DougE

Yes the springs are different. A spring pack for the 1500 has a part #225240 and one for the 3500 has a part #799639 (numbers can be different for various configurations of each). The mfg recommended tire pressure is based on max axle load. Thus the tire on the front is 50 psi while the same tire on the rear is 80 psi. If the load on the rear tire is ALWAYS going to be less than the load on the front tire, there is no reason why you can't run it at 50 psi too (other than the tpms issue). The little jolt you get when you drive over a paving joint will then be lessened, but it shouldn't make any difference in the bounciness.

greenfire

Yep if the van isn't loaded to the max, you can lower the rears a bit, but there is some liability there...

Above mentioned the difference between a 1500 and 3500. The differences are significant, so just swaping springs would not be a good idea. The frame and axels are differerent, etc.

Any spring changes would need to be done by a professional spring shop, but even there too get into the whole liability/saftey issue, the van is a 3500 for a reason.

New shocks and sand bags under the seats sounds like you best option.

canucklehead

Please ignore this.

The rear tires are at 80 psi because the rear is heavier than the front. If you doubt that, go jack up your van from the centre and you will see how much harder it is to lift the rear.
You cannot lower the rear tire pressure to improve ride smoothness. That is just plain stupid. To make any noticeable difference you will wreck your tires and perhaps even have an accident.
My van is a 02 2500 passenger with the 8 lug axle. I have no issues at all with my ride comfort, and I have my tires at 50/80.
Now your van is a 15 passenger extended axle, so it will likely have bigger overloads as the rear will be heavier than a standard length van.
If you take it to an axle shop, they might have some ideas, but anything you change will alter the van's official gvw.

barwick11

Wait a minute... now, I don't plan to lower the rear tire pressure, but... you're telling me that the weight distribution of my 3500 van is closer to "optimal" than a typical sports car? I can't see how this is the case. This thing has a 700+ lb iron block, plus all the accessories, plus cooling, transmission, etc, etc, etc, all centered roughly over top of the front axle or in front of that axle. The majority of the rest of the vehicle is between those two axles, and then the rear axle has a heavy iron solid axle housing, and a differential, and a 4-seat (mine's a 12 passenger) bench seat roughly on top of the axle. Even if it had that 4-seat in the rear, I fail to see how this could yield a 1.6 times increase in rear axle load to require 50 psi front and 80 psi rear.

The season at the local road course is done, but maybe I'll get a hold of one of the guys there to see if I can use their 4-wheel scales. I'd be very surprised if this thing was any more than 60/40.

canucklehead

I have tools in mine. They are evenly distributed front to rear, but perhaps that plays a part in the weight on my truck. However I bet you will find it is close to 50 50 front rear with the van empty. There is a lot of steel hanging out behind the rear axle.....
Also the rear axle is rated for almost 2000 lbs more weight that the front, so that is why the suspension is much stiffer, and why the psi is higher on the tires.
I am not sure that you are easily going to make your ride softer without loading a few hundred pounds of sand in the back.

barwick11

Sand is probably the best bet, but I have to figure out a way to strap it down.

Also, this is an extended (extended wheelbase), not the old extended version with a million miles of steel hanging off behind. Those things are death traps IMHO, and WOULD have a very high rear weight distribution even unloaded, and especially loaded.

DougE

canucklehead, you're a little off on your reply to my last post and you really should soften your language a little. My suggestion for lower rear tire pressures was accurate and included the appropriate precautions. At 80 psi each of the rear tires is good for a total load of about 3000# (each). His actual loads appear to be considerably less and probably less than the load on his front tires. Thus the suggestion that he hunt down a scale and compare the front and rear axle loads in his maximum loaded condition.

greenfire

You are thinking of the old Ford and Dodge extended vans. GM vans always moved the axel back on the extended versions.


The point is a 3500 is designed to carry weight.. more of it in the back, because that is where the payload goes. A 3500 van is not that much different than a 3500 pickup truck. Some think(not you) the 3500 is the "extended version". It is not.. you can buy a 3500 that is the same length as a 1500. The series numbers correlate to the payload capacities (brakes, axel, springs etc), not length, nor engines.

Your van is designed to be full of passengers, its a bus basically...when its full the ride should be smooth. Do the math.. how many passengers do you normally carry, whats the weight and see what your shortage is to say get around 70% of the payload of a 3500.

Put the sandbags over the rear axel if you can. This may not even be a good option.. sand all over etc. You might need a lot of bags?

I guess we have beaten this topic up enough....

canucklehead

Nope. I was spot on.
Anyone who tells someone to go ahead a disregard the manufacturer's tire pressure rating on the door sticker is out of line. You are promoting an unsafe practice, and I'm going to call you on it.
Maybe you should call a dealer and ask them about running 2/3rds pressure in the rears....

in2pro

Checking with the Tire manufacture is also a good resource, granted the door panel label is important, it could be for what was originally installed on the vehicle, if those tires have changed in type and rating, the tire manufactures specs should be used.....

Here is a snip-it from Goodyear's site on adjusting tires for softness:
the full context can be found here: Goodyear Tires

"IMPORTANT: It's a common practice for RV owners to lower tire pressure in their search for a smoother ride. This is not only dangerous, it's relatively ineffective, as the difference in ride quality is not significant. When minimum inflation pressure requirements are not met, tire durability and optimum operating conditions are compromised. Tire inflation pressure should always meet at least the minimum guidelines for vehicle weight."

EDIT: I will add that in certain circumstances that temporarily lowering tire pressure to below minimum is common for getting traction in snow/ice situations