275/70r18’s @ 50psi - tires look under inflated

I started having this issue with my prior set of KO2’s and replaced them at 50k miles.

Discount set new tires to 35psi, which I then aired up to 40psi. I’ve gradually increased pressure to 50pi, but tire still acts like it’s under inflated.

Here are the symptoms:
1. When truck comes to a stop, truck bounces, or rocks, 6-7 times before it’s no longer noticeable.
2.When this happens, I can visually see the sidewall giving/flexing to absorb the movement of the truck through the rim.
3. When I climb into the truck you can see the same reaction in the sidewall.

I know HD trucks run these tires at 60+ psi, but at 50 the ride is stiff and seems excessive for the tundra, even though the tire is rated up to 80psi.

Only change I’ve made was removed a 3/1 spacer lift and replaced with the TRD pro shocks earlier this year. This started sometime after that, from what I recall.

Other than harsh ride due to psi, truck rides food and tires seem to be wearing evenly, so alignment seems to be good.

Any ideas on what could be causing this? I am at a loss - new tires didn’t fix, I can’t see how the TRD suspension could cause it…

 

I have 275/70/18 E rated Coopers at 55 PSI and my truck rides smooth. I had them at 45 for a while but the sidewall looked under inflated. After increasing to 55 I noticed no difference in ride, but the tires looked inflated and my MPG increased. I have Bilstein 5100’s. I think ride quality is so subjective you are going to have a hard time determining what is wrong. What you call harsh, another may call smooth.

 

I run my LT275/70/18 Cooper AT3 LTX's at about 42 psi and they ride and wear great! Got about 10k on them and no issues!

 

Did you put the TRD pro fox coil overs on?

The rock 6-7x your describing is very likely from them if so. I recently installed the icon 2.5s and noticed the same “rock” you describe coming to a stop. Most of the race tuned components suffer at low speed. Fair trade off IMO

 

I cant imagine running 50PSI daily, unloaded, in 275/70s unless you need the support- very heavy loads or huge bumper and armor. Maybe in the rear during heavy tow/haul. If it get pressure up near 45, it can feel like I'm driving a 2500 pickup. I have found that minor air pressure adjustments have a large impact on my tundra. 2-3 lbs difference can really loosen or firm the truck up and found that to be true with the stock size SL tires as well.

Ive run two different sets of 275/70s on my Tundra. 38 to 40 for front, 40/41 in rear if unloaded has given me good handling, excellent tire wear.

You cant inflate a tire based only on visual. Tires are meant to have some bulge, which can look like underinflation. That is how modern radial tires are, now the old poly and glass tires of the 60-70s, if they looked low, they were low. Anyway, Ive used this tool for years when switching tires size or load ratings and it is quite good, has always gotten me close to spot on with maybe a pound or two PSI adjustment depending on load. E load tires, so stiffer and really overkill for a half ton truck, but we have limited load range options for larger tires unless you drop down to 17s, can get some C load tires in those sizes.

No idea on your rocking, maybe at the pressure you are running they are not giving at all and the suspension is taking on the load, and rocking until the suspension settles.

 

Agree that ride quality is very subjective. I’ll try airing up to 55 to see how they respond.

Yes, Fox coilovers. Good to hear - others have experienced the same. If normal, I’m good.

Thanks for the replies!

 

It’s almost like the opposite. Like the suspension isn’t absorbing, so the tires are - but that doesn’t make sense to me and I can feel the shocks working on the highway, etc. I’ll keep playing with it - figured I’d just throw it out to see if the brain trust had any new ideas!

 

I found out no matter what PSI I put at cold, once I drove it for an hour it will raise to 50 PSI…

 

That's me too I guess.

When I got in the truck after work, they were all showing 37-38. After some driving, they creep up to 40-41.

 

I drove all the way down to San Diego from Bay Area with some tools and luggage in bed, maybe depends on the truck weight, I tried 38-47 PSI, while I’m driving I checked the cluster and no matter what I started with I always have 50 PSI while and at the end of my drive

 

My in dash gauge stops at 50 psi. Could be the reason. I’d bet if you checked the 47psi cold tires with a handheld gauge after driving it will be over 50psi when hot. Mine is a 2019.

 

maybe that's why...mine is 19 also...lol

 

I am no expert, but I put 52 psi cold in my rears to tow my boat 2 weeks ago, has read 50 on the dash since, never changed from 50. Hand gauge shows 52 cold still. Bet it’s 57-58 when hot.

 

I get a warning message as soon as my pressure EXCEEDS 50#. I can watch it hit 50# as the tires build heat, but it won’t display 51#. Just a warning that my truck will explode in a fiery ball if I don’t see my dealer, blah, blah, blah.
That said, I run anywhere from 35 to 42, load dependent. I’m also on a different size tire so my pressures are irrelevant. I only posted because of the 50# limit on our TPMS system.

 

No warnings here. Might be a feature on a Platinum? Mine is a fairly basic SR5.

 

My ‘19 stops at 50 as well.

Just to post an update, I increased pressure to 55 psi and the truck does actually ride better. Still have a bit of the rocking, although it’s gotten slightly better.

 

them Fox shocks could handle 55 psi...envy

 

I have Bilstein 5100's and my tire pressure is at 55 psi and it is smooth, not a Fox thing.