Brakes: How Hot?

[944 man]

Im looking to buy an infared thermometer, but Im not sure which temperature range to go for. Does anyone have first hand experience of measuring disc temperatures and if so, can they offer any advice?


Simon

 

[robwright]

Do you mind if I ask why Simon?

 

[944 man]

Of course not. Even ten years ago kit like this cost 100x the price, but now you can buy reasonably accurate devices for between £10 and £30 - even simple colour change indicators used to cost £100-odd from Demon Thieves!

For my £10-£30 I will be able to see how my tyres are working, tell whether my brake cooling is effective, even see hot spots on my cylinder head!

The question has to be: why wouldnt you? []

 

[Neil Haughey]

I have the Sealey one in my kit, as you say why not.

 

[944 man]

Ever read your brake discs temperature? []

 

[Hilux]

Hi temp fluids are rated around 300 - 350 degrees so there's a starting point as the disc would be even hotter

 

[Riverside]

I have what's described as a laser thermometer (infra-red with a laser pointer) for tyre temps, you don't touch the surface but the further away you are the wider circle the temp is averaged over so you need it to be close.

I paid £20 for it a few years ago but IIRC it was on sale from £40 from Maplins & it has a temp range of -60 to +350deg; ideal for tyres, checking the rad (diagnosing stuck thermostat etc), very handy device.

From experience, pointing it at the exhaust manifold at idle will tell you which cylinder is misfiring (as soon as you rev it it goes beyond 350deg though), and pointing it at the front wheel centres helped me find an overheating wheel bearing recently but the disks are way beyond the temp range & tbh I'm struggling to think of a diagnostic reason why you'd need to measure them []

Also, now that I have one to check against I find I can judge tyre temps (inner middle outer) by hand accurately enough for my purposes so on my own car I don't actually use it all that much now.

Most useful for small variations in temp where the hand or eye isn't subtle enough to spot problems, for brake issues I'd look for burnt pads, discolouration & pedal feel etc.

Hope this is of some use.

 

[944 man]

The ranges I was looking at ere 550°, 700° & 900°. Its interesting to see that even a 350° type would be useful, thanks Malc.


Simon

 

[944Turbo]

Well if they get really hot they will glow red, if i remember correctly from school is somewhere between 500 C and 900 C dependant on the brightness - they will not retain that much heat by the time you have stopped to measure them though, so I would have thought the 550 should cover it.
Tony

 

[Eric_Oz_S2]

Mine measure over 350C after the cool down lap with 968 air scoops.

 

[edh]

What's your application Simon? I was wondering why you were planning bigger (very big) brakes

I can see their value in 40 min races, or trackday sessions with a 1500kg car - medium blacks will work with cooling & decent pads, but it doesn't really cost much more to go bigger. 5 years ago I bought some big blacks from OPC Exeter for £400 - never fitted them (sold to John Sims) as I decided that medium blacks actually worked fine & I didn't want to buy 17" rims.

 

[944 man]

The I thermometer and the brake upgrade are separate Ed. The thermometer seemed too good not to buy with their being so cheap (but obviously dearer for each increase in operating range) and the brake upgrade seems to make sense because I need discs and I believe that I have plate lift, from the feel of the brakes.

If I need new discs, pads and work on my calipers then this would be a good time to upgrade as itll be extremely cheap. 928S4 discs dont cost any more to buy and hopefully the extra caliper and adapter cost will be mitigated by my being able to to have all of the work completed in one go, without the car being left off the road.

With a little man-maths this is all possible... []

 

[edh]

Seems to make perfect sense - i wouldn't worry too much about the maths.. [] - be interested to see what you end up with.

 

[George Elliott]

Red hot, or "Cherry" is 900 deg as mentioned above, as seen on older endurance racers disc's[] Darker reds are cooler by approx 100 deg.

Light Straw, Dark Straw, Blue, Mauve etc are in the 280, 350 plus deg range.....as seen on steel manifolds, exhausts etc.

George
944t

 

[944 man]

Thanks George. Even a 550° device should be able to deal with pretty much everything that I will come across then? Cool.

 

[Super_Marv]

I have been meaning to bring my infrared thermometer with me to Europe to see how hot the brakes get after descending a a mountain pass...they can get rather hot on the ones with lots of hairpins!