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I have changed my Kia Carens tire size My original car Kia Carens tire size was 225/45 R17 (total Diameter 25")

I changed the front tires to 225/50 R17 (total Diameter 25.9") Difference 3.6%

And then changed the back tires to 245/45 R17 (total Diameter 25.7") Difference 2.8%

I know the change is above 3% but is it risky, and shall I change it again?

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    What is it you are worried about? Just so we know what we are meant to answer? – HandyHowie Nov 2 '15 at 20:08
  • My worries in order are: First: Increasing the wheels diameter is expected to affect car stability in high speed, to what extend is that effect. Second it also affects engine performance as overall wheel weight increased. Finally the speedometer in will be less than the actual with 3.6% – Sayed Yousef Nov 3 '15 at 21:10
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As long as you have enough clearance, meaning the tires don't come to contact with body panels, etc, you should be fine. No need to change.

The only thing the size change will affect is your odometer and speedometer reading.

To find out exactly how much it would change use this website: https://tiresize.com/speedometer-calibration/

It has a calculator where you can put your model/make and tire sizes.

If you want to calibrate the speed to match your tire size, there are after market devices that let you do that. But these are not easy to install. You have to tap the wire of the speed sensor. Here is one example of such a device. http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=238/prd238.htm

If you are concerned about speeding tickets, use a GPS. GPS speed is almost as accurate if not better than your speedometer.

EDIT: One more thing to keep in mind is that, if you car is AWD, then you have to be very careful about having different size tires in front and back. This can create premature wear on your AWD system. This does not apply to OP's car I believe.

  • Realize with taller tires it takes more braking force to stop a vehicle. This is due to the taller tire applying more torque because it's radius is larger (in effect, it's a longer lever). – Pᴀᴜʟsᴛᴇʀ2 Nov 2 '15 at 22:16
  • Good point. Didn't think about this. But I don't think the size change is significant enough to be concerned. Same can be said for acceleration and top speed. Correct? – rana Nov 2 '15 at 22:20
  • Oh, I completely agree with you that it isn't significant enough to worry about, but that's my opinion. As for acceleration, that too is affected ... it will be slower due to the larger torque requirement. As for top speed, it should theoretically be higher with the taller tire, but that depends on how much power the vehicle has and whether it's a brick rolling down the road ;-) – Pᴀᴜʟsᴛᴇʀ2 Nov 2 '15 at 22:24
  • Thanks for your input. First: I am concerned more about car stability then impact on engine life time by overloading it with extra torque as you have indicated and of course impact ton acceleration. – Sayed Yousef Nov 3 '15 at 21:18

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