Phylodog
Senior Member
- Joined
- Aug 9, 2013
- Posts
- 682
- Reaction score
- 328
- Location
- Arcadia, IN
- Ram Year
- 2012 & 2018
- Engine
- 5.7 Hemi & 6.7L CTD
I bought the speedometer calibrator from HyperTec because the dealership said they weren't sure if they could reprogram it to the tires I have (275/65R20). Goodyear says the tire height is 34.1" and when I measured them I came up with 33.8". I set the calibration for 33.75" but the speedo was running 2mph slow compared to the GPS. I drove it like that for a week then during a trip the speedo suddenly flipped and was running 2mph faster than the GPS.
It's remained that way for a couple of weeks and I've reprogrammed to 34" and now 34.5" and it's still running faster than the GPS. The programmer tells me the process has been successful each time.
What am I missing. I confuse myself thinking about it but I'm thinking larger tires should slow the speedo down to match the GPS. The bigger question is how much does 1/2" in tire size effect the speedo at 60-70 mph? Those are the speeds I'm most concerned with.
Any help?
It's remained that way for a couple of weeks and I've reprogrammed to 34" and now 34.5" and it's still running faster than the GPS. The programmer tells me the process has been successful each time.
What am I missing. I confuse myself thinking about it but I'm thinking larger tires should slow the speedo down to match the GPS. The bigger question is how much does 1/2" in tire size effect the speedo at 60-70 mph? Those are the speeds I'm most concerned with.
Any help?
