Overheating Disc Brakes

timmyotool

Hi,

After a trip to the Lake District, coming down Honister Pass, I realised my disc brakes were overheating/cooking. They started getting spongy, the lever travel reduced (I assume expansion of the hydraulic fluid) and I really struggled to slow down, which was not fun! When I did managed to stop there was a burning smell coming from the brakes.

I know recommended practice is short sharp bursts of braking, which I was trying to do, but when you're going down 20% gradients it's easier said than done, and I had to drag them to slow down enough for the corners.

Now it's not the often I go down something so steep for so long but I'm sure it'd happen if I went abroad. I know there are a number of options to help reduce this issue but I've no idea which are the most effective as to change all will be quite expensive?

Bigger discs - currently 140mm
Different discs - currently Sram centreline
Different pads - currently Swiss stop organic green
Different fluid - currently shimano mineral oil.

cycleclinic

160mm rotors on the front and back. the bigger rotor on the rear is useful as you can use the rear as a drag brake without it overheating.

The brake fluid is fine although if it is still spongy it will need replacing.

Also Shimano's ice tech rotors are the best hands down. Campagnolo calim there new rotors are the best hands down but if you look at the construction of a sandwiched, and finned shimano rotor then you'll know why I say shimano rotors are the best hands down.

So get a set of expensive but worth it XTR freeza rotors or the newer Dura Ace or R8000 rotors. Your over heating issues will fade away.

ugo.santalucia

yep... down those big boys it's easier said that done indeed.

Went down Bwlch Y Groes today... very carefully and stopped twice to take photos and cool the brakes. SHarp short squeezes help, but with those gradients don't help much

https://www.strava.com/activities/1130006755

pedrospedros

I had that front brake ,after looking at the disc , burnt colour ,i do the front quite a lot on big descents ,

cougie

I've done the Alps and the Stelvio and a few climbs out that away. Never overheated my rim brakes either.

Would squirting water on them help or hinder ??

mrb123

cougie wrote:

I've done the Alps and the Stelvio and a few climbs out that away. Never overheated my rim brakes either.

Would squirting water on them help or hinder ??

Totally different. Release you brakes for more than a second or two down Hardknott etc in the wet and you are dangerously out of control.

ugo.santalucia

MrB123 wrote:

cougie wrote:

I've done the Alps and the Stelvio and a few climbs out that away. Never overheated my rim brakes either.

Would squirting water on them help or hinder ??

Totally different. Release you brakes for more than a second or two down Hardknott etc in the wet and you are dangerously out of control.

THIS!

meanredspider

timmyotool wrote:

They started getting spongy, the lever travel reduced (I assume expansion of the hydraulic fluid) and I really struggled to slow down, which was not fun! When I did managed to stop there was a burning smell coming from the brakes.

This bit doesn't make sense. Sponginess is normally because the fluid boils - that leads to longer lever travel. Whilst a fluid is liquid it can't compress.

I'd certainly go for a bigger front disc - 140mm always seemed undersized to me for all but racing snakes. I'm less sure about a 160 rear - it will help with very steep descents but, in normal use, you might find you are locking the rear too easily. Choice is yours.

Agree that Ice Tech is great - I think the new Dura Ace version is even better. And painfully expensive.

Better pads will also almost certainly help. Burning smell is fine.

The very worst thing you can do with any brakes is to drag them - the heat never dissipates - you'll destroy any brakes like this. Disc brakes benefit from short firm application. If you're trying to modulate your speed on a long steep descent, alternate front and rear with firm applications and releases. This promotes heat dissipation. Dragging brakes and travelling slowly is a double-whammy because you don't get the airflow. The ideal is getting some speed up and braking hard and briefly. Takes some confidence though.

Oh - and I expect squirting water on a sizzling disc will warp it.

animal72

Thinking back to my (motor)bike racing days... Are you boiling the brake fluid? I ran DOT5 to mitigate the problem... assume it's the same for pushbikes???

meanredspider

Animal72 wrote:

Thinking back to my (motor)bike racing days... Are you boiling the brake fluid? I ran DOT5 to mitigate the problem... assume it's the same for pushbikes???

Not really - the boiling point of a DOT 5.1 is around 270+C and Shimano Mineral is 280C. I'm also not sure I'd trust all the components to be resistant to DOT fluid. The race grade of DOT 4 fluid I use in my race car gets up to 320C - but these are all marginal. DOT fluids are generally hygroscopic so need replacing.

I'm confused as to whether the fluid even boiled in this case. The OP's symptoms don't make clear sense to me. Boiled fluid would have the levers against the bars...

kajjal

What disc brakes do you currently have ?

meanredspider

Personally I think the combination of small rotors, organic pads and the brake dragging on the steep descent is what happened. I think you got brake fade rather than boiled fluid.

