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Unread 08-18-2013, 08:22 AM   #61
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Originally Posted by mschi772 View Post
Usually this is a matter of placebo effect. Someone expects to feel an big impact, so they end-up thinking they feel one. This is why people's "butt dynos" are useless and never taken seriously when anyone talks about the changes a given mod make them feel. CAI mods are a great example of a place where often people will say they feel a big power increase but a true dyno run usually just says there's been little to no change. People's perceptions are unreliable. There can be other factors, but this is a major player and why I never take anecdotal "butt dyno" testimonies seriously...ever. Regarding tires, this is almost always confounded by the fact that when someone changes their tire weight, they almost always change tire model, diameter, and/or width at the same time. It's hard to tell what's causing what when you change multiple things at once. Tread patterns, compounds, and width can have a profound effect on resistance while different diameter, as all well-informed Jeepers know, don't have to change a whole lot to have big enough effects worthy of regearing.

Take a Jeep TJ with a 2.5 4cyl, 4.10 gears and put a set of 33x12.50R15 (C load rating) BFG T/A KO tires and aluminum wheels on it.

Now on a 2001 Dodge Ram 2500 with a 5.9 Cummins, 4.10 gears put a set of 35X12.50R17 (E load rating) Nitto Mud Grapplers and steel wheels on it.

The Ram obviously has the largest increase in tire size and weight from stock.

Is the "Butt Dyno" incorrect in thinking that the TJ feels the increase in tire size and weight more than the 2500 Ram will?


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Originally Posted by mschi772 View Post
No, the ratio is independent of gear ratios. It's an inertial equivalence. An object (wheel) has inertia whether or not it's attached to an engine and a bunch of gears, and those things don't change its mass or its inertia. They do change how the mass is moved of course. Lower gears make it easier for a given engine to accelerate a given amount of mass and all that etc etc.

If the gear ratio effects how the mass is moved and makes it easier or more difficult to move a given mass, how can a scientific/mathematical ratio be translated to how it actually effects the vehicle that the tires are on if the gear ratio is not accounted for?



Quote:
Originally Posted by mschi772 View Post
Neither I nor Mason have shown the effects on varying masses on the vehicle. We've shown equivalent mass of rotating objects compared to static objects. The effects of either the rotating or static object on something like a vehicle is another can of math worms, but the ratio for the tire/wheel/driveshaft/whatever remains the same and becomes PART of those calculations.

If the scientific/mathematical ratio can't be translated to and show how it ACTUALLY effects the vehicle, isn't it just another useless number being thrown around?

Without considering all of the factors/variables, isn't the scientific/mathematical ratio of 2 to 1 just as useless as the "Butt Dyno"?

I'm not questioning or disagreeing with your scientific/mathematical answer, But how can you determine how significant a number is if it effects all vehicles differently?


If the vehicle's motor horse power/torque and the gear ratio is taken into consideration, would it be safe to say that the ratio would change?

If you included those factors/variables, wouldn't you then have a scientific/mathematical answer that accurately represented how a tires weight effects a vehicle?

Would that ratio also be different from one vehicle to another?

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Unread 08-18-2013, 08:46 AM   #62
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No one will notice an additional 6 pounds in a tire all other things being equal whether it is a TJ or a one ton Ram. And, the energy that it takes, miniscule as it is, to load the tire with kinetic energy in rotation would not be enough to measure outside of a laboratory.

Tire weight is a tradeoff. Its not like a tire is weighed down with a bunch of useless garbage that does not contribute to the durability, strength, dependability, etc. of the tire. It is not at all like making a race car a little faster by taking out the window regulators, truck and hood latches and dashboard. The tire's materials are, get this, necessary. A lighter tire is by definition a lesser tire.

Now there may be a desire to have a lighter tire and a willingness to accept the sacrifices that go with it. But it is not at all true that a lighter tire is, ipso facto, a better tire.
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Unread 08-18-2013, 09:29 AM   #63
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Originally Posted by wilson1010 View Post
No one will notice an additional 6 pounds in a tire all other things being equal whether it is a TJ or a one ton Ram. And, the energy that it takes, miniscule as it is, to load the tire with kinetic energy in rotation would not be enough to measure outside of a laboratory.


At what point does weight become significant?

