A durometer and some brake pads: a hardness experiment

[La Bourde]

Hi,

 

 

I recently got some Coustellier brake pads with an used bike. Somehow, I had the impression that the rear pads did not work well as I know them. I supposed there are old or were contaminated with some kind of chemicals.

So I just did a small experiment to understand what are the hardness of the rubber of different brake pads.

I bought a Shore durometer, to measure the hardness of the rubber.

They are several scales of hardness and thus several durometer types exist. For a tire or a brake pad, the shore A scale is used.

I took some of my brake pads and took 5x measure for each one. I computed the average then.

Here the results:

• Jitsie black: 81,4 A
• Crewkerz yellow (not sure), first pad: 87,2 A
• Crewkerz yellow (not sure),second pad: 88 A
• Crewkerz orange, first pad: 82,6 A
• Crewkerz orange, second pad: 83,4 A
• Coustellier (green), first pad 90,2 A
• Coustellier (green), second pad 90,8 A
• White (brand and model unknown, for rims without grind), first pad 91,2 A
• White (brand and model unknown, for rims without grind), second pad 91,6 A
• Another green Coustellier (not on the picture): 90A

 

The last Coustellier I measured is from the front brake. The two other ones were on the rear brake. Somehow, I could not measure a relevant difference. Maybe I have to compare to the ones of my other bike, that are newer.

 

Measuring hardness with precision and accuracy is quite ... hard (sorry for the pun).

There is a standard (ASTM D2240-15(2021)), that is unfortunately not free (maybe I can have a look at work)

The precision seems to be quite good, I measure a +/-1 shore difference. I had to be careful with the placement of the durometer, all the supporting surface had to be in contact with the rubber of the brake pads. I hold the durometer per hand (no operating stand)

My biggest issue was that, the value was decreasing the longer the durometer was in contact with the rubber. This is due to the elasticity of the rubber. So I just measure the peak value - I guess this is the more relevant value I can measure.

Unfortunately the measure is sensible to the temperature and the durometer has to be calibrated, which is not the case here. Whereas the absolute value might be off (accuracy),  a comparison between the hardness of the different pads shall be valid.

To me, the Coustellier are very powerful and they seem to last quite long. I found the black Jistie amazing, but unfortunately they wear faster and one of them broke in two.

 

Edited March 14, 2023 by La Bourde

[AdamR28]

TartyBikes lists hardness of all their brake pads in the product listing too. Though this offers more information about brake feel (in terms of "squish') than it does performance or longevity.

[La Bourde]

I can't find any hardness information somehow.

 

I also measured some transparent V-brake pads from Odyssey, the shore was 81A.

 

 

[PLIW]

Tartys own pads were the best. I miss them 

[Mark W]

13 hours ago, La Bourde said:

I can't find any hardness information somehow.

From memory, when I was working there we'd measure the durometer out of curiosity, but we didn't list them as they can be a bit misleading. We list tyres durometers as there's a bit more of a correlation between the compound being softer and the tyre being better for trials use, but for brake pads there's more to it. The formulation/composition of the pad material will have a big role to play in how the pad performs, so you could theoretically have two pads that were 90a that would perform differently to each other. To use an example from your own list, the Odyssey pads are 81a and the Jitsie pads are 81a, but if you used them both on a ground rim or both on a smooth rim the pads would perform in completely different ways to each other. 

The other aspect is that - as you've found - a softer or harder compound doesn't really mean a pad will perform better. For example, you found that you really liked the Jitsie pads which you measured at 81a, but a lot of people prefer the Coust pads which are 90a. The performance characteristics people describe from each of them are broadly similar, so how do you really use that durometer information? Is softer 'better' or is harder 'better'? There isn't a right answer to that, so I think that's why we kept the info mainly to ourselves.

Although we didn't/TartyBikes don't list brake pad durometers it made more sense to list them for tyres as a softer durometer tyre will typically offer more grip than a comparable tyre in a harder durometer. More grip is generally more good for trials, so it seems a more legitimate comparison. Equally, some brands were printing Shore numbers on their tyres (e.g. Maxxis saying Slow Reezay was 40a, Super Tacky was 42a and MaxxPro was 60a), so actually measuring them and checking them made more sense. It also helped compare tyres across brands better too.

[AdamR28]

Mark's right. I got confused! Thanks for clearing it up (and remembering the thought process behind it all).

[Mark W]

No worries! I'll be honest, when I read your post I thought they were on there too and it was only when La Bourde said he couldn't find them there (and I checked a few pad product pages) that I remembered what the deal was.

[La Bourde]

Thanks for the comments guys.

I had a look at the other majors properties of rubber, there are quite a few.

Years ago I took out of the bin at work a book about tribilogy and rubber.

Gess it is time to flip through it to get a better understanding.