Do you have any pics of the alloys you have. The T5 as standard would have 205 55 16 my 2.5 ltr had the 195's. I think as standard if you have 16" wheels the profile would be 55. Although I think you can fit 3 diffrent tyre sizes to a wheel without problems.

Tyre sizes fitted as 'standard' on the 850's were (from the owners manual) 185/65 R15, 195/60 R15, 205/55 R15, and 205/50 R16 T5 'std' was 205/50 R16 The R's were fitted with 17" rims

Do you have the T5 alloy wheels? (5 spokes star shape) they should be running on 205/55R16 as far as i know, it seems strange you have wider rear tyres, the car is not rear wheel drive....

Wheel and tyre sizes 

Thanks for your input everyone the tyres are 195/55 16 front 205/50 16 rear will put a photo on maybe tomorrow. According to manual 850 2.5 10V should wear 15 inch wheels,so surely my car will be slightly overgeared will this affect speedo mileometer readings.The wheels look like a starfish with roundish spokes,I also found it strange to find wider tyres on undriven wheels. Thanks again Mick.

if you're on 16" wheels the correct size is 205/50 and not 205/55/16s. these can and do rub on the inner arch on the front.

Cheers irf could 195/55 16 inch rub on arch liner? Will take a look tomorrow.Thanks again Mick.

sorry for wrong info before regarding the profile of the tyres if I were you I will get the 195 changed to 205/50/16

Tyres 

Hi done some quick sums ,205x50 profile =102.5.195x55 profile =107.25 ,107.25-102.50=4.750 divide this by 2 =2.375 mm which is about a gnats dick.Will put 205/50s on soon as poss.Thanks Mick