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4.56 gears with 31" tires sucks


gw33gp

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I recently upgraded my off-road tires to 33" and installed 4.56 gears to work with the taller tires. I run 31" tires for daily use and towing. I knew the 31'" tires would be far from idea with the 4.56 gears but thought it would still be reasonable.

Back and forth to work on So Cal freeways, I typically drive around 80 to keep up with traffic. At 80 mph my speedometer is reading 90 mph and that means I am right on the edge of the speed cutoff and the engine is at the shut down point if I happen to go any faster. I can even feel a slight vibration that normally starts at around 90 mph which I think is a resonance in the driveshaft that gets bad when approaching 95 mph.

I do have a re-flash on the computer that raises the speed cutoff and I can have the speedometer recalibrated but that doesn't change the rpm of the driveshaft at 80 mph. It looks like I am going to have to slow down a little on the freeways when I have these 31" tires mounted and just learn to stay out of the way for faster traffic.

It will make towing easier and I only run about 72 mph when towing so no problem there.

The 31" tires w/ 4.56 is probably going to hurt my gas mileage also. All in all it pretty much sucks.
 


alwaysFlOoReD

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-So get taller tires.
-Try a trade on craigslist or buy used.
-Just drive slower. There's nothing wrong with driving slower than general as long as you are aware of traffic and let people pass safely.
 

bobbywalter

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you may need to shim the springs or trans mounts a bit to help with the vibe at speed unless it simply needs a high speed balance. then again you may be at the rpm limit for those particular rear shafts.

easy button is a used set of 33 in radials like mentioned.


i have to run 37's on my ranger to highway cruise with mere 410 gears due to the diesels primary powerband. ideally i would have 350 gears and 33 in tires for the street and a nice doubler for off road when using bigger tires...but i cant bring myself to spend the money on factory offered gears.

the tires were the simplest and cheapest solutions. i am sure your gear swap was much more then used tires.
 

gw33gp

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Yes, I know my options but I could not find decent street tires in 33" or 32" when I bought the 31" tires about 15K miles ago. I didn't want to run MT tires all the time due to the excessive noise. I didn't realize the BFG MT KM2 were relatively quite or I would have just bought them then and ran them all the time.

If I wanted to sell the 31" tires now, I would lose a lot of money on them so I will just continue to run them until the tread is low enough to get rid of them. I will just have to learn to drive slower.

From what I understand the resonance is inherent in the driveshaft and that is one of the reasons Ford governs the speed to around 92 mph. That and driving a truck at much higher speeds is not very safe.

I am just pointing out some of the drawbacks to running 4.56 gear w/ 31" tires for anyone considering that combination.
 

alwaysFlOoReD

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It's always good to have real world experience reviewed on site,
Thanks.
 

delta.tango

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This may be a bit of a hypothetical question, but do you think you would be happy with your 4.56 gears if you were running 32" tires? For whatever reason, 4.10 gears for the D35 seem to be twice the price of 4.56...
 

Mickey Bitsko

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gw33gp...
You've had your 4:56's for a couple months now, How you liking them with 31's or 33's?
I'm going to oder my 4:56's this week , but I'm gonna hold off on the tires till I get more info on the best on hiway size..make/model

Thanks..
 

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I have 4.56 gears and 29's (235/75R15) and I love them. Then again, I have a 4 cylinder and 80-90 mph never happened even before the swap lol. 70 mph tops, 3000 rpm in overdrive. It's not as bad as it sounds, and my mileage actually increased across the board.
 

Mickey Bitsko

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I have 4.56 gears and 29's (235/75R15) and I love them. Then again, I have a 4 cylinder and 80-90 mph never happened even before the swap lol. 70 mph tops, 3000 rpm in overdrive. It's not as bad as it sounds, and my mileage actually increased across the board.

That's what I like to hear:yahoo:
 

gw33gp

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I have gotten to like them a little better. Acceleration is awesome but I have to be careful with that because it really sucks up the gas. On the freeway I was used to going 80 mph. The truck is not as comfortable with that so I have dropped to 75 mph and that is not so bad. Gas mileage around is still 1 to 1.5 mpg less than it was with the 4.10 gears. I think I just need to learn to short shift with the 4.56 gear and I may be able to gain back some of that mileage.
I am looking forward to my next off-road trip with the 33" MTs. I think I will be very happy the 4.56 gears then.
 

Captain Ledd

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That's what I like to hear:yahoo:
I like to use the analogy that the 2.3L 4 clyinder @ 3000 rpm should be comparable to a 4.6L V8 @ 1500 rpm. When it's put in that context it doesn't sound bad at all, and it's actually fully in the powerband of the engine.

Deep gears are fantastic if you don't need to go really fast. If you can stand 70 or less, err slightly on the deeper side of your gear choices.
 

Sasquatch_Ryda

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With my 97 with the 3.0L and 5spd I had 4.56's in it. Ran 33's in the summer and 265/75r15's in the winter (31" tire) it was perfect with the 31's and I felt it needed more gear with the 33's (the 3.0L likes to rev tho)
 

Mickey Bitsko

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gw33gp: Alrighty, Got my 4:56's in and love them, My power is a 4.0 ohv, a/t 65mph is 2500rpm's not too bad, I don't feel good about going that rpm for 200-300 miles , so , I will go to taller tires this summer. All that being said, what tire, make/model did you go with, are you happy with them and did you get your hiway cruising speed back ?
Thank you
 

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