160 rotor (decide whether you want both ends - it isn't for me on a road bike), sintered pads and different braking technique. And, by all means, upgrade the discs (and the Shimano pads have cooling fins too) for better heat dissipation.

mamil314

When i asked for a front adaptor for a 160mm disc, LBS guy put in big effort into dissuading me from it, claiming it would result in fork breaking apart. I must look really fat for a 76kg guy.

kajjal

thecycleclinic wrote:

160mm rotors on the front and back. the bigger rotor on the rear is useful as you can use the rear as a drag brake without it overheating.

The brake fluid is fine although if it is still spongy it will need replacing.

Also Shimano's ice tech rotors are the best hands down. Campagnolo calim there new rotors are the best hands down but if you look at the construction of a sandwiched, and finned shimano rotor then you'll know why I say shimano rotors are the best hands down.

So get a set of expensive but worth it XTR freeza rotors or the newer Dura Ace or R8000 rotors. Your over heating issues will fade away.

This is exactly what is on my road / gravel bike ,shimano 160mm rt99 freeza rotors and finned pads. So far no problems.

First.Aspect

mamil314 wrote:

When i asked for a front adaptor for a 160mm disc, LBS guy put in big effort into dissuading me from it, claiming it would result in fork breaking apart. I must look really fat for a 76kg guy.

It highly likely that this nothing to worry about. Should be straightforward enough for you to check with the manufacturer and then disregard everything the LBS says.

meanredspider

First Aspect wrote:

mamil314 wrote:

When i asked for a front adaptor for a 160mm disc, LBS guy put in big effort into dissuading me from it, claiming it would result in fork breaking apart. I must look really fat for a 76kg guy.

It highly likely that this nothing to worry about. Should be straightforward enough for you to check with the manufacturer and then disregard everything the LBS says.

Yup - braking forces are as nothing compared with hitting a pot-hole.

sloppyschleckonds

Great thread "get dura ace" "get bigger rotors"

timmyotool

meanredspider wrote:

Animal72 wrote:

Thinking back to my (motor)bike racing days... Are you boiling the brake fluid? I ran DOT5 to mitigate the problem... assume it's the same for pushbikes???

Not really - the boiling point of a DOT 5.1 is around 270+C and Shimano Mineral is 280C. I'm also not sure I'd trust all the components to be resistant to DOT fluid. The race grade of DOT 4 fluid I use in my race car gets up to 320C - but these are all marginal. DOT fluids are generally hygroscopic so need replacing.

I'm confused as to whether the fluid even boiled in this case. The OP's symptoms don't make clear sense to me. Boiled fluid would have the levers against the bars...

I guess that the fluid didn't boil, What I felt was the initial lever travel decrease - to get to a point when the brakes were applied (because the fluid was heating up/expanding?), but then pulling on the levers felt like it had very little bite, and I had to pull them a lot harder and further than usual to slow me down (spongy). Probably brake fade, as you said, either way, I'd like to avoid it. I'll definitely look at the bigger rotors and finned sintered pads for any future trips.

Brake fade is not something I'd noticed before, and I came down Great Dunn Fell that trip with no issues, but it just seemed to be the steepness of the gradient, combined with the corners and cars that caused the problems.

timmyotool

Kajjal wrote:

What disc brakes do you currently have ?

They're Shimano RS685.

kajjal

timmyotool wrote:

Kajjal wrote:

What disc brakes do you currently have ?

They're Shimano RS685.

They are good brakes, based on the m785 xt mountain bike disc brakes. I have the same.

apreading

Another think not mentioned here is finned pads.

Bigger rotors, provided your forks can take them - if the manufacturer only rates them to 140mm then regardless of whether fitting bigger rotors breaks them, it will void the warranty.

Pads with cooling fins, ideally sintered.

Shimano Ice-tec rotors

Shimani freeza finned rotors only come for centre lock wheels - if you can run them then do, but I cannot for this reason.

If you do the above you will be fine - each step makes a big difference.

ugo.santalucia

timmyotool wrote:

Brake fade is not something I'd noticed before, and I came down Great Dunn Fell that trip with no issues, but it just seemed to be the steepness of the gradient, combined with the corners and cars that caused the problems.

Try Bwlch-Y-Groes next... it's like Honister, but longer!

timmyotool

ugo.santalucia wrote:

timmyotool wrote:

Brake fade is not something I'd noticed before, and I came down Great Dunn Fell that trip with no issues, but it just seemed to be the steepness of the gradient, combined with the corners and cars that caused the problems.

Try Bwlch-Y-Groes next... it's like Honister, but longer!

