3.15/3.31 Gear with 3.5L EB - Why Not More Popular?
04-11-2015, 08:14 AM
#41
Senior Member
Quite a few have already been listed, your just not listening... but to recap, some advantages of not having lazy 3.15 highway gearing are:
If your buying a fleet of stripper trucks for your company and putting 50K miles per year on each of them, the 3.15 starts to make sense....
And it's not lack of "independent thinking" that creates this conclusion, it's the combination of personal experience, collective wisdom, and enough seat time in high ratio trucks walking away with the impression, "wow, this gearing really sucks..."
- More fun to drive.
- Better towing performance.
- Better high payload performance.
- Better hill performance.
- Better headwind performance.
- Better high altitude performance.
- Less transmission hunting when you need power.
- Better resale.
- More fun to drive (listed twice, because 3.55 is way more fun than 3.15's)
- About the cost of a Starbucks coffee per week in extra fuel cost.
If your buying a fleet of stripper trucks for your company and putting 50K miles per year on each of them, the 3.15 starts to make sense....
And it's not lack of "independent thinking" that creates this conclusion, it's the combination of personal experience, collective wisdom, and enough seat time in high ratio trucks walking away with the impression, "wow, this gearing really sucks..."
One more: If you are thinking about putting larger tires on it.
Having owned trucks/off road vehicles for 35 years not once did wish I had highway gear set in it.
04-11-2015, 08:34 AM
#42
Quite a few have already been listed, your just not listening... but to recap, some advantages of not having lazy 3.15 highway gearing are:
If your buying a fleet of stripper trucks for your company and putting 50K miles per year on each of them, the 3.15 starts to make sense....
And it's not lack of "independent thinking" that creates this conclusion, it's the combination of personal experience, collective wisdom, and enough seat time in high ratio trucks walking away with the impression, "wow, this gearing really sucks..."
- More fun to drive.
- Better towing performance.
- Better high payload performance.
- Better hill performance.
- Better headwind performance.
- Better high altitude performance.
- Less transmission hunting when you need power.
- Better resale.
- More fun to drive (listed twice, because 3.55 is way more fun than 3.15's)
- About the cost of a Starbucks coffee per week in extra fuel cost.
If your buying a fleet of stripper trucks for your company and putting 50K miles per year on each of them, the 3.15 starts to make sense....
And it's not lack of "independent thinking" that creates this conclusion, it's the combination of personal experience, collective wisdom, and enough seat time in high ratio trucks walking away with the impression, "wow, this gearing really sucks..."
Nothing like the bottom of a shift with an eco they pull like crazy.....a tune doesn't hurt either
04-11-2015, 09:07 AM
#43
Member
331
I got my FX4 5.0L with 3.31 gears too. I'm so out of touch when it comes to gearing. Does 3.31 give more takeoff or more pulling? I told my dealer to put towing package on and he asked what I tow. I explained that I have a 26' camping trailer weighing 2400kg, but I only pull it a few times a year. He said these gears would be good for what I need and still have power to have fun as I do. Any feedback from you guys on this?
04-11-2015, 09:26 AM
#44
Senior Member
04-11-2015, 09:36 AM
#45
Senior Member
I went with 3.55 for some of the reasons listed but also because I am going with taller tires. With the 3.55 it will help the truck get moving better and will have a taller gear ratio with the bigger tires so it will act as if its got around a 3.31 gear
04-11-2015, 10:21 AM
#46
Senior Member
I get a kick out of everyone's take on gear ratios. While it remains true the shorter gears will always out accelerate taller gears to infinity, it is not necessarily true a shorter gear will out accelerate on taller one through a specific distance especially if not coming from rest. If that was the case, every drag car in the world would run 5:14 gears or higher.
While shorter gears will always have a mechanical advantage over taller gears in a specific gear, it may not at a certain speed as the taller gear may be taking advantage of a shorter gear in the transmission. Since these 6 spd's have over a 4:1 first, it has created room for these 3.15 and 3.31 To work. With 8 and 10 spd transmissions, this will translate to different gear ratios using different gears to do the same thing going down the road.
To get the "best" performance you would have to do a "torque to the wheel chart" using a torque chart of your truck over all rpm's, multiplied by the gear ratio in the driveline(transmission included) to the set shift points you want to use. Plot this on a curve against speed and do one for each gear ratio, the one with the largest area under the curve will accelerate the fastest over that specific distance.
In the end and if you are working it, fuel mileage will be less important than capability, if you are traveling on the highway capability may be less important than fuel mileage. There is as many answers to this as there is questions.
While shorter gears will always have a mechanical advantage over taller gears in a specific gear, it may not at a certain speed as the taller gear may be taking advantage of a shorter gear in the transmission. Since these 6 spd's have over a 4:1 first, it has created room for these 3.15 and 3.31 To work. With 8 and 10 spd transmissions, this will translate to different gear ratios using different gears to do the same thing going down the road.
To get the "best" performance you would have to do a "torque to the wheel chart" using a torque chart of your truck over all rpm's, multiplied by the gear ratio in the driveline(transmission included) to the set shift points you want to use. Plot this on a curve against speed and do one for each gear ratio, the one with the largest area under the curve will accelerate the fastest over that specific distance.
In the end and if you are working it, fuel mileage will be less important than capability, if you are traveling on the highway capability may be less important than fuel mileage. There is as many answers to this as there is questions.
Last edited by Smidgy; 04-11-2015 at 05:48 PM.
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MGD (04-11-2015)
04-11-2015, 04:03 PM
#47
So I think I have a reasonable understanding of why 3.55 gearing is preferred over 3.31 and 3.15. Can the same arguments be made for going with 3.73 gearing over 3.55s? 3.73 comes standard with the HD payload package in 2015. Sounds like 3.73s might be preferred when towing or when traveling the mountainous western part of the country. Would 3.73s be even better in these situations? How about when just driving around town empty? So many choices!
04-11-2015, 05:59 PM
#48
Senior Member
All in all 3.15 vs 3.73 is a 16% change in gearing from top to bottom. The 3.55 vs 3.73 is less than 5%. These are not huge changes between one up or down. Will the 3.73's work better than 3.55's well they will have 5% higher torque advantage so if both were in the same gear and you were towing....yes. If you were towing on a back road where the 3.73 was in 6th gear and the 3.55 was to be in 5th, then the 3.55's would have the mechanical advantage until the 3.73's shifted down....sound complicated? It is.....
Pick your motor, figure out how you drive it, pick your differential ratio.
Pick your motor, figure out how you drive it, pick your differential ratio.
Last edited by Smidgy; 04-11-2015 at 07:03 PM.
04-11-2015, 06:52 PM
#49
I love the 3.73's, but Ford has definitely made it more difficult to get in most configurations... But 3.55 e-lockers seem to be available in almost all config's, so that's what I'd probably choose today.
04-11-2015, 09:31 PM
#50
I picked up my truck yesterday with the 3.55 e locker, and so far on my first tank with mixed driving over 240 miles is getting 22.4 MPG based on the computer. It is an XL SCab sport 3.5 eco with a 2166 payload sticker, so it is lighter than a lot of trucks on here.