Tire decision help

[stioc]

....no manufacturer has specified 235/85-16s on a single-rear-wheel pickup truck for over 15 years. Times (and tire technologies) have changed.

Neither does a 285/70/17 right?

While perhaps true for the single-rear-wheel pickups but what do you think is the problem with this tire size? If your concern is about how tall the sidewall is, it's almost the same as the 265 size and less than many of the 32s and 33s in the 15" diameter. If your concern is the width keep in mind that 235s while skinnier than 285s, they're not exactly skinny. Heck many German sports sedans come with 225 width and coming from track experience with fatter tires we couldn't get them hot quickly enough in the first couple of laps to allow them to really hook up there's no way you're going to overheat the 235s with the proper tire pressure.

As for cars' bushings etc being engineered for a particular tire size that's a bit far fetched but the same also applies to going wider. In fact, it's worse with larger and fatter tires. Next time you see a truck with monster tires sticking out 3" to the side keep your distance incase a ball joint, tie-rod etc give

Btw, the 235/85/16 is a very common and abundant tire size.

 

[stioc]

Ok, so good discussion on tire size...

How about the AT3? Is there anyone who has firsthand experience with this tire in mud? I don't expect to be in it too much, but when wheeling in Eastern OK it does happen.

Sorry, no first hand experience but I've heard good things about the Cooper AT3s...actually all popular Cooper tires in general.

 

[Kaisen]

Neither does a 285/70/17 right?

The Hummer H2 came standard with 315/70-17s. My Sub 2500 has the same basic suspension components, and I've upgraded my tie rod ends and ball joints with HD H2 units and run forged H2 wheels that shift the centerline to compensate for the increased width. So in my application, a 6,500 pound SUV, it's a big upgrade. Safer, more stable.

While perhaps true for the single-rear-wheel pickups but what do you think is the problem with this tire size? If your concern is about how tall the sidewall is, it's almost the same as the 265 size and less than many of the 32s and 33s in the 15" diameter.

The LT235/85R16E tire itself is not a problem. It's a problem when you take a tall skinny truck with a high center of gravity, one that was engineered for a 265mm tire with a 70 series sidewall, and fit 4 inches less width per axle, and increase the sidewall aspect ratio over 20%. It's not just the height of the sidewall, and it's not just the width of the tire (although that's the worse offender of the two variables), it's the relationship between a skinnier footprint AND a relatively tall sidewall......note that I said "relative", as the relationship or aspect ratio between the width and height is important in on-road stability. Furthermore, a 32" tire on 15s is typically 10.5" wide or wider. In a LT235/85R16E Cooper AT3, it is less than 7" wide. Less stable.

If your concern is the width keep in mind that 235s while skinnier than 285s, they're not exactly skinny. Heck many German sports sedans come with 225 width and coming from track experience with fatter tires we couldn't get them hot quickly enough in the first couple of laps to allow them to really hook up there's no way you're going to overheat the 235s with the proper tire pressure.

German sports sedans typically have a much lower center of gravity than a top-heavy, skinny SUV like a Montero. On top of that, a typical German sports sedan has a 60 series tire (or lower)....never a 85 series. And even though a Montero isn't super heavy, it's still a lot heavier than a German sports sedan that would wear a 225mm tire.

You've got to be kidding me about the heat build up. That scenario is completely invalid to this discussion.

As for cars' bushings etc being engineered for a particular tire size that's a bit far fetched but the same also applies to going wider. In fact, it's worse with larger and fatter tires. Next time you see a truck with monster tires sticking out 3" to the side keep your distance incase a ball joint, tie-rod etc give

I agree that monster tires sticking out 3" to the side can also be a dumb move. But we're not talking about that, are we?
It's rare that a manufacturer has a steering center (virtual or actual) directly through the center of the tire. So anytime you change width, you change that geometry. Wider or narrower.
Since his truck was engineered for 265mm wide tires, and he's not changing wheels, then a 2" narrower tire and taller sidewalls (remember, both inter-relate) will appear very differently to the entire suspension. A thick swaybar, compliant spring, and off-road shock (that works with 265/70s) could spell disaster when trying to control the sidewall deformation (folding), weight transfer, and pitch (roll-center) that skinny 85 series tire would present in an on-road emergency maneuver.

