OK,I'll run it up to 13.5
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That write up is superb! Thank you! I was taking a test drive (to and from the gas station of course) and noted that at 60mph my rpms at least according to the display was around 1700 (it is a guess on the display as not enough tick marks between the big numbers) I have 33" tires but maybe when pumped up they are 34" per your equation. Either way I see that getting the engine to turn faster at the same vehicle speed (or same thing is making the drive shaft ratio lower) is getting the engine to higher rpms and in its torque band.
Of course the other solution is to downsize the tires to get the rpms up and of course smaller/lighter tires will give less load for the engine to push.
It is clear that when the road goes up a bit of a grade even at 60 that the truck loses speed and engine load really has to pick up to keep it at speed. On the other hand on level highway at 60mph the rpms seem to be a comfortable range given that it only has 4 gears to work with.
Is 4.1 the only other stock option 'above' 3.73? I assume the rating for the front axle uses the same number system so a 3.73 would apply to front and rear on our truck.
I think in time I can convince my son that we can still come up with some really nice rims/tires. We can lose the excessive offset and get most of the rim back under the wheelwells, we can then goa bit skinner and maybe get diameter down an inch and it will still run nice and look nice. That will get rpms up into the sweet spot. I don't think we have time or energy to swap out front and rear axles for a 1mpg or 2 when the more obvious thing relates to how you drive it and the tires/rims and resistance.
I was hoping full tune up would help a bit. Maybe we get lucky and adding the O2 sensor will help a bit. I guess most aim for about 13mpg as a good thing with mix of highway and city given the situation.
To give you a reference, my 1988 K1500 350 TBI/ 700R4 has 4.1 diffs and 33x12.5/15 tires and looking at a recent datalog I can accurately say that on level ground, sitting on 60 mph, I was doing 1800 RPMs with the TCC locked. Hope that helps.That write up is superb! Thank you! I was taking a test drive (to and from the gas station of course) and noted that at 60mph my rpms at least according to the display was around 1700 (it is a guess on the display as not enough tick marks between the big numbers) I have 33" tires but maybe when pumped up they are 34" per your equation. Either way I see that getting the engine to turn faster at the same vehicle speed (or same thing is making the drive shaft ratio lower) is getting the engine to higher rpms and in its torque band.
Of course the other solution is to downsize the tires to get the rpms up and of course smaller/lighter tires will give less load for the engine to push.
It is clear that when the road goes up a bit of a grade even at 60 that the truck loses speed and engine load really has to pick up to keep it at speed. On the other hand on level highway at 60mph the rpms seem to be a comfortable range given that it only has 4 gears to work with.
Is 4.1 the only other stock option 'above' 3.73? I assume the rating for the front axle uses the same number system so a 3.73 would apply to front and rear on our truck.
Small tires may not be as cool but neither is going down the $$$$ rabit hole, at least until he's got a career and a reliable backup car.