think that the three broad families of friction materials used on cars all fall into the category known as "organic" on push bike disc brakes. I'd say that the three families (non-asbestos organic, semi-metallic and low-metal) are vastly different to one another, but it would seem they're alike enough - by comparison with sintered pads - to be lumped in as a single type.

About a decade ago, when I first got disc brakes on my MTB, I had a try at DIY pads by bonding slivers of automotive NAO friction material to a set of backplates. They seemed to work quite nicely until the bonding let go. That was a fun descent . Obviously, I have no idea how they'd go for wear.

tim

[1] One of our overseas sales departments wanted to start buying and on-selling motorcycle pads, and had a few options to choose from. I figured out a dodgy test, cutting and welding the pads to fit in a car caliper that I could test on dyno. They found some tame moto riders to test them. My car brake test - on a cast iron rotor - showed one material had wildly unstable friction and the other was low but stable. The test riders reported the exact opposite - the one I said was stable, they found grabby when cold and useless when hot, but the other one was rock solid under all conditions.

OK understandable lot of variables I guess

[baabaa]

here we go, the peoples who make the brakes, building the forks to suit the brakes, to suit the ...
http://road.cc/content/news/138884-new- ... s-fork-trp" onclick="window.open(this.href);return false;
The fork has a 397mm axle to crown measurement and 47mm offset which makes it a cyclo-cross inclined fork, although a road version is in the pipeline, and there’s clearance in there for a 40mm tyre, so perfect for your gravel racing tyre, and with a 32-ish width cyclo-cross tyre there should be loads of mud clearance.
Cant wait for a heap of dedicated road bike disc headsets to come out.

[MichaelB]

Bit expensive !!!!

[baabaa]

ForkForFreds so yes, needs to be expensive.

[Nate]

I think you put too much consideration on the weight of the bike.

Depends really...
its probably about 8% increase in total.

Maybe that's the tipping point where it went from having 2% safety margin to having -6% safety margin!

[trailgumby]

No way I'd go 180m on a front rotor with roadie slicks. Massive overkill that will likely result in a busted collarbone. I've done it before with 32mm slicks and it was scary - especially in the wet. Much too sudden.

.....

I've run a 180 front disc for last 5 years now, and have not ever had an issue. And I've braked HARD on many opportunities, dry and wet.

Maybe I'm special ???

Maybe you're using Avid?

QFT:

Depends on so many things... at just shy of 80kg I couldn't imagine needing over 180mm on the roadie, even with my crappy Avid BB7 roads... but then when upgrading the MTB from Elixirs to XTs I downsized the front rotor to 160mm on the LBS's recommendation.

[MichaelB]

Maybe you're using Avid?

That's about to change soon

[trailgumby]

Maybe you're using Avid?

That's about to change soon

What are you changing to?

[MichaelB]

RS685/RS785, but maybe a bit of Zee thrown in.

Trial of some BR-517's coming up as well !!

[Nate]

Put on a lovely xt rt86 Ice Tek rotor... been going for a few weeks.

MUCH more meat in the rotor, aaand no fade!
Same route, same loads etc - never any fade.

Buuuut the initial bite hasnt been all that good - so looks like there's some differences in the surfaces of the rotors?!?
Theeeeen the pads started making some gawd awful noises - sounds like the pads were made out of gravel! Brake performance was also down a bit.

Decided to take them off & have a look...
OMGosh... material is cracking & about to come off the backing plate!!!

You can see the squiggly/ragged circle in the middle of the pad:



straight to the bin!
Now back running Braking P21's & loving it.

NEVER NEVER will I use Gigapower/Discobrakes again... insane!

[MichaelB]

What are the Braking P21 you are referring to ? Compound type ?

[Nate]

What are the Braking P21 you are referring to ? Compound type ?

yep - semi metallic organic
google "braking p21 disc pads"

[MichaelB]

Cheers Nate - I'll be using shimano resin one atm in the new setup (going well in the mech calipers that I am using on a Polygon Helios C6X atm).

Will be interesting to see how they perform over the longer term

[Nate]

Cheers Nate - I'll be using shimano resin one atm in the new setup (going well in the mech calipers that I am using on a Polygon Helios C6X atm).
Will be interesting to see how they perform over the longer term

yeah the ice tek (& equiv in other brands) definitely allow the use of resins where it was only possible with sintered before due to heat.
Just wish hydreau wasnt that expensive of an upgrade :\

[CKinnard]

Reading through some of the above tech stuff, I ask myself, wouldn't a rim that conducts and absorbs heat more so, be better and safer?

If the heat is not going into the rim at the same rate, more heat will go into the brake pad, which is more likely to cause brake fade.

Further, the idea is to keep the pad/rim interface cooler. The more conductive the rim, the quicker heat dissipates away from the interface, and into the total mass of the rim. This results in a lower peak heat in any part of the rim. Further high rim conductivity means the heat will be dissipated into the surrounding air quicker, so you get quicker cooling.

I suppose the other safety factors apart from brake fade is rim heat punctures, and tire roll offs.