Newly Released Suspension & Components General

beeb

beeb

Dr. Beebenson, PhD HA, ST, Offset (hons)
dazz said:
Err, not sure if...
View attachment 399134
But it doesn't work like that...
Click to expand...
Yep, serious (I might be wrong, but would rather learn something if I am...).

Braking force is created from friction between pad and disc. More surface area allows more friction, no? Why is there brakes with larger pads if the extra surface area doesn't do anything? (Yes, I understand larger piston/multiple pistons area will create more pressure on the pad). And yeah, larger rotors provide more 'leverage', and a little additional mass to absorb the heat generated, but if there's only a tiny amount of surface area touching the pad that braking track is still going to heat up/overheat faster than a 'less open' disc design and provide less friction.

What am I missing?
 
Oddjob

Oddjob

Merry fucking Xmas to you assholes
beeb said:
Yep, serious (I might be wrong, but would rather learn something if I am...).

Braking force is created from friction between pad and disc. More surface area allows more friction, no? Why is there brakes with larger pads if the extra surface area doesn't do anything? (Yes, I understand larger piston/multiple pistons area will create more pressure on the pad). And yeah, larger rotors provide more 'leverage', and a little additional mass to absorb the heat generated, but if there's only a tiny amount of surface area touching the pad that braking track is still going to heat up/overheat faster than a 'less open' disc design and provide less friction.

What am I missing?
Click to expand...
Sublimation of the pad material at the braking surface. Without holes to ventilate the gas the friction co-effecient takes a dive.

Sent from my M2012K11AG using Tapatalk
 
Freediver

Freediver

I can go full Karen
It doesn't decrease the braking force, that comes from the pistons. If you halve the area you double the force per unit of area.
 
dazz

dazz

Downhill Dazz
beeb said:
Yep, serious (I might be wrong, but would rather learn something if I am...).

Braking force is created from friction between pad and disc. More surface area allows more friction, no? Why is there brakes with larger pads if the extra surface area doesn't do anything? (Yes, I understand larger piston/multiple pistons area will create more pressure on the pad). And yeah, larger rotors provide more 'leverage', and a little additional mass to absorb the heat generated, but if there's only a tiny amount of surface area touching the pad that braking track is still going to heat up/overheat faster than a 'less open' disc design and provide less friction.

What am I missing?
Click to expand...
Cool! I get to do the engineering nerd thing.
The thing that initially appears counter intuitive is that friction force is independent of the contact area.
1682550981016.png

It is directly proportional to the normal force. The normal force is related to the ratio of piston area between the caliper and the master cylinder.
Brakes with larger pads are simply a result of them having more piston area. If you designed a 6 piston caliper but kept the pad size small, you would have a lot of trouble achieving even wear and your pistons would likely cock sideways and jam as a result. As a bonus more pad material lasts longer because, well, there's more of it. For a given rotor diameter, a multi piston caliper is better than a single piston of the same pad area because the geometric centre the pad contacts at a greater radius. Or put another way, the middle of the long narrow pad is closer to the OD of the rotor than the middle of a square pad.

Now for the rotors.
There's a few things we want/need from our rotors. We want them to be of a large diameter and fully support the pad to keep the pistons nice and square to the caliper. We want them to not overheat or buckle, so make them nice and fat with no holes in them, that gives us lot's of thermal capacity and a strong brake rotor/flywheel. But wait! We also want them light, so make them thin and put lots of holes in them, but also make sure those holes don't clog up with mud or compromise the support of the caliper pistons. The holes also aid cooling by increasing surface area, but you are trading off thermal mass.

So it's a balancing act between performance, weight and cost. (I'm lumping robustness in with performance here)

@Freediver is on the money! Clamping force is what gives you the friction force. F = P*A For a given force, increasing pad size just decreases the pressure.

