Rubicon stock rims with 35x12.50R17LT

[AlwaysRecord]

The JT in my avitar (not mine) was outfitted from the dealership with General grabber X3's 35x12.50R17LT - when I look up the specs for that tire it lists the approved rim width as 8.5 - 10.0 - 11.0.

Is this a problem since its my understanding the stock rubicon rims are 7.5' width???

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[bgenlvtex]

7.5" wheel is much too narrow for a 12.5" cross section.

That said, people do it all the time and I have seen people get good service from their tires even under these conditions.

There is a "design" rim width which is exactly what it sounds like, is where all criteria are established and will provide best service.

Then there is "approved rim widths", which are also exactly what they sound like. The manufacturer expects the tire to function reasonably with no conditions that would affect the tire warranty detrimentally.

Outside those approved and design rim widths(which overlap obviously) there is reasonable cause to expect that conditions may occur because of those incorrect dimensions, that will negatively impact the tire and/or create a failure outside of warranty conditions.

Typically problems with too narrow a rim width show up in irregular tread wear problems (exacerbated by more aggressive tread designs) some of which can be mitigated with air pressure.

However, belt edge separation, separation at the termination of the turn up (seen as cracking above the GG ring, gutter erosion in the bead area, and torque cracking are all functions of an improperly paired tire/wheel combination and/or the result of too low air pressure used to mitigate the previously mentioned tread wear problems.

So the short answer is no, it is not correct.

People will be along to tell you that they have done it for years without any evidence of detriment, I'm not saying they didn't and will not argue them down. But what I am telling you is what you will find to be true with any manufacturer where their engineering data is published.

The General X3's are some nice tires too. If the 35's don't prove to be a power/fuel mileage problem I'd keep them and just buy a correct set of wheels.

 

[AlwaysRecord]

7.5" wheel is much too narrow for a 12.5" cross section.

That said, people do it all the time and I have seen people get good service from their tires even under these conditions.

There is a "design" rim width which is exactly what it sounds like, is where all criteria are established and will provide best service.

Then there is "approved rim widths", which are also exactly what they sound like. The manufacturer expects the tire to function reasonably with no conditions that would affect the tire warranty detrimentally.

Outside those approved and design rim widths(which overlap obviously) there is reasonable cause to expect that conditions may occur because of those incorrect dimensions, that will negatively impact the tire and/or create a failure outside of warranty conditions.

Typically problems with too narrow a rim width show up in irregular tread wear problems (exacerbated by more aggressive tread designs) some of which can be mitigated with air pressure.

However, belt edge separation, separation at the termination of the turn up (seen as cracking above the GG ring, gutter erosion in the bead area, and torque cracking are all functions of an improperly paired tire/wheel combination and/or the result of too low air pressure used to mitigate the previously mentioned tread wear problems.

So the short answer is no, it is not correct.

People will be along to tell you that they have done it for years without any evidence of detriment, I'm not saying they didn't and will not argue them down. But what I am telling you is what you will find to be true with any manufacturer where their engineering data is published.

The General X3's are some nice tires too. If the 35's don't prove to be a power/fuel mileage problem I'd keep them and just buy a correct set of wheels.

@bgenlvtex - Thank You!! much appreciated. I have a JT coming (in JB) and trying to pick out some tires and like the General X3's on my friends JT Rubi.....but once I started looking in to the sizes I started to get confused.....

On my own I may keep the stock wheels and skin them with the General X3's but in the 295/70R17 version - what I don't like though is that these spec out at a overall diameter of 33.3" - which isn't all the much bigger than the OEM Falkens......like to get in to a 35" tire

 

[bgenlvtex]

@bgenlvtex - Thank You!! much appreciated. I have a JT coming (in JB) and trying to pick out some tires and like the General X3's on my friends JT Rubi.....but once I started looking in to the sizes I started to get confused.....

