17" to 15": Toyota tech says don't do it

What difference could it possibly make? Going to a 15" wheel could only make it easier on the power steering system during tight maneuvering. I say do it if that's what you want.

 

It would be an extremely dumb engineering decision to do it that way. I am not saying it might not happen.

People change tires all the time. Winter tires, summer tires, upgrade to aftermarket rims. If the car self destructs, there will be lawsuits.

 

If I'm not mistaken Toyota also uses a different steering ratio for different wheel/tire combinations.

 

FWIW, the V has the brushless motor, with the better steering ratio. I asked about this way before the first car hit the ground last spring. I have not seen any suggestion in any of the many threads discussing this that there could be any detriment to going to 15 inch wheels. I'm not a gear head, but it's hard to think of any reason that could be a problem. Surely the steering ratio is not "too quick" if you use 15 inch wheels.

 

As others have said the new brushless motor (there is no pump), used because of the quicker steering ratio in the PriusV, has more power than the normal motor. Going to smaller width tires would make it's job easier. What this mechanic told you makes no sense at all.

If someone wants to go the other way, wider tires with the old style motor, that seems to work OK too. Quite a few of us put wider tires on the Gen2 and several have put them on the Gen3 II through IV with no reported problems. In fact in some Toyota regions, I have been told, the wider tires for the II through IV are a port installed option as they were for the Gen2.

I believe that, unfortunately, a lot of our present generation of Prius technicians seem to lack the ability to think things out for themselves. Perhaps they are told not to.

 

I went from stock-sized 17" to stock-sized 15" steelies for wintertime. There was no way on God's green earth the 17s would have survived a Chicagoland winter unscathed.

I'm sure I'll be in for my first service before the snows come off, so I'll be interested to see if anyone makes a comment.

 

If anything, you can do damage to the hubs by putting heavy rims/tires on it. But then you are talking about over a LONG time

 

Going from 17" to 15" will be just fine. The power steering will work even better.
Going from 15" to 17" will cause the power steering to work extra hard. It -may- feel like the steering has gone "heavy". Over years it could shorten the life of the power steering unit. Note that the power steering doesn't do much after you get above 10-20 MPH. So low speed steering might get heavy, but at high speed you won't notice.

What you DO want to watch is to avoid putting on a wheel/tire combo that is -much- heavier than stock. This will overload the shocks and -may- cause a dangerous response to bumps. Things like wheel hop and associated braking problems.

 

Yes it is. But the amount of rubber present is different. Imagine if you had a 1" wheel and rest of it tires will it cause problem with your car? Yes probably because it wasn't designed to be used with a 1" wheel. You will probably be wobbling about.

If you have the SUN roof you can only got with the smaller wheels anyway. I don't see the harm going from 17 to 15 at all except it won't look as good.

 

1" is just to drive a point to point out the extreme to see it better.
Of course with different wheel side your handling is going to be different. What is it that you don't buy? You don't think that it makes any difference at all to the handeling if you change the size of the wheel?

 

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Vehicles with 15 inch wheels use brush type motor which does not require a boost converter. Vehicles with 17 in wheels use brushless.This system includes a boost converter in the power steering ecu and a rotation angle sensor in the steering column assembly. The boost converter converts batt voltage to the level required by the brushless motor.
Yes the toyota tech is correct

 

As to the wearing things out faster idea. Driving on secondary roads will wear the tire/steering faster. Driving in the city will wear things out faster. Driving over potholes will wear things out faster. Driving 80 mph will wear things out faster. Putting on tires with more traction will wear things faster. Having a passenger will wear things faster.

I believe that these minor increase in wear is within design parameters. Of course things will wear faster - but so would a lot of other things. And consider the prevalence of the other things (passengers, luggage, potholes, driving fast, etc), switching tires will be minor.

Having new wheels probably put less stress on steering than having a car full of passengers. So if you really want to save the car, don't carry passengers.

 

I'm not technical enough to understand your point.

What is it about the facts you present that make the technician's statement right?

 

I do not understand your point. The reasons you stated do not seem to support your conclusion.

All of the Prius models with VSC, that would be all Gen3 and most Gen2 cars, have a steering angle sensor so that is not a factor. If the steering motor works with wider tires on 17" wheels it would have to work with narrower tires on 15" wheels, they are easier to turn. The stuff about a boost converter is totally irrelevant, the OP was talking about changing tire and wheel sizes not steering motors or ECUs.

 

As long as the OD - Outside Diameter - of the tire is the same, why should it matter? The speedo/odo will retain their accuracy, but with more sidewall the following will happen:

1. Ride will be softer. This is a GOOD thing over frost heaves and potholes

2. Cornering will be a bit sloppier. In winter, only fools take corners at high speed

As an example, my FJ came with P265 70 17 wheels and tires. The correct minus 1 size is P265 65 16. I actually prefer the 16's for overall ride quality

 

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