just picked up my new plat this morning. Love it all cept the ride seemed like it should be a bit smoother. Does anyone think if I changed the perellis out to michelins MS2s in the same size 275 55 R20, that the ride would improve substantially? Or change out to same size Nitto Terra Grapplers? Just seemed like I could feel every crack/seam in the road while driving it home. Dont really want to change speedo / computer.

 

While I do suggest/endorse the LTX M/S2 (I have them on my '06) I would also suggest looking into one aspect ratio larger. The 275/60/20 gains you about .9" in overall height, and looks a little better too as it fills out the wheel wells a little more. Price from the 275/55/20 to the 275/60/20 is only a few $$.

I too have the 275/60/20 on my '06 and they're great for my needs/uses. They are far smoother than other tires I've had in the past.

 

i wouldnt mind going to the next size to improve the ride but i dont want my speedometer or mileage etc to be incorrect. I wonder how much diff it would make in the speedo and the mileage?

 

You can easily get the tire size changed in the PCM. I really dont think different tires are going to make a noticable difference in ride.

 

Less than 3%. In my case the speedo went from reading slightly high with the 55 series to being dead accurate (gps tested) through 80mph with the 60 series installed.

 

Just to confirm your observation of a rough ride, I also had a 2010 Plat with those very same tires and absolutely hated them. Thankfully, my new truck doesn't have them.

 

Jacknbella, did you do anything to correct the ride or did you just get rid of the truck? You think it is correctable with diff tires? or diff size tires?

 

Tire construction is a large part of the ride quality.
One 10ply should ride very similarly to another 10ply.
A lower #ply should be more compliant/soft than the 10ply.

I do believe that the tires I have ride much better than the previous set I took off that had less than 5k miles on them. Was it the tire? Was it the step up in aspect? I think both contribute.
One thing you might want to check with the pirellis is pressure. Its possible the dealer could have inflated to max pressure. Most run the pirellis (in an empty/non loaded or hauling truck) around 36psi. I run my M/S2 at 38psi cold.

 

How much air pressure did they have? Mine had 42psi when I took delivery of my truck. They rode pretty good but I think 42 psi was a few over. You may want to try different air pressure to see how it effects the ride. I swapped my stock Pirellis out mostly because they looked too small on such a large truck and I also heard they weren't good in snow. Besides that I thought the Pirellis rode pretty good.

 

I test drove a 2010 Lariat and a 2010 Plat within minutes of each other and the 1st comment I made to the salesman was about the rough ride of the Plat. He told me the suspension was different but I knew better. But, like an idiot, I still went with the more expensive Plat. Much happier now with my 2011 XLT EB!!! I think different tires would probably smooth your ride though.

 

I too think the aspect ratio (sidewall height) makes a big difference in ride. I had an 05 SD EC short box with 265/65x17 Pirellis and now own an 06 F150 EC 6.5' box. The SD had a GVWR of 10,000 lbs and the F150 has a GVWR of 7200 lbs. The F150 has 255/70x17 Generals. The wheelbase is similar. The SD rode much better than the F150 does. In my opinion it's because the SD tires had a much taller sidewall than the F150 has. The short sidewalls of a 55 series tire will give a much harsher ride than a 70 series that the XLT uses because there is less sidewall to absorb bumps. Sidewall hieght as well as air pressure do effect the overall spring rate which does effect ride and handling.

 

does anyone know how far off my speedometer would be if I went with a 65 or 70 eries tire vs the 55 series? And am I right in asuming that a dealer could reflash for this size so that the speedo etc is correct?

 

Not for sure. But you can figure the % of difference dividing the smaller diameter tire by the larger diameter and get pretty close. Since you are going larger in diameter you subtract the % u arrive at from 100% and either multiply or divide the new size by that percentage converted to a decimal equivalent of course. Example: if you are going to a larger Dia. tire that is 10% larger, you would subtract .1 from 1.00 to give you .90. Mutiply the larger dia. times .9 and that will give the amount of mph with new tire size. If you were going to go to a smaller Dia. tire you would divide the size by .9 to give you the correct speedo readings. I'm just using the 10% as an example. You'll have to actually calculate the numbers yourself. Just remeber that the tire width is in metric. Divide that number by 25.4 to convert to inches. That is the sidewall height of the tire. Mutiply that dimension times the aspect ratio (.55 in your case) and mutiply that number times 2 and add the wheel diameter. That will give the diameter of the tire. Or you can go to Tire Rack's website and they'll have the diameters of all the tire sizes listed in the specs.

 

Use this calculator to find the % differences and speedo issues.
Tire Size Calculator - tire & wheel plus sizing

 

I can tell you for a fact that the michelin MS2s will ride better. As my Perelli's were cracking olny 13,000 on them so i got credit under warranty and used it for the MS2's. After doing this even if i had to pay full price i would to get the perelli's off my truck. I went with the stock 275 55 20 as well and you can add on that they look much better on the truck as well.