Difference Between Sprung & Unsprung Weight

[Wildman]

I would like to further discuss as well. How much weight would it take to actually make a difference?

Loading the tires should lower the CoG. By how much? Who knows.

I can say that if we approximate a 35" tire on a 17 in wheel, there should be around 25 gallons of available volume to fill with something. If we choose water, we now have loaded our tires with an additional 207 lbs, each. That's 828 lbs total, all located lower than the unloaded CoG. Does it matter? How much does it "flatten" the box?

Oh... This rig with loaded tires is going to be an absolute pig to drive. But for the purpose of discussion, let's ignore that for now.

What is the difference in weight between a 15" tire and a 17" tire? Or a biased ply compared to a radial?

Size	Aspect Ratio	Section Width	Weight	Tire Tread Width	Tire Tread Depth

36x13.5/15LT

36

13.5

66

11

21/32

36x13.5/16LT

36

13.5

65

12

21/32

36x13.5/17LT

36

13.5

66

12

21/32

36x13.5/16.5LT

36

13.5

67

12

21/32

Now for Radial

36x13.5R15LT

36

13.5

81

11

21/32

36x13.5R16LT

36

13.5

85

11

21/32

36x13.5R17LT

36

13.5

84 lb

11

21/32

36x13.5R16.5LT

36

13.5

86

11

21/32

So not much weight difference in rim size but 15 to 20 lbs heavier if we are talking about a radial compared to a bias ply tire. Since most of everyone now days runs a radial tire are you adding 80 to 100 lbs of weight to your rig? And what if any difference is it making in traction off-road?

 

[Wildman]

Mike H asked and I'll ask again. How much makes a difference? If I change from steel to aluminum corners will I notice a difference? Or is it a complete package where I need to change my corners, front fenders & skid plates all to aluminum to make a difference?

 

[TJ Hunnicutt]

On the tire diff between bias and radial, it really is (IMHO) a no-brainer. Even though the radials have more weight (check into the belt configuration of these tires; I'm thinking we may be comparing nylon belts to steel belts, which would account for a lot of the weight diff), the radials are going to outperform the bias-ply in pretty much every circumstance.
Bias-ply tires have relatively rigid sidewalls that do not give much under side-load (turning, off-camber situations). This means that their footprint is going to be flat against the terrain only when the vehicle itself is sitting flat against the terrain. Introduce side load (turning or off-camber) and bias plies will "bend", causing the tread to lift on the inside of the turn/lean so that only the outside of the tread fully contracts the terrain.
Radials, on the other hand, have softer, more pliable sidewalls which allows them to flex under these circumstances and keep the tread much more perpendicular to the terrain; dramatically increasing your effective tread footprint...and grip. There are lots of places on the net to check radial vs. bias-ply performance and functionality.

 

[Bill M.]

Remember guys water in a tire does not rotate with the tire at low speeds like rock crawling.

 

[TJ Hunnicutt]

I should also add that radial tires, as a rule, absorb impact (like hitting a rock) much better that bias plies...again, because of the more pliable sidewalls. So, this also makes up a lot for their greater weight (I still wonder about the belt materials in your list).

 

[TJ Hunnicutt]

OK, I should also mention that, because (especially for radials) the majority of the weight of a tire is at its outer diameter (i.e the tread), a larger diameter tire of exactly the same weight as a smaller diameter tire will exert greater forces (as previously detailed) on the drive train, etc. than the smaller tire because the weight will be farther away from the center of rotation. Think of rotating a sledge hammer by holding it by the head (swinging the handle around) as compared to swinging it by the handle (swinging the head around)...big diff.

 

[Wildman]

OK, I should also mention that, because (especially for radials) the majority of the weight of a tire is at its outer diameter (i.e the tread), a larger diameter tire of exactly the same weight as a smaller diameter tire will exert greater forces (as previously detailed) on the drive train, etc. than the smaller tire because the weight will be farther away from the center of rotation. Think of rotating a sledge hammer by holding it by the head (swinging the handle around) as compared to swinging it by the handle (swinging the head around)...big diff.

And what does that weight at the outer diameter do to your rig? Good or bad? I'm not going to debate which is a better type of tire I am just interested in discussing what the weight does.

And no one has offered their insight on how much weight does your rig have to lose to make a difference?

 

[JMT]

And what does that weight at the outer diameter do to your rig? Good or bad? I'm not going to debate which is a better type of tire I am just interested in discussing what the weight does.

And no one has offered their insight on how much weight does your rig have to lose to make a difference?

Every pound counts, just like inches in the bedroom!

 

[JMT]

Rotational inertia. I’ll go with lighter any and every day if diameter remains the same. 20-25% makes a huge difference in mountain biking. Everyone know a carbon wheel set is the best weight savings you can pony up for. Practically, with Jeep’s, I don’t think any of us will be able to tell a difference. If you do it’s in the first few days of a change. Run the same trail with two sets of tires with different weights back to back (e.g 33x12.5 and 33x10.5) and report back.

 

[TJ Hunnicutt]

The weight at the outer diameter acts just the same as weight of the tire overall, just moreso because the further from the center, the greater the effective load [lever principle]). The heavier the tire, the more it will have rotational mass and change-of-direction mass (I'm sure there is a technical term for that). Any increase in mass will adversely affect your drivetrain because it will increase loads as speed changes and as trajectory (direction of travel) changes.

