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Discussion Starter #1
Why do folks want to change to the 245 tire? I think they are about 3/4 inch wider. Are they taller also? I see where some of the 245s are rubbing the fenders. Better stability? Softer ride? Just better lookin'? More choices? Seems like 225 tire would get the better mpg, just guessing.
 

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For me it's better looking, better traction, more damage resistant tire, and there semed to be more choices also. A 245/75/16 is taller as well as wider than a 225/75/16.

The height is calculated as 75% of 245 or 225. So a 205/50/15 tire the height would be calculated as 50% of 205mm . Some tires listed as the same size still have different dimensions however. If you look on a good tire site such as tire rack you can find their exact diameter etc though.

I thought I had a bit of a fender liner rubbing, but it was just a fender liner sticking out instead of being behind another liner where it should have been. Fixed it and no rubbing now.

Most likely it will get a bit worse mpg, but not enough to deter me from switching.

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Discussion Starter #3
thanks for the info. I didn't know about the height calculation.
 

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greetings,
here is a tire size comparison calculator for your doodling pleasure. It is what i have used on each of my builds.

I decided to stick with the stock size on our 2017 PM (225/75r16) but put on BFG KO2 all season/all terrain that really make a big difference IMO on handling and looks. With all the wet road conditions i must endure on the Oregon Coast i always side with narrow tires to cut through the standing water (we get ~80" a year rainfall).

Looks fine to me : )



Thom
 

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Discussion Starter #5 (Edited)
Thanks for the online calculator. That is awesome and fun to mess with. Really educational. The 245s are 1.2 inches taller and .7 inches wider according to the calculator. Your tires look good, are they noisey with that tread?
 

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Thanks for the online calculator. That is awesome and fun to mess with. Really educational. The 245s are 1.2 inches taller and .7 inches wider according to the calculator. Your tires look good, are they noisey with that tread?
Resurrecting a slightly old thread because I'm new here.

I too would like to hear about people's experiences with the K02's with regard to increased noise. Is there much difference?

The PMs on the lot use Nexen tires. Mine's being built and so I'm not sure what tires they'll come with.
 

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While playing with the tire size calculator look at a 245/70-16 tire. Slightly wider and about the same overall diameter. When looking at wider tires, another spec to look at is the range of rim width allowed. The PM has 6" wide wheels. Not all 245 tires are suggested for that width of rim. If you go to a wider tire with a lower profile, to maintain overall diameter, odds are you will need to get a wider rim. If you want to go crazy you can get a BFG KO/2 in an LT265/60-18 which is only an inch bigger than stock, but it needs a minimum of a 7.5 inch rim. While the diameter may fit, the extra width may not unless you can find a proper wheel offset. That same web site quoted above has a page to compare wheel offset.

https://tiresize.com/wheel-offset-calculator/


While there are still several wheel size and tire size combos that will technically fit, any change you make will have a beneficial effect AND a detrimental effect. A heavier wheel/tire combo will slow down suspension response. The OEM suspension was made for a specific weight of tire. Changing diameter of a tire is the same as changing gearing slightly. A larger diameter will be a little slower to accelerate, but will cruise at a lower RPM on the highway. This lower RPM may translate to better highway mpg, but since you can't tell your PM the tires are larger the speedometer and odometer don't know about the difference so calculating your speed and mileage are affected. At 60 mph on your speedometer with a 245/75-16 you will travel at 62.4 mph. While the stock tire will turn 712 times in a mile, the 245/75-16 only turns 684 times in a mile since it is larger in diameter, so when you have travelled 100 miles, your odo will report that you have only travelled 96 miles.

Confusing, isn't it? In order to determine your true miles per gallon, a lot more math is needed! :D
 

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Yeah, I've wondered about the speedometer/odometer/MPG thing. Way back in the '60s, I worked in a Dodge dealer parts department. We could change the speedometer drive gear (ratio) to compensate. But I guess that's no longer possible in a digital world, eh?
 

