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MY PUP Speedo Issues Going to 19 inch Wheels?

DaveORD

Member
Mar 12, 2020
727
628
Chicagoland
The MY PUP has a staggered wheel config, 255/35R21 front, and 275/35R21 rears. Looking at winter tire options and I decided to go with a set of four 19 inch x 8.5 wheels and 255/45R19 tires and no longer stagger.

According to tiresize.com the 19 inch config is an identical match to the PUP fronts - 28 inch diameter and 720 rev per mile - but when compared to the rears on the PUP the 19 inch config will be different - the rear on the PUP is 28.6 and 706 rev per mile. So now the question is what effect, if any, will this have on my sensed speed and distance.

If there is a change by changing to 19, I am looking at displayed 60 MPH is actually 58.7 MPH, so I will travel less than reported by the odometer. The MY has a wheel configuration option for 19/20/21 inch which I assume is only for range estimates, have not seen anything about speedometer changes.

My questions, for anybody who has already figured this out or know:

1) How is the speed measured on the MY, and will the 19 config on a PUP result in a change in reported speed and miles traveled?

2) If there is a change, do I submit a service request for a speedo re-cal and then again next spring when I switch back to the staggered config? Or do I just live with it? I might just sell the 21 Ubers and buy another set of wheels if this gets too complicated.

TIA... :confused:
 

RoBoRaT

Zero Farts Given!
Nov 22, 2018
1,388
1,228
NorthSoCal
The MY PUP has a staggered wheel config, 255/35R21 front, and 275/35R21 rears. Looking at winter tire options and I decided to go with a set of four 19 inch x 8.5 wheels and 255/45R19 tires and no longer stagger.

According to tiresize.com the 19 inch config is an identical match to the PUP fronts - 28 inch diameter and 720 rev per mile - but when compared to the rears on the PUP the 19 inch config will be different - the rear on the PUP is 28.6 and 706 rev per mile. So now the question is what effect, if any, will this have on my sensed speed and distance.

If there is a change by changing to 19, I am looking at displayed 60 MPH is actually 58.7 MPH, so I will travel less than reported by the odometer. The MY has a wheel configuration option for 19/20/21 inch which I assume is only for range estimates, have not seen anything about speedometer changes.

My questions, for anybody who has already figured this out or know:

1) How is the speed measured on the MY, and will the 19 config on a PUP result in a change in reported speed and miles traveled?

2) If there is a change, do I submit a service request for a speedo re-cal and then again next spring when I switch back to the staggered config? Or do I just live with it? I might just sell the 21 Ubers and buy another set of wheels if this gets too complicated.

TIA... :confused:

I have changed my staggered 21" Uberturbines to square 19" Geminis with stock wheels 255/45R19 without speedometer issues (tracked GPS vs Y Speedometer).

The Y has 4 speed sensors, one each wheel. Since the tires have the same diameter, 21 front 255/35R21 vs 19 square 255/45R19 l, there should be no speedometer issues. Besides other Model Ys run on 255/45R19s.

You can use the Wheel Configuration function in the car to effect the change - matching estimated range for squared 255 tire on 19s.

Screenshot_20201011-092820_Samsung Internet.jpg 20200620_110613.jpg
 

DaveORD

Member
Mar 12, 2020
727
628
Chicagoland
Thx. The fronts have the same diameter whether 19 or 21 and both should report the same speed. I was concerned about the rears since the 21 have a larger diameter than the 19, so I was wondering how the MY handled that, the fronts reporting a speed different than the rears and which speed it would use. From your response, looks like it will use the fronts, or the highest reported speed I guess.
 

RoBoRaT

Zero Farts Given!
Nov 22, 2018
1,388
1,228
NorthSoCal
And, for your current staggered 21" set up - this what I think is happening:

2 front tires 255/35s @ 90 mph
2 rear tires 275/35s @ 91.9 mph
Average: (90 + 91.9) / 2 = 90.95 mph

So, staggered 21s at 90.95 mph is 90 mph on squared 19s on 255/45R19 tires.Screenshot_20201011-094622_Samsung Internet.jpg
 

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