My cars stock size was 185/65R14. Every time I put on my toyo 350 175/80R14 my gearing is about 9% taller. Also my fuel economy becomes about 9% better. So in my 1.9 TDI Seat taller gearing works very well. Best way to test this is to get used tires from local tire shop for free and just test it. No sense to buy new tires in my opinion. Also best way to see if any changes will work is to make it so big that effects will be propably be big if it works. Otherwise you need to drive a lot to see the difference. On my case I notice it from the first tank when I put the tires on
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One thing that also counts is that tires should not weight much. I have also tested 1% even taller tires and got much worse fuel economy. So if your first tire does not work it does not mean that it wont work with some other tire. I would recommend that Toyo because it has worked like dream with my car.