bouncing d-90

[Rick Carlisle]

Several months ago I changed out my tires to BFG M/T KM 285/75/16s. They look great but since the change I have noticed a lot of bouncing from the rear of the truck especially. I notice this mainly with in-town driving where there are speed bumps and bad asphalt. I previously install Bilstein shocks and LR HD springs up front and medium duty springs at rear.

Any advice on how to eliminate the bouncing? Are there better choices for shocks and/or springs for mostly in-town driving? I really like the tires and do not want to change them.

Thanks.

[TDI Guy]

what about the tire pressure? what are you running in them?

[chrisvonc]

We've run the same tires as you and the only time we see this problem is on higways where the jointing was sloppy. Mostly only on concrete slab roadways. The feeling is like if you have ever driven a truck when the rear shocks have gone bad. If you have some shocks bad, it would definatly pronounce the bouncing.

I run 45-50psi in my BFGs on road.

[Rick Carlisle]

That is the feeling....like bad shocks but these Bilsteins are only 6 months old. And I noticed the bouncing immediately with the new tires.
Randy, I checked the pressure and it was around 53 psi in the rears. I just took it down to 45 psi each and maybe that will help.
As for shocks, is there a better shock for in-town driving that I should consider?
Thanks.

[chrisvonc]

Also, is it possible that the shocks are not the right rate?

[Mike Hippert]

Do you have any of the old shocks to try? 53 psi is crazy, I run from 25 to 35 PSI. I have driven for a bit on one shock in the rear (Don't even think it) and it handled the same as you describe. So you could pull one shock and if it does not get worse then I would say bad shock or like Chris said not the right rate.

[wicks]

Factory sugg. is in the 20s. I run 26 front 32 rear for in town, which seems ideal.

How much lift did the LR HD springs provide?

[Rick Carlisle]

I just checked one of the tires and it says "max. load 3000 lbs. at 65 psi". And the shop that mounted them had set the pressure at 53 psi. I would assume the pressure requirements are different for these tires vs. ones from the factory.
So now I wonder what the right pressure should be for everyday driving (NOT max. loads) for these tires?
Wicks, the lift was about 2" with the spring change. But I did the spring change a while ago when I still had the factory tires and there was no bouncing.
Mike, I don't have one of the older shocks to try. I ordered the Bilsteins and spring setup from Rovers North. I guess I didn't even consider the shocks could be rated incorrectly. How do you tell? And from the lack of comment, I guess there is no better alternative for street driving than the Bilsteins?
Thanks.

[Mike Hippert]

Forgot to comment on shocks but I have only run Rancho 9000s in the rear, they are great because you can adjust them to what you like. I would think if you bought the shocks from Rovers North that they would be the correct shocks.

[Rick Carlisle]

Thanks Mike. I have heard a lot of positives on the Rancho shocks. That was one in my mind that I may look at to replace the Bilsteins. Of course, I had heard the Bilsteins were the "best" for on-road driving before I purchased them.

[wicks]

No on tire pressure - many people are misdirected by the load rating with high pressure. High-load tires show max pressure (with the high load). Run them at normal pressure ranges while not carrying a load of gold bullion in the back.

[Rick Carlisle]

So Wicks, do you know what pressure I should be running in these specific tires with a no-gold-bullion-load?

[TDI Guy]

I would try to run no more then 35...... that is in the front and rear..Try it Rick, you can always air up again but i bet it will ride great.

[Rick Carlisle]

I realize you don't run the max. psi in the itres and was only referencing what was listed on these tires. But nowhere in the information I received when I bought the tires did I read what the recommended pressure was under normal load conditions.
So Randy. I will give what you recommend a try. Thanks.

[Mike Hippert]

Rick, they cannot recommend a tire pressure for you or anyone because they don't know all of the different conditions. For example if they only had to worry about weight then they could make a chart of tire inflation per pound of vehicle. but the hight of the vehicle comes into play when you corner so they would also have to consider the COG. There are other things to consider (rim width, front to rear ratio of vehicle weight, offsets of the rim, track width, and wheel base all play some roll) so there is no exact pressure that that anyone could pin down for a specific tire and vehicle without doing some testing and that would take for ever as they would have to test every possible scenario.

So whats all that crap mean, put what feels right in your tire. I have 35" MTRs and I run 25 for around town/light off road and 35 for long highway rides as it stiffens the ride and gives a little better high speed control.

[Rick Carlisle]

Mike,

Mostly this makes sense even though it does make me wonder how the factory can suggest an inflation rate but BFG cannot. Nontheless, I agree with the "what feels right" concept and I am going to try Randy's idea at 35 psi. If that still leaves some bouncing, I will go down until it feels better.

I don't understand why Tire Kingdom inflated them to 53 psi.

Just to illustrate how bad the bouncing has been, I started noticing a loud knocking coming from the rear of the truck about two weeks ago. I had my daughter sit in the back Sunday and we drove around. She kept telling me it sounded like the knocking was coming from the spare tire. So when I stopped, I checked my Mantec tire carrier and all of the bolts that were holding it to the body of the truck had worked themselves loose. I could take the carrier and move it back and forth away from the truck. So the bouncing was not only annoying it was loosening things up a bit in the back.

Thanks to all who responded.

Rick

[RyanS]

My guess is that the inflation was set high when they were seating the beads, and they forgot to reset the pressure afterwards.

I think a good starting point for inflation is to do it based on weight. It would be best to get the weight on each axle measured, but for rough numbers assume everything's equal. If your rig weighs 4500 lbs fully loaded, then each tire carries about 1125 lbs. If the tire is rated for 3000 lbs at 65 psi, then at 1000 lbs the corresponding pressure would be 24 psi (65*1125/3000). I would look at this as only a starting point, and would tend to run a higher pressure on the street. And if you can get real axle weights, then you can get even more precise. But still tweak from there based on the other factors already mentioned by others.

Be careful about underinflating for a softer ride especially if you do a lot of highway miles (tires will run hotter). Remember Firestone :(

[Rick Carlisle]

Good info. Thanks Ryan.