Prius 2013 skids while driving today

Sounds good, but I’m used to CDN $’s and prices lol. For what it’s worth i think the X-Tours are the same tire, Michelin rebadged the Defenders for Costco.

Are they currently having a discount at Costco, that helps?

 

Not just ABS, but also the vehicle stability control, VSC, expects matched tire sizes. I agree that the mismatch didn't cause the skid, but it certainly upsets the VSC's ability to respond.

If the mismatch is large enough, it will light the VSC warning icon during regular driving and probably disable its function. Apparently this mismatch wasn't enough to trigger that warning, but it would have degraded its response.

If it was black ice (likely though unconfirmed), then driver inexperience with winter conditions is also a contributor. But such drivers still have a much better chance of safely handling it when ABS and VSC are fully functioning, so that set of 4 new matched tires will help.

Back to the other descriptions at the very start:

There is a separate problem when braking lightly over bumps, when the car is using primarily regenerative braking, not friction brakes. Momentary traction loss on the bump (or wet manhole cover or railroad track, etc.) disengages the regen braking and the car switches to 4 wheel ABS, but with a momentary delay. To many drivers, this delay feels like a complete loss of braking, or even an accelertion, and can induce panic or cause them to release the brake pedal. The best response is to just keep your foot on the brake pedal, even increase the pressure, as full friction braking will engage in a few tenths of a second. This isn't known to happen under medium and hard braking, which exceed the regen capacity so already have the friction brakes engaged.

The rest of what you descibe here is plausibly related to the tire mismatch.

 

Exactly. Rat them out to Toyota USA? And maybe some US government transport/safety body?

The flip side: sometimes it’s complying with an oddball customer request that gets tire shops in trouble, but seems very unlikely in this case.