6lb per tire and 10lb per wheel is a total of 16lb per corner and 64lbs total for 4 tires and wheels. If you include the spare (it's not rotating, but it is still there), that makes it an 80lb difference in actual weight. That doesn't take the rotating weight aspect into consideration. That's also just a possible difference in weight in the same size tire and wheel. If you account for the difference in weight from the stock size to the new size, the difference is even more drastic.

Would a 4cyl TJ be able to feel a 150lb difference in just the tires?

Add that to the other areas that could see substantial weight savings and you can easily be looking at a 500lb difference.

Would a 4cyl TJ be able to feel a 500lb difference?

Would that same 500lbs have the same effect on the Ram?

At what point do all of the insignificant weights cause a major impact?
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Unread 08-18-2013, 10:17 AM   #64
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Originally Posted by SLADE View Post
If the gear ratio effects how the mass is moved and makes it easier or more difficult to move a given mass, how can a scientific/mathematical ratio be translated to how it actually effects the vehicle that the tires are on if the gear ratio is not accounted for?
Because no matter how you move something and with what kind of leverage, its mass stays the same, and it carries the same inertia at a given velocity.

Spinning an automobile wheel/tire up to a given speed will require appox 2x the same energy as carrying that wheel/tire up to that given speed. That won't change. You can use leverage to reduce the energy necessary to do these things, but the ratio between the two will always be the same.

Here, I'll really super fantastically simplify this and use some fake numbers (this won't be the most accurate of math; it's just to demonstrate an idea):
  • You have a wheel that weights 10 g.
  • With X leverage/gearing, it costs 10 J to accelerate it (not spinning) to 10 m/s. Spinning it up to 10 m/s would be like accelerating a 20 g wheel to 10 m/s. I do not know if this would be equivalent to 20 J or not at this time.
  • If you change your leverage/gearing to Y, it may cost 100 J to accelerate the static 10 g. To spin it up to 10 m/s, it will still be like accelerating a static mass of 20 g. The ratio has NOT changed. All that has changed is what you're using to exert force on the wheel.

I suspect that the "J" figure does not change in a linear fashion as gearing changes; no, I haven't done any math here because I frankly lack the motivation to go that far. Just like the relationship between tire diameter and gearing isn't a linear one either (I assume most Jeepers around here are quite familiar with the relationship between diameter and gearing).

Regarding your TJ vs Ram analogy, the flaw there is that while the Ram may still have received an even bigger increase in weight compared to the TJ, you have to keep it in perspective. It's still a much smaller % of the whole mass of the Ram. Adding 300 lbs to a 3000 lb vehicle, for example. Is a 10% increase in weight. Adding 300 lbs to a 5000 lb vehicle is only a 6% increase. Your analogy is also confounded by the different engines (totally different power curves) and transmissions (different gear ratios and shift points) involved. Throw a bunch of bricks in to the back of a Corolla, and you'll probably notice quite clearly that you're hauling a bunch of bricks in your Corolla. Throw those bricks into the back of the Ram, and they'll still have the same mass and still exert the same exact forces on the Ram as they did on the Corolla, but it'll probably not be as noticeable for a variety of reasons. My point is that the physical characteristics of the item/cargo in question never changes whether it's a full-size spare, a spinning wheel, or a bunch of bricks.



A lot of people keep trying to cite real-world comparisons/analogies, but they're full of tons of extraneous variables: different tires, different sizes, different gears, different trannies, different engines, different vehicles, etc. If you want to experience a real-world comparison, you have to change NOTHING else other than the mass of the wheel or tire. That's very difficult for tires since it's nearly impossible to get a particular model of tire that is identical in every way except weight--there's no reason for a manufacturer to do that. Differing load ratings is probably the closest way to accomplish this, but even then the tires might differ slightly other than just weight, and the weight difference probably isn't very much anyhow which would make comparing them extremely difficult if not impossible for the butt dyno.

So wheels it is. Drive you Jeep. Now change ONLY the wheels to wheels of the exact same diameter, backspace/offset, and width but different weight. You MUST use the same Jeep and the same tires. Drive again. My math suggests a 1.5-2 to 1 ratio. I know the butt dyno won't be able to calculate ratios or any other numbers, but if you can be as unbiased/objective as possible, hopefully you can roughly guesstimate whether or not it's a 2:1ish or 10:1ish ratio.

