255/85 R16 Owners Experience

So far they've been great. This is my first mud terrain so not much to compare too, but I did just come back from a 3-day mojave road trip and they performed flawlessly. Plus they're 8-ply so they're a little lighter and they're cheap!(er) haha

 

16" x 7 Trd Trail team Fj wheels fit with 255s without spacers? Or if I decide to go 16x8 255 are still safe right. second gen

 

Joined BFG Mud Terrain A/T KM2. Ome BP51s w/Dakars. Wheel spacers because I have to with stock steel wheels and spindle gussets.

 

Still enjoying mine. The size is just perfect for me. Height for ground clearance. Skinny enough to keep the weight down.

 

No pictures, but I recently swapped from 275 KO2s to 255/80r17 ST Maxx. Oddly the 255s look as wide as the KO2s and I feel like mine look wider than most of the pictures I see on here. They're on 8" wheels though, whereas a lot of people are on stock wheels.

Did a 2k mile trip with them. They're louder than the KO2s, but they are also softer and steer easier, which was expected. Did some twisties on HWY 1 in Cali and they're not the best option for that. Gas mileage is essentially the same as the 275s, but initial power is better with the 255s. I am happier overall with them than I was with the KO2s and will probably stick with this size in the future.

 

One of these days I will probably try them out. I hear good and bad, but the price sure is right.

 

First off, nice truck! Second, I know this is an old post, but as someone with a good handle on engineering, physics, and math, this drove me crazy; you have a total misunderstanding of some concepts and I don't like seeing misinformation spread.

This is completely backwards. A larger tire size (diameter) will exacerbate any problems with a too-low gear ratio. That is why many people who put on larger tires change to HIGHER gears, ie 3.55 to 4.10.

You're completely contradicting yourself. The middle post is correct, that friction is not affected by area, it is determined by the coefficient of friction and normal force. Your assertion that higher tire pressure = more friction is also wrong. PSI and tire width do not change the normal force, or the coefficient of friction, and therefore do not affect friction in any way. Friction will be the same because mass (which will determine normal force) is the same. Imagine a clay brick smooth on all sides. Lay it on the large side, or lay it on it's narrower edge, but normal force and coefficient of friction (ergo, friction) remain the same.

An important thing to realize, now that you have a better understanding of how friction works, is that friction would only be the main consideration if our wheels didn't rotate and we were dragging our trucks across a surface. Since vehicles move by rotating their wheels, friction is not the only thing determines traction. I'm not sure where you pulled "surface molding" out of, but if you think that a higher PSI tire is going to mold to a surface better, we better tell all those idiots airing down their tires for off-roading that they're doin' it wrong.

Just for fun, as a military guy myself, I can tell you that this vague statement about military vehicles not using the widest tires has little to do with "needing them to perform". Wider tires would perform better off-road, but cost more and get much worse fuel economy. Not to mentioned we're not going to go around trimming the underbody of every 1197 so we could fit wider tires. We do typically run narrow tires at higher PSI, because we're not the ones who buy them, and fuel economy in a convoy of vehicles going down the highway matters more than a little more off-road capability from a wider tread.

AND on a side note, I am probably going 255/85/16 on the stock rims if I pick up the new TRD Pro. That's how I tumbled down this rabbit hole.

 

This has been covered ad nauseam on the web... And i think we're saying the same thing - but I can't help throw in my .02.

Basically traction comes from two things happening between the tire and the ground: friction - which is, as you state, not dependent on area, but just normal force and coefficients of friction - and interlocking, which is where the tire and substrate actually push against eachother like a tiny and/or even microscopic gear teeth. This happens for two reasons: both due to the geometry of tread and surface of the substrate, and also from the deformation of the tire's rubber compound around the substrate's surface geometry. And that factor is affected by area, and a lot of other things, like durometer of the rubber, roughness of the substrate, compliance of the tire's body (from it's inflation pressure) etc... So, interestingly, the depth of interlocking and the amount of interlocking are affected by area in opposite ways. Smaller contact patch means higher psi so more deformation and "deeper" interlocking, but larger contact patch means a greater number of interlockings...

Rolling adds a whole new dimension to the system, but i think is relatively unimportant for crawling.

 

Yeah we're in agreement

I mentioned friction not determining traction as it relates to tire pressure. The coefficient of friction will be determined by the tire compound and the material it is contacting, but friction is constant as it relates to tire pressure.

 

Hey Guys- I'm running 255/85/16 KM2's on stock 2012 TRD Off-Road rims with a 2.5 inch lift.

I'm thinking I'd like to put on wheel spacers to get the tires out just a bit.

I'm looking for recommendations on spacer size. I don't know much about spacers. Also, any pics from folks that have a similar setup as mine with spacers are of course welcome.

 

I don't have it backwards, you're arguing semantics. I said higher as in numerically higher. I think he was saying 6th gear is too low, as in 6th gear ratio is too low (RPMs too low, lacking power), often referred to as taller or "slower" gears (fewer revolutions).

I have never heard someone refer to a lower gear ratio as "higher gears", but I see where you're coming from, since I have heard people say they need to lower their gears after a lift/tires so they obviously don't mean a lower ratio (heck, that's why 4-LO is called that). I have always talked about gears in terms of ratios (i.e. 2.83, 3.55, 3.73, 4.10) so I would say after a larger tire I need to regear to a higher ratio.

 

Woof

 

URE(offroad) this weekend, rubbubububub, gonna have to cut and hamma.

 

I finally made the move and got them. I got the Cooper ST MAXX and these don't look skinny compared to the km2. Also these ride really quiet for a A/T tire and absolutely no rubbing anywhere. So glad that I didn't get 285s!

 

I've got wheels that are the equivalent of 1/2" spacers, and i have a bit of rubbing, so be forewarned...

 

Offroading will make them rub too.

 

Stock height or lifted?

And where does it rub?

 

Seriously, are you trolling or are you being serious?

It is not semantics. Going to a lower gear ratio means only one thing. Lower gears require more revolutions of the input shaft to turn the output shaft one complete turn. As the gears get lower, the number of turns required of the input shaft increases. That's why one of the numbers in the ratio gets larger. No one EVER refers to that as a higher ratio, except for you.

Or think of it this way, a 1:1 ratio is high ratio because output is high in relation to input. The engine does not have to work hard to have a high output. A 4:1 ratio is a low ratio because output is low in relation to input. The engine has to work 4 times as hard to get one turn output. Lower gears provide a lower output. (That explanation is ignoring the transmission gear reduction for simplicity)

As tires get larger in diameter, you need lower gears to keep your engine working in the proper RPM range.

 

kodiak has it right. Take truck gears out of the equation. If I have a 20:1 gearbox for an electric motor, it has a lower gear ratio than a 10:1 or direct drive. So a 4.56:1 gear ratio is lower than a 3.73:1.

 

Lifting doesn't matter, unless you are talking a body lift. but, yes, lifted a bit - OME springs and 5100's on the lowest setting. Mine are rubbing more on the left than right (not sure why the camber adjustment is maxed out on the left, not the right) and it rubs in the back of the wheel arch near the pinchweld. I guess that mod is next. I am thinking i should have just had them mounted up on stock wheels!