My 4.88s are not quite broken in yet, but on 34s with the inch bumper I was getting 20 mpg on the highway for a stretch I ran 50-55mph during the break-in, and I'm seeing about 14-14.5 around town. I'll know in a couple weeks what the mileage really looks like and was planning to report in at that time, but if it stays even within 10% of that I have to seriously agree with
@grinchy and others that have said you just can't have too much gear, as by rights I should be running a bit under 4.30. Then again I suspect if I try to cruise at 100 mph on the highway my mileage might not improve, but at reasonable speeds more gear actually seems to help.
FWIW if you think of the amount of effort it takes to get a bicycle started from a stop in 1st gear vs 21st gear, imagine your legs as the engine and you can see why shorter gears really help mileage even though the ratio implies it shouldn't. Because it's much less work for the engine, you're not dumping fuel into the cylinders to try and compensate for the "challenging" gear ratios created by taller tires.
This is great to hear. Sounds like your hypermilling is on point to touch those kind of numbers! Interested to hear your impressions outside of breaking in, but I trust you'll find as much success as
@grinchy found with this combo.
Towing may be a different story, at least for my setup. Your aero and setup differs so your experience may be different. Just something for others to be aware of as they pick and choose how they might tailor their rigs.
From my earlier post
here
Freeway MPG efficiency with trailer in tow - this is an interesting area as it wasn't necessarily an improvement. Previously, with 3.9s and 33s, for my rig and its weight and aero, the preferred cruise gear was 4th, putting me at ~2500 rpm at ~65mph. Note with 33 tires, 4th works out to be about an ideal 4.5 gear. This worked great with enough margin to lockup the torque converter, and still handle slight grades and wind. With the re-gear at 65mph, it puts things a bit too high and too low. 4th is now too high at 3k rpm with more gearing (windage losses) than I need to cruise. 5th is barely workable and will just lockup the torque converter on flats, with RPM a bit low at ~2150 rpm. So while pulling on hills improved, cruise is now a bit more inefficient with ~.5mpg loss.
To help others analyze how this plays out. Those of us with 6-speeds don't have as fine selection with the in-between gears so it's a big rpm jump between usable gears. A .5MPG decrease is what I saw re-gearing with 33s. Reason is I find that the optimal towing RPM to be about 2600 for my aero profile and load at 65mph. For those that tow a lot, this may be how to assess where you want to be, at least for hauling MPG.
As from my earlier post, I got the best MPG with
- (1) stock gearing with 33s. This 2673 RPM @65 was great as it kept the torque converter locked, while having torque reserves for some minor wind and hills, and kept excess RPM down.
- (2) My experience going to 4.3s with 33s was as I quoted above. Excess RPM @2941 for the same 65mph, meaning windage losses while keeping excess power reserve in gear. Losing about .5MPG vs (1).
- (3) Now that I have 35s with 4.3s, I have 100 more RPM to turn bigger tires, but relatively the same as (1), so I'm probably spitting distance in MPG minus minor losses hauling around the bigger 35s.
So a way to look at this for heavy towing usage is to find combos that put you around 2600rpm @65mph as a first approximation. Again, I'm stock aero, 1" lift, 35x12.5s. If you have bumpers, add ~100rpm to your target rpm. Roof rack, add another ~100rpm. That sort of thing. Try the different gears in your towing setup now to come up with a sense of where you think the car wants to be in RPM when laden, to cross check the optimal gearing (for efficiency).
@linuxgod the orange is where you'll roughly land with your 4.88 setup. If you towed in 4th gear prior with stock gearing and 34s, that was probably around 2600rpm as a reference. It'll be interesting if you can grab 5th with the new setup. Though I know you also tend to keep a higher speed so 5th gearing may work out per the 75MPH table below and you have a chance at sitting pretty.
