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Truck tires quick question

Old 07-12-2019, 07:23 AM
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Just my opinion but the OEM tires already look too small for the truck. I've always gone bigger.
Old 07-12-2019, 07:27 AM
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Originally Posted by avalonandl View Post
I believe the 265's are OE. With the OE wheel (which is skinny) you really should NOT go wider if you load up the rear....
a lot of these trucks came OE with 245/75/16's, which were comically small

I would not go wider than 285 wide on the 6.5" wide stock wheels, although I know plenty of people that run 315/75/16's that have never had an issue, one guy dragging a skid steer every day of the week
Old 07-12-2019, 07:50 AM
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Originally Posted by dawgsfish View Post
a lot of these trucks came OE with 245/75/16's, which were comically small

I would not go wider than 285 wide on the 6.5" wide stock wheels, although I know plenty of people that run 315/75/16's that have never had an issue, one guy dragging a skid steer every day of the week

Mine came with 245s. I ran those for the first 207,000 miles and just got tired of looking at it with what looked like small donuts. Mine was really bad because my truck is white with black wheel well moldings. The combination of white truck, black moldings and relatively small tires made it look like the tires were 4-5 sizes too small. At 207k, I switched over to 265s and have run those for the last 196,000 miles. A 3.7% increase in tire circumference. Knocks my speedo off by 2 mph at 70 and throws my odometer off by 37 miles for every thousand but those are really the only 2 differences I can tell. No change in mpg, how it drives or rides or tows. And it looks a whole lot better. Anything bigger would require lifting the front end to clear bigger tires.
Old 07-12-2019, 08:24 AM
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Originally Posted by Back-in-Black View Post
Mine came with 245s. I ran those for the first 207,000 miles and just got tired of looking at it with what looked like small donuts. Mine was really bad because my truck is white with black wheel well moldings. The combination of white truck, black moldings and relatively small tires made it look like the tires were 4-5 sizes too small. At 207k, I switched over to 265s and have run those for the last 196,000 miles. A 3.7% increase in tire circumference. Knocks my speedo off by 2 mph at 70 and throws my odometer off by 37 miles for every thousand but those are really the only 2 differences I can tell. No change in mpg, how it drives or rides or tows. And it looks a whole lot better. Anything bigger would require lifting the front end to clear bigger tires.
Yeah my torsion bars are turned up just a little to take some take out and clear 285's. I don't have any rubbing issues. I may have lost a mpg on the highway coming up from the 265s, really not significant though.
Old 07-12-2019, 09:04 AM
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Originally Posted by Garett View Post
Your on board computers will make the adjustments for the tire size and retune your injector settings and timing.
As others have mentioned, that's a negative, ghost rider.

I've run many different tires in the 300K I've put on my Duramax, from stock 245s to the current 285/70/17s. I've found that the main factor in fuel mileage on my truck is the tread pattern, not necessarily the size. On the highway, with highway tread, I actually get better fuel mileage with a slightly taller tire (.8-1mpg). I assume this is due to running a slightly lower RPM at the same speed. Around town with the taller tire, MPG is about identical. I've been running 285/70/17s for the last few sets of tires, the odometer/speedometer is off 8-11% with new tires of that size, my current new BFG KO2s are off 9.5%. I had a set of Cooper STTs on there in that size a few years ago, they cut mileage 15% (2-3mpg) all around. The truck would not do any better than 18mpg in any situation, where 21 was fairly easily attainable with highway tires. The BFG and Toyo ATs drop mileage 5-8% from highway tread, but they look so much better that I don't care.
Old 07-12-2019, 09:41 AM
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Originally Posted by ParkRanger View Post
As others have mentioned, that's a negative, ghost rider.

I've run many different tires in the 300K I've put on my Duramax, from stock 245s to the current 285/70/17s. I've found that the main factor in fuel mileage on my truck is the tread pattern, not necessarily the size. On the highway, with highway tread, I actually get better fuel mileage with a slightly taller tire (.8-1mpg). I assume this is due to running a slightly lower RPM at the same speed. Around town with the taller tire, MPG is about identical. I've been running 285/70/17s for the last few sets of tires, the odometer/speedometer is off 8-11% with new tires of that size, my current new BFG KO2s are off 9.5%. I had a set of Cooper STTs on there in that size a few years ago, they cut mileage 15% (2-3mpg) all around. The truck would not do any better than 18mpg in any situation, where 21 was fairly easily attainable with highway tires. The BFG and Toyo ATs drop mileage 5-8% from highway tread, but they look so much better that I don't care.
The tires I have on now are 285 Cooper Discoverers (truck came with them and they were brand new when i got the truck.) My average on the highway both hand calculated and via Edge CTS2 is around 21-23. I got about 45k out of them and honestly never recalled rotating them or anything so thats pretty damn good!

