I am thinking of putting on a set of tires on my montero that will be two different sizes, on the front will be 50 series on the rear will be 55 series so the 55 series are probably taller by perhaps 3/4" max.

I normally only use the 4wd when it is snowey. Is there any danger to the 4wd system in this mismatch of tires?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

First questions: True 4x4 or AWD? Manual locking hubs or automatic? What disconnects the front axle drive, transfer case or axle disconnect?

While all these questions can make a difference, the best answer is still not to do it. Perhaps if you vary the width of the tires so that the overall height is still nearly the same, but frankly, that's a hassle, keeps you from ever being able to rotate them, and isn't really any cheaper. Why mess with it... Just do it right the first time.

MV

I'll assume a selectable 4WD system with only these transfer case selections available: 2HI-N-4HI-4LO. As you probably realize, selection of 4HI and 4LO will cause the transfer case to attempt to dictate nearly identical rotational speeds to the front and rear drive wheels. Your plan to install tires of a smaller diameter on one axle will mean that on a high-traction surface, some driveline "wind-up" or binding will occur. On a low-traction surface, the tires on at least one axle will periodically break traction and skip a bit to relieve the wind-up. Could that very brief break in traction occur at a bad time and cause a skid on a curve? Possible. Likely? Probably not. Would I install tires of differing diameters on a 4WD vehicle? No.

It is a truck I use pretty much only to push snow or on occasion other duties. if the pavement is dry i use 2h. yes it has 2h, 4h and 4low and neutral.

I am swithcing the tires off it for other use and have this set from my Miata which has a lot of tread left.

I am most concerned about damaging the center diff. I believe some of the old subies didn't actually have a center diff.

The Montero appears to have a nice hd solid rear axle and a proper transfer case.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Maybe you could put the 2 tires in the shed for now & once you have 2 more, do a full swap. I have broken a tail shaft on a 6WD road grader by putting lower profile tires on the front. Was not happy !! You dont need "wind up"!!

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Tom, if this truck does not have an AWD system usable on a dry road, it probably does not have a center differential. One of the purposes of the center differential in an AWD system is to act as a buffer (think of a briefly slipping clutch) between the front axle differential and rear axle differential, as even with tires of the same labeled size on all four wheels, some differences in tire rotational speeds occur between each tire while driving. With the buffer in play, the "wind-up" of driveline components will not occur.

That is likely correct. If you still have the owner's manual, and the manual cautions against driving in 4HI or 4LO on a paved dry surface, it definitely does not have a center differential, and the concerns discussed in this thread about using tires of mixed diameters on the Montero would apply.

I realize that you indicated the vehicle sees light use, but I would also be concerned that the Miata tires have insufficient capacity to accomodate the weight of a fully loaded Montero.

Well they will get it home and I can figure out what to do permanently later.

I may pull the tires from my utility traier and put them on the seldom used montero and get new tires for the utility trailer. I put the new tires on the Montero when I put in service because I thought I would be driving it on the highway. I think I did once so far to check the fuel economy or something. It is not a normal thing for me to do.

Thanks for the prompt and thoughtful replys!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Trailer tires dont belong on a truck. What size tires does the truck need?

I wont mismatch tires on a 4wd truck.

~Nate

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95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

The trailer does not have proper trailer tires.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.