Speedo Correction Confusion

[pezboy]

Hello,

I am trying to figure out which parameters I need to change to correct my speedometer for a change in tire size on my 2009 Chevy Silverado 5.3L 4L60E. My stock tune is attached.

My stock tires measure at 2465 mm circumference (H0139 and H0140) which is pretty close to stock. However, the revs per k on that tire (H0136) are 406 which is nowhere near what the stock tune says. The tires I am going to measure at 2683 circumference and 373 revs per k.

Why would H0136 be off by so much? Does it not change anything? Is it compensating for an error somewhere else? Should I change it to 91.87% of what it is now or should I change it to the correct amount? Should I change the tire circumference to 108.84% of the current size? What other values do I need to change?

Thanks!

Dustin

[johnv]

If the Speedo was reading correctly with previous tyres, just click on the "speedo calculator" tab , in that window click on speedo calculator and fill in new tyre specs then click apply.

If after that speedo is still of a bit , click on the "speedo fine tuning" tab and using a GPS log your actual speed verses displayed speed and put the values in and click apply.

Would also pay to do the shift point correction as well.