How important is weight when upgrading tires/wheels?

[A Sober Animal]

So I'm new to the world of offroad wheels and tires, and I'm trying to understand all the factors that go into sizing up once I get my 2.5" Teraflex CT2 install done. I know I'll be going straight to 37s, and with the 2.0L engine I feel like limiting the increase in weight is something I should heavily consider, based on comments I've read on various threads. The more the weight, the more I lose performance and cause additional stress on the vehicle.

Help me understand the impact of increasing the weight of my wheels/tires. I know that the stock Rubicon setup is about 73 lbs per wheel, and I'm happy with the BFG KO2s performance so far. The lowest weight option I've found would be a light 17" wheel around 35 lbs, and a lighter tire such as the KO2 at 65 lbs - for a total of 100 lbs, a 37% increase in weight from stock. Every 10 lbs I increase equates to another 13% increase, which seems like a high number to me, but maybe I'm overthinking this.

How important is it to limit the weight when I upgrade? Is there really a substantial difference between going with a 100 lbs per tire setup versus a 120 lbs setup?

While the jeep is my primary vehicle, I live in the city and barely drive 100 mi/month unless I'm taking a road trip to camp, wheel, or visit friends. As such, my aim is to build up the Jeep with a focus towards off-road performance over daily driver comfort, but still has to be decent on long highway trips.

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[roaniecowpony]

IMO, the weight affects ride quality and contact with the ground, especially during cornering and braking on bumpy surfaces. How much? That's not easy to quantify. But you'll notice it going from 33s to any 37. Fuel economy, IMO, will not change much between tires of the same diameter and tread style, regardless of weight differences. Diameter, width and tread style will play bigger roles, IMO. I would not put weight concerns on the top of my list of criteria.

 

[J0E]

So I'm new to the world of offroad wheels and tires, and I'm trying to understand all the factors that go into sizing up once I get my 2.5" Teraflex CT2 install done. I know I'll be going straight to 37s, and with the 2.0L engine I feel like limiting the increase in weight is something I should heavily consider, based on comments I've read on various threads. The more the weight, the more I lose performance and cause additional stress on the vehicle.

Help me understand the impact of increasing the weight of my wheels/tires. I know that the stock Rubicon setup is about 73 lbs per wheel, and I'm happy with the BFG KO2s performance so far. The lowest weight option I've found would be a light 17" wheel around 35 lbs, and a lighter tire such as the KO2 at 65 lbs - for a total of 100 lbs, a 37% increase in weight from stock. Every 10 lbs I increase equates to another 13% increase, which seems like a high number to me, but maybe I'm overthinking this.

How important is it to limit the weight when I upgrade? Is there really a substantial difference between going with a 100 lbs per tire setup versus a 120 lbs setup?

While the jeep is my primary vehicle, I live in the city and barely drive 100 mi/month unless I'm taking a road trip to camp, wheel, or visit friends. As such, my aim is to build up the Jeep with a focus towards off-road performance over daily driver comfort, but still has to be decent on long highway trips.

based on comments I've read on various threads.

True, that's one of the most quoted myths on the interweb.

The rotational inertia:

I = 1/2 * m * r^2

where:

• I is the moment of inertia
• m is the mass of the wheel and tire combination
• r is the radius of the wheel and tire combination

Is important for high acceleration, not constant velocity. The mass of the vehicle is far more important for the performance.

If you want to maximize off road performance, get a strong heavy tire like a Nitto. It will do fine on the road.

 

[andy29847]

Heavier weight will wear out suspension components faster.

Tire weights are fairly easy to find ( Tire Size Chart ) . Wheel weights seem to be a mystery. I have kept my stock wheels and am running a Toyo 35x11.5r17 ATIII. I have been happy with the combo and it weighs virtually the same as stock wheel/Falken Wildpeak MT combo that came stock on my Jeep..