You can go a step further after driving on the two different wheels by going back to the lighter wheels then adding static weight to the vehicle until it feels the way the heavier wheels felt. I would probably just try-out two different weights and just decide which feels most similar: weight equivalent to 2x the difference of the wheels and a 10x. Taking stabs in the dark or gradually changing weight might make it difficult to compare or even remember the feel of what you're comparing to.



Quote:
Originally Posted by SLADE View Post
At what point does weight become significant?

At what point do all of the insignificant weights cause a major impact?
Significance is up to you. What you can perceive and what you feel is a worthwhile/significant weight increase/decrease is subjective. There's no equation to provide THE answer to this one. We all draw our own lines.
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Unread 08-18-2013, 01:40 PM   #65
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I think while 16 lbs would be hard to notice, what you do notice is the different tire diameter taking more torque to turn. That's noticeable. Add the weight and its even more noticeable.

I just swapped from a stock wheeled four door to a 2dr 35 inch jeep JK. I think the accel is better in the two door, with bigger tires, because I'm dragging around 600lbs less weight. Weight matters but it needs to be a much larger component.
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Unread 08-18-2013, 02:05 PM   #66
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Originally Posted by mschi772 View Post

A lot of people keep trying to cite real-world comparisons/analogies, but they're full of tons of extraneous variables: different tires, different sizes, different gears, different trannies, different engines, different vehicles, etc.

How does your scientific/ mathematical ratio have any real-world relevance or real-world value if it does not take all of the real-world variables into consideration?

I'm not saying that your ratio is not scientifically/ mathematically accurate, but wouldn't real-world variables need to be considered for it to have any real-world value?


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Originally Posted by mschi772 View Post
Significance is up to you. What you can perceive and what you feel is a worthwhile/significant weight increase/decrease is subjective. There's no equation to provide THE answer to this one. We all draw our own lines.

Wouldn't the significance be up to the vehicle? You said it yourself when you pointed out the "flaws" in the TJ/Ram comparison, what is significant for one vehicle isn't significant for a different vehicle. The "flaw" you pointed out was actually the point I wanted to make.
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Unread 08-18-2013, 03:18 PM   #67
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Originally Posted by SLADE View Post
How does your scientific/ mathematical ratio have any real-world relevance or real-world value if it does not take all of the real-world variables into consideration?

I'm not saying that your ratio is not scientifically/ mathematically accurate, but wouldn't real-world variables need to be considered for it to have any real-world value?





Wouldn't the significance be up to the vehicle? You said it yourself when you pointed out the "flaws" in the TJ/Ram comparison, what is significant for one vehicle isn't significant for a different vehicle. The "flaw" you pointed out was actually the point I wanted to make.
Just because it's math doesn't make it somehow "unreal." You keep asking the same thing over and over, and at first I thought I knew what you wanted, but I don't know anymore. This may be a matter of neither of us being able to think on the same level. A spinning 30 lb tire generates inertia equivalent to 60 lb of cargo. I mean, I don't know what else to say. You seem to be wanting math for the entire vehicle and all its moving parts. You might as well be asking me to give a lecture on chaos theory.

Regarding that messy analogy of yours, let me clean it up. Given identical attributes other than mass, the effect of a given wheel/tire will be EXACTLY the same on a 3000 lb TJ as it will be on a 5000 lb TJ (that would be one fat TJ, huh?). It will be more noticeable to you in the 3000 lb TJ, but that doesn't mean it's actually having more of an effect on the TJ. It's simply a matter of perception. The effects are identical.
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Unread 08-18-2013, 06:23 PM   #68
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Originally Posted by mschi772 View Post
Just because it's math doesn't make it somehow "unreal." You keep asking the same thing over and over, and at first I thought I knew what you wanted, but I don't know anymore. This may be a matter of neither of us being able to think on the same level. A spinning 30 lb tire generates inertia equivalent to 60 lb of cargo. I mean, I don't know what else to say. You seem to be wanting math for the entire vehicle and all its moving parts. You might as well be asking me to give a lecture on chaos theory.

I never said math was "unreal".

I'm looking for the significance of your science/math in how a given vehicle's performance is effected/ impacted by it.

I'm having a hard time righting tire weight off as being insignificant.

Get out of your "I'm smarter than everyone else on this forum" mindset/ "thinking" and back to the real world level. I know your smarter than I am, I'm not doubting that.

Your Scientific/ mathematic answers are just numbers unless they can be translated into real-world impacts. After all, the real-world impacts are what really matters.


