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I want to get a new car but just put new tires on the old car that died. The dealership has no problem taking the tires from the old to the new as they are just taking the old car to auction. However, they said because the size is not right, they will not do it. The new car has 225/55 17 tires on it and I want to put 225/65 17 tires on it. Will this damage the vehicle or create a safety issue?

  • And to add to the answer you might find someone willing to purchase them for a better price than the dealer... – Solar Mike May 16 '19 at 15:29
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The difference in the dimension of the two tyres is purely in the aspect ratio of the sidewall so the /65 tyres will have a bigger sidewall (note that the number is 65% of the width, not 65 somethings - i.e. 165.75mm vs 140.25mm and that's effectively doubled because you're taking radius, not diameter) and therefore making the overall circumference of the wheel and tyre combination bigger.

This will have the knock-on effect of throwing the speedometer out, so when the speedo indicated 65mph, the vehicle will actually be travelling at 70mph. You may find that this throws out the gear ratios of the car too so acceleration will be slower.

You'll also need to check that the speed and weight ratings of the old tyres suit the new car. You may potentially run into insurance issues if you fit underweight or under-speed tyres in certain jurisdictions.

Finally, you have the complication of trying to establish what pressure you ought to run the tyres at for optimum wear, grip and ride. There is also a possibility that you'll affect the handling of the car because you'll be adding 25.5mm to the end of the wishbones so they'll be running at an odd angle and potentially reach their extent of travel sooner. There is of course a chance they'll foul the bodywork of the car although this is unlikely given how close in size they are.

I'd speak directly to the manufacturer of the new vehicle and ask them what sized tyres the vehicle is homologated to run. Typically there will be multiple sizes listed and if 225/65R17 are listed and the speed and load ratings of the tyres you have are appropriate, go for it.

If they won't fit, haggle the price of them into the part-exchange deal.

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