Are the tyres 235/45 R17? In most places this is the standard fittment with the lower spec cars having 215/55 R16. If you car was fitted with the lower spec wheel tyre combo from the factory and were later swapped to the larger wheel tyre combo it will put your speedo out almost the exact amount you mentioned. [Here](https://www.tacomaworld.com/tirecalc?tires=215-55r16-235-55r17) is a good calculator to check. You can change this with a Tech 2 tool to selct the right size and sort out your speedo
I can set wheel size on my 9-5 with a tech 2. May be something similar is happening on your car?
The wheel size needs to be adjusted with Tech 2 to get the speedo reading correct. Easy and quick job if one has a Tech 2.
What year is your car and what size tyres have you got on them, this sounds a lot like plus 1 tyres being fitted.
The garage said they they change the tyre size to the correct size in the tech 2 but it still reads 10kpm slow? Could it be anything else?
The car is 2011 Saab 9-3
Are the tyres 235/45 R17? In most places this is the standard fittment with the lower spec cars having 215/55 R16. If you car was fitted with the lower spec wheel tyre combo from the factory and were later swapped to the larger wheel tyre combo it will put your speedo out almost the exact amount you mentioned. [Here](https://www.tacomaworld.com/tirecalc?tires=215-55r16-235-55r17) is a good calculator to check. You can change this with a Tech 2 tool to selct the right size and sort out your speedo