LT tires for a RWD truck?

[giantcone]

I've been using my RWD 720 for carrying motorcycles around for some time. It seems that recently I'm noticing that there's a lot of side-to-side swaying in the truck bed when I'm loading a motorcycle.  I've had some close calls of dumping the bike when I'm on the bed of the truck.  I was suspecting that issue was due to the  shocks. I replaced the shocks with what I think are decent grade Gabriel shocks, but that didn't solve the problem. I also ensure that I inflate the rear tires (P 195/75 R14 XL load rating) to around 38 psi, but the rocking is still there.  I'm beginning to suspect that it's all due to the passenger tires and the fact that there isn't much sidewall strength (even for XL rated passenger tires), and that the swaying during the loading of a motorcycle is due to the sidewall flex. 

 

I found LT tires that are commonly used on VW Vanagons: Yokohama Y356 (going for ~ $119 a tire). They're summer only tires.  Would this be an option that I should be considering if I wan't to cure the swaying issue?  I'll be hauling 2 motorcycles (around 950 lbs) across country in late April.  On paper the passenger tires I have should be adequate to do the job, but the sidewall flex is a bit unnerving.

 

Also, could anyone comment on the driver door jamb tire pressure numbers given for the P195/75 R14 tires.  My label states 24 psi in the front and 32 psi for the rear,  that front amount seems rather low.

 

My big official Nissan Service Manual has those same numbers for a "Heavy Load" on the back of the book, but also suggests running 24 psi front and rear for "normal load",  that seems too low in my opinion.  The LT tire inflation for LT 195/75 R14 tires are given at 35 front and 65 rear (if I remember correctly). Any comments on this info (whether the label or manual figures should be followed or not) would be greatly appreciated.

 

¡Mucho Thanks!

[bottomwatcher]

This will get Mike riled but I had issues with my rear swaying when towing a trailer. I put polyurethane bushings in the leaf springs and the rear firmed right up.

[weldingrod]

Are they radial tires? They are designed with a flexible sidewall. Recently moved a couple of loads of bricks,  1500 lbs. per load without any problem in my 84 720 4x4.

[datzenmike]

Get someone to shove the back of the truck side to side, what I think you'll see is the tire tread firmly planted on the ground, with the rims (and the rest of the truck) moving side to side with the side walls flexing. Go with the recommended tires and pressures on the label. If you go to higher ply tires with strengthened sidewalls it will ride like a tank and you'll need four. Tires are part of the suspension. You know it rocks so it may annoy you, but shouldn't surprise you.

[giantcone]

So just to update this thread before it gets too stale, I did replace the leaf spring rubber bushings with polyurethane bushings (around the same time I did the clutch work). While I was driving it (before my transmission front counter-shaft bearing decided to grenade), I did feel that the ass end of the truck no longer felt like it was swaying during fast turns.  While the ride is a bit harsher, the truck did ride better.  I put some 3M 08946 silicone paste on the  bushings, so there's no squeaking either (hopefully it stays that way).

 

As for the sidewall flexing issue with the P-rated tires I have (Discount Tire Sentury P195/75-R14 X-load rated supposedly), I'm just going to live with it as that's just the way it is. While the truck was running, I increased the pressures to Front:30 psi, Rear: 40 psi.  That selection gives the same ratio of front to rear pressures on the door jamb plate which specifies a Front: 24 psi, Rear: 32 psi, while running at 80% of the maximum pressure (49 psi) for those X-load P-rated tires for the rears.  That also seemed to improve handling of the truck as well.  I just felt that 24 psi in the front was a bit low (although I had been running that pressure for years).  I really like the fact that the available tires for the 14" wheels are quite affordable. I'll live with what I got; given everything else going on, I have enough to fuss over for now.