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Moving to 35s - what causes the most change - diameter OR weight?

vh5150

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Hi all - how much of the changes attributed to moving to 35s is actually due to the diameter of the tire? I've researched a ton and as you all already know weight is a common & major part of the discussion. That said, how much of the change in diameter causes things like sluggishness and drops in mpgs and overall drop in performance when staying on stock 3.73 gears?

The reason I ask is that, like many I continually go back and forth between going 33s to 35s, but even then some of the 33s I like are essentially the same weight of 35s, example being 285/70 Nitto Ridge Grapplers compared to a BFG KO2 315/70 C rated give or take a pound or two.
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Jeeperjamie

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I feel like weight is a huge factor, not that the diameter doesn't matter, but weight I think would play more of a factor, especially on components like ball bearings and things like that. When I ran 35's on my JKU, I first had Geolander M/Ts and I averaged about 15.5 MPGs at best. 35's in a KO2 and i could get around 16.7 mpgs. The Geolanders weighed about 16lbs more each than the KO2s. Gearing and resetting your computer plays a factor as well.
 
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vh5150

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I feel like weight is a huge factor, not that the diameter doesn't matter, but weight I think would play more of a factor, especially on components like ball bearings and things like that. When I ran 35's on my JKU, I first had Geolander M/Ts and I averaged about 15.5 MPGs at best. 35's in a KO2 and i could get around 16.7 mpgs. The Geolanders weighed about 16lbs more each than the KO2s. Gearing and resetting your computer plays a factor as well.
Thanks, that is my thinking as well, so I was like if I am going to get a 60 lb tire, why not the BfG KO2 c and go 35s. Wanted to make sure I wasnt missing something...
 

AZJT

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I did Nitto Ridge Grapplers (285/75/18) on my Overland. Discount site says these are 70 lbs. each. I did feel a little sluggishness on Day 1 after install, but you kinda just get used to it. I only lost a few MPG due to the added weight - maybe 1-3 MPG loss, depending on where I'm driving. Aside from that, simple physics (at least for my simple mind) tells me that in most cases, additional diameter will equal more weight. Overland is also 3.73 gears, FYI. I'm still hitting about 19MPG overall (per on-board computer calculations).
 

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In my opinion, weight. But ALSO where that weight is! Meaning two different size tires that weigh the same will have different impacts due to the weight being further out.

The weight concern is what drove me to a C rated 35x11.50x17 on the stock, lightweight, alloy wheels. It's a pretty light package for a 35 (Tire = 63lb, wheel = 22lb).
 

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Aonarch

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Weight. Tires are unsprung weight. A loose formula is to multiple the unsprung weight. by 4.

So if your tire weighs 30 lbs more than stock, multiple that by 4. Since you have 4 tires, multiple that by 4 as well.
 
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vh5150

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Appreciate all the responses and super helpful! Love this forum
 

Aonarch

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Also we do not need load range E tires.

My 35 KO2s are C rated, saves a ton of weight.
 
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vh5150

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Also we do not need load range E tires.

My 35 KO2s are C rated, saves a ton of weight.
Will be only going for C rated tires, thanks!
 

jorbasaurus

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I’ve got about 1,000 miles on my 315 k02s and rode a set of takeoff falken ATs for 1,000ish prior. K02s are a pound or so heavier, I haven’t noticed a significant change in MPG & it actually seems to hold 8th better coming home from the mountains now with the larger tires. 3.73 gears for now.
 

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dcmdon

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Moving to larger tires affect 2 things primarily. It also affects weight, which is pretty minor.

1) gearing. This isn't really a big thing other than annoyance. The fact that the transmission rarely uses 8th gear or is more likely to hunt between 7th and 8th could get tiring.

But overall, taller gearing works to IMPROVE fuel economy.

2) Resistance. There are several types of resistance that are increased.

a) rolling resistance - bigger tires don't necessarily have higher rolling resistance but more off road focused ones do. The reality is most people are replacing stock tires with "chunkier" tires so they won't roll as well. If you run less air pressure in the larger tires, that will also increase rolling resistance.

Rolling resistance isn't going to impact you much accelerating at low speed because there simply isn't much of it. It increases linearly, rather than at a square rate like aerodynamic resistance, so its generally less important than aerodynamic drag.

b) aerodynamic resistance -- the truck will sit taller and will move more air. With greater air entering the turbulent area under the truck. This one hurts a lot on the highway because it increases as a square function of speed. So if you go 25% faster, aerodynamic resistance increases by 56%. So a small bump makes for a big difference on the highway.

So aerodynamic resistance has little impact on acceleration or economy at low speeds but more impact at high speeds.

Weight certainly affects things. But wheels and tires are significant because you aren'g just moving them forward you are spinning them.
1) more weight takes more power to accelerate at a given rate.
2) polar moment of inertia a/k/a flywheel effect. When you accelerate you are spinning up 4 flywheels. Make the flywheel larger in diameter, even if the weight is the same and it still takes more power to accelerate it and more brake to decelerate it.

Make that larger flywheel heaver and you compound the impact.

Note that both aspects of weight really only impact acceleration, not steady state driving. So the weight won't really impact fuel economy much. But will impact how responsive the truck feels.

Hopefully this isn't too geeky. I just wanted to break everything down.
 
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Fastwake

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12:50 35sToyo. No problem with power loss drives and handles great with a 2” Mopar lift. Very quiet and has now problems staying in 8th gear on the flat With 373s
 
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vh5150

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12:50 35sToyo. No problem with power loss drives and handles great with a 2” Mopar lift. Very quiet and has now problems staying in 8th gear on the flat With 373s
AT3's?
 

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What dcmdon said. That is spot on. Unsprung weight deals more with ride, spring rates, rebounding, etc.
With the same size tires, but heavier load range, (ie steel belting / tread, etc) most of the weight is in the face or outermost diameter of the tire. Sure, some is in the sidewall, but not most. That outer diameter is where the most resistance to rotation occurs.
In theory, and probably in space where there is no gravity and no aerodynamic needs, the taller tire would yield higher mileage. Not gonna happen here on earth.
Is a lighter load range better? Not for me. I live on a gravel road and don't want to deal with punctures. Come see me with your 4 ply tires a couple of times and you'll see what I mean.
 

MrKnowitall

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With the 8spd auto, definitely weight. The trans can do an amazing job in making up for the change in effective gearing, but it just takes more power to get heavier tires moving. Look for light wheel/tires, unless you're planning to re-gear. This will help with ride, too.
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