Tire size causing traction control to improperly engage?

I've recently started to have issues where when I get up over 55/60 mph the traction control will engage and limit the accelleration of my 2009 prius. I took the car into my local Toyota dealership and they claim it is because of the size tire I have.

I recently purchased a set of Hankook Optimo H727 replacement tires. After having done my research (mostly on these forums) I decided to go with the P195/60R15 tire size.

Now I have several reasons to believe that the dealership has misdiagnosed the issue:

1. There are loads of people on this site who have installed 195 size tires (and larger) without issue as far as I can tell.
2. The issue did not begin immediately after installing the new tires, but rather a couple months later.
3. My brother installed the same exact tires on his 2005 Prius and does a lot more freeway driving than I do and has not had an issue.
4. My understanding from reading here is that in some other countries Priuses come with 195 size tires stock.

Despite explaining all this to the guy at the dealership he insisted that all these other people should be having the same problem and I should be using a 185 tire size. They put 185 size tires back on the car and took it out for a drive and said they didn't experience the issue. My thinking is that it could possibly be some defect with this particular set of tires rather than the size itself that is causing the issue. They did not try it with a different set of 195 size tires.

So I guess what I'm looking for are any ideas as to what else might be causing this problem. Is there maybe some adjustment that needs to be made to the car when installing a bigger tire that the dealership neglected to perform? Any other ideas?

Any feedback is much appreciated. I'd like to avoid having to buy a whole other set of tires if that is not the problem as I suspect. Thanks in advance.

 

You guys are awesome.

So when I got the new tires I only checked one of the tires to make sure it was the size I had ordered. I just looked at them all and the back right tire is indeed the wrong size - 65 instead of 60.

I feel like a dummy (though the trained techs at two different dealerships are even bigger dummies), but am very happy to have the problem worked out. Thank you!

I have a couple more questions at this point if you guys have another second to spare...

1. I have had the new tires for a few months (and driven maybe a few thousand miles) now and I know you're supposed to try to keep the wear even on pairs of tires. Should I try to have them replace both back tires so they are not uneven? Has it been long enough to worry about?

2. Is it possible this has caused any other damage to my car? Is there anything else I should bring up with them or have them look at as a result of this?

Thanks again!

 

Sweet. Thanks so much again for the advice.

While scolding them for installing the wrong size tire I'll be sure to slip in a little gratitude for making sure they did it on the rear wheel

 

Thanks again as well Tom.