Quote:
Originally Posted by mschi772 View Post
Regarding that messy analogy of yours, let me clean it up. Given identical attributes other than mass, the effect of a given wheel/tire will be EXACTLY the same on a 3000 lb TJ as it will be on a 5000 lb TJ (that would be one fat TJ, huh?). It will be more noticeable to you in the 3000 lb TJ, but that doesn't mean it's actually having more of an effect on the TJ. It's simply a matter of perception. The effects are identical.
Wouldn't any added weight be more significant /noticeable on the one that is pushing it's maximum weight capacity?

My analogy wasn't messy. I meant to use 2 entirely different vehicles to show how a large increase in tire weight doesn't effect one (the Ram) as much as the smaller increase in tire weight effects the other (the TJ).

My point was to show that the vehicle the increased tire weight is added to is more of a factor on how the tire weight impacts the vehicle than the tire weight itself.

Your science/ math stays the same but the impacts are VERY different.
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Unread 08-18-2013, 08:19 PM   #69
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I have heard this too. I just never paid much mind to it because my XJ came factory with the oversized calipers. (Sadly it has the tendency to generate waaaaay to much heat.. Lol). As long as I can stop fast and hard without locking up with my tires.. I'm happy.
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Unread 08-19-2013, 05:55 AM   #70
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Wouldn't any added weight be more significant /noticeable on the one that is pushing it's maximum weight capacity?

My analogy wasn't messy. I meant to use 2 entirely different vehicles to show how a large increase in tire weight doesn't effect one (the Ram) as much as the smaller increase in tire weight effects the other (the TJ).

My point was to show that the vehicle the increased tire weight is added to is more of a factor on how the tire weight impacts the vehicle than the tire weight itself.

Your science/ math stays the same but the impacts are VERY different.
I know what you meant to do with your analogy, but it just didn't work because you didn't account for all the extraneous variables that also change when the vehicle changes. That's why I used a 3k vs 5k TJ in a hypothetical world where neither one's powertrain is overloaded with weight (since a 5k TJ would probably just give-up and go home; they only have a 3500 to rating, right?). Even in your analogy, weight increases would exert the same forces on the Ram as they would on the TJ, and the rotating masses would still have the same equivalent static mass in either vehicle.

The bottom line, and why I was quite thankful to have found Mason's page, is that I'm quite bad at explaining some things. This would be one of those things. Yeah, it gets frustrating when I can't convey what I need to, but please don't think that I'm one of those pricks who thinks he's better than people who aren't as smart/educated as he.

I can't find any flaws in my math, but that doesn't mean there are none. I also KNOW I simplified some figures to make the math a little easier. I'd welcome being proven wrong just as much as being proven right. I wish I had the time and resources to do a real experiment to go along with this math. I'd love to do some MPG and dyno runs while only changing wheel/tire weight (nothing else; can't stress that enough).
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Unread 08-19-2013, 09:13 PM   #71
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I can't find any flaws in my math, but that doesn't mean there are none.

Your flaw is in your ability to apply it to real world impacts. We don't live in a hypothetical world.

Even using your 2 to 1 ratio, when you change a tires weight by 10lbs, 20lbs, or even 30lbs+ without even taking an increase in tire height into consideration, it makes an impact. Using your math turns that into a 20lb, 40lb, and 60lb+ per tire increase. The weight alone is enough to impact a vehicles handling and performance. The impact the weight has will vary from vehicle to vehicle and even Jeep to Jeep.


Your wrong in saying that a tires weight is not worth consideration.
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Unread 08-20-2013, 01:32 PM   #72
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Originally Posted by SLADE

Your flaw is in your ability to apply it to real world impacts. We don't live in a hypothetical world.

Even using your 2 to 1 ratio, when you change a tires weight by 10lbs, 20lbs, or even 30lbs+ without even taking an increase in tire height into consideration, it makes an impact. Using your math turns that into a 20lb, 40lb, and 60lb+ per tire increase. The weight alone is enough to impact a vehicles handling and performance. The impact the weight has will vary from vehicle to vehicle and even Jeep to Jeep.

