Improved braking when hot - but why?

[thenortherner]

I had new grooved StopTech discs and pads fitted a few months ago. When cold, the initial bite and power is pretty lousy. They only seem to have any real stopping power after the brakes have been used fairly heavily for over a couple of miles.

Question is, why? I'm guessing there's some sort of happy medium between getting up to temperature and decent performance, and overheating and resultant fade.

[Fleckers]

sounds like you have fast road or race pads fitted that do not work until hot

bet its fun in the very cold weather trundeling around town

[thenortherner]

Quite possibly. I'd read the StopTech pads were pretty decent, so went for them over anything else.

Fortunately I don't really do any stop/start town driving - I work shifts and the commute consists of 70% back road blasting.

When they're up to temperature the difference is night and day. I did notice last week after 25 minutes of hard driving smoke coming from the calipers.

[WeirdNeville]

I had Ferodo DS2500's on my 200SX and their performance was exactly as you describe. Horrible on the first application, brilliant thereafter. I got into the habit of performing a rolling brake test at the start of every drive. I also live on a steep hill which helps!

[thenortherner]

WeirdNeville said:

I had Ferodo DS2500's on my 200SX and their performance was exactly as you describe. Horrible on the first application, brilliant thereafter. I got into the habit of performing a rolling brake test at the start of every drive. I also live on a steep hill which helps!

I do the same myself. A few bouts of hard braking at the start of a drive and they're fine.

[DAVEVO9]

thenortherner said:

They only seem to have any real stopping power after the brakes have been used fairly heavily for over a couple of miles.

Something is not right there. Did you have any bedding in instructions with your new discs/pads?

Fast road/race pads need bedding in properly from new.. This procedure normally involves several high speed stops starting with gentle braking to introduce heat into the pads.

You are effectively "heat curing" the pads and transferring pad deposits to the disc. This is very important to do to make them perform correctly even from cold.

The pads I use are Carbotech XP10's which are essentially a race pad. I will not bore you with the bedding in details of these pads but it was pretty brutal! From cold I have fairly good brakes, after only a couple of applications they are very strong. By the time I have got out of my village they are savage!

You should have a decent pedal feel even after a few stops, not a few miles of heavy braking? Do you have a "wooden" feel with your brakes?

If you do you may have "glazed" your pads by not bedding them in properly to start with. You could try taking out the pads, cleaning them up with some coarse wet and dry paper on a flat surface like a piece of glass/mirror and cleaning off the discs too.

Bed the brakes in again by getting them warm to start with then do plenty of high speed stops with a few cooling down periods between. This should get everything nice and hot gradually and place some pad deposits onto the discs.

Once you have done this park your car up and leave overnight to cool. Your brakes should be better now and have more feel from cold and will not need much use to be effective.

HTH.

[thenortherner]

DAVEVO9 said:

Something is not right there. Did you have any bedding in instructions with your new discs/pads?

Fast road/race pads need bedding in properly from new.. This procedure normally involves several high speed stops starting with gentle braking to introduce heat into the pads.

You are effectively "heat curing" the pads and transferring pad deposits to the disc. This is very important to do to make them perform correctly even from cold.

The pads I use are Carbotech XP10's which are essentially a race pad. I will not bore you with the bedding in details of these pads but it was pretty brutal! From cold I have fairly good brakes, after only a couple of applications they are very strong. By the time I have got out of my village they are savage!

You should have a decent pedal feel even after a few stops, not a few miles of heavy braking? Do you have a "wooden" feel with your brakes?

If you do you may have "glazed" your pads by not bedding them in properly to start with. You could try taking out the pads, cleaning them up with some coarse wet and dry paper on a flat surface like a piece of glass/mirror and cleaning off the discs too.

Bed the brakes in again by getting them warm to start with then do plenty of high speed stops with a few cooling down periods between. This should get everything nice and hot gradually and place some pad deposits onto the discs.

Once you have done this park your car up and leave overnight to cool. Your brakes should be better now and have more feel from cold and will not need much use to be effective.

HTH.

Dave, thanks a lot for your reply,

I was advised of any specific instructions re. bedding in. I was cautious of the high speed braking way of bedding them in - I'd always thought this is what causes the glazing. I reckon you're right, the pads are fast road/race spec and probably should have been bedded using the method you suggested.

I don't think I was clear enough when I said it takes a few miles to get them working properly. Three or four bouts of heavy braking sees them right. They're then powerful enough to make the back of the car step out under heavy braking.

Still, it might be worth skimming them as you suggested. The local Honda dealership - whom I've found to be trust worthy - advise that the pads have worn 25%, and I've probably only covered 4k miles at best since they were fitted. No track days etc since they were fitted, and only handful of hard use sessions on the road.

[PJ S]

As your discs are grooved, then highly unlikely yourvpads are glazed, that's part of the point of grooved discs!
Sounds like just a simple case of lack of temperature meaning the coefficient of friction is on the low side - a parameter of their design as part of the trade-off for being effective repeatedly at the high temp they'd see on track or twisty roads with spirited driving between the bends.
I'd say you've nothing to worry about, and a couple of good jabs before you need to rely upon them is de rigeur.

[Dave Brand]

PJ S said:

As your discs are grooved, then highly unlikely yourvpads are glazed, that's part of the point of grooved discs!

Sounds like just a simple case of lack of temperature meaning the coefficient of friction is on the low side - a parameter of their design as part of the trade-off for being effective repeatedly at the high temp they'd see on track or twisty roads with spirited driving between the bends.
I'd say you've nothing to worry about, and a couple of good jabs before you need to rely upon them is de rigeur.

Glazing is a very misunderstood phenomenon. So many people see pads with a shiny surface & think they are glazed, when in reality what they are looking at is a perfectly normal pad. Glazing is the condition where the friction surface, usually because of excess operating temperatures, becomes resin-rich & therefore has a reduced coefficient of friction.

I'd go along with your comment on temperature. An inherent property of organic brake pads is that pads which give high friction levels when cold tend to fade when hot while pads which have good friction at high temperature don't have very good cold friction. Over the years friction materials have been developed to the point where they five such consistent performance over a wide heat range that for just about all road car applications they perform well under any conditions & do not need any special bedding-in procedures to ensure optimum performance.

[thenortherner]

Cheers guys.