Q: front brake discs replacement Yamaha Diversion XJ900s

For the Diversion specialists

already two years now driving a Yamaha Diversion XJ900s (2002 built)
thirty thousand kilometers (18.641 miles) and today the two front-brake
discs are replaced in an 'extended' small service visit.

The new discs have 4mm thickness whilst the old discs were 4.5mm.
Back-brake disc has some 5mm left.
I assume the discs thickness is relevant for heat dissipation and
preventing the discs to warp (not sure whether this is proper English,
hope it is clear to you all)

In short, can someone explain when brake-discs are to be replaced. Next
what replacements are ok for a Diversion XJ900s 2002.

Didn't find an answer on the net. Googling the new discs partnumber (on
receipt) (4km2582t0000 ) shows to somewhat obscure sites
(http://www.yamaha-motor.it/Images/Fastmove2004_tcm39-46881.pdf en
http://62.5.189.98/yamahaeur/exist/moto/Motorcycle)
Neither found genuine Yamaha spare parts.

Thanks in advance.

Yes, tomorrow I'll also call the garage and find out their explanation
too. But I do appreciate an indipendent answer from this NG.

 

When nthey are worn thinner than their service limts; when they are
badly scored; when they are badly warped.

EBC.

 

I find them next to useless. On the Guzzi they can barely knock the rust
off the discs and in the MZ the OE East German linings are better
(astonishingly).