Stupid Tire Question
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From: Kansas City, KS
Stupid Tire Question
79 F150 4x4 351m. My first 4x4, so please forgive the dumb question...any particular reason that I would have 225s on the front and 235s on the rear?
That can't be right, can it?
Don't all four have to be the same size?
That can't be right, can it?
Don't all four have to be the same size?
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Not unless someone was trying to compensate for mismatched differentials.
In a 4x4 you want the front tires to be pulling the rear ever so slightly so normally the tires are the same and the gears are slightly different like a 4.10 in front with a 4.11 in the rear.
In a 4x4 you want the front tires to be pulling the rear ever so slightly so normally the tires are the same and the gears are slightly different like a 4.10 in front with a 4.11 in the rear.
Last edited by Torque1st; Nov 8, 2006 at 02:48 PM.
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From: Kansas City, KS
Well, I'm fairly certain that the rear end on this truck is not original. Suppose I should pick the whole truck up, put it in four wheel drive and use ropes on the drive shafts to find ratios?
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From: Nebraska
There is an easier way just jack the back up mark a spot on the ds like tdc then turn your wheel by hand if it an open diff if your tire turns say a lil over 4 times then you would have 4.10 or 4.11's then do the same for the front. That is 4 to 1 turn of your ds.
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From: Kansas City, KS
Originally Posted by Mil1ion
The main difference is in the 2nd tire reference.
70R ,75R,78R,80R
The 225-235 is the tread width.
70R ,75R,78R,80R
The 225-235 is the tread width.
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No,
I'm saying that if a 235 R75 and a 225 R78 are close to the same diameter.
or
There is only a 3% difference in diameter between the 235 R75 and the 225 R75
I'm saying that if a 235 R75 and a 225 R78 are close to the same diameter.
or
There is only a 3% difference in diameter between the 235 R75 and the 225 R75
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From: Delavan, IL
Mil1ion is correct. the 70/75/80 are a percentage or tread width.
225-75R15 = 225mm tread width [75% x 225 = 168.75 sidewall height] R15 < Rim diameter
168.75mm x 2(2 sections of sidewall) + 15" rim = 28.29" tire diameter
All in theory though. The rolling radius varies depending on width, material, weight per tire, etc, etc.
225-75R15 = 225mm tread width [75% x 225 = 168.75 sidewall height] R15 < Rim diameter
168.75mm x 2(2 sections of sidewall) + 15" rim = 28.29" tire diameter
All in theory though. The rolling radius varies depending on width, material, weight per tire, etc, etc.
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From: Kansas City, KS
Thanks for the replies...but I'm still confused. I've got a 4x4 with 225s on the front and 235s on the rear. Is it safe/wise to engage four wheel drive while I've got smaller tires on the front?
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From: Kansas City, KS
Originally Posted by DOUBLEF222
To Know What Ratio U Got Look For The Gear Ratio Tag Or Pull The Covers The Ratio Is Stamped On The Ring Gear
At the moment, I'm more just curious/ concerned about putting the truck into four wheel drive with two different sized tires on it...
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From: Nebraska
What you have is a Ford 9 inch so in your case the tag would on the front of the diff and if not you will have to drop your ds and pull the 3rd member out the front after you pull the axles out a bit so you can pull the 3rd member. Or do as posted earlier make two marks one on your ds and the other right across from it on stationary axle housing jack up the rear turn your tires and count how many times your tires turn to one rotation of your ds that will give you the gear ratio without taking it all apart.
More Turbo
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Running those 2 size tires shouldn't make a difference, unless you are driving on pavement in 4wd (which is bad). This could cause a slight bind in the transfer case. Off road, the difference in tire size is so minimal, that you could see the same difference if all 4 tires were the same, but had different air pressures in them. You have a ford 9" rear which doesn't have a cover. It has a removable 3rd member that unbolts from the front of the axle. This was the standard rear for a 79 150
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TC .....what's your axle code number.
Here's the scoop.
Normally a 4x4 has either: the same ratio gears in each axle
or
The front axles is different from the rear axle by a Min'ute amount.
ie:
F= 3.54
R= 3.54
or
Rear = 4.11
Front = 4.10
This is so the two axles are exactly the same in rotation as in ie 1
or
The front axle is being pushed by the rear axle in ie 2.
In your case,
Your rear tires are slightly larger in diameter and turn a SLOWER rotation than the front.
Which is the same as the offset ratio front to rear.
Tires on 4.10's rotate faster than 4.11's
You should be fine.
Here's the scoop.
Normally a 4x4 has either: the same ratio gears in each axle
or
The front axles is different from the rear axle by a Min'ute amount.
ie:
F= 3.54
R= 3.54
or
Rear = 4.11
Front = 4.10
This is so the two axles are exactly the same in rotation as in ie 1
or
The front axle is being pushed by the rear axle in ie 2.
In your case,
Your rear tires are slightly larger in diameter and turn a SLOWER rotation than the front.
Which is the same as the offset ratio front to rear.
Tires on 4.10's rotate faster than 4.11's
You should be fine.
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From: Gadsden Purchase
Cool thread. :) Learned quite a bit. :)
I have a friend that has a '65 Chevy 4 wheel drive he bought new that still has the original 4 wheel drive equipment in it. :) No big deal with tire sizes etc for that guy (dumb cowboy, heck he uses whatever tires he's got that'll hold air) he just doesn't engage the 4 wheel drive until he needs it then stops and disengages it as soon as he don't need it.
Simple as that. :)
What's your plan for your 4 wheel drive, TC? :)
Alvin in AZ (retired dumb railroader)
I have a friend that has a '65 Chevy 4 wheel drive he bought new that still has the original 4 wheel drive equipment in it. :) No big deal with tire sizes etc for that guy (dumb cowboy, heck he uses whatever tires he's got that'll hold air) he just doesn't engage the 4 wheel drive until he needs it then stops and disengages it as soon as he don't need it.
Simple as that. :)
What's your plan for your 4 wheel drive, TC? :)
Alvin in AZ (retired dumb railroader)