[Innate]

I wanted the exact 20" tire diameter on my Ltd to get a matching diameter 17" tire. Don't want to screw around guestimating the mph when there is a uniformed state, county or city sworn official pointing a laser at me or in my rearview. Well here it is....

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[soldthetaco]

the OEM 245/50/R20 and 245/60/R18 tires are exact size
there is no exact tire size downsizing the wheel to R17, the closest is 245/65/R17 or 265/60/R17 with -0.3% diameter, at 90mph, your true speed is 89.7mph

 

[WI.EC]

I thought I saw a way somewhere that you can adjust the speed in the settings to adjust for tire sizes. It stuck with me bc I thought that was a cool feature to have.

 

[Walking Black Bear]

If that is in the settings, that would be amazing! Then it really wouldn't matter what size you go with. Honestly, everything is computerized now, it's all calculated. A far cry from the days of a spinning cable attached to a gear in the transmission moving a magnetized needle in the dashboard. (Which, to be fair, was some brilliant engineering for the era it was created in.) So a setting that lets you type in a new tire size? That would kick @$$.

 

[LittleBokey]

I thought I saw a way somewhere that you can adjust the speed in the settings to adjust for tire sizes. It stuck with me bc I thought that was a cool feature to have.

That was what I read too.. it may be a hidden setting done only through the OBD port. Otherwise, we are talking a physical gear change in the speedo. (is that not electronic now?)

The only thing in the manual is for adjusting the adaptive cruise control speed.

 

[Innate]

the OEM 245/50/R20 and 245/60/R18 tires are exact size
there is no exact tire size downsizing the wheel to R17, the closest is 245/65/R17 or 265/60/R17 with -0.3% diameter, at 90mph, your true speed is 89.7mph

Yep, thats why I'm going with Amer. Racing Torq Flight 17"x7.5"/5x4.5" 45mm wheels with 245/65/R17 Michelin Crossclimate2's tires and new TPMS sensors. Only .2" diameter smaller difference so thats OK with me. Doubt it will even be noticable but that 50 up to 65 profile should improve the ride. For $2200... I would sure hope so!