THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

Hi all. I have read the thread of Jose's about his tire replacement from 2021, and since I don't think my problem is similar, the question bears trying again. My car, 77903, currently has 205/70/15 tires on it. We got them shortly after we got the car- it was desperate for tires. I did not have a spare made up at the time as it wasn't deemed needed as the car was "moveable" but not "roadworthy,." It still has the original 640-15 spare in the trunk which has never been used (and does not hold air). I want to start using the car more this year, as I 'think' I have it safe, legal, and have dialed out the largest of the leaks. I am trying to research an issue- beyond lack of a proper spare on a Wire wheel. My speedometer reads 10% fast. This is according to the speedometer app which I put in my phone for this very reason.
Getting around to the question, does anyone know if a 205/75/15 would help the speedo issue and at the same time fit into the wheelwell? My other somewhat more drug induced question is can I get a different gear which I could use to make up the 10% disparity?
Weird Al Yankovic did a song called "First World Problems."

I will attempt to answer my own somewhat simple question. I measured my current 205/70/15 tires at 26 inches diameter on the car. I went to both Tire Rack and Coker Tire's websites and compared their specs of near sized tires' "actual" mounted and inflated diameters. As was mentioned in Jose's thread (on Jag forums) the 195/75/15 does seem to be the correct size. It is about .3 to .5 taller than mine depending on brand. 205/75/15 are more in the range of 26-1/2 to 27 inches diameter. I then used a trolley jack to lift the car and remove a rear tire as an experiment. I found that (and certainly should have known) its as much the height of the tire as its width- along with having a jack of some sort that will lift the body high enough to allow clearance. Lifting by the hub will get you nothing but tired. None of this directly answers the speedometer question, but the spec charts on the 2 websites did list revolutions per mile so I'll need to look at that again. Maybe someone can say how much difference one would get on the speedo with a 1/2 inch tire. I have put this in as a starting point for others looking for a tire specific thread. hope it helps someone.