3.31 2wd vs 3:55 4wd?
03-10-2016, 01:35 PM
#1
Senior Member
Thread Starter
3.31 2wd vs 3:55 4wd?
Due to the weight difference in the 4x2 and 4x4 will the 3:31 in the 4x2 tow just as well once you are moving as the 3:55 in the 4x4?
The reason I ask, is when I bought mine, I went off the specs listed on the web listing of the truck I bought and didn't look at the sticker. Well the listing on the web was wrong. So I ended up with the 3:31 instead of the 3:55. I can change it if I have to, but I don't think it would be worth the trouble or expense unless I went to a 3:73, however evidence on the web shows the 3:55 in the 4x4 pulls fine.
The reason I ask, is when I bought mine, I went off the specs listed on the web listing of the truck I bought and didn't look at the sticker. Well the listing on the web was wrong. So I ended up with the 3:31 instead of the 3:55. I can change it if I have to, but I don't think it would be worth the trouble or expense unless I went to a 3:73, however evidence on the web shows the 3:55 in the 4x4 pulls fine.
03-10-2016, 07:16 PM
#2
Grumpy Old Man
3.2% difference in engine RPM at the same road speed. I don't know about the 2.7L, but my 3.5L EcoBoost with 3.15 axle ratio has no problem towing an 8,000 pound trailer from Austin to Midland thru the Texas Hill Country.
IOW, don't worry about your axle ratio. Worry about not exceeding the payload capacity of your F-150. If you don't exceed the GVWR (and payload capacity) of your F-150, then your Mighty Mouse 2.7L turbo boosted engine should have no problem pulling any trailer you can hook up to, regardless of whether you have 3.15, 3.31. 3.55 or 3.73 axle ratio.
On one trip I towed a 20,000 pound gooseneck trailer thru the Hill Country. No problem pulling the load, but those twin turbos had to work hard so the result was only 6.5 MPG.
In case you haven't heard it yet, with an EcoBoost engine you can have Economy or you can have Boost, but you cannot have both economy and boost at the same time. When those twin turbos go to work, MPG goes in the gutter.
IOW, don't worry about your axle ratio. Worry about not exceeding the payload capacity of your F-150. If you don't exceed the GVWR (and payload capacity) of your F-150, then your Mighty Mouse 2.7L turbo boosted engine should have no problem pulling any trailer you can hook up to, regardless of whether you have 3.15, 3.31. 3.55 or 3.73 axle ratio.
On one trip I towed a 20,000 pound gooseneck trailer thru the Hill Country. No problem pulling the load, but those twin turbos had to work hard so the result was only 6.5 MPG.
In case you haven't heard it yet, with an EcoBoost engine you can have Economy or you can have Boost, but you cannot have both economy and boost at the same time. When those twin turbos go to work, MPG goes in the gutter.
Last edited by smokeywren; 03-10-2016 at 08:52 PM.
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03-10-2016, 08:02 PM
#3
Senior Member
Thread Starter
I didn't realize the difference was only 7%. From a vehicle perspective, I knew the difference was marginal, I just wasn't sure about towing.
I have been reading your posts and those of others and understand about payload. I don't have anything added to the truck so I can take full advantage of the capacity of the truck.
As for eco or boost, I was aware of that and even note in in my signature. I also have an 87 S10 pickup with a V8 in it. It is the same. It is reasonably economical if you can keep your foot out of it, but here is not much fun in that.
I have been reading your posts and those of others and understand about payload. I don't have anything added to the truck so I can take full advantage of the capacity of the truck.
As for eco or boost, I was aware of that and even note in in my signature. I also have an 87 S10 pickup with a V8 in it. It is the same. It is reasonably economical if you can keep your foot out of it, but here is not much fun in that.
03-10-2016, 08:51 PM
#4
Grumpy Old Man
Well, the old MBA screwed up the math. Fat fingers on my cheap hand-held calculator.
Speedo, odo, trip meter, axle ratio and engine RPM all change as the percentage of change in tire revs/mile, at least on a Ford.
275/65R18 KO2 tires have 648 revs/mile,
275/70R19 KO2 tires have 627 revs/mile.
648 minus 627 = 21, 21 divided by 648 = 3.2%.
So your engine RPM would decrease by 3.2% with the taller tires. So 2000 RPM with the 65 profile tires would be 1,936 RPM at the same road speed with the taller 70 profile tires.
400 miles per the trip meter on a tank of gas would be an actual 412.8 miles. That could make a slight difference in your mpg calculation.
Taller tires result in longer legs. So a 3.55 axle ratio will feel like a 3.44. Not a big difference, but some.