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Yeah, I've wondered about the speedometer/odometer/MPG thing. Way back in the '60s, I worked in a Dodge dealer parts department. We could change the speedometer drive gear (ratio) to compensate. But I guess that's no longer possible in a digital world, eh?
In the motorcycle world there is a digital conversion box you can get to fix your speedo, but then the odo will be off in the other direction by the same amount. It's a great way to have your 36,000 mile warranty expire in 32,000 miles !
 

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Most GPS units will give you very accurate speedometer readings. After switching to oversized tires on my Scion to improve the ride, I got the side-benefit that my speedometer is much more accurate now per my gps. The downside is my fuel mileage is a bit less. I hadn’t bothered to do the math to determine whether the old tires giving inaccurate odometer readings was the cause of this or the different gearing or a bit of both. It’s likely the something similar would happen to fuel mileage estimates you get from the trip computer.
 

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Most GPS units will give you very accurate speedometer readings. After switching to oversized tires on my Scion to improve the ride, I got the side-benefit that my speedometer is much more accurate now per my gps. The downside is my fuel mileage is a bit less. I hadn’t bothered to do the math to determine whether the old tires giving inaccurate odometer readings was the cause of this or the different gearing or a bit of both. It’s likely the something similar would happen to fuel mileage estimates you get from the trip computer.
I could see that your fuel mileage as estimated by the car computer would be less as it thinks it burned the same amount of fuel but, as far as it knows, you went fewer miles.

But in reality, did your mileage improve? That is, because of the slightly higher gearing, did you get to where you wanted to go but burned less gas than with the smaller tires?

That'd be what I would be expecting, but then humans have a tendency to complicate things. For example, if it's geared higher, a car will accelerate slower and theoretically be more economical. But then someone could want to get similar acceleration as before with the lower gearing, and thus step on the gas pedal further, negating any economy gains.
 

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i had a chance to get an odd size tire but by the time i researched it the guy sold them. they were firestone mud tires in a 215/85/16 after looking into it them seem to be a great option for a larger tire. they are just a tiny bit shorter than the 245 but taller than the 225 and what i liked is that they were not as wide as the 245's. i hope this link works but here is the 215/85 compaired to the stock size. https://tiresize.com/comparison/
 

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I just wanted to add to this thread. I read this thread before I got my promaster, and made up my mind I wanted the larger BFG all terrains in the 245 size. I have a 1 ton long wheel base high roof. I live in minnesota and the stock nexens, or whatever were terrible, ,like driving pure summer tires when it snowed.
With my 245 BFGs I can go down the highway with confidence. Just got back from a 3000 mile road trip from MN to Idaho with no issues, snowed the whole time. I know its not the tire size that helps out so much as the tires, but 245s do fit. There is only about 1/2 inch of clearance in the rear, but I doubt I will ever max out the cargo weight of my Promaster to test the clearance when loaded. Having said that, I do plan to modify the rear fender area if I decide to pull a trailer, because they do look like they would rub eventually.
BFG!
 

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my 2018 3500 ext came with nexxan tires. I planed to rotate them at 40k, but yesterday night i hit some debris on the highway. Tires have 33k miles on them. I took a nap a couple hours later. When i awoke the left front tire was flat. I aired it up and drove it home 400 miles to the tire store. I am an expeditor. I carry loads through all kinds of weather and sometimes heavy loads. I was hoping for at least 80k from the original set. I bought 2 Firestone HT 225/75R16 for the front and swapped side with the rears. I have used this tire on my last promaster and had great luck with wear and handling. At 40k i'll buy 2 more and mount them on the front.
 

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They will fit...some clearance issue in the rear...hammer fixed that...my biggest reason whas because of the availabilty and load rating...its a more pooular tire ...in case of replacement irs easier to find and replace if nessesary since most pickups use this size...second ..they have a higher load rating per tire..never iverload..just peace of mind....

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6.5-8” wide rims
 
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