NissanDiesel Forums

Okay, I've been searching/reading the the forums for a little bit now and have a couple of questions relating to tire pressure and front end alignment.
My '82 KC SD22 has 225/70-14's, which are going to be on there a long time considering they are pretty much new and price of everything right now..., and Les Schwab has them pumped up to 35 psi.
As you know, the door plate read 24 psi for the front and 32 psi for the rear, but that is based on 1982 tire technology. Obviously todays standard of 35-ish psi is too much, but considering the tire size, where should I start in trying to fine-tune my tire pressure?
I get the wobbly front end on rough roads, there are vibrations around 48~51 mph and 54~56 mph, the steering is heavy, and there is alot of body-roll when turning. As I understand, lowering the tire pressure should help with this, but I am also concerned with mpg, and I can handle some heaviness and vibration for the sake of mpg, but I want to make sure that no damage is occuring.
Regarding the body-roll, I should probably mention that this in my first 720 and I've been driving a tight and well-aligned 620 for about eight years and am not familiar with the 720's particulars.
Also, considering the tire size, and where I end up with tire pressure, are there any ideas as to the particulars for alignment?
I plan on installing a sway-bar, if someone would be so kind as to remind me what will fit and maybe give advice on bolts, bushings, etc., and installing load-assisting firestone air-bags on the rear, to be used only when I carry a load and otherwise left low.
Thank you, everyone, in advance for your assistance.
Clark
Salem, OR

Hey, Clark! I was through Salem twice yesterday (dragged a car back from Springfield). Used to live there, 1987-9.

Zeyemurgy wrote:Okay, I've been searching/reading the the forums for a little bit now and have a couple of questions relating to tire pressure and front end alignment.
My '82 KC SD22 has 225/70-14's . . .

Yow! That's w-i-d-e rubber for a 720.

. . . Les Schwab has them pumped up to 35 psi.

It seems that Les Schwab's company policy is to inflate to the tire's maximum load spec rating, not the vehicle mfgr's spec. I've always thought that was particularly stupid, esp. for a "tire store". It's almost never appropriate to inflate a tire to the number on the tire's sidewall. That number is a Federally-mandated do-not-exceed tire load rating spec., not a recommendation!

However, Nissan's front spec of 24 is a bit low for a non-PS truck. While there are modern vehicles that run tire pressure that low (Toyota RAV4? KIA Sportage? One of those runs 23 all around), they have power steering and are also lighter built than the 720. With stock rubber, a 720 can be turned at parking lot speeds with 24 PSI, but anything wider and it's a real wrestling match.

You might experiment with around 28-30-ish for the front.

As you know, the door plate read 24 psi for the front and 32 psi for the rear, but that is based on 1982 tire technology. Obviously todays standard of 35-ish psi is too much . . .

While there are many vehicles that spec 35 PSI today, they are primarily SUVs (and Fords); the Hondas, Mazdas, Toyotas are lower-spec'd, and the German cars (VW, Audi, MB) are all higher, up to 44 and higher. IOW, it depends on the suspension variables.

I get the wobbly front end on rough roads, there are vibrations around 48~51 mph and 54~56 mph . . .

Check out the "Idler Arm" thread -- slop there is a very common problem, and there are different designs in the replacements. There should be no oscillation at any speed. Tire pressure adjustment to avoid shaking is a patch, not a fix.

. . . the steering is heavy . . .

No kidding!

. . . and there is alot of body-roll when turning.

They do lean, stock, and can I assume you've cranked up the torsion bars to get enough clearance to run the oversized rubber? That's going to make the lean worse, of course.

While lower tire pressure will affect mileage, it's not a huge factor. If you are running larger rubber than stock, reduced mileage is a trade-off you're going to have to live with.

I plan on installing a sway-bar, if someone would be so kind as to remind me what will fit and maybe give advice on bolts, bushings, etc.,

Philip and at least one other have installed the later OEM sway bar from a JY donor rig. There are pictures in one post. Use Search on " sway AND bar" and I'm sure the thread'll turn up.

. . . and installing load-assisting firestone air-bags on the rear, to be used only when I carry a load and otherwise left low.

There were a set of those on my first diesel 720, as it had a camper on it most of its life, and a telescoping rear bumper.

Al, Thanks so much for all the info.
Yeah, I know it's wide. It's what I had on my '73 620 (with no issues) and when I got the 720 in January the tires were undersized, and not much tread, so in the interest of econimics I swapped. I only get fender-rub on the firewall when turning to the lock, and sometimes on a speed bumb. I haven't touched the torsion bars, so the body roll is probably pretty close to normal, just a touch exagerated due to the height of the tires. I'll just have to get used to it.

I've got all new ball joints and shock, so the idler arm is the next palce to look, isn't it.

I'll re-read the idler arm and swap bar threads and hit NAPA and the junk yards.

Thanks again.