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View Full Version : different size tires on front and back of a 4x4


tomtoc
02-17-2009, 08:32 AM
i know it's not ideal, but it's just for a couple months. i don't plan on using 4 wheel drive at all. am i right that if i NEED it for a short distance on slippery ground, it'll be fine.

i'm talking a snow covered gravel driveway, muddy trail, etc.

front 265's ~ 29.5"
back 235's ~ 28"

not ideal, but you'll be fine
-or-
you're an idiot

UTfball68
02-17-2009, 08:39 AM
Alright...I dunno what the metric numbers convert to...but I will say, if you can keep the tire height difference around 1" you should be fine...like you said, not ideal, but liveable. I mean hell, there's some guys out there who have that much tread wear difference between front and rear...haha. Just remember, don't force anything, or if you feel any binding...get out of it.

Skandocious
02-17-2009, 10:41 AM
Tom I'd really advice against doing so unless you REALLY need to... Even on snowy gravel/pavement-- if those tires all get traction for even a couple seconds you could do do some damage...

Bricks
02-17-2009, 10:56 AM
I wouldn't do it, slippery surface or not. Too much to lose.....

SuperCab
02-17-2009, 10:59 AM
are 265s and 235s that much of a difference?

What size are they?

I'm thinking of 265/75/R16 and 235/85/R16, which are both nearly identical in size, IIRC

tomtoc
02-17-2009, 11:05 AM
235/70/R15
265/70/R15

pretty sure they're about 1.4" different

O'Rattlecan
02-17-2009, 11:21 AM
you sure the smaller one is that size? Is it 235/75/15? If it is, they're about an inch different. If your numbers are correct... I wouldn't do it.

Ryan

Skandocious
02-17-2009, 11:28 AM
Just as future reference for the people who do not know-- with metric tire sizes, the first number does not give much indication about the DIAMETER of the tire without giving us the latter 2 numbers also....

The first number is how many millimeters WIDE the tire is. The 2nd number is the size of the sidewall of the tire in units of "percentage of width". So a 265/70 tire has 265mm width, and (.70)(265) = 185.5mm sidewall; which equates to 7.30 inches. Multiply that times 2 and add the diameter of the wheel (third number) and you get (7.3)(2) + 15 = 29.6" diameter

Of course you can do all this math or just use online tire size converters :p


Normally I $$$$$ about how our jacked up system of units in the US sucks-- but this is the one case where I think the metric system really blows. Giving the tire diameter in inches seems so much more logical...

Skandocious
02-17-2009, 11:48 AM
And by the way-- they are 1.64" inches difference in diameter-- I just ran the calculations.

UTfball68
02-17-2009, 11:53 AM
And by the way-- they are 1.64" inches difference in diameter-- I just ran the calculations.



Well if that's the case...then tomtoc, I wouldn't consider running 4x4 at all. The absolute max I would even consider engaging 4x4 is no more than 1" difference, and I personally probably wouldn't go over .5-.75".

tomtoc
02-17-2009, 11:54 AM
you sure the smaller one is that size? Is it 235/75/15? If it is, they're about an inch different. If your numbers are correct... I wouldn't do it.

Ryan
i think he's right *75* not 70 on the old ones. the new ones are 70.

was going off memory and not actual tire size. i think the new ones were a different %. sorry if that messes up the whole thread :)

Skandocious
02-17-2009, 11:56 AM
That would make .724" difference between the two...

So the correct tire sizes are:
235/75/15
265/70/15

?

tomtoc
02-17-2009, 11:58 AM
That would make .724" difference between the two...

So the correct tire sizes are:
235/75/15
265/70/15

?
correct - massive confustion, sorry

EDIT: if a mod/admin is bored, they can clean up the old/irrelevant posts mentioning old tires sizes and inch difference based on wrong values

UTfball68
02-17-2009, 12:03 PM
That would make .724" difference between the two...

So the correct tire sizes are:
235/75/15
265/70/15

?


Chris...thanks for clearing up how to figure up what the tire size actually is...I never knew how to figure it before. And I got the same numbers you got...so in my book, I say go for it...only in extreme cases though.

CowboyBilly9Mile
02-17-2009, 12:04 PM
Using the numbers (in inches) you gave in your first post, that works out to a 5.1% difference (assuming 29.5 >>28). The difference in the lineal distance traveled (straight travel, not a curve) between the two works out to ~4 3/4" per rev. I feel that it goes without saying that this is not going to be good on drive train components and not a smart thing to do. Will it break anything or shorten the life of it? The jury is out on that one for now. Personally, I wouldn't do it, but if you must, then reserve it for solid ice or usage after you get stuck.

*I can't help but wonder what the numbers look like for a vehicle that has four shoes of the same size, 4X locked, and the vehicle is making a sharp turn...........