Moving, say, 2" wider and proportionately taller (staying 70 series) would affect the suspension geometry too. But not in a way that would affect lateral stability or loss of control, or the propensity of a tall skinny truck to roll over.

Speaking of tall skinny trucks rolling over.....the 2001-up Mitsubishi Montero is known for it. Google "Montero rollover" and it's very easy to find. Consumer Reports made a huge deal over how badly the 2001-up Montero failed their rollover tests. There are lawyers that specialize in suing over Montero rollover accidents.

And now you're going to amplify that by fitting taller skinnier tires!?!?!

Really good advice here on these forums. Well done!

http://www.rockcrawler.com/features/newsshorts/01june/montero.asp

 

[2scars]

I just picked up a set of the Cooper ATP's, close friend to the AT3, and SO FAR I like them. Will be taking them out this weekend to see how they do in dirt. Nothing crazy, fire roads, but that is why I have them. Very smooth compared to my old KM1s. I will update later on.

 

[stioc]

The Hummer H2 came standard with 315/70-17s. My Sub 2500 has the same basic suspension components, and I've upgraded my tie rod ends and ball joints with HD H2 units and run forged H2 wheels that shift the centerline to compensate for the increased width. So in my application, a 6,500 pound SUV, it's a big upgrade. Safer, more stable.

Wow, you just contradicted yourself and proved my point by saying the H2 has the same basic suspension components as your Sub yet the Sub came with skinnier tires. In other words going wider to skinnier tire or vice-versa, to an extent, is well within the design limits of the suspension components. Does the skinnier tire make the Subs more dangerous because the H2s have wider tires or perhaps the excessively wider tires are nothing more than the 'cool' factor as well as selling to a particular market.
Just because a car came with one type of tire, filter, exhaust doesn't mean it has to be absolutely the same from that point on or you're messing with the engineering limits. Sure there are compromises with every change but then every car/truck comes from the factory as a compromise because different people have different needs.

The LT235/85R16E tire itself is not a problem. It's a problem when you take a tall skinny truck with a high center of gravity, one that was engineered for a 265mm tire with a 70 series sidewall, and fit 4 inches less width per axle, and increase the sidewall aspect ratio over 20%. It's not just the height of the sidewall, and it's not just the width of the tire (although that's the worse offender of the two variables), it's the relationship between a skinnier footprint AND a relatively tall sidewall......note that I said "relative", as the relationship or aspect ratio between the width and height is important in on-road stability.

Agreed.

Furthermore, a 32" tire on 15s is typically 10.5" wide or wider. In a LT235/85R16E Cooper AT3, it is less than 7" wide. Less stable.

Unless Cooper is building some weird tire a 235mm tire is 9.4" wide.

German sports sedans typically have a much lower center of gravity than a top-heavy, skinny SUV like a Montero. On top of that, a typical German sports sedan has a 60 series tire (or lower)....never a 85 series. And even though a Montero isn't super heavy, it's still a lot heavier than a German sports sedan that would wear a 225mm tire.

Obviously, but my point was the 235 width may "seem" skinnier by today's standards in the monster truck world but 9.5" of contact patch x 4 is not a joke either.

You've got to be kidding me about the heat build up. That scenario is completely invalid to this discussion.

I wasn't kidding but you're right tire temps have nothing to do with this discussion. I threw that in there in trying to understand your angle on this whole 'Expo recommends skinnier but they're all stupid, I know what I'm talking about because...?'.

