Here's one I'm having a hard time figuring out:
>
> My truck is a 90 Chev 1/2 Ton 4x4 reg cab longbox.
> Stock tires were a LT225/75R16, door sticker recommends 45psi.
> Current tires are LT 265/75R16's (IIRC load range D)
> They're Canadian Tire M&S tires. (Thought I wanted the ground clearance
> for winter - they're the largest stock size you could get on that truck,
> but now I'm wishing I hadn't bothered.)
>
> Normally I was running them around 40-45psi, and the truck drove fine,
> but like a 17 year old truck. When I was towing my race car this
> summer, I bumped them up to max pressure (65 psi) because we're fully
> loaded with gear, car, and trailer.
>
> I forgot to lower the pressure after - and the truck rides SMOOTHER.
> Enough smoother that my wife was wondering if I changed the shocks or
> something and hadn't told her. This is completely the opposite of what
> I was expecting - I was expecting the back tires to be just about
> bouncing off the pavement over bumps.
>
> Can anybody explain how adding 20 psi to the tires would smoothen the
> ride out on an old truck?
>
> (The shocks aren't new, only had the truck 2 years, so I'd guess they're
> probably 5 years old and this thing was a farm truck for the first 15
> years of existence...)
>
> Ray
========
That's a good question. The recommended tire pressure in my manual for an '06 Camry LE is 29 psi. 29 psi also appears on the sticker in the door jam.
29 psi produces a nice, smooth ride. When I pumped up the stock P205/65R15 tires by 5 psi to 34 psi, I definitely experienced a rougher ride--could easily feel the bumps. Didn't like it much at all. But my gas mileage seemed to improve from 20 mpg city driving to
24 mpg city driving, a 20 percent improvement. 20 percent seems like a lot. Is that even possible? I was expecting
5 percent at most.
Anyway, I next pumped up the tires to 38 psi, 9 psi over the recommended 29 psi. The stock Goodyear Integrity tires have a maximum cold tire inflation pressure of 44 psi, according to the sidewall, so I'm within the safety margin. Well, I don't know if it's just in my mind, but 38 psi feels smoother to me than 34 psi--I don't feel the bumps as much, and I like the ride as much as at the recommended 29 psi.