On my own I may keep the stock wheels and skin them with the General X3's but in the 295/70R17 version - what I don't like though is that these spec out at a overall diameter of 33.3" - which isn't all the much bigger than the OEM Falkens......like to get in to a 35" tire

There are just no free rides on this deal. You could use 285/75R17 on the same wheel (correctly) and get a 34" tire, but there are not many choices in that size. And for what? You would be gaining an (virtually imperceptible) 1/2" of ground clearance.

There are diminishing returns on this stuff. If it is a purely cosmetic consideration and you will not be using the truck as an actual truck where your field expedient final drive ratio adjustment becomes a factor, then increasing the O. D. of the tire is easy enough to do.

But at the end of the day, if you want your shit to be right on your new truck. Then you will need to come to grips with what I already said. There are no free rides.

One final note is to pay attention to the weight of your tire and wheel choices. Additional unsprung weight, and additional weight in rotating mass are the enemies of everything meaningful in your vehicle.

 

[bgenlvtex]

As an additional note, I would really like to see tire manufacturers expand the 75 series offerings.

For example in this case 285/75R17 34", 295/75R17 35", 305/75R17 36".

All could be used on wheels that come OEM on many different trucks, afford more ground clearance and present less irregular wear issues. I have always been a fan of narrower and taller tires on trucks, they work.

P78-15, Q78-15, 900-16 some of my favorite sizes.

 

[TennesseePA]

OK I am going to ask a few questions about the many posts above and then offer my analysis of the 12.5 on 7.5. I read the words "approved rim width" a lot up there but I have never read it in a tire spec sheet. I have read "recommended rim width" in spec sheets though. I will admit right here in front of God and all His children that I have not read all manufacturer spec sheets, I haven't even read a lot of them but I have read a few and none of the ones I have personally seen stated "allowed."

Now on to my opinion and how I got to it. I think we can all agree now that a modern tire's tread surface is formed by the dual plies of steel belts that are part of its construction. Given that fact, squeezing the bead cannot affect the tread shape. Many people argue that putting a 12.5 on a 7.5 will cause the tire to run on the center of the tread causing uneven tread wear. That is not the case in my personal experience as well as the thousands and thousands of thread posts on every single forum that addresses the issue. So why do manufacturers RECOMMEND an 8.5-10.5 rim width for most 12.5 tires? Glad you asked. If you mount your tire on a more narrow rim you squeeze the bead into a more narrow space. Since we have already established that the steel belts do not stretch and, therefore, the overall diameter of the tire cannot change the only dimension that can change is the section width. So if you mount a 35x12.5r17 tire on a 7.5x17 rim you will not realize the entire 12.5 section width that you paid for. I personally do not care about that since my goal has always been to keep my tires under my Jeep. I have an LE with a 2 inch Mopar lift kit and 37x12.5r17 BFG KO2s on the stock LE rims. I picked the truck up with 12 miles on it already converted to this configuration and it now has 3300 miles on it and I have experienced zero ill effects. Now as an unofficial anecdote to my opinion go to the Discount Tire website and look up any old 35x12.5r17 tire and you will see that they recommend 7.5-10.5 rim width on the tires. The manufacturers recommend the width of the rims based on their advertised section width. They do this so that a guy doesn't put their tires on a 7.5 and complain when he realizes that his effective section width is only 11.5. That is my scientifically unsupported but well thought out opinion on the matter. But if you do a little digging you can see examples of where automobile manufacturers have sent cars out of their factories with tires mounted outside of the "recommended rim width." I have posted links to the articles cited here in other threads on the subject. The only one that comes to mind is the LE on 35s in the show and tell category.

edited to add that if you want your 35 to fall in the "recommended rim width" take a look at the Nitto 35x11.5r17. Since that is the effective section width you will get with a 12.5 tire anyway.

second edit to add that I just noticed the Nitto does in deed say "approved"

 

[bgenlvtex]

OK I am going to ask a few questions about the many posts above and then offer my analysis of the 12.5 on 7.5. I read the words "approved rim width" a lot up there but I have never read it in a tire spec sheet. I have read "recommended rim width" in spec sheets though. I will admit right here in front of God and all His children that I have not read all manufacturer spec sheets, I haven't even read a lot of them but I have read a few and none of the ones I have personally seen stated "allowed."

