Ride quality of skinnies (eg 255/80r17)

[str8flexed]

Correct me if I’m wrong, but a skinny tire under the same PSI deforms more and thus you get less ground clearance than a wider tire of the same diameter.

Thus, to get the same ride height you need higher PSI’s to counter the deformation (40-60 psi?), and you will have a harder and harsher ride because of this.

Of course, being E-rated incresss harshness too. I’ve noticed all 255/80’s are E-rated, presumably to give more sidewall stability or to decrease the roll of the tire under itself when turning/cornering. There must be a reason manufacturers don’t offer this size in C-rated.

This is all theoretical mumbo jumbo I’ve conjured up in my head, but wanted to correlate with any real world experiences.

I do prefer a slightly softer ride now with my stock size KO’s usually around 35psi to balance out the stiff Bilstein 5100’s...

 

[chiz45]

Harshness is going to be subjective to the end user, of course, especially if the driver is coming from P rated or even a car. With that said, I have had E rated tires on trucks since 2003 (GY MT/Rs, Terra Grapplers, KO2s) and currently 2 sets of 255/80s on two difference trucks. I have used these ST Maxx since 2014, for around 50k miles combined. I run 37-39PSI. While there is a noticeable difference in noise, weight, and harshness, compared to the stock Duelers, I do not find it unbearable.

I'd be surprised if you would be able to notice a change in ground clearance due to tire pressure. Are your tires C rated?

 

[str8flexed]

Harshness is going to be subjective to the end user, of course, especially if the driver is coming from P rated or even a car. With that said, I have had E rated tires on trucks since 2003 (GY MT/Rs, Terra Grapplers, KO2s) and currently 2 sets of 255/80s on two difference trucks. I have used these ST Maxx since 2014, for around 50k miles combined. I run 37-39PSI. While there is a noticeable difference in noise, weight, and harshness, compared to the stock Duelers, I do not find it unbearable.

I'd be surprised if you would be able to notice a change in ground clearance due to tire pressure. Are your tires C rated?

Currently running C-rated 265/70r17 KO’2’s...

Yes, I think the theoretical loss of ground clearance is minimal but still could be maybe 1/4-1/2 inch, and that’s a tire size or two worth of ground clearance...

I just heard that the 255/80’s while larger in theoretical diameter than 285/70, they appear smaller/lower (yes I know there is a lot of variation between actual tire sizes between brands, too)

 

[Jetboy]

The general idea is that a tire is actually holding up the wheel from the top, not pushing up from the bottom. The tire does push down against the ground. So there's a bit of a complex situation between the road and wheel. As far as the shock transferred to the wheel, I don't think you can say one is more or less. It depends a lot on the shape of the bump. As a general rule a lower psi tire will deform more and transfer less. However a wider tire at the same pressure has a footprint that's shorter and wider. A narrower tire has a longer narrower footprint. So the simple example is a rumble strip. Because of the longer footprint and bridging effect of the tread, a narrower tire at the same pressure could be smoother. On the other hand most of the time a wider tire on the same vehicle would be run at lower pressure. In that case the lower pressure may balance it out.

So I don't think there's a one size fits all solution.

Also FWIW, most 75 or 80 profile tires are intended for dually trucks. They are narrow so they don't rub together. That's why they're almost always e rated. No one would buy a dually and run c rated tires.

 

[Monkey Wrench]

After running 255/80r17s (maxxis bighorn, Cooper ST Maxx), 255/75r17 KM, 235/80r17 KO2, 265/70r17 KO2 on 4th gen 4Runner and 2nd gen Tacoma- 285/70r17 KO2 in C load is the smoothest ride out of all of them. Most of it is probably the C rating but the extra air volume from the added width helps.

The 34x10.5r17 KO2 is the ideal tire, but are way too expensive for a 33.3ish tire.

 

[MAST4R]

Interesting discussion.

If you look at 255 75 17, there are plenty of LT-C choices. The combo of height and C rating should make for a smooth ride. The load and speed ratings, otoh, are marginal, 111Q.

The ground clearance difference on my LT-D KO2s was half an inch between 40 psi and 20 psi on a Subaru.

Basically, if you go up 1" in diameter but have to air down for offroad, you end up with the clearance of a P-metric tire that is stock size and that, being P metric, needs not be aired down and should not be aired down unless you deal with deep sand.

The P metric Wildpeaks I have offer plenty of flex and comfort at 33 psi.