Just had the wifes' '95 855T in the shop for a check up. The mechanic told me the front rotors and pads need to be replaced. I just had the rotors and pads replaced less than 30K miles ago. I opted for the new pads but not the rotors. How long should the rotors last?

JJF

My 850 rotor to pad ratio, 2 sets of pads per 1 set front brakes.

The rear brakes pads are usually replaced with every other set of front pads.

my front rotors lasted 40k miles...

I was just talking about such stuff with a local tech the other day.
He had an Accura up on the lift--rear rotors about shot after 20,000 miles.
He said that is not unusual these days--pads have been made harder, to stop complaints about brake noise. As a result, rotors wear faster.

No set time or mileage--depends on the quality/hardness of the pads and the type driving being done. City driving with lots of stop and go will wear stuff a lot faster than rolling on the interstate for hours a day.

On my 850 and S70 front pads go about 30K and front
rotors about 60K.

You could measure the rotor thickness with a 30mm micrometer.
The minimum size is stamped right on the rotor near the hub.
If it is under the minimum size, it needs replacement.

I replace my rotors every other brake job. They aren't that expensive: about $50 for the 2 front rotors.

Where do you get your rotors for $50 a pair?

I got the Brembos through an import parts dealer in the Washington DC area: Olympic Auto Parts. Great place to get parts for imports.

I just got my front pads replaced and rotors resurfaced. Pads lasted 45k! Rotor was new 45k ago.

Volvo rotors aren't designed to be turned. They are designed for two sets of pads and then disposal.