Is MPH accurate if all filled in information is correct. Trying to figure out how far my I'm off and who's lying,  my speedo, GPS or quad. 

My truck info 6spd, 3.55, 285/70/17 Tire circumference comes out to 102.7 in. I have to have it at 97 in. to match my speedo at 70mph, GPS says I'm going 70.7 mph. If i set it to 102.7 quad will jump to 75 mph. 

Like I'm in the same boat. 5 Speed transmission, 3.55 gears and tires measure out at 99.7 inches and it shows +2 high on the Quadzilla (67) vs Speedometer (65) and the GPS (65). 

Edited March 8, 20187 yr by Mopar1973Man

The Quadzilla is using math so it can't really "lie".  that doesn't mean however that the circumfrence is %100 accurate based on tire size etc.   Treat it as fuzzy math and the GPS is always right.

Thanks Nick, that was my thoughts too. I know tires are not what they are a advertised,  if you get 35" tires different brands measure different hight. Most of time a 35 will be 34 so circumference will be off. I'm just going to leave it at 97 maybe bump it to 98 so I'm closer to GPS.

This brings another question, is your MPG mode depending on correct circumference I assume. 

oh gesh....I dont remember lol    

 

It would have to be....

 

 

 

Yes it is. I think

The Quad is done by calculation. Your GPS is probably the most accurate unless going up or down steep hills. Even then, they probably have figured out how to take that into consideration if you have access to more than 4 satellites for your location. 

What happens in the Adrenaline is that it calculates based off a stock tire size of 95.7" in circumference. 

If you put in a tire size of 97" it is going to multiply the incoming MPH x (97/95.7) or ~1.014 to increase your speed by a little bit. It will then use that corrected value in calculating gear and transmission slip based off the other drive train info. 

 

MPG calculation is going to rely more heavily on the MPG Offset than on the tire size. You will have to calibrate that yourself. Once you start running in wire-tap levels, its more of a hazy general idea than an actual MPG used. 

 

 Well either way I got it pretty close, my main concern was on mph. My mpg offset is at 150 and really close to my actual numbers. What I've noticed is anything above 65 my MPG drops like a rock. Just going from 65 to 70 equals to 18-19mpg to 13-14mpg according to quad and I know it's fairly accurate. What's weird is if I go 75-77mph then I actually gain a little bit 14-15mpg but up hills it'll drop even more. This is also on my daily tune that I've modified since I've posted it, it's a bit aggressive and not made for mpg. But the passing power is what I what love 

 

Thanks for posting this @Dieselfuture!   We have the same tire size and I've noticed the speed differences a lot being I usually run interstate speeds and I could never figure out if my speedo was off or the Quad was high at those speeds.

As for your mpg findings, I see very similar things. I run around on my "speshul tune" (read: idiot race tune) most of the time, and 65-70 I read 18-19 mpg, 75-80 reads 15-16, and 85 reads 17-18.  My engine load stays pretty constant through all those speeds as well, so I don't have any ideas why it's so different.

rpm changes. as rpms increase you are burning more fuel even though the same amount is injected per stroke.