how hot do calipers get?
bluechair84
Posts: 4,352
Pretty simple really, I'd like to know how hot the piston and the oil behind it can get whilst braking... can anyone point to an article covering the science behind a bikes caliper or hazzard a guess at how hot is hot?
0
Comments
-
-
Simple term is F/H.
Most mechanics know what this means.
0 -
turned my disks blue once or twice and i think thats about 300-400oc ish for steel depending on the type0
-
One of the numbers to know is that the DOT 4 standard means that the fluid doesn't boil until 230 degrees c when dry, after which point, you are pretty well ****ed
(also tells you why you need to change your fluid from time to time and need to keep it dry, that drops to about 150 degrees when wet)
Not sure about that 300 degrees c from Shimano, that'll do nasty things to mineral oil, it usually boils at about 250 degrees IIRC though that varies a bit. 300 degrees fahrenheit maybe? Even a really good DOT 5.1 would be pushing it there.
The fluid does tend to stay cooler than the pads mind, there's a cooling reservoir effect there.
If you ever get your discs to glow, that's about 600 degrees for most steels You see this sometimes on brake testing videos but mtb brakes won't stand for it, not for long anyway. Melted a sticking motorbike brake this way, I thought I'd got away with it til I came back to the bike in the morning and all the fluid had leaked out, the seals had melted :shock: Uncompromising extremist0 -
-
The friction surface could possibly be that hot I reckon. Not sure about that but it doesn't seem too unreasonable.Uncompromising extremist0
-
That's the rotor temp though, that won't be transferred to the pads/piston/fluid, most heat will be lost to the surroundings.
I wouldn't think the calliper itself gets that hot at all.0 -
Not to confuse the temperature of the discs / pad faces and that of the piston and oil.
The pad itself is quite a good insulator.
If you use sintered pads on a long downhill and hit the brakes a lot, your oil will boil, because the high metal content of these pads means that they are obviously less efficient insulators.
It's shocking because the boiling point of any liquid depends on the pressure, so as long as you are dragging the brakes and keeping the fluid pressurised then all is well, you release the brakes for a millisecond, and the fluid in the calliper becomes vapour... you re-apply the brakes and your lever hits the bars (and if unlucky, you hit something too...)
This is also not to be confused with brake fade wherein the frictional properties of the pads/disc changes due to temperature.Giant Reign X10 -
I've never had hot brakes... :-(
I live in the fens though 0 -
my hazzard guess based on knowing nothing but instinct would say.. umm... 150DC. I'm in the process of designing something for the caliper based on these figures. I might give Hope a call and see if they have any data related to it.
Never turned my discs blue / red / black / white...
Turned my finger red touching the rotor after a descent once. what temp is that? 0 -
bluechair84 wrote:Turned my finger red touching the rotor after a descent once. what temp is that?
Scorched the leather palm of my gloves once touching a rotor after a descent. taught me never to do that again, especially without gloves on.FCN 9 - 2008 Kona Cinder Cone
FCN 9 - Custom Build On-One 456
FCN 5 - 2010 Boardman Team Carbon0 -
We tested a load at WMB 3 years ago - the oil in some got upto 500c in some.0
-
A friend of mine had some lightning discs (old hopes rotors with lightning bolts pattern). After a long descent and a misplaced leg had a lovely lightning burn on his leg. Humour. Also, in Afan another friend set fire to his pads. Literally on fire.A Flock of Birds
+ some other bikes.0 -
njee20 wrote:That's the rotor temp though, that won't be transferred to the pads/piston/fluid, most heat will be lost to the surroundings.
Sure, in short use that's the case but if the rotor's running consistently hot the rest will too- most heat's lost to the air but a decent proportion goes into the caliper and fluid. Mostly brakes stay pretty cool just because they don't get used much, they add a lot of heat in short cycles but then lose it again. Which is why people say how great their brakes are then go somewhere with a real mountain and spend the whole week complaining about brake fade and worrying about funny smells
Depends on intended use I guess.Uncompromising extremist0 -
I would think brakes get up to about 150-180°c as they heve no trouble turning water into steamI assume this is French petrol - be careful in reverse - the car will retreat rapidly at the least provocation.0
-
-
pugaltitude wrote:Simple term is F/H.
Most mechanics know what this means.
Just like when you do up a bolt you do it F/T 0 -
thecremeegg wrote:pugaltitude wrote:Simple term is F/H.
Most mechanics know what this means.
Just like when you do up a bolt you do it F/T
and risk F the T Giant Reign X10 -
I was pretty sure that "brake fade" was the name given to the reduction in brakes due to ANY actions, either overheating pads, discs, boiling fluid, etc.konadawg wrote:This is also not to be confused with brake fade wherein the frictional properties of the pads/disc changes due to temperature.0 -
Brake fade is when you exceed the operating temp of the resin that binds the pad together. The resin goes from being a binding and friction agent to lubricating the pad disc interface. The pad surface will then be dry and will only have around 70% of the normal friction after it has cooled back down. The dry pad material needs to be removed by re-facing the pads.
On our bike brakes, the pads are so thin that they are pretty much FUBAR if you get a serious fade event.Boardman Elite SLR 9.2S
Boardman FS Pro0 -
... I think we have all don the put finger on the disc to see how hot it gets and done go f******* hell!!!
as ^^^, the pad is a good insulator and the area of contact between the piston and pad is quite small (pistons are usually hollow; also if stainless steel which is not a particulalry good conductor of heat compared to say copper.
interesting question though .. and good point about the pressure and boiling point.
my theory of braking down a hill is to apply brakes hard, slow down a lot to put a fair bit of heat into them then release and repeat instead of keeping them on all the way at lower pressure - this is due to Newtons law of cooling where more heat is transfered from a hotter object than a cooler one - but I digress.
It is possible to buy LCD temperature stick on strips that permantantly change colour when a certain temperature is reached and try it out.
we could have a compo for who gets the highest temp ?0
