Heavy 35's vs lighter 37's

[Twisted Patriot]

Question for people with more knowledge than me on this.. if someone had a heavy set of 35's vs someone with a set of 37's that were lighter than those 35's .. would the person with 37's still be at the disadvantage with regards to power and wear and tear on suspension parts and needing to regear due to rotational mass? Or would it kinda equal out? Example.. say the 35's were 71 pounds a piece and the 37's were 65 pounds a piece.

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[Old Jeeper]

Question for people with more knowledge than me on this.. if someone had a heavy set of 35's vs someone with a set of 37's that were lighter than those 35's .. would the person with 37's still be at the disadvantage with regards to power and wear and tear on suspension parts and needing to regear due to rotational mass? Or would it kinda equal out? Example.. say the 35's were 71 pounds a piece and the 37's were 65 pounds a piece.

I would say that is not enough of a Delta to show up before the tires were worn out or replaced.

The weight come in the tread, are you looking at specialty tires of some kind or different widths, like 12:50 vs 13:50 or US vs China???

 

[Twisted Patriot]

I would say that is not enough of a Delta to show up before the tires were worn out or replaced.

The weight come in the tread, are you looking at specialty tires of some kind or different widths, like 12:50 vs 13:50 or US vs China???

I'm just saying people say you should regear for 37's.. but what if the 37 you want to run is lighter than the 35's you currently run?.. 35x12.50 vs 37x12.50.. would you still be at a higher wear and tear.. and need for regearing even though the 37 is lighter just due to more rotational mass?

 

[21JLURDG]

A physics question! And my kids said you'd NE-VER use it in real life. Ha! But I'm guessing you don't want to discuss derivatives, so let's simplify with some basic assumptions. A tire with equal radius but greater weight will have greater momentum (like a heavier flywheel), and therefore require greater rotational force or mechanical advantage to change angular speed. This also applies to a tire of equal weight but larger radius. So a larger tire with smaller weight will require the same rotational force as a smaller but heavier tire at a specific size and weight combination, but now you have to do the math. Of course there are other considerations, such as hits to the bank account, tire carcass strength, axle clearance, etc. that should lead to: "it's not worth considering it."

 

[entropy]

I looked into this months ago. A larger tire will put more stress on components because of size. Re-gearing is about the size of the tire and what it takes to get it to do a full rotation. Of course a heavier tire does take more energy to rotate than a lighter tire, so your engine would work harder and you'll burn more gas. But differential gearing takes radius into the equation and not weight.

I think it goes like this:
1) Pick tire size you want.
2) Pick tire taking weight into consideration.
3) re-gear.

With the heavy 35inch tire you might see a decrease in city MPG vs. the lighter 37 because of the amount of energy it takes the tire to rotate, or maybe MPG would be close to the same. On the highway you should get better MPG with the 35 even though it is heavier. The 35 might be more difficult to stop if you need to brake. The 37inch tire will always have an advantage on the trail over the 35 regardless of weight. It can simply climb over bigger obstacles and have better reach when flexing.

 

[Old Jeeper]

I'm just saying people say you should regear for 37's.. but what if the 37 you want to run is lighter than the 35's you currently run?.. 35x12.50 vs 37x12.50.. would you still be at a higher wear and tear.. and need for regearing even though the 37 is lighter just due to more rotational mass?

Combo of 2 things, mass and height, granted mass is the biggie due to rotating mass and newtons laws but height plays a role also.

My question to you is: How much high-speed hwy driving do you do? If its significant then I would go with the lighter tire. If like most of us, more city than highway then it will all even out. You have a 6 lb delta overall not significant unless you are rolling at speed and rolling hard.

 

[mgroeger]

The real question is which weighs more... a pound of lead or a pound of feathers?

 

[BIGW0RM]

Ive been going through myself. I have a Rubicon. I don't want 37's since I have 4.10's. Nor do I want to deal with all the added stuff you should do to run them properly. Most spring lifts are well over 2.5" which makes 35's look funny on the Rubicon. So I only want a 1.5" lift and some 35's.

Looking at 35's I have seen weights of them range from 52lbs to 80lbs in 35x12x7 or 315/70/17 a tire.

While I don't want 37's I did check their weights and the KO2 seemed to be one of the lowest weight options at 71lbs a tire.

Some Nittos are 80lbs a 35" tire! Where as the lightest 35 I found was 52 for a GY terrority. Next in line was a KO2 35" at 62lbs.

