Tires and transmissions

[Eric Wettschreck]

I went to get some newer, more aggressive tires today for my 91 chev. This is a truck I recently upgraded from my 89 chev.

I wanted a little taller and skinner tires so I can get through the snow better. Tire dude told me the last thing I want to do is put on a taller tire due to the 700r4 tranny in the truck. He said these trannies don't like taller tires and I should stick with the manufactures specs. He said skinnier is fine but don't go taller.

Background- tire dude is a friend of mine, wouldn't steer me wrong, and I didn't buy anything from him. Also, a few years ago I roached a tranny (700r4) doing the back and forth thing in deep snow trying to get un-stuck. Yeah, I'm sure I got it real hot so I won't blame tires, I'll blame myself. Let's just say I put my right foot into things and no doubt the tranny got pretty darn hot.

So, the question I have is............is my friend the tire dude off his rocker saying don't put taller tires on this truck or are we all on crack?????

[Macgyver55]

Any idea what the gear ratio is in the differentials?

[Tom7227]

If you are going to spend the money for new wheels and tires it will get a bit spendy, might be better off putting that dough towards a newer truck.

If all you're going to do is come up with a tire design that has more sidewall then I have to wonder if that extra half inch of clearance is really going to make that much difference.

I heard the same thing from a tire shop when I was thinking about taking a couple of new tires from an old truck and putting them on a new truck. I think it was going from a 15 to a 16 or viceversa.

[Eric Wettschreck]

Any idea what the gear ratio is in the differentials?

Not a clue.

[Gordie]

When you go taller Eric it takes more power to get them rolling to full speed and that is what puts the stress on the transmission, I did the same thing on my 89 suburban and fried the 700r4 so I upgraded, so to speak and had a turbo 350 rebuilt for it, and never looked back. That is not something you can do because of all the electronic do hickys on those newer trucks.

If you gear your trucks differentials to a lower gear it will be easier on the tranny because it will not have to work as hard to get the power to the tire.

I would stick with what they say for the tire size if you have a 700r4 tranny.

I'm not a big fan of those trannies because of the Overdrive in them I think that is what makes them weak.

[Macgyver55]

If you were to have the 3.73 it probably wouldnt be as much of a problem. But those trucks were built back when horsepower was down and trying to get mileage was becoming more important so many of them came with a 3.08 ratio (I believe) Putting a taller tire on that is like having an even higher ratio than that which is pretty much asking for trouble. The only other thing you can do is not use OD when pulling but its not a cure-all by any means.

My advice would be to stay with stock size but to find a tire highly rated for traction.

[Eric Wettschreck]

Thanks guys. For the record, this isn't my everyday driving machine. I doubt I'll put 1000 miles on it this year, and I can get my tires pretty darn cheap.

Having spewed out all that, sounds like I'll be sticking to stock size and getting something really aggressive. I'll put the ones I have on now back on in the spring. I really don't feel like replacing a tranny. Been there, done that, don't like it.