Largest Rim/Tyre that will Fit a Cortina Mk3 ?

Years since I've done wheels on a MK 111 , cant really advise on it .Depends on where your getting wheels from and whether new or s/hand . If new , most suppliers should be able to give you the info you need by phoning or going in to store /accessory shop .If getting wheels off a scapyard , these guys are usually pretty good at letting you know what wheels will fit and swap over o.k .Just got to check all clearances when fitted if not sure and double check they are not fouling anywhere .Remember you will have to notify your insurance if you replace them or you could be in the s*** if not and have a claim later on .

at the moment I'm having a 12'' Rim as I know Yeah I better do that thanks.

Some info to consider ,

Ford Cortina MK3 Rebuild: Fender Flaring 101.

About 17" is the largest you can go on the MK3 Cortina. You could try to push for 18" but you would have to have very low profile tyres on them.