Yesterday i went to Discount and NTB to compare a 265 and 285 in person. I just can't do it. 265 is a bigger difference than I thought it was. The sad part is, NTB has 265 Discoverers buy 3 get one right now.. so out the door with road hazard it'd be $683 which is awesome! But, I can't do it. So I'm having 285's put on today at Discount. I'm going to start looking around on Craigslist too for the stock rims on my truck.


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Old 07-12-2019, 10:00 AM
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Originally Posted by ondarvr1 View Post


It doesn’t work that way.
You can say it doesn't work like that all you want but I've had two different truck's computers that would say otherwise. So you can go with what you think you know and I'll go with what I've experienced first hand.

Each time the tire size went up or down the trucks would run like crap for a day while the computer was trying to figure out how to change the settings and to what.....sort'of like the truck was sick for a day.
Old 07-12-2019, 10:07 AM
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that would be the transmission shift points re-learning in the TCM, not the "computer", which I assume you mean ECM, changing engine parameters like you mentioned previously

you can manually program a trans-relearn through various tuning capabilities and feel the same thing as it relearns.
Old 07-12-2019, 10:09 AM
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Originally Posted by Manoverboard123 View Post
The tires I have on now are 285 Cooper Discoverers (truck came with them and they were brand new when i got the truck.) My average on the highway both hand calculated and via Edge CTS2 is around 21-23. I got about 45k out of them and honestly never recalled rotating them or anything so thats pretty damn good!

Yesterday i went to Discount and NTB to compare a 265 and 285 in person. I just can't do it. 265 is a bigger difference than I thought it was. The sad part is, NTB has 265 Discoverers buy 3 get one right now.. so out the door with road hazard it'd be $683 which is awesome! But, I can't do it. So I'm having 285's put on today at Discount. I'm going to start looking around on Craigslist too for the stock rims on my truck.

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I have the Discoverer HT Plus tires on my Ram, 275/60R20s and just put on my second set. They are great highway tires that are aggressive enough for light off road and dirt road capabilities. Got about 50K miles from first set.
Old 07-12-2019, 10:24 AM
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Originally Posted by Garett View Post
You can say it doesn't work like that all you want but I've had two different truck's computers that would say otherwise. So you can go with what you think you know and I'll go with what I've experienced first hand.

Each time the tire size went up or down the trucks would run like crap for a day while the computer was trying to figure out how to change the settings and to what.....sort'of like the truck was sick for a day.
As an old EFILive tuner who is quite familiar with the workings of the ECMs and TCMs we are talking about, I can assure you that the ECU doesn't adjust anything based on tire size without additional human intervention. All the computers see is load and perceived speed. The TCM is constantly learning/changing based on load and power output, but it doesn't care about your tire size. Fuel quantity and timing are set in tables in the ECU, they do not change just because you spent $1000 at the local Discount Tire.

Last edited by ParkRanger; 07-12-2019 at 12:11 PM.
Old 07-12-2019, 11:55 AM
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Originally Posted by Garett View Post
You can say it doesn't work like that all you want but I've had two different truck's computers that would say otherwise. So you can go with what you think you know and I'll go with what I've experienced first hand.

Each time the tire size went up or down the trucks would run like crap for a day while the computer was trying to figure out how to change the settings and to what.....sort'of like the truck was sick for a day.
Unless you manually reset the tire size in the system it has no clue what they are.

Although if they disconnected the battery long enough it may need to re-learn and reprogram itself, which may cause it to run rough for a bit.

This still has nothing to do with it knowing the tire size though. And if there is enough of a change in tire type or size your mileage will change.

Last edited by ondarvr1; 07-14-2019 at 06:55 AM.
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Old 07-12-2019, 02:16 PM
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Just found the pictures I was looking-for! My 2006 E-Cab with the stock 245/75R16 tires on custom wheels.



Same truck, same wheels, but 285/75R16 tires.



Same wheels, different truck, 265/75R16 tires

Old 07-12-2019, 03:24 PM
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Mine currently has 245/75, stock is 265.

