Bigger tires & speedo calibration?

[umpire19]

If I put bigger tires (33's) on my BB do I need to do have speedometer recalibrated?

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[Woody '73]

If I put bigger tires (33's) on my BB do I need to do have speedometer recalibrated?

Yes. Larger circumference of the tire means it takes longer to complete a full rotation. Speedometer will read slower and odometer will clock less miles.

 

[Hyfly]

You can use this link and it’ll show you how off your Speedometer will be
https://tiresize.com/comparison/

 

[BroncoAZ]

Yes. Larger circumference of the tire means it takes longer to complete a full rotation. Speedometer will read slower and odometer will clock less miles.

And the problem with that is what, exactly? The bigger issue is recalibrating for the auto trans.

 

[Woody '73]

And the problem with that is what, exactly? The bigger issue is recalibrating for the auto trans.

Agreed. Just answering the question about the speedometer.

 

[kodiakisland]

Need to? No. You may want to however. Lots of us with 4wds add bigger tires and don't worry about it. My tires add about 4mph at highway speeds. I can do the math on the fly. Or not. I rarely look at the speedo anyway. Yeah, sure, my odometer will also be slightly off, but I don't care. Oil change intervals aren't that sensitive. Overall, I just don't care.

 

[BR0NCO]

It’s a good idea with an automatic transmission to get the shift points back to where they should be

 

[kodiakisland]

It’s a good idea with an automatic transmission to get the shift points back to where they should be

I don't own an auto, but are you saying today's autos shift based on MPH instead of RPMs?

 

[BroncoAZ]

I don't own an auto, but are you saying today's autos shift based on MPH instead of RPMs?

Today’s autos take a lot of parameters into consideration. If the tires are significantly larger the auto might not be able to respond correctly when picking a gear to downshift, and maybe it drops 2 gears instead of three.

 

[EStepCG2022]

Yes. Larger circumference of the tire means it takes longer to complete a full rotation. Speedometer will read slower and odometer will clock less miles.

Wouldn't the car's MPG readout technically be off too? I would assume it just uses the odometer mileage data to track that.

 

[Big Boss]

Wouldn't the car's MPG readout technically be off too? I would assume it just uses the odometer mileage data to track that.

The MPG readout is already off LOL. Mine has not been accurate since day 1. Always 2 to 3.5 MPG optimistic, compared to hand calculated

 

[EStepCG2022]

The MPG readout is already off LOL. Mine has not been accurate since day 1. Always 2 to 3.5 MPG optimistic, compared to hand calculated

That's probably true, but my point still stands that the readout would be further affected by a tire size increase.

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