 

[Tech Tim]

Question for people with more knowledge than me on this.. if someone had a heavy set of 35's vs someone with a set of 37's that were lighter than those 35's .. would the person with 37's still be at the disadvantage with regards to power and wear and tear on suspension parts and needing to regear due to rotational mass? Or would it kinda equal out? Example.. say the 35's were 71 pounds a piece and the 37's were 65 pounds a piece.

On the tech side, it is an interesting equation with multiple variables.

Weight-
Location of that weight-
Actual Tire Diameter-
Width of tire-

Rotation weight is a huge performance killer and could trump just about all the other variables.

The tread is the heaviest part of the tire, by going to a larger diameter tire, you're moving the heaviest part of the tire (the tread) further from the axle centerline. So even if the tires weighed the same, the 37 has the weight further from the axle centerline (a larger torque arm).

And it is exponential as you move that weight further out.

But, is all the added weight in the tread (the furthest from the wheel center) or is some of it in the sidewall?

And then are you going from a true 35" tire to a 37" tire that only measures 36"s? Or going from a 35" that only measures 33.5" up to a 37" that measures 36.5"?

The width matters, because now you're looking at increased friction or rolling resistance.

On the reality side of things, run the tire you want and then make changes to gearing if you feel you need to.

Add me to the group that says you should regear for 37s. Most people won't notice a big change going to 35s, but usually feel a move up to 37s.

 

[Old Jeeper]

Ive been going through myself. I have a Rubicon. I don't want 37's since I have 4.10's. Nor do I want to deal with all the added stuff you should do to run them properly. Most spring lifts are well over 2.5" which makes 35's look funny on the Rubicon. So I only want a 1.5" lift and some 35's.

Looking at 35's I have seen weights of them range from 52lbs to 80lbs in 35x12x7 or 315/70/17 a tire.

While I don't want 37's I did check their weights and the KO2 seemed to be one of the lowest weight options at 71lbs a tire.

Some Nittos are 80lbs a 35" tire! Where as the lightest 35 I found was 52 for a GY terrority. Next in line was a KO2 35" at 62lbs.

Worm Man, do you do any kind of off roading at all? Tire weight can say a lot of things. I had some Toyo 35s on my Jeep and theyu were incredibly heavy, but they were steel belted, good grief and IIRC correctly they were a 12 ply rated tire and yes OMG were they heavy.

That said weight may not be your friend because you don't 12 ply tires. Maybe just a good all-around tire would work best.

Here are a couple of tires at a good price point for tires today, they may fit the bill. They are both 12:50 x 35 x 17

WRANGLER ULTRA TERRAIN AT

COOPER EVOLUTION M/T

Give them a look: https://www.discounttire.com/compare/product

 

[roaniecowpony]

Of course weight and where that weight is located play a role. But I think you'll find that the moment arm is the over riding characteristic in terms of bending stress on steering and suspension, braking, and acceleration over a handful of pounds between tires. That moment arm is the radius from the axle center to the ground. Think of your tire like a torque wrench with your engine trying to spin the socket and the weight of the vehicle resisting movement (in the case of accelerating) with a long torque wrench. If you make that wrench longer it requires more torque to move the force holding the other end stationary (and visa versa for braking).

You can put a taller tire on a vehicle that weighs exactly the same as the shorter tire and you'll still loose acceleration and braking capacity.

 

[hoag4147]

But wait…. Isn’t 38s the new 35s in our Jeeping world ?

My 37s look smaller every time I look at them lol

 

[21JLURDG]

The real question is which weighs more... a pound of lead or a pound of feathers?

Please specify if on Earth or the Moon. The real stumper is if an airplane has a load of pigeons and you scare them to fly off the floor right at take-off, does the airplane see a performance increase? Inquiring minds want to know....

 

[dragoneggs]

A physics question! And my kids said you'd NE-VER use it in real life. Ha! But I'm guessing you don't want to discuss derivatives, so let's simplify with some basic assumptions. A tire with equal radius but greater weight will have greater momentum (like a heavier flywheel), and therefore require greater rotational force or mechanical advantage to change angular speed. This also applies to a tire of equal weight but larger radius. So a larger tire with smaller weight will require the same rotational force as a smaller but heavier tire at a specific size and weight combination, but now you have to do the math. Of course there are other considerations, such as hits to the bank account, tire carcass strength, axle clearance, etc. that should lead to: "it's not worth considering it."

Ha ha Bill, I earlier started crafting a reply pretty much like yours with words such as angular momentum and center of mass and then just decided to use the 'delete' button.

 

[mgroeger]

Please specify if on Earth or the Moon. The real stumper is if an airplane has a load of pigeons and you scare them to fly off the floor right at take-off, does the airplane see a performance increase? Inquiring minds want to know....

My bad... Moon.

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