Issues with changing wheels on a Prime XSE from 19" to 17"

1. Speedo would be 0.5mph off at 25mph, 1mph off at 55mph, and 1.5mph off at 80mph.
2. My math might be wrong, but I think it's actually 1 mile for every 53 miles. (so 190 miles off for every 10,000 miles)
3. Height of the car would be altered by 0.25". BTW, that's a similar amount to how much a tire changes over the course of its life(most have a tread depth life of 9/32" = 0.28")

Cars are built for their tires to have a margin of error because not all tires are exactly the same size, and tires change size over the course of their lifespan as the rubber wears away. I believe the safety margin for changing the size of your tire is typically between 2-3%. The tire size difference between the 19" and 17" wheels is 1.9%.

In other words, it feels like your service rep is full of s#$t. This isn't a case of going from a standard size to a non-standard size. This is going from one standard size to another. If you were changing tire sizes and the new tires were an inch or two taller/shorter, yeah, you'd have problems. But a quarter of an inch in height? 1.5" in circumference? I don't buy it unless I hear it from someone several levels higher than a generic service rep.

 

You can find a tire+wheel combo that keeps the overall size of the tire+wheel the same. This would be a non-issue. The only difference you may notice is that with a 17" wheel, there is more tire between the wheel and the road to absorb the shocks from the road and thusly less "responsive" or "sporty".

 

Any info on how much the mileage would increase with 17-inchers? And another question: looking at the 17" wheels on Toyota's website (see just below), it looks like there are wheel covers because I can't see any wheel nuts, but what lies underneath those covers? I assume alloy wheels, but what do they look like?

 

Answer to the first question is: "it depends". If you get a set of stock 17" wheels and the wheel covers, you should gain 3-5mpg. If you get the stock wheels but no wheel covers, maybe a touch less(2-4mpg?). If you get aftermarket 17" wheels, then it depends on the weight and aerodynamics of the aftermarket wheel. Could be more than 5mpg, could theoretically be worse than the stock 19".

As for the second question, beauty is in the eye of the beholder, but I think they're ugly. Not as ugly as the wheel covers, but giving them a run for their money. But come to your own opinion:

 

What sensor? Do you mean odometer/speedometer accuracy? You can compare the rev's per mile for the two tire sizes; there's online tire calculators for that. IIRC the 17's OD is slightly less, which is the opposite of 3rd/4th gen.

Almost like the 19's are the "base" model, and the odo is set to that.

FWIW, in Canada the only 2023 Prius offered are 19". And AWD. If and when they ever show up.

 

I think they mean parking sensor accuracy. If you were to raise or lower the car to a significant degree, it's possible the parking sensors would either give false alerts(in a lowered car) or not enough alerts(in a raised car). But common sense would suggest the height difference would have to be far more than the 0.25"/6mm difference when switching between stock 17" and 19" tire sizes.

 

My own opinion is... ugh-lee (both cover and wheel). Maybe a super light 19" aftermarket wheel would be the way to go. The standard 19-inchers look great but I'll bet they're pretty weighty. Does anyone have any specs?

 

I like your little side note on 147 fill-ups and 64 mpg.

 

Here's a couple of links on the subject of aerodynamic wheels and wheel covers:

80sHERO: July 2013 | Car wheels, Wheel, Wheels and tires
12 Aero disc wheels ideas | rims for cars, wheel rims, car wheels

It seems there was more interest in the subject years ago, but I assume the interest will return with the need to reduce aerodynamic drag from EV wheels. A flat face with slots or vanes along the edges seems to make sense.

One of my favourites is the wheel design of the 1982 Porsche 956 (I assume those are wheel covers and were used at Le Mans and other high-speed tracks):






Or how about something like the Rotiform VCE? It's forged but I don't know how light (or not) it is.


Maybe the best solution would be a super-light forged (or carbon fibre) wheel with a flat, thin and slotted/vaned wheel cover. Hey, let's dream in Technicolour!

 

Or how about this wheel cover from the McLaren Speedtail along with a very lightweight wheel behind it?