As for the total weight of your vehicle and how much you might "need to loose" to make a difference; quite frankly, that is impossible to answer. It would depend on your total vehicle's weight, its sprung weight vs. unsprung weight, its suspension compliance (softness), gearing, engine, tire grip, etc., etc., etc.
All I can say is, to repeat what others have stated; in general, lighter is better. Will 10 pounds of steel replaced by aluminum make a big difference?...almost certainly not. Will a cumulative 120 pounds of X replaced by Y make a difference?...probably so (though, it may not be really obvious, depending on your vehicle).
Yeah, I know, wishy-washy as hell, but that's the deal...just keep it as light as you reasonably can.

 

[Wildman]

Alright keep it as light as you can. Now how does unsprung weight affect the way your rig handles? Sprung weight plays a part as has been stated. Going aluminum over steel armor will make a difference.

 

[BuildBreakRepeat]

Alright keep it as light as you can. Now how does unsprung weight affect the way your rig handles? Sprung weight plays a part as has been stated. Going aluminum over steel armor will make a difference.

I see the benefits of lightweight - mostly in making hill climbs and stability in off camber situations.

 

[Bill M.]

Alright keep it as light as you can. Now how does unsprung weight affect the way your rig handles? Sprung weight plays a part as has been stated. Going aluminum over steel armor will make a difference.

I think you need to further define your question. What is the final goal, better rock crawling, overlanding, desert whoops or highway?

 

[Wildman]

I think you need to further define your question. What is the final goal, better rock crawling, overlanding, desert whoops or highway?

Well the answer would be ALL of the above.

What works for a rig that sees all types of terrain and types of soil? My main question is how does each type of weight affect your rig? If you have a rig say with Dana 60's and larger tires w/beadlock rims how does this unsprung weight affect how your rig handles compared to a rig on a Dana 30 & Dana 44 with aluminum rims & 33/35" tires?
And then how does a rig with steel armor compare to a rig with all aluminum armor? And just to make it more interesting the rig with Dana 60's has all steel armor also. Or has all aluminum. How does this affect the rig.

Part of my problem is that I haven't been wheelin for over 8 years and aluminum armor was just becoming popular back then. So I haven't seen rigs that are lighter compared to rigs on steel armor.
And I see everyone saying go lighter but I don't see people applying this to their unsprung weight as much. So I'm trying to understand how each type of weight affects our rigs.

 

[Bill M.]

Well the answer would be ALL of the above.

What works for a rig that sees all types of terrain and types of soil? My main question is how does each type of weight affect your rig? If you have a rig say with Dana 60's and larger tires w/beadlock rims how does this unsprung weight affect how your rig handles compared to a rig on a Dana 30 & Dana 44 with aluminum rims & 33/35" tires?
And then how does a rig with steel armor compare to a rig with all aluminum armor? And just to make it more interesting the rig with Dana 60's has all steel armor also. Or has all aluminum. How does this affect the rig.

Part of my problem is that I haven't been wheelin for over 8 years and aluminum armor was just becoming popular back then. So I haven't seen rigs that are lighter compared to rigs on steel armor.
And I see everyone saying go lighter but I don't see people applying this to their unsprung weight as much. So I'm trying to understand how each type of weight affects our rigs.

If you are the guy with D60s and 44" tires crawling I don't think unsprung weight is a big concern. Then again if you the running desert whoops at high speed then unsprung weight is everything. There is no middle ground where you can do both because of aluminum fenders and bumpers.

 

[pagrey]

That bears some very deliberate discussion and research. I could very well be fully wrong but the way I remember my conversations with folks smarter than me is the COG doesn't really change. To tip a TJ over or any vehicle for that matter, once the COG moves outside the tire box, it's going over no matter what it weighs. Change my mind.

This make sense?

 

[Wildman]

If you are the guy with D60s and 44" tires crawling I don't think unsprung weight is a big concern. Then again if you the running desert whoops at high speed then unsprung weight is everything. There is no middle ground where you can do both because of aluminum fenders and bumpers.

Not running 44's but 36-37" tires and a Dana 60 rear and Ford Dana 44 front. And not interested in doing high speed whoops are anything close to that.

 

[mrblaine]

View attachment 164262

This make sense?

I get that part perfectly. What I didn't fully get is how adding weight to the tires changes the COG that much. And then I finally recall how COG is determined and see that it will lower the COG by adding weight to the tires. One of those things I have think through to get again.

 

[pagrey]

I don't wheel in these tough situations but from what I've heard you say it seems that total weight of the rig makes more difference than the distribution. My pictures just show the rollover angle and that might not make much real difference in the dirt.

 

[mrblaine]

I don't wheel in these tough situations but from what I've heard you say it seems that total weight of the rig makes more difference than the distribution. My pictures just show the rollover angle and that might not make much real difference in the dirt.

We've played with it a bunch. Tie a strap between the tops of two rigs at the cage. Then drive on the side of a steep walled wash with the top rig holding the other one from going over by keeping the strap tight. You can drive on a steeper surface across the face than you are ever comfortable doing. You are literally holding onto the oh shit handle from the driver seat to keep from just being wadded up against the door. And the rig don't fall over.

However, that is at slow speed and as that increases, the dynamic forces go way up and can upset the apple cart. Hit one football size rock and the tire spring will likely make bad things happen.