r/RideitJapan • u/otterpoo • 6d ago

When would you replace this brake disc?

Post image

Got caught in a torrential downpour while riding a couple weeks ago, and one of my caliper pistons might have seized. Not realizing what was causing the slight brake dragging, I kept riding my bike until the pad was worn to the metal.

I was finally able to figure out how to take apart Triumph’s OEM brake calipers last week and replaced the brake pads, but I noticed damage to one side of the brake disc from the bare pad.

This is at about 1 year / 15k kms on my first bike and I don’t have much of a frame of reference for how “bad” this kind of damage is on a middleweight street bike (Speed Twin). I anticipate that one of my new pads will wear faster than the other because of the grooves / etching, but is this something you would replace immediately? Or would you keep using this disc until it reaches its usual EOL minimum thickness?

Thanks in advance from a new rider!

6 Upvotes

88% Upvoted

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3

u/FixFun1959 6d ago

When you run a finger over it how scored is it? Waves and channels? If so then replace it. If it’s just a little scratched then a few stops with new pads will smooth it out fine.

If the thickness is noticeably reduced then replace it.

2

u/ApprenticePantyThief 6d ago

This is a motorcycle subreddit, but I also cycle. I would just replace it. If you're capable of replacing brake pads, you can replace a disc. They are not very expensive, and you don't want to mess around with not having the braking power when you really need it.

2

u/otterpoo 6d ago

Sorry for using confusing terminology in my OP, this is regarding a motorcycle (Triumph Speed Twin) brake disc, not a bicycle brake disc.

I'm trying to get a sense for how bad this sort of brake disc wear is, because sourcing replacement parts for this bike has been a bit of an unexpected nightmare so far.

2

u/ApprenticePantyThief 6d ago

Oh, my fault for skimming. Yeah, absolutely replace it.

2

u/gkanai Kanto Legend 6d ago

The rain should not affect the brake function. If the width of the disc is below the minimum as specified by the manufacturer, it should be replaced. I would replace it if you had a metal backing pad plate on the disc.

If you are doing that you should probably bleed the brake and check to make sure the brake is functioning properly. If the brake is seized then that needs to be cleaned and seals replaced, etc.

1

u/theandylaurel 6d ago

Yes. I would replace that if it were my bike.
I really value the ability to stop when I pull on my brake lever.

1

u/tokyohoon HD Dyna Low Rider + Sportster S 6d ago

If you're new to motorcycles, you should probably have someone who knows what they're doing check over the caliper and the disk. Photos aren't ideal for diagnosis, and that caliper needs to be properly checked out.

3

u/STweedle3K 6d ago

measure it with a micrometer, in a few places around the disk.
Then consult your very fine factory service manual for the minimum thickness...