20" vs. 22" wheels and rotational mass

[vvv90]

So it's come down to me really wanting to get 22" wheels for my 3SRT, but I always hated the thought of losing performance.

The biggest misconception is wheel weight. The overall wheel weight doesn't have as much to do with accelleration, or lack there of as rotational mass does.

It's simple physics really, the further away from the hub that a majority of the weight is, the more energy it takes to move it.

Just like spinning around on a tire swing when you're a kid. If you pull your legs in you go faster yet your overall weight never changed.

22" wheel hoops are further away from the center and a majority of the weight of the wheel.

However, the overall diameter of a 22" wheel tire combo is probably about the same as my stock 20" wheel tire combo.

I'm just trying to figure out if it's a moot point and that if there's some way to determine the rotational resistances comparatively.

I know there's very heavy 22" wheels out there that look pretty....Not interested....I'm assuming I'll have to go with a very strong forged light weight (and expensive) wheel.

But how expensive I wonder?

Does anybody have any idea how I can determine this? Is there any wheel makers out there that have these facts?

Thanks!

[Bornagainultimatum]

First, you have to think about the performance charachteristics of your car currently. For drag racing, assuming you are not using slicks or sticky drag radials, you probably see considerable wheel spin with your SRT. If your hemi has enough torque to create excessive wheel spin, the added rotational mass associated with going from 20's to 22's won't be a significant factor in performance. If you were hooking up using a good set of slicks and had limited wheel spin to begin with, the added rotational mass of 22's might bog the car during your launch. Go with the 22's and trust the hemi's torque to do the job even with the 22's.

[vvv90]

First, you have to think about the performance charachteristics of your car currently. For drag racing, assuming you are not using slicks or sticky drag radials, you probably see considerable wheel spin with your SRT. If your hemi has enough torque to create excessive wheel spin, the added rotational mass associated with going from 20's to 22's won't be a significant factor in performance. If you were hooking up using a good set of slicks and had limited wheel spin to begin with, the added rotational mass of 22's might bog the car during your launch. Go with the 22's and trust the hemi's torque to do the job even with the 22's.

I may be wrong, but I don't think that's necessarily true.

I believe the difference in rotational mass would seriously affect the performance of the car all the way down the track/at high speeds.

I don't have a formula to prove it, but just what common sense is telling me that at higher speeds there will also be a resistance against a taller wheel as long as you're accelerating.

The benefit of having 22" wheels at speed will allow you to coast further if you take your foot off the gas.









(haha --- > "Why you're a Gillette Man I see" )

[done]

So it's come down to me really wanting to get 22" wheels for my 3SRT, but I always hated the thought of losing performance.

The biggest misconception is wheel weight. The overall wheel weight doesn't have as much to do with accelleration, or lack there of as rotational mass does.

It's simple physics really, the further away from the hub that a majority of the weight is, the more energy it takes to move it.

Just like spinning around on a tire swing when you're a kid. If you pull your legs in you go faster yet your overall weight never changed.

22" wheel hoops are further away from the center and a majority of the weight of the wheel.

However, the overall diameter of a 22" wheel tire combo is probably about the same as my stock 20" wheel tire combo.

I'm just trying to figure out if it's a moot point and that if there's some way to determine the rotational resistances comparatively.

I know there's very heavy 22" wheels out there that look pretty....Not interested....I'm assuming I'll have to go with a very strong forged light weight (and expensive) wheel.

But how expensive I wonder?

Does anybody have any idea how I can determine this? Is there any wheel makers out there that have these facts?

Thanks!

I would suggest that the difference due to rotational mass is not going to be significant.

If you are comparing forged wheels, the 22 would likley be about 3 or 4 pounds heavier. Then you would have to condsider the style of the wheel and where the weight is concentrated. The difference in tire weight could be as little as 1 pound bewteen a 20 and a 22.

Compared to moving the mass of a 4500 pound car, this difference is not an issue.

[MagnumRT05]

Personally, 24s fill the wheel well perfectly. Even with my 22s, they still look very small, but I dont think you want 24s with a rubberband as a tire. I say 22s if youre not gonna be an all out racer and you plan to watch out for curbs

[Super T]

Come up with the weight of the spokes, the weight of the hoops, and the weight of the hubs for both size wheels, and i can tell you the difference in polar inertia between them. The equation includes taking the radius (the distance from the mass to the axis of rotation) to the fourth power... so double the distance means 16 times the inertia to overcome. It can be a pretty huge difference. From a weight standpoint, which only matters if you put 'em in your trunk, then no, you probably wouldn't notice the difference.

[done]

Come up with the weight of the spokes, the weight of the hoops, and the weight of the hubs for both size wheels, and i can tell you the difference in polar inertia between them. The equation includes taking the radius (the distance from the mass to the axis of rotation) to the fourth power... so double the distance means 16 times the inertia to overcome. It can be a pretty huge difference. From a weight standpoint, which only matters if you put 'em in your trunk, then no, you probably wouldn't notice the difference.

Not a valid arguement. The radius from a 20 to a 22 is only 1 inch, a 10% increase. Once the wheel is in motion, then you would have greater rotational inertia. However, the few pounds of increased rotational mass is nothing compared to the weight of the car itself. This whole debate is about the size of a flea on an elephant.