Now on to my opinion and how I got to it. I think we can all agree now that a modern tire's tread surface is formed by the dual plies of steel belts that are part of its construction. Given that fact, squeezing the bead cannot affect the tread shape. Many people argue that putting a 12.5 on a 7.5 will cause the tire to run on the center of the tread causing uneven tread wear. That is not the case in my personal experience as well as the thousands and thousands of thread posts on every single forum that addresses the issue. So why do manufacturers RECOMMEND an 8.5-10.5 rim width for most 12.5 tires? Glad you asked. If you mount your tire on a more narrow rim you squeeze the bead into a more narrow space. Since we have already established that the steel belts do not stretch and, therefore, the overall diameter of the tire cannot change the only dimension that can change is the section width. So if you mount a 35x12.5r17 tire on a 7.5x17 rim you will not realize the entire 12.5 section width that you paid for. I personally do not care about that since my goal has always been to keep my tires under my Jeep. I have an LE with a 2 inch Mopar lift kit and 37x12.5r17 BFG KO2s on the stock LE rims. I picked the truck up with 12 miles on it already converted to this configuration and it now has 3300 miles on it and I have experienced zero ill effects. Now as an unofficial anecdote to my opinion go to the Discount Tire website and look up any old 35x12.5r17 tire and you will see that they recommend 7.5-10.5 rim width on the tires. The manufacturers recommend the width of the rims based on their advertised section width. They do this so that a guy doesn't put their tires on a 7.5 and complain when he realizes that his effective section width is only 11.5. That is my scientifically unsupported but well thought out opinion on the matter. But if you do a little digging you can see examples of where automobile manufacturers have sent cars out of their factories with tires mounted outside of the "recommended rim width." I have posted links to the articles cited here in other threads on the subject. The only one that comes to mind is the LE on 35s in the show and tell category.

edited to add that if you want your 35 to fall in the "recommended rim width" take a look at the Nitto 35x11.5r17. Since that is the effective section width you will get with a 12.5 tire anyway.

second edit to add that I just noticed the Nitto does in deed say "approved"

I said in my original post I would not argue people down and I will not.

I will tell you however that your supposition that the tread face does not distort by altering section width is absolutely wrong regardless how well thought your opinion may be. The "belt" is not a piece of steel, it is flexible and responsive to what the body ply(s) are doing. You can easily distort the tread shoulder simply by mis-mounting on the correct design wheel (bad lubrication, not clean, flange distortion,etc.)

Design rim width- the advertised section width (and all other engineering data) is established using this width
Approved rim width- section width will vary +/- based on width of wheel, but the tire will perform as intended

Outside of those parameters you are in territory that the manufacture of the tire does not recommend for best service and safest operation.

 

[TennesseePA]

https://www.discounttiredirect.com/buy-tires/bfgoodrich-all-terrain-t-a-ko2/p/29037

I will argue with 100% certainty that the steel belts in fact do limit the overall tire diameter regardless of rim width and inflation pressure. Please read through the citation above and you will see that the author of that article agrees with me. The steel belt plies are installed in a manner where the steel belts run at a 45 degree angle to the direction of travel. Each of the two plies are installed so that the steel belts run perpendicular to each other so what you end up with is multiple steel wires arranged at a 90 degree angle to one another across the tread. The cited article spells this out very clear. The tire will perform as engineered outside of the designated parameters BUT it will NOT conform to the advertised dimensions.
https://www.discounttiredirect.com/buy-tires/bfgoodrich-all-terrain-t-a-ko2/p/29037
Here is Discount Tire's opinion on the matter. Wouldn't it stand to reason that a company as big and as smart as DTD would ask a lawyer or two to review that before they put it out there for the world? If you are correct I can go crash my JT on my way to work and then I can sue them for selling me those tires and telling me it is OK to put them on my truck. Problem is that it is OK to put them on my truck so...Oh, guess what? She is retired now but my mom worked for a little company called Bridgestone just south of Nashville in the town of Smyrna, TN. I am in healthcare now but before deciding to get into medicine I was a senior in mechanical engineering. Granted I did not graduate as an engineer but I was one semester away from it. I have had the materials science classes and the statics classes that engineers use to design these things. You are free to have your thoughts on the issue. I will let the articles cited along with my experience, logic and knowledge be measured against your experience, logic and knowledge and whoever reads this can decide for themselves. I really do love to learn about all things science so if you can cite and provide evidence for your opinion I would love to read through it and compare to what I have cited. This is not an argument here, this is an attempt to gain knowledge.

