What's my ratio?
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What's my ratio?
I have a '92 F-250 4x4 supercab with a 5.8 Litre engine and Electronicly controlled 4 speed automatic transmision (E4OD I think)
I would like to know the axle ratio to aid me in a decision about what tire size to go with.
The Axle code given on the sticker in the drivers side door is 'C9'.
I have looked in the owners manual but this code is not listed. However I have noticed that all of the codes that end in 9 are 3:55 ratio whereas all the codes that end in 5 are 4:10 ratio.
The rpm's @ 100km/hr (60 MPH) are about 1650 with the overdrive on the transmision engaged. The tires are 265/75/16.
I know it is not likely but I am hoping that the ratio is 4:10 rather than 3:55 as I would really like to increase the tire size to 335/75/16 (same height as 35" I think). Would It be possable to run the 35's with the 3:55 axle ratio or would I just be lugging the motor too much? Also does that axle code tell whether or not it is a limited slip rear end?
I would like to know the axle ratio to aid me in a decision about what tire size to go with.
The Axle code given on the sticker in the drivers side door is 'C9'.
I have looked in the owners manual but this code is not listed. However I have noticed that all of the codes that end in 9 are 3:55 ratio whereas all the codes that end in 5 are 4:10 ratio.
The rpm's @ 100km/hr (60 MPH) are about 1650 with the overdrive on the transmision engaged. The tires are 265/75/16.
I know it is not likely but I am hoping that the ratio is 4:10 rather than 3:55 as I would really like to increase the tire size to 335/75/16 (same height as 35" I think). Would It be possable to run the 35's with the 3:55 axle ratio or would I just be lugging the motor too much? Also does that axle code tell whether or not it is a limited slip rear end?
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I was afraid of that...
It sounds like I am gonna have to swap the gears then.
So what would you recomend? I plan to tow a boat and possibly have a small camper as well. Would 4.10's be low enough or should I go even lower?
The truck has a lot of miles on it and the 5.8 is not exactly a power house even when new. I am going into this expecting to have to re-build the motor in the next year or two. When I do that I will probably go with an RV cam and maybe some work done to the heads to boost the power output and make a little more torque in the lower range.
It sounds like I am gonna have to swap the gears then.
So what would you recomend? I plan to tow a boat and possibly have a small camper as well. Would 4.10's be low enough or should I go even lower?
The truck has a lot of miles on it and the 5.8 is not exactly a power house even when new. I am going into this expecting to have to re-build the motor in the next year or two. When I do that I will probably go with an RV cam and maybe some work done to the heads to boost the power output and make a little more torque in the lower range.
Posting Guru
Joined: Dec 1999
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From: Copley, OH
Well the stock tires on an F150 are 29." IIRC on the f250 they're 30." Yours are 31.6."
To get back to the equivalent of stock performance with the 335/75-16 (35.7") you'd need to go to
3.55 * (35.7/31) = 4.08. I certainly wouldnt go smaller than 4.10 and I'd seriously consider larger if you tow or haul a lot.
To get back to the equivalent of stock performance with the 335/75-16 (35.7") you'd need to go to
3.55 * (35.7/31) = 4.08. I certainly wouldnt go smaller than 4.10 and I'd seriously consider larger if you tow or haul a lot.
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Joined: Nov 2003
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From: Hallettsville, Texas
You can also look for a metal tag bolted to a cover bolt on your rear axle to find your ratio, if it is still there. It should tell you what your ratio is. Ex; 3.55 = open carrier, 3L.55 = Limited Slip. Same goes for the 4.10 ratio. I have an `86 truck that has the original gears from the factory in it. Door tag shows C5 which equals to 4.10 w/limited slip but my tags on front and rear axles show 3L.55. In actuality, the truck has 3.55s w/limited slip. Your C9 should be the 3L.55 but I would check the tags. Sounds right with the rpms you are turning.
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Joined: Dec 2002
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From: USA
With 35"-36" tires in that heavy truck with a smallblock, used for towing, I would go all the way to 4.56 gears. I'm running 4.56 w/ 33's in my '92 F350 Crew Cab 4x4 351 and it is a major improvement in power from the 3.55's that were in the truck stock. Since you have an overdrive trans, 4.56 will still be very comfortable on the freeway with 35" tires. I have a C6, no overdrive, so I go pretty slow on the freeway, but if I had an overdrive gear, the setup would be perfect for me. I know what you mean about the 351 not being a real powerhouse. In our heavy trucks, it needs some gearing help for towing.
You could even go to 4.88's with overdrive and 35"-36" tires, but you will lose a little freeway speed and unloaded gas mileage there. I actually get better mileage now under most circumstances (except cruising on the freeway unloaded over 60mph) with the 4.56's than I did with the 3.55's, especially on hills and when loaded. Better gas mileage, and more power, can't beat that
.
You could even go to 4.88's with overdrive and 35"-36" tires, but you will lose a little freeway speed and unloaded gas mileage there. I actually get better mileage now under most circumstances (except cruising on the freeway unloaded over 60mph) with the 4.56's than I did with the 3.55's, especially on hills and when loaded. Better gas mileage, and more power, can't beat that
.
Last edited by SoCalDesertRider; Mar 22, 2004 at 10:07 PM.
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I likes the sound of that!
"Better gas mileage, and more power, can't beat that."
Thanks SoCalDesertRider, I think I now know how I am going to explain to my wife why I need to spend all this money on my truck...lol
Do you find that the 35's are alot noiseyer than simialarly treaded smaller tires? The truck already has BFG All Terain TA's and they don't seem to be very noisey at all, so I will probably stick with the same in the 35's.
Thanks SoCalDesertRider, I think I now know how I am going to explain to my wife why I need to spend all this money on my truck...lol
Do you find that the 35's are alot noiseyer than simialarly treaded smaller tires? The truck already has BFG All Terain TA's and they don't seem to be very noisey at all, so I will probably stick with the same in the 35's.
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Joined: Dec 2002
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From: USA
LOL. Good luck selling the idea to the wife 
I spent about $1650 on my gear change + locking rear diff, but to me it was worth every penny.
I have 33" BFG All Terrains on mine, and they are very quiet and well mannered on the street. I haven't run 35's on this truck but on my old Chevy I had some 35's, I think they were Goodyears, they were an all-terrain tread anyways and I didn't notice that they were all that noisey. If you keep the tire pressure high on the highway, the 35's should be descently quiet.
I spent about $1650 on my gear change + locking rear diff, but to me it was worth every penny. I have 33" BFG All Terrains on mine, and they are very quiet and well mannered on the street. I haven't run 35's on this truck but on my old Chevy I had some 35's, I think they were Goodyears, they were an all-terrain tread anyways and I didn't notice that they were all that noisey. If you keep the tire pressure high on the highway, the 35's should be descently quiet.
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