I agree that monster tires sticking out 3" to the side can also be a dumb move. But we're not talking about that, are we?
It's rare that a manufacturer has a steering center (virtual or actual) directly through the center of the tire. So anytime you change width, you change that geometry. Wider or narrower.
Since his truck was engineered for 265mm wide tires, and he's not changing wheels, then a 2" narrower tire and taller sidewalls (remember, both inter-relate) will appear very differently to the entire suspension. A thick swaybar, compliant spring, and off-road shock (that works with 265/70s) could spell disaster when trying to control the sidewall deformation (folding), weight transfer, and pitch (roll-center) that skinny 85 series tire would present in an on-road emergency maneuver.

Moving, say, 2" wider and proportionately taller (staying 70 series) would affect the suspension geometry too. But not in a way that would affect lateral stability or loss of control, or the propensity of a tall skinny truck to roll over.

Partially correct; just by reducing the width of the tire you're not affecting the suspension geometry and you're not changing the track by going wider or skinnier- unless you change the offset/backspacing on the wheels.

Speaking of tall skinny trucks rolling over.....the 2001-up Mitsubishi Montero is known for it. Google "Montero rollover" and it's very easy to find. Consumer Reports made a huge deal over how badly the 2001-up Montero failed their rollover tests. There are lawyers that specialize in suing over Montero rollover accidents.

And now you're going to amplify that by fitting taller skinnier tires!?!?!

Really good advice here on these forums. Well done!

http://www.rockcrawler.com/features/newsshorts/01june/montero.asp

Agreed, anytime you lift a truck you increase its CoG, that combined with 'stickier' tires is what causes rollovers, it has very little to do with the width of a tire.

Nice pic and there're are plenty of similar pics of many other rolled trucks with massive tires too...also, at one point or another CS has reported various vehicles having the same issue mind you these are all stock with the original suspension geometry, tires etc. The Isuzu Trooper, 4runner, Explorers etc were found to be unsafe in emergency maneuvers. So the take away is we should all drive Lotus Elises because they wouldn't exhibit this behavior in a 50mph emergency maneuver

Going back to this discussion I think on a Montero a 255 tire would look great and be just fine if the OP wants more height too. The 235 will look a bit too skinny and is still 32". So my suggestion is to stick with the 265s if you're not looking for additional clearance under the diffs.

 

[no-pistons]

235's are way too wide!:sombrero:

I got 215/85-16s! Cooper AT3 too. Very happy with them, ride nice and are quiet.

OH No, I'm going to flip over and the E rating is going to be so stiff that my teeth will fall out!

 

[Kaisen]

Wow, you just contradicted yourself and proved my point by saying the H2 has the same basic suspension components as your Sub yet the Sub came with skinnier tires. In other words going wider to skinnier tire or vice-versa, to an extent, is well within the design limits of the suspension components.

No. Please re-read my post. I fit different H2 upper and lower ball joints and H2 tie rod ends. I also fit factory wheels that have the correct offset for the wider tires.

Does the skinnier tire make the Subs more dangerous because the H2s have wider tires or perhaps the excessively wider tires are nothing more than the 'cool' factor as well as selling to a particular market.

The truck handles significantly better (more stable) with the 285/70-17s, but my biggest reason for fitting them was the gearing change that the taller tire gave. The width is simply a function of the height, the corrective 17" wheel, and wanting to stay in the 70-75% aspect ratio. H2s fitted 315/70-17 for ground clearance, stability, an off-road capability. Since I run 3.73s and not 4.10s, the 315s weren't for me, nor would they clear without trimming.

Just because a car came with one type of tire, filter, exhaust doesn't mean it has to be absolutely the same from that point on or you're messing with the engineering limits. Sure there are compromises with every change but then every car/truck comes from the factory as a compromise because different people have different needs.

In what world is taking a vehicle with relatively poor stability and making modifications that make those attributes worse (and potentially unsafe) an acceptable compromise?

Unless Cooper is building some weird tire a 235mm tire is 9.4" wide.

Nope. The LT235/85R16E Cooper AT3 is 6.7" at the tread. The part that matters. The only part that makes contact with the road.