 

[bgenlvtex]

You're using the term diameter when you mean circumference.

If you let 15 pounds of air out of the tire what happens to the radius, and as a matter of consequence the diameter? That's right it changes and the belt package does not limit that.

The deformation and all consequent problems occur at the shoulder ( the juncture of the body ply(s) and the belt package) with regards to correct or incorrect rim widths.

@AlwaysRecord , If you need further input IM and I'll help you as much as I can.

 

[TennesseePA]

How does the use of circumference vs diameter affect my point. Circumference cannot be measured without first knowing diameter right? Because of the contact patch tires are not really a circle anyway.
I will concede the diameter vs circumference point. Now other than semantics what proof do you have that a more narrow rim has the ability to change the length of the steel belt plies thereby affecting the overall circumference of the tire? Once again I am attempting to gain knowledge here. I am well aware that the inherent flaw of the radial tire design is the disunion of the tread plies from the sidewalls at the shoulder. But there are also design elements such as adding extra material at the shoulder to disperse the forces. https://www.sciencedirect.com/topics/engineering/radial-tire
https://www.sema.org/files/attachments/WTC-2011-05-Bias-vs-Radial-Tire-Wheel-Fitment.pdf
Some interesting reading on the subject.

 

[WXman]

There are just no free rides on this deal. You could use 285/75R17 on the same wheel (correctly) and get a 34" tire, but there are not many choices in that size. And for what? You would be gaining an (virtually imperceptible) 1/2" of ground clearance.

There are diminishing returns on this stuff. If it is a purely cosmetic consideration and you will not be using the truck as an actual truck where your field expedient final drive ratio adjustment becomes a factor, then increasing the O. D. of the tire is easy enough to do.

But at the end of the day, if you want your shit to be right on your new truck. Then you will need to come to grips with what I already said. There are no free rides.

One final note is to pay attention to the weight of your tire and wheel choices. Additional unsprung weight, and additional weight in rotating mass are the enemies of everything meaningful in your vehicle.

As an additional note, I would really like to see tire manufacturers expand the 75 series offerings.

For example in this case 285/75R17 34", 295/75R17 35", 305/75R17 36".

All could be used on wheels that come OEM on many different trucks, afford more ground clearance and present less irregular wear issues. I have always been a fan of narrower and taller tires on trucks, they work.

P78-15, Q78-15, 900-16 some of my favorite sizes.

I agree with most of this. Additional ground clearance is halved when upsizing tires, so from a functional point of view it's many times not worth it. This is why I try to remind all the people desparately searching for Rubicon take-offs that spending $1,200 for 0.5" of ground clearance is usually a silly thing to do.

Also, weight is a BIG deal on a midsize truck and the General X3 happens to be one of the heaviest tires on the market.

And yeah, the 75-series aspect ratios are nice. More sidewall is better for ride quality, ground clearance, and other reasons.

Pick your tires carefully! Personally I think 285/75-17 is my favorite all-around tire size. My set measured a true 33" tall while on the Jeep and they looked nice too.

 

[bgenlvtex]

I agree with most of this. Additional ground clearance is halved when upsizing tires, so from a functional point of view it's many times not worth it. This is why I try to remind all the people desparately searching for Rubicon take-offs that spending $1,200 for 0.5" of ground clearance is usually a silly thing to do.

Also, weight is a BIG deal on a midsize truck and the General X3 happens to be one of the heaviest tires on the market.

And yeah, the 75-series aspect ratios are nice. More sidewall is better for ride quality, ground clearance, and other reasons.