 

[oldcjguy]

Weight has a big effect on acceleration and braking. Use extremes to visualize it. Picture spinning and stopping a wheel on a 10 speed bike with your hands. Now picture spinning a grinding stone of the same size. How easy will it be to spin that stone up to the same speed and how quickly can you stop it from spinning. Tires and wheels fall into the category of "unsprung weight". adding 1 pound of unsprung weight is equivalent to approximately 5 pounds of cargo. If you go from 73lbs per wheel to 120lbs per wheel that's roughly 50lbs per wheel increase. 200lbs total added unspring weight. (The spare is not unsprung, it's cargo) Plus the taller tire effectively raises your gearing (numerically lowers). Expect your performance (accelerating and breaking) to change about the same as if you added almost 1000lbs of cargo (plus you went taller with the tire, so there is the added leverage effect). You'll feel that, especially when stopping. But you'll get used to it. Gearing can help get acceleration back. Honestly, with a 2.0 and 4.10 factory gears, I think you'll be ok. But that's just an opinion. Depends on how you like to drive. Stopping you'll need to adjust to.

 

[Mudduck]

This is one of the areas on this forum where you ask a question and get 20 different answers. None of them are really wrong. It all comes down to what is acceptable trade-offs for you, and there are always trade offs to any mod.

I think you'd do far better to ask a specific question to a specific group of folks that have done the same thing you are wanting to do, for the most realistic real world set up/Jeep spec'd driver input.

 

[J0E]

Weight has a big effect on acceleration and braking. Use extremes to visualize it. Picture spinning and stopping a wheel on a 10 speed bike with your hands. Now picture spinning a grinding stone of the same size. How easy will it be to spin that stone up to the same speed and how quickly can you stop it from spinning. Tires and wheels fall into the category of "unsprung weight". adding 1 pound of unsprung weight is equivalent to approximately 5 pounds of cargo. If you go from 73lbs per wheel to 120lbs per wheel that's roughly 50lbs per wheel increase. 200lbs total added unspring weight. (The spare is not unsprung, it's cargo) Plus the taller tire effectively raises your gearing (numerically lowers). Expect your performance (accelerating and breaking) to change about the same as if you added almost 1000lbs of cargo (plus you went taller with the tire, so there is the added leverage effect). You'll feel that, especially when stopping. But you'll get used to it. Gearing can help get acceleration back. Honestly, with a 2.0 and 4.10 factory gears, I think you'll be ok. But that's just an opinion. Depends on how you like to drive. Stopping you'll need to adjust to.

Tires and wheels fall into the category of "unsprung weight". adding 1 pound of unsprung weight is equivalent to approximately 5 pounds of cargo.

Where did you get that? So going from a D44 to a D60 you need to multiply the difference in weight by 5?

It's the rotational inertia that has an impact, but only under acceleration.

Picture spinning and stopping a wheel on a 10 speed bike with your hands.

Here's a better test. Put the bike on a stand and turn the petals. Really easy. Now put your butt in the seat, much hard to accelerate. The combined mass dominates.

 

[oldcjguy]

Tires and wheels fall into the category of "unsprung weight". adding 1 pound of unsprung weight is equivalent to approximately 5 pounds of cargo.

Where did you get that? So going from a D44 to a D60 you need to multiply the difference in weight by 5?

It's the rotational inertia that has an impact, but only under acceleration.
Picture spinning and stopping a wheel on a 10 speed bike with your hands.

Here's a better test. Put the bike on a stand and turn the petals. Really easy. Now put your butt in the seat, much hard to accelerate. The combined mass dominates.

Where did I get that you multiply unsprung vs sprung weight? Physics. Where did I get that actual number of 5? That's an approximation because "it depends". That number can be anywhere between 2 and 10+. Yes, going from a D44 to a D60 you need to multiply the weight if you are trying to determine the effect on performance. Acceleration/deceleration performance is what we're talking about here. Physics tells us it's harder to accelerate a rotating mass than it is a non-rotating mass. Much of the weight in a D44 to D60 is still rotating mass. Bigger, stronger axles, carrier, pinion, ring gear, rotors, etc... The case and brackets have less of an effect but still carry more of an effect than the same weight added to the passenger compartment. When dealing with rims and tires that unsprung mass is also rotating mass so it's really making a difference. Add to that the increase in height.