Obviously, but my point was the 235 width may "seem" skinnier by today's standards in the monster truck world but 9.5" of contact patch x 4 is not a joke either.

Maybe not, but 6.7" of contact patch x 4 is a joke on a high center of gravity skinny 4x4 SUV

Agreed, anytime you lift a truck you increase its CoG, that combined with 'stickier' tires is what causes rollovers, it has very little to do with the width of a tire.

In the case of a 2001 Montero with LT235/85R16E AT3s, in a high-speed emergency maneuver the tire would roll onto its sidewall, allowing the weight to transfer further, allowing the angle/attitude of the truck to dip a couple degrees further, and pitching the truck further towards roll. Amplified, perhaps, by faster (twitchier) turn-in of skinnier tires.

Nice pic and there're are plenty of similar pics of many other rolled trucks with massive tires too...also, at one point or another CS has reported various vehicles having the same issue mind you these are all stock with the original suspension geometry, tires etc. The Isuzu Trooper, 4runner, Explorers etc were found to be unsafe in emergency maneuvers. So the take away is we should all drive Lotus Elises because they wouldn't exhibit this behavior in a 50mph emergency maneuver

Consumer Reports found exactly three vehicles in 30+ years of testing that exhibited an unsafe propensity to rollover....the 2001 Montero, the Suzuki Samurai, and the Isuzu Trooper. What do they all have in common?

The take away is that "expedition vehicles" with high centers of gravity (and maybe a roof rack full of gear) need to fully understand the trade-offs between safe on-road stability and better off-road characteristics. If your rig sees more trail than road, and you want to fit tall skinny tires, then understand those limitations when you are on the street. Take it easy, and load weight low. Don't unload all of your normal gear and cargo but leave your spare wheel/tire, hi-lift, and full jerry cans on your roof rack and run 75mph on the freeway.

Going back to this discussion I think on a Montero a 255 tire would look great and be just fine if the OP wants more height too. The 235 will look a bit too skinny and is still 32". So my suggestion is to stick with the 265s if you're not looking for additional clearance under the diffs.

A 255/85-16 would be better for this truck. Agreed.

 

[Kaisen]

Forgot the 6.7" tread proof:

 

[stioc]

The actual tread width is never the same as the section width i.e. even a 265 which has a section width of ~10.5" is only 7.8" for the tread width for the AT3s. Interestingly enough I measured my 235 Duratracs' tread width and it's approx. 8" same as a 265 AT3!

Anyway, I understand your point (a valid one) about putting skinny tires on tall and narrow SUVs but it's all relative. I would hope the owners would do some due-diligence on their own, evaluate how they'll use their truck etc before taking suggestions from anyone on the Internet. I was a bit put off when I saw your two recent posts basically saying 'Expo recommends Tacomas and skinny tires because it's ExPo and there's no rhyme or reason for the suggestions'. There're all kinds of awesome Expo trucks here, some ingenious solutions, ideas and suggestions from members just like you who're helping others out by sharing their own experiences and lessons learned. I think overall the ExPo site and the community is an awesome one-stop shop for anyone interested in overlanding, where else can you find sections on camping food to GPS to HAM to vehicle modifications to overland medicine etc all in a single site.

 

[magoh76]

I've really been dithering back and forth on tire size, but I've found a solution. I bought a set of 4 235/85r16 BFG KO tires off Craigslist that came mounted on some Chevy steel wheels. Bolted right up to the Monty. Paid $130 for the whole shebang. They are about 30% tread life left, but it gives me a chance to try out the skinny tires without a huge $$ commitment. Drove to my out-laws tonight, a trip that includes 75-mph turnpike, twisty two lane highway, rough blacktop, and "mountain" (as close as we get in NE OK) dirt roads that get graded about once a year. Driveability seems fine, did great on the twisties. Definitely a stiffer ride thanks to the E rating. Only problem I encountered was a shimmy at 70 mph. I'll get them balanced and drive it for a month or so then decide what new tires I'm purchasing. Here's a picture of the Monty with the "new" wheels and tires.

