Hi All
E-Lad, Gresley and myself have spent the last three days in the Lake District. Our small convoy of Gresley's Stag, E-Lad's Stag, my Stag and my wife's GT6 had a very pleasant drive on Monday from Cheshire to near Keswick via a scenic route through Pendleton, Gisburn. Settle, Ribblehead, Dent, Sedburgh, Windermere, Ambleside. Tops down or roof open(GT6) all the way
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We came back home today directly down the M6 and it gave me an opportunity to do direct comparisons between our Stag and GT6 whilst on a long journey, something which very rarely happens for obvious reasons!
Anyway, I know my Stag under reads on the speedo and mileage clock because it has a 3.45 diff fitted. However, I am surprised at the large difference in mileage recorded between the services near Lancaster and Crewe. The GT6 recorded it as 82 miles whilst the Stag says 67 miles. According to my calcs below the Stag is under reading by 10% which means it has physically covered 1.1 miles for every 1 mile recorded on the clock. So. 67 miles +10% is 74 miles so why the difference of 6 miles between the two cars? I think I need to take both cars out with the Satnav and see what they record over a measured mile. I also think I need to check the ratio of the diff fitted to the GT6!
Can someone please check my calcs below for the Stag?
Thanks
Bruce
E-Lad, Gresley and myself have spent the last three days in the Lake District. Our small convoy of Gresley's Stag, E-Lad's Stag, my Stag and my wife's GT6 had a very pleasant drive on Monday from Cheshire to near Keswick via a scenic route through Pendleton, Gisburn. Settle, Ribblehead, Dent, Sedburgh, Windermere, Ambleside. Tops down or roof open(GT6) all the way
.We came back home today directly down the M6 and it gave me an opportunity to do direct comparisons between our Stag and GT6 whilst on a long journey, something which very rarely happens for obvious reasons!
Anyway, I know my Stag under reads on the speedo and mileage clock because it has a 3.45 diff fitted. However, I am surprised at the large difference in mileage recorded between the services near Lancaster and Crewe. The GT6 recorded it as 82 miles whilst the Stag says 67 miles. According to my calcs below the Stag is under reading by 10% which means it has physically covered 1.1 miles for every 1 mile recorded on the clock. So. 67 miles +10% is 74 miles so why the difference of 6 miles between the two cars? I think I need to take both cars out with the Satnav and see what they record over a measured mile. I also think I need to check the ratio of the diff fitted to the GT6!
Can someone please check my calcs below for the Stag?
Thanks
Bruce
| 3.45 diff fitted | 3.7 diff fitted | ||
| in a mile | in a mile | ||
| yards | 1760 | 1760 | no. of yards in a mile |
| inches | 63360 | 63360 | yards x 36 |
| revolutions of a tyre (rolling circumference is 78.61 inches) | 806.00 | 806.00 | inches in a mile divided by the circumference of the tyre |
| revolutions of the propshaft | 2781 | 3039 | wheel revolutions multiplied by the diff ratio (3.45 or 3.7) |
| engine revolutions in 4th OD (0.82) | 2280 | 2492 | propshaft revs multiplied by the gearbox ratio in 4th gear + Overdrive |
| Difference in engine revs between the two diffs | 211 | engine revs for a 3.7 diff minus that for a 3.45 diff | |
| % difference | 9.28% | ||
| Note : Car fitted with a A type Overdrive | |||
as I had been basing them on the recorded miles off the clock which is at least 7% under reading the actual mileage
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