The 245s look small, but I had them and they were new, so I stuck them on. They’re just about done now, so I’m looking around.
Old 07-13-2019, 03:14 PM
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Went with 285's! Thanks guys.. I'll get to see her with new shoes in about an hour
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Old 07-13-2019, 07:08 PM
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Well, got the tires on.. I'm happy with them, but not so happy with Discount. So i pick the truck up right when they close.. I drive home, and on the way I notice a loud ticking/clacking noise coming from my front driver. The faster the vehicle, the faster/louder the noise.

I get home, pull the wheel off, and comes to find out the weights they used to balance the tire were hitting the mounting bracket for the caliper.. one strip of weights already had fallen off, the other strip came right off when I barely pulled on them.

To top that off, when I pulled the wheel off i noticed my hub cap was a little loose. Pull the wheel, cap falls off, and I find that they broke 2 of the clips that hold the cap on.

They are going to have a very welcoming Monday morning.....
Old 07-13-2019, 09:40 PM
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This is why I hate getting tires at a big dealer. Went to NTB once, dropped the Jeep off. Came back and 5 oz of weights were hammered on for a 235/75/15 tire.

BTW, all the new guys work on Saturday, and they’re packed. Go on a Tuesday.
Old 07-14-2019, 03:40 AM
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Originally Posted by Garett View Post
You can say it doesn't work like that all you want but I've had two different truck's computers that would say otherwise. So you can go with what you think you know and I'll go with what I've experienced first hand.

Each time the tire size went up or down the trucks would run like crap for a day while the computer was trying to figure out how to change the settings and to what.....sort'of like the truck was sick for a day.
That may indeed be what you are experiencing; sure, but you’re misunderstanding what that is.
Old 07-15-2019, 09:15 AM
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Originally Posted by JKBrad View Post
This is why I hate getting tires at a big dealer. Went to NTB once, dropped the Jeep off. Came back and 5 oz of weights were hammered on for a 235/75/15 tire.

BTW, all the new guys work on Saturday, and they’re packed. Go on a Tuesday.
Didn't even have to raise hell. Simply told them the issue, they got me fixed me up no problem.. 1hr wait and they put me up front to get it taken care of. All is good
Old 07-15-2019, 10:52 AM
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Originally Posted by ParkRanger View Post
As an old EFILive tuner who is quite familiar with the workings of the ECMs and TCMs we are talking about, I can assure you that the ECU doesn't adjust anything based on tire size without additional human intervention. All the computers see is load and perceived speed. The TCM is constantly learning/changing based on load and power output, but it doesn't care about your tire size. Fuel quantity and timing are set in tables in the ECU, they do not change just because you spent $1000 at the local Discount Tire.
Now all of those abbreviations are over my head and that really doesn't matter I guess. but what year vehicles are we talking here that ECM's and TCM's apply to? My reference is back to an 88 & 89 Nissan 300 V6 King Cab 4x4. Now those two vehicles definitely knew something was changed and got all screwed up for a day, then back to normal and no change in fuel mileage. Change the tire size back down or factory size and the same thing would happen all over again....another day of the truck being sick. ????
Old 07-15-2019, 11:11 AM
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Originally Posted by IcutMetl View Post


That may indeed be what you are experiencing; sure, but you’re misunderstanding what that is.
That is possible. I just know in the case of my 88 that engine Never had a problem with anything, it Always ran like a top. (I put about 500km's on that engine and it had plenty of life left in it - compression up and everything). The only time I had a problem with the motor was when I put a set of General (I forget the size now, but they were 33" tall apposed to the factory 31.5" tall tires that came on the vehicle. I drove the truck into the shop to have the tires changed and the minute I left the shop that engine ran like total crap, it ran like that for the remainder of the day, The next day that engine was back to a happy camper and I never did a thing to it to cause a change.

Now long story short, General agreed that the tires they sold me was to much tire for the weight of my truck and agreed to replace them for free. So I went back to the factory sized tires 31.5" tall tire. Again the minute my truck left the shop with the new tires on that engine instantly became sick for another day. So I don't know how you cut it any other way? Now in saying that, a person I knew with the 89 Nissan King Cab 300V6 4x4 did the same thing as I did, he went the next size tire up but did not go with Generals. Again the minute he drove out of the tire shop his truck ran like crap for the remainder of the day, but after that ran fine again.

So were the Nissan 300V6's governed by ECM's or TCM's, I have no idea? I do know with my 88 I tried several times to change the timing and tried to lean out the gas but that truck would NEVER let me. I could drastically change out the time on that engine and the on board computer would change it right back to factory settings.

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