Yes I saw the Strava, it looked brutal! That second ascent was a long way at 13% average!
I found Honister a lot tougher than I expected (up and down), put me off sufficiently from taking a trip to Hardknotts Pass.

timmyotool

apreading wrote:

Another think not mentioned here is finned pads.

Bigger rotors, provided your forks can take them - if the manufacturer only rates them to 140mm then regardless of whether fitting bigger rotors breaks them, it will void the warranty.

Pads with cooling fins, ideally sintered.

Shimano Ice-tec rotors

Shimani freeza finned rotors only come for centre lock wheels - if you can run them then do, but I cannot for this reason.

If you do the above you will be fine - each step makes a big difference.

Thanks, mine are 6 bolt also unfortunately, but I've seen the shimano pads with fins, its a shame because I switched to organic to avoid the brake squeal of sintered.

ugo.santalucia

timmyotool wrote:

ugo.santalucia wrote:

timmyotool wrote:

Brake fade is not something I'd noticed before, and I came down Great Dunn Fell that trip with no issues, but it just seemed to be the steepness of the gradient, combined with the corners and cars that caused the problems.

Try Bwlch-Y-Groes next... it's like Honister, but longer!

Yes I saw the Strava, it looked brutal! That second ascent was a long way at 13% average!
I found Honister a lot tougher than I expected (up and down), put me off sufficiently from taking a trip to Hardknotts Pass.

Hardknott is very technical, because it's not only very steep, but also very twisty... negotiating those 25-30% bends is very tricky.
Bwlch Y Groes is identical to the west side of Honister, just a lot longer. There is a 18% section which lasts forever and when it finally drops a bit after the junction with Lake Vyrnwy it feels almost flat, but it's still 12% :shock:

I am going to put together a Brevet Challenge, much like the Cingles du Ventoux... obviously nowhere near as gruelling, but adding a time limit element should make it interesting! :twisted:

meanredspider

timmyotool wrote:

Thanks, mine are 6 bolt also unfortunately, but I've seen the shimano pads with fins, its a shame because I switched to organic to avoid the brake squeal of sintered.

It's a 2-minute job to put the sintered pads in when you need them. I ride organic most of the time but there are times when sintered are useful so just pop a set in and hoik them out when you don't need them.

timmyotool

ugo.santalucia wrote:

Hardknott is very technical, because it's not only very steep, but also very twisty... negotiating those 25-30% bends is very tricky.
Bwlch Y Groes is identical to the west side of Honister, just a lot longer. There is a 18% section which lasts forever and when it finally drops a bit after the junction with Lake Vyrnwy it feels almost flat, but it's still 12% :shock:

I am going to put together a Brevet Challenge, much like the Cingles du Ventoux... obviously nowhere near as gruelling, but adding a time limit element should make it interesting! :twisted:

Sounds like a tough challenge! The other two ascents don't seem quite as bad as from the South, luckily!

ugo.santalucia

timmyotool wrote:

ugo.santalucia wrote:

Hardknott is very technical, because it's not only very steep, but also very twisty... negotiating those 25-30% bends is very tricky.
Bwlch Y Groes is identical to the west side of Honister, just a lot longer. There is a 18% section which lasts forever and when it finally drops a bit after the junction with Lake Vyrnwy it feels almost flat, but it's still 12% :shock:

I am going to put together a Brevet Challenge, much like the Cingles du Ventoux... obviously nowhere near as gruelling, but adding a time limit element should make it interesting! :twisted:

Sounds like a tough challenge! The other two ascents don't seem quite as bad as from the South, luckily!

Nowhere near, but they add up

buckmulligan

timmyotool wrote:

Thanks, mine are 6 bolt also unfortunately, but I've seen the shimano pads with fins, its a shame because I switched to organic to avoid the brake squeal of sintered.

How do you find the Swissstops compared to the stock Shimano finned pads? In my experience, the Shimano pads only squeal in the wet, but need really good bedding in if you contaminate/clean your rotors.

apreading

Shimano do resin pads with the fins - they are cheaper too. Search J02a as opposed to J04c (those are the metal ones).

http://www.chainreactioncycles.com/shim ... prod130823

timmyotool

BuckMulligan wrote:

timmyotool wrote:

Thanks, mine are 6 bolt also unfortunately, but I've seen the shimano pads with fins, its a shame because I switched to organic to avoid the brake squeal of sintered.

How do you find the Swissstops compared to the stock Shimano finned pads? In my experience, the Shimano pads only squeal in the wet, but need really good bedding in if you contaminate/clean your rotors.

I've never had the finned stock pads, I think mine originally came with G02A pads, which are Shimano organic. If I'm honest I can't remember why I changed them, but I think they were more squealy than the Swiss stop.