New Tires/First Trip/Speedo Correction/MPG

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Nov 30, 2014
Nashville, TN
Hey guys!

Put a new set of tires on my 80 last week. Went with 285/75R16 BFG AT KO2's. I love them so far. I like the look a lot and they don't seem overly loud compared to the dry rotted stock size Michelin LTX's that were on there.

I took my first long trip this weekend from Nashville to Knoxville for a wedding. About 180 miles each way.

Before we left, I popped my scangauge II in and set up RPM, MPH, Coolant and AVG MPG. Hopped on to see what my new MPH would be with the bigger tires. It ends up being about 5% faster than what the speedometer states.

The scangauge has a section for adjusting the speed. I punched in 5%. Matched that up with GPS and it was spot on.

Here's my question. The scangauge showed 15.2 MPG coming back from Knoxville --> Nashville. Do I need to multiply that by 1.05 (the 5% speed difference) or has the scangauge already done that math for me?

When I go to calculate MPG by hand at the pump, I will need to multiply the initial MPG by 1.05 to get the true number, correct? This is because the car is actually moving 5% farther than the odometer actually states.

Anyways, if the scangauge does in fact do the math, 15.2 MPG seems pretty good to me with 285's on there. I never calculated nor took a trip with the stock 275's. Ballpark wise, how many MPG's have yall lost w/ bump up to 285's? I traveled 70 MPH (corrected) at about 2280-2310 RPM's. Knoxville to Nashville has you scale up onto a plateau en route to Nashville.

Final thoughts : I thought the 80 was great on the trip. It's a little loud but it's a 18 year old "true LC." I didn't find it dropping out of OD too much to keep up speed.

If you went in and corrected the scangauge by 5% then the numbers showing on the scangauge are corrected. Check the trip mileage on the scangauge and check your trip odometer on the dash. The scangauge should be 5% higher.

Users who are viewing this thread

Top Bottom