Pick your tires carefully! Personally I think 285/75-17 is my favorite all-around tire size. My set measured a true 33" tall while on the Jeep and they looked nice too.

285/75R17 is a great size, unfortunately they are not produced by very many manufacturers.

Static loaded radius is the number to be concerned with where ground clearance is concerned. Remember that that number is not determined at 15psi. So if you air down that radius is reduced and as a matter of consequence so is ground clearance.

So if you invest heavily to gain that extra half inch or inch, remember that when you air down, that gain will be lost.

 

[WMWHV]

Not sure if it is better to wake up this thread or start a new one, but I appreciate the analytical, if divergent views expressed above and figure you guys may be following this thread and hence will see my questions. First of all, to stay relevant to the thread, I note that Mopar has a number of 8.5 inch wide wheels available. Why can’t they just offer 35s with 8.5 wheels as a factory option? (End rant.) I am struggling with what tire diameter I want on my hopefully soon to be available eco diesel JTR. I have 33s on my LJ, but sold the 35s that were on it when I bought it because I thought they were too heavy and too much for the Jeep. So, what do I get from a bigger diameter tire? An inch of axle and overall clearance for every two inches of tire diameter. Is there something else positive I am missing, because everything else seem negative to me? More weight, potential to rub when at maximum flex, poorer braking, messing up gear ratios, etc. I am less concerned about looking cool than true performance. My use case is 99% on highway just like almost everybody else. To drive to anyplace fun to wheel from Houston takes 10 hours on a highway, so road manners are a must. I do volunteer search and rescue work, so I want serious off road ability the few times important stuff like lives might depend on it, but most of my overland driving does not require hairy rock crawling. I tried it and am not a fan. I need height to get through Houston floods, where every inch can count. My proposed solution is maybe 35s and a modest lift. Maybe the 2 inch lift and keep the 33s. I am thinking the ultimate solution to the departure and break over angles is belly armor and a winch rather than bigger tires and more lift. Thoughts?

 

[Renegade]

Not sure if it is better to wake up this thread or start a new one, but I appreciate the analytical, if divergent views expressed above and figure you guys may be following this thread and hence will see my questions. First of all, to stay relevant to the thread, I note that Mopar has a number of 8.5 inch wide wheels available. Why can’t they just offer 35s with 8.5 wheels as a factory option? (End rant.) I am struggling with what tire diameter I want on my hopefully soon to be available eco diesel JTR. I have 33s on my LJ, but sold the 35s that were on it when I bought it because I thought they were too heavy and too much for the Jeep. So, what do I get from a bigger diameter tire? An inch of axle and overall clearance for every two inches of tire diameter. Is there something else positive I am missing, because everything else seem negative to me? More weight, potential to rub when at maximum flex, poorer braking, messing up gear ratios, etc. I am less concerned about looking cool than true performance. My use case is 99% on highway just like almost everybody else. To drive to anyplace fun to wheel from Houston takes 10 hours on a highway, so road manners are a must. I do volunteer search and rescue work, so I want serious off road ability the few times important stuff like lives might depend on it, but most of my overland driving does not require hairy rock crawling. I tried it and am not a fan. I need height to get through Houston floods, where every inch can count. My proposed solution is maybe 35s and a modest lift. Maybe the 2 inch lift and keep the 33s. I am thinking the ultimate solution to the departure and break over angles is belly armor and a winch rather than bigger tires and more lift. Thoughts?

Do whatever makes YOU happy, but rest assure that the JT handles 35s and larger tires very well, especially with the automatic transmission. I also had an LJ on 33s, and my JT on 37s will blow the LJ away in pretty much every way.

 

[rafaelsmith]

I am still waiting for my JTR to be delivered so will have some time before I need new tires.. At that point the decision will be a tough one....I want to go bigger...35s....maybe a 2" "budget" lift....but really hate the idea of having to throw $$ at new wheels. Just not a wheel guy so almost always have stuck with whatever vehicle came with. Really wish Jeep would use more "upgrade proof" wheels.

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