Front brake rotors - What's the go-to?

[Speedfrog]

Brake discs (or rotors) have a nominal thickness when new and a minimum thickness under which they are supposed to be replaced. That minimum thickness is usually printed on the disc.

[GuzziMoto]

1 hour ago, Speedfrog said:

Brake discs (or rotors) have a nominal thickness when new and a minimum thickness under which they are supposed to be replaced. That minimum thickness is usually printed on the disc.

While that is sound advice, that is usually more important for car brake rotors where they are turned down to resurface. There is a limit to how much you can turn them down before the reach their minimum thickness. Motorcycle brake rotors rarely wear enough for thickness to be an issue. I would say, if you have no braking issues you don't need to replace the rotors. If you have any pulsing or vibration in the brakes and it isn't the pads I would look into the rotors being the cause.

To be fair, I haven't turned down car brake rotors in a long time. They have gotten cheap enough that I just replace them. Some car manufacturers don't even allow for turning down the rotors, they just replace them with the pads.

Odd side note, as a brake rotor wears it looses mass. That reduced mass can lead to the brakes running hotter, the same amount of heat fed into a rotor with less mass results in the rotors temp being higher.

[Lucky Phil]

10 hours ago, GuzziMoto said:

While that is sound advice, that is usually more important for car brake rotors where they are turned down to resurface. There is a limit to how much you can turn them down before the reach their minimum thickness. Motorcycle brake rotors rarely wear enough for thickness to be an issue. I would say, if you have no braking issues you don't need to replace the rotors. If you have any pulsing or vibration in the brakes and it isn't the pads I would look into the rotors being the cause.

To be fair, I haven't turned down car brake rotors in a long time. They have gotten cheap enough that I just replace them. Some car manufacturers don't even allow for turning down the rotors, they just replace them with the pads.

Odd side note, as a brake rotor wears it looses mass. That reduced mass can lead to the brakes running hotter, the same amount of heat fed into a rotor with less mass results in the rotors temp being higher.

The front Brembo rotors on my 1000SS were below min thickness in 13,000klms that's one reason I replaced them. The original owner used to do a lot of pillioning. The rear disk on my DucatiST2 I had to replace at 42,000klms of previous owner miles due to being under spec. Wouldn't pass a rego check.

[Speedfrog]

23 hours ago, GuzziMoto said:

Motorcycle brake rotors rarely wear enough for thickness to be an issue.

Street motorcycle brake rotors DO wear under normal usage. How long does it take for them to wear below the recommended minimal thickness varies, depending on several factors; how aggressively you use your brakes, how much weight is on the bike, mountain roads riding...etc, but most importantly, the pads you're using; aggressive pads will wear the rotors out a lot faster than softer ones.

Checking the rotors thickness with calipers only takes a couple of minutes and should be part of routine maintenance.

The minimum thickness stamped on the rotors by the manufacturer is a good indication that, as a wear item, they need to be replaced eventually to remain optimally efficient and safe.

Can you keep riding a bike with its front rotors worn thinner than recommended? Sure ...would the brakes still operate normally? Probably ...how far are you willing to go to find out the failing point of your main safety component?...

Just like you would replace tires long before the rubber is worn through to the cord... or not.  

[docc]

On 9/29/2023 at 12:14 AM, Speedfrog said:

Street motorcycle brake rotors DO wear under normal usage. How long does it take for them to wear below the recommended minimal thickness varies, depending on several factors; how aggressively you use your brakes, how much weight is on the bike, mountain roads riding...etc, but most importantly, the pads you're using; aggressive pads will wear the rotors out a lot faster than softer ones.

Checking the rotors thickness with calipers only takes a couple of minutes and should be part of routine maintenance.

The minimum thickness stamped on the rotors by the manufacturer is a good indication that, as a wear item, they need to be replaced eventually to remain optimally efficient and safe.

Can you keep riding a bike with its front rotors worn thinner than recommended? Sure ...would the brakes still operate normally? Probably ...how far are you willing to go to find out the failing point of your main safety component?...

Just like you would replace tires long before the rubber is worn through to the cord... or not.  

This has certainly been my experience. After using aggressive HH front pads (along with my characteristic Jackrabbit-on-hot-lava riding style ), my front rotors reached minimum thickness at an embarrassing 50,000 miles/ 80.500 km. (The replacements are at 82,500 miles now and holding up fine.)

 I learned to use pads spec'd for the Brembo rotors (FF, GF, or GG) and also changed my service by restoring the piston movement at fluid changes, and my rear rotor made 114,000 miles/185.000 km before reaching minimum thickness.

Seriously YMMV . . .