[Super T]

Not a valid arguement. The radius from a 20 to a 22 is only 1 inch, a 10% increase. Once the wheel is in motion, then you would have greater rotational inertia. However, the few pounds of increased rotational mass is nothing compared to the weight of the car itself. This whole debate is about the size of a flea on an elephant.

Nay, my friend, the object has the same polar inertia whether it is stationary or moving. It's the Momentum that changes with speed. Again, it's not the weight that counts, it's the fact that it takes a lot to get the wheel spinning.

[done]

Nay, my friend, the object has the same polar inertia whether it is stationary or moving. It's the Momentum that changes with speed. Again, it's not the weight that counts, it's the fact that it takes a lot to get the wheel spinning.

Are you aware that this concept was actually tested at one of the GIFO's with 18's and 20's and no measurable difference was reported?

[krusty]

I thought the rule was ...
The angle of the dangle is allways proportionate
to the heat of the beat.

If all this wheel size jargon is true then why isn't everyone at the track using 15 inch wheels with small tires?

If you like 22s Buy 22s.
To the people out there with 22s.
When you went from the stock 18s to your 22s
did your gas milage change?
If your milage went down noticably you have your answer.
If it uses more fuel its stealing your power.


That just logical Captain.I could be wrong, I usually am.

[Super T]

Are you aware that this concept was actually tested at one of the GIFO's with 18's and 20's and no measurable difference was reported?

I read that. I've also read lots of counts of people losing .2 in the 1/4 with no changes to their car other than wheels. I can tell you with certainty that it makes a difference. I spent $100,000 learning that How big a drop in the bucket that is? Without knowing numbers I couldn't tell ya. But unless you're dropping $3,000 for three piece forged (i.e., light but strong) 22's that have lighter hoops and tires than whatever you had stock, they're going to be heavier and make a notable difference. It obviously varies by wheel. High quality mesh type wheels might not make any difference, while wide-spoked cast wheels might make a huge difference. It's not something to overlook if you're genuinely concerned with your track times while considering wheels, that's my point. Ya shouldn't be surprised if you upsize and your times drop.

[done]

I read that. I've also read lots of counts of people losing .2 in the 1/4 with no changes to their car other than wheels. I can tell you with certainty that it makes a difference. I spent $100,000 learning that How big a drop in the bucket that is? Without knowing numbers I couldn't tell ya. But unless you're dropping $3,000 for three piece forged (i.e., light but strong) 22's that have lighter hoops and tires than whatever you had stock, they're going to be heavier and make a notable difference. It obviously varies by wheel. High quality mesh type wheels might not make any difference, while wide-spoked cast wheels might make a huge difference. It's not something to overlook if you're genuinely concerned with your track times while considering wheels, that's my point. Ya shouldn't be surprised if you upsize and your times drop.

But did those reports include swapping wheels at the track and making back to back runs. I have seen 2 tenths variations from week to week on my car without changes, other than temperature and humidity.

I don't dispute that there is some difference, but the difference is more likely due to increased weight of the wheels/tires than to differences in rotational mass. But even that difference is slight.

For the serious guys, those in the low 12's and below, short drag radials are far more important and used.

It doesn't take much power to move a 50 pound wheel, it takes a lot of power to move a 4500 pound car.

[vvv90]

It doesn't take much power to move a 50 pound wheel, it takes a lot of power to move a 4500 pound car.

This is a good quote:

SO the math is 11"/10" squared = 1.21, or 21% more inertia on 25 pounds of a 50 pound wheel/tire. Roughly 10% total added inertia per wheel.

SO if it takes 25 HP to spin each wheel, that's 100HP total. The 10% extra suggest 10 more HP to spin the wheel, costing you about 1/10th in the 1/4 mile.

The biegger problem is when you take than 50 pound 20" combo and turn it into a 60 lb 22" combo. Now that extra 20% weight turns into nearly 60% more inertia. (1.20 squared = 1.44 times the 10% up above = 1.584, or 58.4%)

So now instead of 100HP to spin the wheels, it takes 158 HP, cutting your net effect by up to 58 hp, costing you over half a second in 1/4 mile performance.

That was just an example but the math is pertinent.

Bottom line is that .2 tenths is about what could be expected and I'm not willing to drop $3k for wheels to find out the hard way. Heck, that would negate my Predator purchase. I'm not willing to do that. Whether the overall weight is more important, that's what I want to find out because if the same wheel/tire combo weight is the same for good 22's as it is for my stock 20's, I should be alright.

For craps and giggles, what is the GIFO study? I'd like to take a look and judge for myself.

[Bornagainultimatum]

Sounds like the 22s will work for you. I have been involved in drag racing all of my life. My brother currently has the quickest NHRA stock eliminator car in the country. All of the issues surrounding wheels for regular drag racers have to do with the overall weight of the vehicle including wheels, tires and driver as compared to the horsepower of the engine/trans combination. This is the basis for NHRAs classification system. If you intend to compete regularly at NHRA events, you probably won't want to go with 20s or 22s. Then, the concern will be achieving the optimum launch, at the minimum weight for the class, and sustaining max horsepower and torque throughout the rpm band of the run. All that and reaction time too. But for all around good looks and the need to clean somone's clock occasionally on the weekends, the 22s shouldn't hurt.

[RT NOMAD]

A Good Rule:

No advantage is insignificant.