 

[Bobmog]

7.50X16 transplant

Transplanted 7.50x16 XZLs from G-Wagen to Pinz. A little too narrow for the 280GE.

 

[Martinjmpr]

Forgot the 6.7" tread proof:

View attachment 173716

Did you notice that the tread width for the 265/75 is only 7.8"?

Point being that whether you are measuring section width or tread width, the difference between 265 and 235 is only a little over an inch.

I went from 265/70/16 (stock tires) on my 04 Taco to 235/85/16s and couldn't tell any difference in handling, nor in traction.

It's also worth noting that I couldn't tell any difference in MPG.

That's experience, not opinion, but of course YMMV. :ylsmoke:

FWIW I went from 265/70/16s on my current 4th gen 4runner to slightly skinnier 255/75/17s. Haven't noticed any difference in handling but of course going to a taller tire + going from snow/AT tires (Cooper Discoverer M+S) to MTs (BFG MTs) accounts for the biggest difference.

I'm actually fairly agnostic on the 235 vs bigger subject. When I went to put new tires on my '99 T4R I initially wanted 235s but they didn't have any in stock so I went with 265/75's. After looking at the vehicle with them on, I figured the 265's looked better than the skinnier tires would have. Honestly once my MTs wear out I'll probably go to a BFG AT in 265 width (since I have a set of both 17s and 16s I can pick and choose between 265/75/16 or 265/70/17. Most likely I'll stick with the 17s even though they're a bit more expensive because I like my FJ Cruiser black steelies better than the factory alloys.)

Seems to me if you're testing the traction limits of your tires on a big, top-heavy SUV, you're doing it wrong anyway.

 

[Kaisen]

Did you notice that the tread width for the 265/75 is only 7.8"?

Point being that whether you are measuring section width or tread width, the difference between 265 and 235 is only a little over an inch.

Ummmm..... he has 265/70R16s on his Monty.....look at the chart and they are 8.70" so that's two inches per tire, two tires per axle, so 4" of lost tread width at the ground. EXACTLY what I said in the first place.

It doesn't matter anyway. ExPoers will load a couple hundred pounds of 'expedition' crap on their roof, disconnect their swaybars, overload their suspensons, and fit 100 series foldable-sidewall tires no matter what I say. Which is fine for navigating the ox paths in Patagonia, where they clearly spend 99% of their time.

 

[Co-opski]

Ummmm..... he has 265/70R16s on his Monty.....look at the chart and they are 8.70" so that's two inches per tire, two tires per axle, so 4" of lost tread width at the ground. EXACTLY what I said in the first place.

It doesn't matter anyway. ExPoers will load a couple hundred pounds of 'expedition' crap on their roof, disconnect their swaybars, overload their suspensons, and fit 100 series foldable-sidewall tires no matter what I say. Which is fine for navigating the ox paths in Patagonia, where they clearly spend 99% of their time.

Sorry to hear you are not in Patagonia at the moment, I heard the skiing is going off.

Please tell us more on how you feel about the import drivers stretching side walls and the Cali-lean Chevy Trucks.

My 235/85 16 did not stretch that far on my 7 inch wide Isuzu wheel and I want the JDM Hella Flush look on my Nissan. And you drive a Chevy and I think you guys invented the Cali-lean, If I were to take off my OME dakar springs would this new look adversely change my aerodynamics of a RTT?

 

[no-pistons]

...no matter what I say.

Out of curiosity, who are you to tell anybody what to do?

Are you just sitting there looking at numbers on a screen or do you have real experience with skinnier tires?

BTW, I drove a bunch of winding mountain roads this weekend with a Discovery on 215/85-16 tires and no rear sway bar. No problems whatsoever. Most cars couldn't even keep up with me!

My much bigger and heavier 100 Series Land Cruiser is sitting on 255/85-16. No problems there either.

Both trucks drive and corner nicely on the roads, and perform great off road.


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