Sublimation of the pad material likely only occurs under very specific conditions. There are a hell of a lot of vehicle brakes that work just fine with solid rotors so I suspect this is more marketing BS than any real significant factor.
 
beeb

beeb

Dr. Beebenson, PhD HA, ST, Offset (hons)
Freediver said:
It doesn't decrease the braking force, that comes from the pistons. If you halve the area you double the force per unit of area.
Click to expand...
Ha! I can't believe I'd forgotten that... :eek:

dazz said:
Cool! I get to do the engineering nerd thing.
The thing that initially appears counter intuitive is that friction force is independent of the contact area.
View attachment 399138
It is directly proportional to the normal force. The normal force is related to the ratio of piston area between the caliper and the master cylinder.
Brakes with larger pads are simply a result of them having more piston area. If you designed a 6 piston caliper but kept the pad size small, you would have a lot of trouble achieving even wear and your pistons would likely cock sideways and jam as a result. As a bonus more pad material lasts longer because, well, there's more of it. For a given rotor diameter, a multi piston caliper is better than a single piston of the same pad area because the geometric centre the pad contacts at a greater radius. Or put another way, the middle of the long narrow pad is closer to the OD of the rotor than the middle of a square pad.

Now for the rotors.
There's a few things we want/need from our rotors. We want them to be of a large diameter and fully support the pad to keep the pistons nice and square to the caliper. We want them to not overheat or buckle, so make them nice and fat with no holes in them, that gives us lot's of thermal capacity and a strong brake rotor/flywheel. But wait! We also want them light, so make them thin and put lots of holes in them, but also make sure those holes don't clog up with mud or compromise the support of the caliper pistons. The holes also aid cooling by increasing surface area, but you are trading off thermal mass.

So it's a balancing act between performance, weight and cost. (I'm lumping robustness in with performance here)

@Freediver is on the money! Clamping force is what gives you the friction force. F = P*A For a given force, increasing pad size just decreases the pressure.

Sublimation of the pad material likely only occurs under very specific conditions. There are a hell of a lot of vehicle brakes that work just fine with solid rotors so I suspect this is more marketing BS than any real significant factor.
Click to expand...
That makes perfect sense. Thank you both! :)

Now off to buy some gigantic rotors! (Though still not with giant friggen holes in them - because my fat-arse fearful hack riding 'style' needs maximum braking mass!)
 
dazz

dazz

Downhill Dazz
Oddjob said:
Speaking as a fat fuck who has done a megavalanche and Maydena, I know all about brake pad sublimation.

Sent from my M2012K11AG using Tapatalk
Click to expand...
I assumed the primary reason for the drop in mu at high temps was more to do with the rotor material than the pad material. Seems I learned something, thanks.

Can you post pics of your rotors, Oddjob? I'd like to see the pattern used.

I still don't think the slots/holes primary function would be to ventilate the gases under the pad, more so to dissipate heat from the rotor to prevent sublimation in the first place.
As heat dissipation is primarily about surface area, lots of smaller holes/slots is better than fewer large holes. BUT! Small holes clog with mud more easily, negating the cooling effect. The holes also need to be large enough to get a reasonable flow of air through them.

I just had an idea!!
Perhaps you have a favourable body type to test a spoke mounted cooling fan. As the wheel rotates, air is directed at the rotor?

*Edit*
1682561211953.png

https://www.bendix.com.au/news-events/what-causes-brake-fade-and-how-to-minimise-it


1682561477270.png

https://alconkits.com/drmassets/Brake-Fade-Solved.pdf
 
Last edited:
fjohn860

fjohn860

Alice in diaperland
The burning question for me:

Is there an optimal rotor hole shape (round, rhombus, dick shaped etc) and do the holes suit different pad shapes/brake manufacturers or are the manufacturers just making their holes different, just to be different?
 
dazz

dazz

Downhill Dazz
fjohn860 said:
The burning question for me:

Is there an optimal rotor hole shape (round, rhombus, dick shaped etc) and do the holes suit different pad shapes/brake manufacturers or are the manufacturers just making their holes different, just to be different?
Click to expand...
I think there would be, yes. But that optimal shape and size would be specific to each combo of rider/track/conditions.

Rorschach said:
It's also the whole point of ICE Tech rotors
Click to expand...
Yes, some solid eng theory going on with those! Lot of $$ for that extra performance though.
1682562110511.png
 
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