Tire inflation on '78 Suburban, and leaf springs to keep back end up?

[Shareen]

Hello fellow oldies!

I have a '78 that I use for basically nothing except towing horses. I recently had some trailer tire issues so asked my friend in another state about what to do about that since that is her family's business. Besides the advice on what tires to get on that, I asked her how much to inflate the tires on the Suburban. It goes up to 80 psi, and it's so old, there is no plate on the door that says what it should be. It says look at the certificate. Ha! I've had them at 50 because thats what the tire pros said to do. She said go about 75 and that a lot of tire pros do less because they wear the walls faster. What is the way to go?

I was thinking more would be better because the back end sags when I have horses in the trailer.  On that line, it does ride low behind with horses. Would it be a good idea to install some heavy duty leaf springs back there to keep the back end higher?

It's an old park vehicle because it was light green when I got it, and it only has 5 digits on the odometer, so could have close to 3 or 400000 miles on it. It's a 350 3 speed with a granny low that makes it like a tractor if need be.

Thanks for ANY advice. And if you're really nice, I'll share a picture of how I painted it.

[Mike81K10]

Can you post some pics? I feel it is most likely a leaf spring problem. Max tire pressure is on tires and typically tires are not inflated to the max. As you drive and tires heat up - tire pressure will increase a little bit. Max inflation can cause a rougher ride for your horses and you. Don't think max tire pressure will fix the sag. Not enough can be bad as well. If they say 80 PSI, I would go about 65-70 PSI and see how they ride. However, your vehicle should have a recommended tire size and tire pressure. Perhaps in addition to some pics of your trailer, you can post a pic of the side of a tire with the tire pressure and info. Michelin tires have been pretty good on the highway.

[Shareen]

Thanks Mike,

The pictures won't load right now. I will work on it.

The tires are pretty new and have 80 psi max. I'm thinking if I've been at 50, that's not great. I will try 65-70 and see how it goes.

I agree it seems to be a leaf spring issue. It's what makes sense. And so I'm thinking a heavy duty leaf spring to keep it up at normal height so it doesn't drop seems to the way to go. Right?

[bigben5054]

I don't know what the ideal tire pressure should be.  But I don't think you can or should fix a sagging rear end by adding more air in the tires.  I like your idea of looking at the leaf springs.  Either swap them out with some heavier duty ones, or I think they make "helper springs" or "add-a-leaf" kits that give some additional stiffness.  Yet another good alternative is to use a weight distributing hitch (if you aren't already). 

[Shareen]

Thanks Ben,

Yeah. I'm not really thinking tire inflation to prop the back end up, but I might be making it worse because I am way underinflating. I do have a weight distribution hitch, so glad others think the leaves are a good idea.

[bd]

Just a quick note.  If you plan to address an insufficient spring rate, replace the entire spring packs in pairs as opposed to add-a-leafs.  The reason should be obvious but is often overlooked to save money in the short run.  Unless a leaf is actually broken, sagging high-mileage springs are due to the entire pack losing arch.  Adding leaves transfers a major burden of load to the new leaves, "leaving" them to do the work.  ( )   It may not be long before the suspension begins to sag again.  Another option may be to install air springs that will adjust for the load.

[Shareen]

Thanks bd. Yes, that was the plan. They're not that expensive, and adding on to 43 year old springs would not seem like a good idea.