Different tire sizes question
Post Fiend
Joined: Jan 2005
Posts: 7,147
Likes: 0
When I drove around with different sized tires, they were 60's and 70's era cars, no harm no foul. I don't know how it would effect the newer rigs now that they have abs. speed sensors and wheel sensors, tire monitors and so fourth.
Thread Starter
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More Turbo
Joined: Feb 2006
Posts: 685
Likes: 25
From: East Central Indiana
I understand what you are saying (at least I THINK I do). Think of this whole thing like an equation.
you have driveshaft speed which equals 100%, then you have the 2 wheels that whose speeds add up to 100%, but it can change back and forth depending on how sharply you're turning in either direction. If you're going straight, it's 50% on each side.
So here's the equation under normal circumstances
Left tire speed + right tire speed = drive shaft speed
if you're going straight here's the values for the equation
left 50% + right 50% = driveshaft 100%
if you have a taller wheel on one side, it causes that axle to turn slower, which causes the other side to turn faster
left 40% + right 60% = driveshaft 100%
but, this is the same thing that happens when you turn. Which means either one side is going to spin some, or the other will drag some, or binding will occur and break something.
Please bear in mind that I am not trying to be annoying, or trying to prove anything, or mean or rude in any way. It's just that this makes 100% sense to me, and I feel you guys may not be understanding my thoughts on this.
If you still disagree with me after reading this, I won't press the point any longer, I promise.
you have driveshaft speed which equals 100%, then you have the 2 wheels that whose speeds add up to 100%, but it can change back and forth depending on how sharply you're turning in either direction. If you're going straight, it's 50% on each side.
So here's the equation under normal circumstances
Left tire speed + right tire speed = drive shaft speed
if you're going straight here's the values for the equation
left 50% + right 50% = driveshaft 100%
if you have a taller wheel on one side, it causes that axle to turn slower, which causes the other side to turn faster
left 40% + right 60% = driveshaft 100%
but, this is the same thing that happens when you turn. Which means either one side is going to spin some, or the other will drag some, or binding will occur and break something.
Please bear in mind that I am not trying to be annoying, or trying to prove anything, or mean or rude in any way. It's just that this makes 100% sense to me, and I feel you guys may not be understanding my thoughts on this.
If you still disagree with me after reading this, I won't press the point any longer, I promise.
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
I think you've got a solid grip on it, good man!
Now the thing is - IS THE AXLE on your truck limited slip or not? That's what we need to know.
If it isn't, then SURE! It may look funky, but you can get away with running odd sizes until you can get a replacement.
NON LIMITED SLIP AXLES are designed and intended for opposite wheels to run at different speeds, and they run like that constantly. They're built for it, and it's constant.
It doesn't hurt anything.
*To the best of my knowlege there is no sensor system installed in any Ford truck which eventually calls an error code that means:
"YO MAN! YOU TURNIN' LEFT WAY TOO MUCH - STOP IT!!!"
(For the Craftsman Truck Racing fans out there....)
Now the thing is - IS THE AXLE on your truck limited slip or not? That's what we need to know.
If it isn't, then SURE! It may look funky, but you can get away with running odd sizes until you can get a replacement.
NON LIMITED SLIP AXLES are designed and intended for opposite wheels to run at different speeds, and they run like that constantly. They're built for it, and it's constant.
It doesn't hurt anything.
*To the best of my knowlege there is no sensor system installed in any Ford truck which eventually calls an error code that means:
"YO MAN! YOU TURNIN' LEFT WAY TOO MUCH - STOP IT!!!"
(For the Craftsman Truck Racing fans out there....)
Last edited by Greywolf; Feb 7, 2008 at 04:38 PM.
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
Excellent - then you should be alright.
It won't handle as nice as it might - the brakes may pull to one side. But it will get you to work until you can match things up again.
(Braking force is 75% applied on the front tires, 25% applied at the rear)
The difference should be very marginal.
Based on that, putting the odd tire out on the front is a bad idea....
(Do you follow that?)
It won't handle as nice as it might - the brakes may pull to one side. But it will get you to work until you can match things up again.
(Braking force is 75% applied on the front tires, 25% applied at the rear)
The difference should be very marginal.
Based on that, putting the odd tire out on the front is a bad idea....
(Do you follow that?)
Last edited by Greywolf; Feb 7, 2008 at 05:15 PM.
Thread Starter
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More Turbo
Joined: Feb 2006
Posts: 685
Likes: 25
From: East Central Indiana
once again, not to argue, but while the bigger wheel may pull to that side when braking, it also has more leverage in resisting the brake. So it may sort of equal out.
But let's not get started on that, my head's already hurting...lol
But let's not get started on that, my head's already hurting...lol
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Elder User
Joined: Jan 2003
Posts: 586
Likes: 1
you can run one size off for a shorter period of time. like weeks or months, just not years. This is how they can get away with the mini-spare.
On the front, yes, you may feel a slight pull to the small tire side, but nothing more than if you were down a few lbs. of pressure on one side. Or even on a road with a steep pitch towards the shoulder. I suppose you could run the small tire at 35 psi and the taller tire at like 29 and they'd be pretty close, while still at a safe air pressure setting.
Also, if the 195 is pretty worn and the 185 is almost new they will be pretty close. The tire gets shorter as the rubber wears off.
On the front, yes, you may feel a slight pull to the small tire side, but nothing more than if you were down a few lbs. of pressure on one side. Or even on a road with a steep pitch towards the shoulder. I suppose you could run the small tire at 35 psi and the taller tire at like 29 and they'd be pretty close, while still at a safe air pressure setting.
Also, if the 195 is pretty worn and the 185 is almost new they will be pretty close. The tire gets shorter as the rubber wears off.
Thread Starter
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More Turbo
Joined: Feb 2006
Posts: 685
Likes: 25
From: East Central Indiana
I could see it pitting chrome or aluminum rims maybe, but would it do it to steel?
I got the tire put on, it actually seems slightly smaller than my stocks. It does seem to pull ever so slightly to that side.
Thanks for all the help guys.
I got the tire put on, it actually seems slightly smaller than my stocks. It does seem to pull ever so slightly to that side.
Thanks for all the help guys.