**FYI - the difference between 1.5" and 1.64" will not significantly change the outcome of the above numbers.

tomtoc
02-17-2009, 12:07 PM
*I can't help but wonder what the numbers look like for a vehicle that has four shoes of the same size, 4X locked, and the vehicle is making a sharp turn...........
good point - hadn't considered that that scenario would be similar

although...is that more side to side (axle) tension than front to back (driveshafts/t-case)

CowboyBilly9Mile
02-17-2009, 12:12 PM
Different turning radii will equate to different distances traveled between the tires on the front/rear axles; this is, why they "buck" with 4X engaged and the vehicle is on dry pavement (or any surface where moderate traction is gained). The thing is, what percentage of a vehicles life, or for that matter an average trip, is spent turning?

*I can create bucking on ice while turning (sharp turn @ ultra low speed), proved that again yesterday and I will again today. And I can't say I like it much either.

tomtoc
02-17-2009, 12:16 PM
The thing is, what percentage of a vehicles life, or for that matter an average trip, is spent turning?
agreed - and is that percentage any different than the off chance that in the next month or two i'll need it for 50 feet getting up my gravel driveway.

reading my past posts, i don't mean to come across as stubborn, or unwilling to accept an answer, just want to make sure we have all the facts right before saying "NO WAY". i hate when 100 people tell someone NO and they refuse to accept that. let me know if you think i'm that guy

CowboyBilly9Mile
02-17-2009, 12:37 PM
agreed - and is that percentage any different than the off chance that in the next month or two i'll need it for 50 feet getting up my gravel driveway.

reading my past posts, i don't mean to come across as stubborn, or unwilling to accept an answer, just want to make sure we have all the facts right before saying "NO WAY". i hate when 100 people tell someone NO and they refuse to accept that. let me know if you think i'm that guy

No, you're not being stubborn, you're just being like me is all. You want good answers. But what we the readers don't know is what your driveway situation is or how you will drive it if you start to slip; this is why I won't say "go for it, no biggie".

.............Will it break anything or shorten the life of it? The jury is out on that one for now. Personally, I wouldn't do it, but if you must, then reserve it for solid ice or usage after you get stuck............

I'll stick by that. Like I noted, there is a maneuver that I take a handful of times every week that requires using 4X with the wheel nearly cranked. I cringe when I do this because I know it's not good, I know it's hard on equipment, but I don't think it's going to grenade anything. I also think it's sucking a little bit of life out of it each time it happens. I also know my drive train is sound with 53K miles on it and I haven't severely abused it so I don't think I'm compromising reliability that I enjoy when out in the middle of nowhere and the doing get's rough. Come another 100K and it'll be someone else problem, I don't care, I'll go buy a new one.

*Tires that have tread that make it harder for them to slip that needed amount will add to the concern, as will surfaces that add traction.

UTfball68
02-17-2009, 12:37 PM
I personally think you'll be fine IF you use 4wd extremely sparingly and ONLY in the most extreme conditions. But that's just me...I highly doubt you'll have any catastrophic failure in the next 2 months if you engage the tcase for 50 feet...even once a week.

Skandocious
02-17-2009, 01:02 PM
Disclaimer: Whatever you decide to do-- don't come back blaming us saying "you guys told me it would be okay!!" :p Just wanted to put that out there :D

tomtoc
02-17-2009, 01:04 PM
Disclaimer: Whatever you decide to do-- don't come back blaming us saying "you guys told me it would be okay!!" :p Just wanted to put that out there :D

:) got it.

thanks, guys. i'll keep it out of 4x4 unless absolutely necessary, and bump the matching set of tires higher up on the list.

LEB Paul
02-17-2009, 01:30 PM
You'll be fine if it's low traction. Guys run staggered sets at mud bogs all the time. Hell I ran 36 on the front and 39 on the back of my bronco last year at one race. So- if you're an a situation that actually requires 4 wheel drive then use it all you want and don't worry about it.

Mike C.
02-17-2009, 06:27 PM
I did this same thing with tires on my F150 4x4 and it got real hairy at times. I had studded tires as it was during ice and snow storm. Not good as I am no youngster, 62.

LEB Paul
02-17-2009, 06:47 PM
Oh and if you're really concerned about it you can put the bigger ones on the front because a taller tire will spin faster and "pull" the truck along. This would look pretty silly though and put more stress on the TTsuck

cipsmithers
02-28-2009, 02:40 PM
After buying the new tires, I am considering running different ones this summer, as to not wear the good ones out when im not gunna be doing much offroading. I figured if it was a huge difference, Id take the front drive line out, just so Im not tempted. But id never do that in the winter.

surewhynot
02-28-2009, 03:57 PM
If you have to lock it in, pay close attention to how it feels. If you feel it starting to bind, take it out before you break something. I had a set of swampers on a mud truck that gave me troubles. I bought them used and the fronts had about 25% tread while the rears had about 75%. That was enough size difference to make it bind up now and then.