[Oldguy]

Hello, All!
New member here. I have installed 215/70/15 tires on ARE 15x8 wheels on my 2010 Scion XB and need to know how to recalibrate my speedometer so it reads correctly. Can anybody help me?
Thanks!
Oldguy
PS: If you want to know how I got 15" wheels on the back of my XB, i'll tell you. By the way, it wasn't easy!

 

[WaggOn]

I had the same concern when I up sized, I have a Garmin GPS that shows your speed. My speed was off by 1mph ( if i was doing 70, gps said 69) before with stock wheels and after I put 18", it stayed the same. Yours may not be off by as much as you think.

 

[TartanJack]

Hello, All!
New member here. I have installed 215/70/15 tires on ARE 15x8 wheels on my 2010 Scion XB and need to know how to recalibrate my speedometer so it reads correctly. Can anybody help me?
Thanks!
Oldguy

All (are at least the VAST majority) modern speedometers are designed to read slightly high, so as to keep drivers who want to "push" the envelope slightly. It's pretty standard across the industry, going back a few decades- at least. Also, as tires wear down, the total rolling circumfrence reduces somewhat- changing the speedometer accuracy slightly too (b/c it physically changes the gear ratio in connection to what tracks the speedo calibration).
The real issue is how the overall diameter compares to the stock one- 205/55/16.

(I use 225/50/16 rubber which happens to be extremely close to the 205/55/16 size and looks neat on the rims- besides theoretical performance advantages on tight roads (I say theoretical b/c some say it helps significantly and others say it won't do much)

PS: If you want to know how I got 15" wheels on the back of my XB, i'll tell you. By the way, it wasn't easy!

I'll bet it involves spacers to make it clear-> OR smaller brakes . . .

 

[Oldguy]

OK, here's what I did to make 15" wheels fit on the back of my XB, which, by the way voided what remains of the warranty on my back brakes: I bought 2 new rear rotors and had a machine shop reduce thier radius by 3/8". I then marked and drilled new holes in the wheel hub and caliper mounting plates on the swing arm. The holes were drilled 3/8" inward toward the centerline of the hub and downward on the plate to prevent the new holes from overlapping the stock holes. I also fashioned two 1/2" steel spacer plates that I installed between the hub assembly and the swiing arm mounting plates to bring the rear wheels out to approx. the same width as the front wheels. I then had the spacers welded to the swing arm plates to prevent any possibility of the spacers slipping or shifting. I used the stock calipers, caliper brackets, and brake pads and everything works perfectly. Now, the reasons I did all that are these: I hate the look and ride of low profile tires and I wanted to see if I could do it. And I did! Also, according to Miata.net's tire size calculator, 215/70/15 tires are almost 2" larger in diameter than the stock 205/55/16 tires my XB came with and make my speedometer read 5mph slower than my real speed which is why I want to find a way to recalibrate it. Any ideas anybody?Later!Oldguy

 

[TartanJack]

It's all digital, so it has to be changed in the programming.

 

[Oldguy]

I know it's all digital and all in the programming. What I don't know is how to change the programming. There has to be a way to reset the speedo software to reflect the new tire size. Anybody?