Sorry neosin, this is a rare case and we've decided not to add features like this that will only affect a small number of users. We have a long laundry list of features to add to the site including better graphing, better reporting, and much more.
Maybe there's a way to adjust your stats as you enter them and make a note of your changes?
It's easy enough to approximate the difference (your trip & odometer are hardly precision instruments them selves!). You need to know the % difference between the tyre profiles then apply that to the mileage. A quick n' dirty way is to use the tyre profiles, tread width is divided by the profile as a % then doubled & applied to the wheel diameter. If we take 195/45R15 then we get:
(the 25.4 is covering millimetres into inches)
Say I'm going to move to 195/40R16 tyres I have the result 22.14"
You then use the two numbers you got to get the difference in %, 1.05% in this case. So I'd add 1.05% to my mileage total.
With Scan Gauge you can adust your speed offset when you set it up. You will need GPS and then adjust so that the gauge is reading the correct MPH. I do this in my jetta as it is off just a bit. I then use all the info in Scan Gauge when filling up and inputing it here on Fuley. I am off just a few miles every tankfull with my odometer but Scan Gauge is right! LOL!
Thanks guys, I've installed a scangauge2 and did the setup with a GPS, it is off about 4MPH. I do not know yet if the odometer is off yet, i've heard some people on tdiclub say that the speedo is off but the odometer is spot on, I haven't checked that yet.
On my next road trip to dallas (from houston) about 400 miles, I will check odometer/GPS/Scangauge2 and tell you what the diff is. At least in my case and then I'll know what adjustments I should make.
By the way PB, love the site. Can't wait to see better graphs and other fun things.
Here's a thought how about a graph of you and your friends that would be fun...