Rear Axle ratio question
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Rear Axle ratio question
I am in the process looking at a ’06 supercrew xlt (w/ 6.5' bed) to replace my old ’97 S-10 – need something bigger to handle the kids and still want a truck. My question relates to the rear axle ratios. What advantage does the 3.55 have over the 3.73? Is the 3.55 a ‘lower’ gear ratio so that it is better for towing/pulling, etc? Does it affect gas mileage? I mostly would be using for a daily driver to work (mixed use) with some summer trips on the highway (500 mile +/- round trip) and do not plan on doing any towing. Thanks for any information - I've found answers to several little questions here already.
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Joined: Dec 2004
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From: Boise, ID
The 3.55 is actually a higher gear ratio. All things being equal, the 3.55 will give slightly less acceleration and slightly better fuel mileage at cruise as the engine will be turning less rpm. Depending on how you drive, stop and go mileage could be better or worse as you may want to put your foot in it more with the 3.55s to get the truck moving.
If you load the truck down or ever do any trailering, the 3.73s allow for a higher gross vehicle weight than the 3.55s. You can find the exact amount in the trailering guide on the Ford website.
If you load the truck down or ever do any trailering, the 3.73s allow for a higher gross vehicle weight than the 3.55s. You can find the exact amount in the trailering guide on the Ford website.
Postmaster
Joined: Aug 2001
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From: Trussville, Alabama
Welcome to FTE! Glad to have you here.
A little more info to add to the above.
The gear ratio is the number of times the pinion gear (that which is driven by the drive shaft) rotates to create one rotation of the ring gear (that which drives the axels).
Think back to a 10 speed bike.
1st gear is more like a 3.73 or 4.11 rear end. You pedal fast (drive shaft) but go slower (final drive to axles). This is good for power/towing but not so good for crusing down the hiway.
10th gear is more like a 3.08 or 3.31 rear end. Harder to get things going but doesn't spin quite so fast cruising down the road.
The 3.55 rear end is kind of in the middle. A decent balance of the two extremes.
Based on what you describe, the 3.55 would be just fine.
In general: start with the 3.55 rear end (it's in the middle)
lower number = lower towing = lower cruising rpm
higher number = higher towing = higher cruising rpm.
A little more info to add to the above.
The gear ratio is the number of times the pinion gear (that which is driven by the drive shaft) rotates to create one rotation of the ring gear (that which drives the axels).
Think back to a 10 speed bike.
1st gear is more like a 3.73 or 4.11 rear end. You pedal fast (drive shaft) but go slower (final drive to axles). This is good for power/towing but not so good for crusing down the hiway.
10th gear is more like a 3.08 or 3.31 rear end. Harder to get things going but doesn't spin quite so fast cruising down the road.
The 3.55 rear end is kind of in the middle. A decent balance of the two extremes.
Based on what you describe, the 3.55 would be just fine.
In general: start with the 3.55 rear end (it's in the middle)
lower number = lower towing = lower cruising rpm
higher number = higher towing = higher cruising rpm.
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Buying or Leasing? It may be easier to unload a 3.73 rear axle truck as it does have a much higher tow capacity. If it is a lease it doesn't make a differnece. Personally I would get the 3.73. What we cannot make up for in displacement we can make in gear!
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From: Marion, VA
In your situation, I would get a 3.73 with the 4.6 and a 3.55 with the 5.4. The smaller engine will work much better with the lower gear. I have a 5.4 with 3.73 and prefer it that way but that is just me and my need to tow.
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Originally Posted by BruceFX4
...mileage could be better or worse as you may want to put your foot in it more with the 3.55s to get the truck moving...
Tuned
Joined: Dec 1999
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From: Bismarck USA
One thing you're not taking into consideration also is tire size. A 3.55 would probably be the wrong gearing if you're on 20 inch tires.
Given that tires sizes have gone from 15 inches when 3.55 was norm gear, on up to 17's and 18's being the norm, I wouldn't personally consider any truck without a 3.73 gear or more. 3.55 is outdated for the give tire size.
Besides, if postings on here are any indication, the gear ratio has less to do with mileage than speed and driver. My 03 with 3.73's gets as good and better than some with 3.55's.
Given that tires sizes have gone from 15 inches when 3.55 was norm gear, on up to 17's and 18's being the norm, I wouldn't personally consider any truck without a 3.73 gear or more. 3.55 is outdated for the give tire size.
Besides, if postings on here are any indication, the gear ratio has less to do with mileage than speed and driver. My 03 with 3.73's gets as good and better than some with 3.55's.
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Postmaster
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From: Trussville, Alabama
Originally Posted by RI_guy
I mostly would be using for a daily driver to work (mixed use) with some summer trips on the highway (500 mile +/- round trip) and do not plan on doing any towing. [/size]
On average, the difference in max towing capacity for a 5.4 with the 3.55 -vs- 3.73 rear end, is 400-500 lbs. This is in the 6,000 - 8,000 lb max towing range, so 500 lbs. is not a huge difference, especially if the only towing to be done is light to moderate.
More antecdotal than important, but I'd wager a significant percentage of the drivers of trucks on the road today have no idea what rear end is under their truck, and even fewer would know what it meant if the knew.
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From: MA
Although the 3.55s are theoretically better for what you have seemed to describe, they are too tall for these trucks in my opinion. Ive driven them with both gear sets, and the 3.73s are better all around.... hands down. Ive found that the 3.55 trucks struggle on any sort of incline at highway speeds.
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The 5.4 with 3:73 will tow 9500lbs, with 3:55 8500lbs. Don't know where the 500 to 600lbs difference came form in a previous post. Owning a 5.4 with 3:73 rear, my feeling is the 3:73 is a much match to the 5.4 and transmission. In fact most comments on this board as it relates to gas mileage, the difference is so negligable that it is more outweighed by the better match of the 3:73's. HWY driving in OD will produce just about the same gas mileage.
Last edited by KevinM; Feb 8, 2006 at 09:54 AM.
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From: Boise, ID
Originally Posted by RangerWask
So, what you are saying is, the more you put your foot into the 4.6/ 3.55 the better the gas mileage?
Everyone has their own opinion as to what is acceptable. For me, I do not want anything slower than my 5.4 with 3.73s.
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From: Brandon, MS
3.55 rear end
More antecdotal than important, but I'd wager a significant percentage of the drivers of trucks on the road today have no idea what rear end is under their truck, and even fewer would know what it meant if the knew.
On top of that, we purchased a used travel trailer last year. Even though what I'm pulling (loaded) is under my weight rating capacity, it really struggles on anything but flat highways/roadways. I'm looking at regearing (preferably to 4.10's) but, as someone previously stated, it won't be a cheap job (with the 4x4, have to do the front as well).
Just my $.02 based on my experience.
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There is a tire size difference in the 3.55 close to a 31" and the 3.73 which has close to a 32" tire. It is not a huge difference at the between the two at the final ratio. The 3.73 is a better choice if you ever think you might put on 33" tires or want to go with the 32" tires with the 3.55. These will kill your power, I have done it and regeared. If you plan to the 3.55 at stock I thought was a power killer which you will notice anytime you go up a hill. Go with the 3.73, and if you plan to go to bigger tires think about the 4.11. The cost to change gears is around 1500 for front and rear.