Not only under acceleration performance, but deceleration as well.

Yes, putting my 200lb butt in the seat will make much it harder to accelerate LOL. But, not as hard as if the wheels weigh 200lb more.

In off-road vehicles (depending on the type of off-roading you do) we don't care as much about acceleration/deceleration. When cruising and crawling off-road that mass isn't hurting much at all, and in many cases, will actually help. But, on the street and at speed it will be noticeable.

 

[J0E]

Where did I get that you multiply unsprung vs sprung weight? Physics. Where did I get that actual number of 5? That's an approximation because "it depends". That number can be anywhere between 2 and 10+. Yes, going from a D44 to a D60 you need to multiply the weight if you are trying to determine the effect on performance. Acceleration/deceleration performance is what we're talking about here. Physics tells us it's harder to accelerate a rotating mass than it is a non-rotating mass. Much of the weight in a D44 to D60 is still rotating mass. Bigger, stronger axles, carrier, pinion, ring gear, rotors, etc... The case and brackets have less of an effect but still carry more of an effect than the same weight added to the passenger compartment. When dealing with rims and tires that unsprung mass is also rotating mass so it's really making a difference. Add to that the increase in height.

Not only under acceleration performance, but deceleration as well.

Yes, putting my 200lb butt in the seat will make much it harder to accelerate LOL. But, not as hard as if the wheels weigh 200lb more.

In off-road vehicles (depending on the type of off-roading you do) we don't care as much about acceleration/deceleration. When cruising and crawling off-road that mass isn't hurting much at all, and in many cases, will actually help. But, on the street and at speed it will be noticeable.

Much of the weight in a D44 to D60 is still rotating mass

The rotational inertia:

I = 1/2 * m * r^2

And the Radius of the axle shafts are very small.

Where did I get that you multiply unsprung vs sprung weight? Physics. Where did I get that actual number of 5? That's an approximation because "it depends". That number can be anywhere between 2 and 10+

Can you site the physics forum you got that from? So all the non-rotating parts on my massive ProRock 80 rear axle count between 2 and 10+ times the same sprung mass?

 

[oldcjguy]

Much of the weight in a D44 to D60 is still rotating mass

The rotational inertia:

I = 1/2 * m * r^2

And the Radius of the axle shafts are very small.

Where did I get that you multiply unsprung vs sprung weight? Physics. Where did I get that actual number of 5? That's an approximation because "it depends". That number can be anywhere between 2 and 10+

Can you site the physics forum you got that from? So all the non-rotating parts on my massive ProRock 80 rear axle count between 2 and 10+ times the same sprung mass?

Yes, I believe those axles will affect performance (even the nonrotating pieces). But... if you're bouncing int he rocks, you need it and that's the cost of the sport. Most any performance modification is going to sacrifice performance in one area for more performance in another. Figuring it all out has always been part of the fun.
It's been many years since I built a car where I was shaving pounds and ounces and most of what I learned came from books and teams. Yup, I'm old. I try not to site from internet forums. They're filled with some really smart and some really dumb people and we can't always tell the difference. There's plenty of good information out there if you're interested. (Much of it is around automotive and motorcycle handling, but physics is physics. We just don't care about hitting 1G is a turn.) Google is your friend. I take no offense if you disagree with me, I never take anyone else's word as gold either.

cheers

 

[grimmjeeper]

Weight is a small factor that is alway over blown by people.

It boils down to this.

Tire diameter determines what axle ratio you want

Original gear ratio × new tire rolling diameter ÷ old tire rolling diameter = target gear ratio.

Weight and rolling resistance is why you round up to the next higher available ratio.

 

[GMONEY]

Does anyone know the weight of Rubicon stock wheel/tire combo

Really should have grabbed scale when rotating tire the other day

 

[A Sober Animal]

Should be 73 lbs per wheel/tire if running the KO2s

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