How Can I Check Discs Are Straight?

[TotalGSXR]

I've a pair of discs which I would like to check are not bent or warped. They are not attached to the bike and all the methods I've read about involve the discs being attached to the bike.

How can I achieve this?

[andym]

I checked mine on a worktop with feeler gauges.... not sure if that was good enough or not, but I still put them back on the bike as they were within the limits listed in the book

[Ollie1995]

Put a metal ruler next to it in a few different places? Or if its removed find a flat surface and place it on that?
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XR 125, DT125 LC, Greeves Scottish, RS200, XS400, GPX600r

Theory Passed - 18/7/13 MOD1 Booked - 24/9/13

[c_dug]

Ideally they need to be on something you can spin them on, I'm assuming they aren't on a wheel? If possible either mount them to a wheel or knock up something they can be spun on.

If that isn't possible then find a flat surface and lay them on it and look across them from level with the disk, any big warping will show as a gap between the disk and surface.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[c_dug]

Or I suppose you could coat the disk in something that will leave a print then place it flat on a sheet of paper and check for any points that don't leave a print, these will be raised points and show warping.

Obviously the disks would need a really good clean after.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[TotalGSXR]

I've use a ruler to check them and they certainly appear straight, but there is a pulsing through the brake lever, so I'm fairly certain that something's not right with them.

They're not on the wheel due to my wheel being on the bike which I use daily to commute, so it's not that easy for me to swap the discs over. I'm interested with other ideas, if anyone knows any. The bobbins make it impossible to lay flat on a sheet or glass to see any warps. Why did the lazy Susan fade out of vogue?

[andym]

If they've already been on the bike but appear to be straight when you are checking them, make sure you clean the area under the disc and tighten all the bolts evenly... I made the same mistake and thought the discs were warped, but turns out it was crap behind the disc that was causing it

[WULFSTAN]

If there is pulsing then its fair to say they are warped. Got warped discs on the cbr i don't really worry about them.
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Your backside is better enough for you to run again, if need be – bristle up the courage of the cornered rat, put on a bold front, and to hell with them. Bluff my boy – bluff, shift and lie for the sake of your neck and the honour of Old England

[Ja7]

[WULFSTAN]