Your wrong in saying that a tires weight is not worth consideration.
Of course even a 2:1 ratio makes an impact. I never said it didn't. The ratio itself IS real-world. Do some "real world" physics tests, and you'll likely confirm the ratio. If not, let me know. I honestly don't have a clue what you want to know anymore, but it seems like you want something other than what I created this thread to discuss. Do you want to know what impact additional weight in wheels has on a vehicle? Handling-wise, I don't know; that's above my head. Otherwise, it's the same as double that weight as static cargo--to tell you that is the whole point of the equivalency ratio in the first place. Do you want to know what impact static weight has on a vehicle? That's a bit more intuitive and a totally different topic for discussion.

It is my opinion that tire weight is not with consideration, not a statement of fact. Feel free to disagree with me, but that won't change my opinion. There are more important aspects to consider when getting tires IMO, and I always have made a tire choice long before having to look at weight to help me decide.
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Unread 08-21-2013, 10:35 AM   #73
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This topic cannot be discussed ignoring "real world differences" in tire design/construction and looking at pure theoretical physics. We're not in a lab using scientific instruments and free spinning weights machined to exacting weight distribution. The best real world test is to use two tires of the same line in different widths. The "close enough" diameter eliminates it as a variable (for real world tests, not lab-grade tests).

33x9.5 vs 33x10.5 vs 33x12.5
The BFG AT K0 is available in all 3 sizes (maybe not 9.5 anymore). All are a 15" wheel, and C load sidewall. Any difference in weight comes primarily from the increase tread width.

Now, go to a race track and run the tank dry for each of the three sizes (Mythbusters did something similar for their tailgate experiment). Since stop/go driving is where it matters, use cones every 300ft to imitate stop lights/signs. Use a robotics to control throttle and brake input to keep it consistent.

The tire that traveled the farthest has the least effect on the vehicle as a whole.

R&T does 0-60-0 on almost every car they review. The same test could be done for testing tire effects, again using robotics for consistent input.

Test a 30x9.5 against the 33x9.5 (If it still exists). We already know weight's effect on the system. Predict the diameter's effect and compare that to actual results.

No, it's not a lab grade experiment. But we aren't the tire engineers living in a lab. We live in the real world with predetermined choices for tires, and infinitely changing variables. All we can control is which tire is on our vehicle & and how much input we use while driving. Using robotic inputs and a controlled environment eliminates the biggest variables.
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Unread 08-21-2013, 11:20 AM   #74
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Quote:
Originally Posted by mike_dippert
This topic cannot be discussed ignoring "real world differences" in tire design/construction and looking at pure theoretical physics. We're not in a lab using scientific instruments and free spinning weights machined to exacting weight distribution. The best real world test is to use two tires of the same line in different widths. The "close enough" diameter eliminates it as a variable (for real world tests, not lab-grade tests).

33x9.5 vs 33x10.5 vs 33x12.5
The BFG AT K0 is available in all 3 sizes (maybe not 9.5 anymore). All are a 15" wheel, and C load sidewall. Any difference in weight comes primarily from the increase tread width.

Now, go to a race track and run the tank dry for each of the three sizes (Mythbusters did something similar for their tailgate experiment). Since stop/go driving is where it matters, use cones every 300ft to imitate stop lights/signs. Use a robotics to control throttle and brake input to keep it consistent.

The tire that traveled the farthest has the least effect on the vehicle as a whole.

R&T does 0-60-0 on almost every car they review. The same test could be done for testing tire effects, again using robotics for consistent input.

Test a 30x9.5 against the 33x9.5 (If it still exists). We already know weight's effect on the system. Predict the diameter's effect and compare that to actual results.

No, it's not a lab grade experiment. But we aren't the tire engineers living in a lab. We live in the real world with predetermined choices for tires, and infinitely changing variables. All we can control is which tire is on our vehicle & and how much input we use while driving. Using robotic inputs and a controlled environment eliminates the biggest variables.
I like the experiment you've outlined. I don't like that the tires have to be different widths because they'll be less aerodynamic and have more drag from their larger contact patch, but I'd rather accept width differences in order to keep everything else the same. Since no one makes a tire identical in every way but weight, something has to give. I'd definitely run this experiment if I could.
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Unread 08-21-2013, 01:04 PM   #75
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Originally Posted by mschi772 View Post

I like the experiment you've outlined. I don't like that the tires have to be different widths because they'll be less aerodynamic and have more drag from their larger contact patch, but I'd rather accept width differences in order to keep everything else the same. Since no one makes a tire identical in every way but weight, something has to give. I'd definitely run this experiment if I could.
You could always glue weights to the inside of the tire. Keeping the wheel balanced would be tricky though.
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