Decisions.....Decisions.....35's or 37's??

Thunder_God_69

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Hey guys, I'm new here. I am really curious as to what most of you will think in regard to my tire size question. I have a 1988 F350 with the 7.3 IDI.....it is stock, so no turbo. I have been restoring the truck, and am about to do some Alcan offroad leaf springs front and rear. They will be a 3" lift in the front, and a 2" lift in the back. The truck would easily fit 35's now with no issues, I am currently running 33's with LOADS of room to spare. The truck is a manual ZF5 with 3.55 gears. I have thought about changing the gears to something more aggressive, but honestly I don't use the truck to tow, and the most it ever hauls is a load of firewood. Also, the 3.55's make it really nice to drive on the road.....I can roll along at very respectable speeds, and the motor is not screaming. With even bigger tires.....it will be even nicer once cruising, in my opinion, cause the motor will be at even lower RPM's.....and if I hit a hill it can't pull, I can always just grab another gear. Now I have done the calculations, and going to 35's will lower my RPM's around 100, 37's will lower them around 200.....pretty much across the board. I did the calculations in 4th gear 1:1 and in 5th gear .77:1.....I honestly think that the truck would still be fine with 37's.....it still has a lot of low end torque, even with no turbo, and 1st gear is sooooo low, that I don't think it will affect it much off the line. I do have 150 acres of land, and that is where it would shine.....in first gear, and low range.....tire size will not be an issue, lolol.....it is unstoppable with the gear reduction it seems. Anyway, I would really like some input on this, as my leaf springs will be in soon.....and once I put them on, I'll be buying the new tires for it. Thanks in advance for any advice you can give me.
 
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Clb

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Well.....
deep subject yea haha


Anyhow, here's my .02 from a different outlook.

my yota rockcrawling rig is at 175:1 final drive on 31" tires
( stock was 28" ) running 410:1 r\p.
First gear low range ,under, it would do 1.3 mph at redline crawling.
It would cruize the hwy in 5th at 80 easy pulling around 3 k rpms....
stepped it up to 35" tires, it basically lost 5 th gear and leaving a stop requires a touch of finess.
Now offroad I can still get out and walk it over stuff at idle but its much less "stout" than it was.
The extra mass takes some engine away the 7.3 vs my 2.4 you win but will see some Drive ability issues me thinks.
should be ok shy of the loss of grunt with the bed full.
 

u2slow

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My experience with 35's is they just kiss the springs at full steering lock. I think 37's would grab quite a bit more.
 

Thunder_God_69

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You guys make some good points.....perhaps sticking with 35's will be a better bet, I honestly don't think I'll notice a difference at all going from the 33's to the 35's. Also, I don't think it will rub at all either, being that my new leaf springs will be providing 3" of lift.
 

Black dawg

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As bad as the first and reverse ratios suck in these transmissions, (especially with 3.55)...........

I had 35s on mine for awhile, and it was ok......kinda......until I would actually use it as a truck, and then it pretty much sucked. And this was with 4.10 gears.
 

u2slow

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You guys make some good points.....perhaps sticking with 35's will be a better bet, I honestly don't think I'll notice a difference at all going from the 33's to the 35's. Also, I don't think it will rub at all either, being that my new leaf springs will be providing 3" of lift.

In case its not clear, lift doesn't increase the spring vs tire clearance. My F350 rubbed the leafs with 4" lift and 315/75R16 on fairly neutral-offset 8" wide wheels.

EDIT: pic for reference
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Thunder_God_69

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My current wheels are a -12 offset.....and my 33's are WAY far from my springs at full lock
 

Thunder_God_69

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In case its not clear, lift doesn't increase the spring vs tire clearance. My F350 rubbed the leafs with 4" lift and 315/75R16 on fairly neutral-offset 8" wide wheels.

EDIT: pic for reference
You must be registered for see images attach
What year is that truck.....looks like early 90's to me.....in doing my research it seems the older trucks had more generous amounts of room for bigger tires.
 

u2slow

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95. leaf springs are in the same place. Tire/body contact was never an issue. It fit skinny 35's at stock height.
 

Thunder_God_69

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95. leaf springs are in the same place. Tire/body contact was never an issue. It fit skinny 35's at stock height.
Well, maybe I'll kick the wheels out a bit farther.....I am running -12 now.....maybe I'll go with like -25 or like -38
 

Clb

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Wadda#$%@ is -12 ect?
Backspace is what moves the wheel away from the engine bay and hub...
 

Thunder_God_69

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Wadda#$%@ is -12 ect?
Backspace is what moves the wheel away from the engine bay and hub...
I am referring to the offset.....and the two are directly related.....the higher the - the further away from the suspension.....the higher the + the closer.
 

u2slow

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Offset has little meaning without knowing the wheel width (i.e. to determine total backspacing).

The more negative offset you have, the greater the swing of the tire, and more chance of hitting the fender fore and aft.

EDIT: I imagine there's some variability in where your steering stops are set at. I never touched mine. With a long crew, I didn't want to steer any less sharp either LOL
 
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Thunder_God_69

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Offset has little meaning without knowing the wheel width (i.e. to determine total backspacing).

The more negative offset you have, the greater the swing of the tire, and more chance of hitting the fender fore and aft.
My current wheels are Backspace 4.500.....Offset -12.....Diameter 16.....Width 8

I will be going with Backspace 4.500 or possibly 3.750 or even 3.500.....Diameter will be 17, and Width will be 9.....I am not sure what the offset will be yet.....but if I go with the 4.500 Backspace they are -12.....if I go with one of the others I'll have to check and see what they are.
 

Thunder_God_69

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I feel like if I stay with 33's on 3" of lift.....that it is going to look really stupid
 

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