Mismatched tires?

[Bruceifer]

Hi folks
I am new to tractor ownership and the forum.
I recently bought a 1996 Zetor 6340 (4x4) and am told it has the wrong size wheels on the rear.
When I look this up, every spec I can find on the internet says it should have 12.4-24 on the front, which it does, and 16.9-34 on the rear, which it does not, it instead has 16.9-30 on the rear.
The wheels all match and the tires also all math, all made in Check republic and are all weather cracked bad enough that they could be original. The 4x4 does appear to be working and in 4x4 the tractor will gently coast down a slight grade without disturbing the gravel.
Could anyone shed some light on this, is it possible some models had different gearing to accommodate this odd tire combination?

Thanks for your help.

 

[LouNY]

If it will coast on a slight down grade and not disturb the gravel,
I'd say your front to rear tire sizing is good.
Is that a manual mechanical front drive?
If so and it engages with no grinding or chattering while moving that would be another confirmation.

 

[Bruceifer]

Yes mechanical, haven’t tried that yet.
I will at some need to be certain about tire size, don’t want to spend $4000 replacing rotten tires and buy the wrong size. Haha

 

[90cummins]

If it will coast on a slight down grade and not disturb the gravel,
I'd say your front to rear tire sizing is good.
Is that a manual mechanical front drive?
If so and it engages with no grinding or chattering while moving that would be another confirmation.

Note; It must be in 4x4 for this coast test.
90cummins

 

[LouNY]

^^^^^
Yes, and actually I would recommend engaging and disengaging the 4wd drive while rolling to listen for gear grinding and ease of engaging and disengaging. And to see how much and sudden any speed change occurs as any binding will reduce the travel speed.
The tread disturbance can tell you which axle is turning the slower as it will be pushing the dirt ahead of the tire lugs.

 

[ROUSTABOUT]

Lift both ends of one side on jacks. Put in 4x4 with trans in neutral. Put a mark on top of front and rear tires. Piece of tape or whatever. Rotate tires a complete round and see how your tape looks in relation to each other then. Should be the same. Within a 1/4 turn is okay but no more difference than that. See how that looks and post back. I have the formula to figure tire sizes.