You can run any tire size you want as long as your drive the rig accordingly.
Even if I have 29" tires and a crawler, I could break stock Birfields all day long if I allowed the truck to hop with the wheels pegged to the turning stops.
Remember that Toy 8" birfields and Dana 44 axles were originally only intended with 27 or 29" tires from the factory (and you wonder what Toyota was thinking when they offered 31s on IFS SR5 package trucks
), so when people go 33, 35, 37, etc. they have to realize the actual physical limitations of their truck.
That's cool that you have the amazing longs in there. If he is right and they are about the equivalence of a D60, then Im sure 38-40 and up tires should be jus' fine but now you will be breaking other things if you really tried to. If you remove the birfield "fuse" and run the stronger axle's which is another missing fuse, then what's next? Sure the stubs on the longfields are what is failing, but that's on a dyno bench and not in a practical rear world condition. Are you going to brake a hub? Bend the housing? Break a knuckle? Blow a pinion? Rip the third member out of the housing because it only has whimpy 8mm bolts?
I know we all try to drive our trucks for what they are worth, but just to toss the idea around a bit more, My truck is using stock birfields with some *temporary* bald 33s underneath a tripple overkill
Crawler with a 510:1 Crawl ratio. And when I was at the hammers, there were a couple of times where I had to peg my wheels to make a corner, and I know that this is the worst possible situation to be in so I was careful not to push so much torque while I had my wheels turned so sharp.
And this is what I believe is the practical aspect of tire size.
It's not what practical size you run, but rather how practical you are with the size of tires you've got. I'm sure someone with stock birfields could run 40s if they knew how
not to break parts. Maybe that's not very practical, but the driver can be.
Hey check out this cool *very old article* I wrote along time ago for our webpage back when our Marfields first came out..
Sorry its pretty elementary, but just go along with it
Birfield Information A Birfield joint. So what makes this part so significant on my Toyota truck? Well, without it, power to the front wheels would not be possible while turning. So what's special about this joint? Well a Birfield joint is a true 100% constant velocity joint. Unlike a Universal joint, which vibrates and spins with unequal power transfers, a Birfield joint produces an ultra smooth and constant transfer rate of torque. This makes for a smooth operation with less stress on the axles. Then why do Birfield joints fail? A Birfield joint, like the Universal joint found on a Dana 44, fail because from the factory, it was only intended to turn 29" tires. And we all know that a tire size greater than 29" is a definite requirement on the trails.
33-inch and greater are most common on the trail today. And with the lower gear ratios needed to spin these huge tires slowly comes a lot more torque to pass through each Birfield joint. Someone might say, "But I've got 33" tires and I have never broken a Birfield joint." 90% of the time, Birfield joints fail when the vehicles wheels are turned all of the way to the steering lock, and maximum torque is delivered to the joints. Consider yourself lucky.
 | Shown in the sketch to the left is a Toyota style Outer and Inner Axle assembly (the outer axle being the Birfield). Sketched first is an axle and joint positioned at 0 degrees, or straight. At this point, maximum torque can be transferred through the Birfield with the least possibility of joint failure.
But below it, is an example shown at a maximum steering angle. This is when the torque transfers are carried to the outer most ridge of the unit. It is here where a failure is most likely to occur. And since torque figures are * greatly increased with lower gearing, joint failures become more and more common.
*139% more torque with a differential ratio of 5.71:1 compared to a 4.11:1, and 300% more torque when comparing a stock crawl ratio of 36:1 to a moderately-advanced crawl ratio of 108:1. |
BigMike
