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Discussion Starter · #1 ·
Please can someone help with this.

I have a Magnum RT with 18" stock wheels. I truly LOVE IT!!!
I am ready to add 22" chrome wheels, however the wheel people that I went to see said that I will notice a reduction in acceleration with the 22's.

Is this correct, is it that noticable? I am a performance freak and will just die if I cant get off the mark as quickly as I normally do. I can't sacrifice that.

Please, if you had 18" and changed to 22" what did you experience?

Please post as many replies as you can, I am sure there are many people that need to know this.

Also, what tire specs should go on 22's, some say 265/30/22 others say 265/35/22. Which is the right choice without change to the computer?

Thank you!!
 

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I'm no mechanic but basically the bigger the tire the more the car has to "push" its self to make the wheel go round. Also I heard some one say that with the bigger rims your mileage meter thingy is also a little off i think?
 

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'75 Power Wagon
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it depends on what the actual diameter of your tires are.. not just bigger rims.. but say you have 18 rims with 20 tires.. its 20.. and then say you get 22s with 24 tires.. then your speedo will be off.

But i think the added weight of the rims may slow your car down a bit, i don't know how much or anyting though.
 

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Discussion Starter · #4 ·
Thanks the75powerwagon for your post.
Does ANYONE know the weight of the stock rims+tires.
If I get 22's and keep weight close to the stock... and keep the o/d of the tires the same, surely I cant lose acceleration.... or am I just wrong with this theory?
 

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The number of revs/mile is what determines how accurate the speedo will be with the new tires. Continental says that our tires are 734 revs/mile. The spec sheet on a tire you are considering will tell you the revs/mile for that tire.

It looks like the 265/30-22's will be a nearly perfect match with weight and revs/mile. The weight of the wheels and the fact that the weight is further out from the center will then become the deciding factors on performance. Good luck and post some pictures when you get your new wheels and tires!
 
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Any chromed steel wheels will be heavier. I got 20" D'Vinci Havocs, which are chromed steel, and they are considerably heavier, maybe 10lbs heavier each. My tire diameter also increased by half an inch, and yes, there is a slight difference. Still a fast car. My mileage may have increased slightly though on the freeway.

The only wheel that will come close to your stock ones will have to be a polished aluminum wheel, most likely a billet type wheel.
 

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AWD is the right way
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Assumig that you retain the stock diameter, any adverse effect would be in the hundreths of a scond range. Unless you are getting forged wheels, the new wheel tire combo will add 10 to 15 pounds per wheel. This extra weight will have more effect on ride and handling than acceleration performance.
 

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It's absolutely true the heavier the wheels, the more HP it will take to move the mass. Think about how much energy it would take you to push a huge tractor tire compared to the energy it would take you to push a bicycle tire. Is the difference in weight enough that you would notice driving your car on a daily basis, more than likely not. It's like putting groceries in your car, you really don't notice the weight difference in normal driving.

Here's a good tire wheel size comparison chart that simple to use:
http://www.miata.net/garage/tirecalcold.html
 

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Here's the deal. You will take a double or triple perforamnce hit on going to 22" wheels.

First hit is the absolute weight of the wheels. 22" wheels will almost certainly weigh more than the stock 18" wheels because it takes much more material to form the rim. Also steel chromed wheels which is what most 22's are made of weighs much more than aluminum.

Second hit which you will take (and the hardest one to understand) is the rotational moment of the wheel is certainly higher than the 18" rims. The further from the center of the wheel the mass is the greater the energy required to get the mass moving. A good example of this is figure skating. If you've ever seen a figure skater doing a spin. The further from her body the mass is (sticking arms and free leg out) the slower the rotation. The closer to the body her mass is (pulling in arms and leg) the faster she spins without having to increase the energy input. You can also think of the wheel as a circuar lever, the further out the mass is on the lever the harder it is to support or move the mass, against gravity.

Third hit which you may or may not have is a change in tire diameter. Tires that are bigger in diameter will require more torque to get them to rotate. You might pick up a little top end but you are in essense changing the gearing of the car to the detriment of low end acceleration.
 

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Discussion Starter · #12 · (Edited)
dantodd said:
Here's the deal. You will take a double or triple perforamnce hit on going to 22" wheels.

First hit is the absolute weight of the wheels. 22" wheels will almost certainly weigh more than the stock 18" wheels because it takes much more material to form the rim. Also steel chromed wheels which is what most 22's are made of weighs much more than aluminum.

Second hit which you will take (and the hardest one to understand) is the rotational moment of the wheel is certainly higher than the 18" rims. The further from the center of the wheel the mass is the greater the energy required to get the mass moving. A good example of this is figure skating. If you've ever seen a figure skater doing a spin. The further from her body the mass is (sticking arms and free leg out) the slower the rotation. The closer to the body her mass is (pulling in arms and leg) the faster she spins without having to increase the energy input. You can also think of the wheel as a circuar lever, the further out the mass is on the lever the harder it is to support or move the mass, against gravity.

Third hit which you may or may not have is a change in tire diameter. Tires that are bigger in diameter will require more torque to get them to rotate. You might pick up a little top end but you are in essense changing the gearing of the car to the detriment of low end acceleration.

Dantodd, that was well put. Whilst I accept and understand the physics of all of this, to what degree has anyone that changed from 18" to 22" experienced a loss in acc? Is it that noticable and is the cool looking trade off actually worth the $5000 investment?

I am sure that I would be able to find 3 spoke 22" wheels so the weight would come down relatively. Whilst the centre of gravity (c.o.g) is at the axis, the centre of mass from the axis to the rim is somewhere along that line. Ideally we want to keep that c.o.m as close to the axis also. Thus, all the wheels where the spokes get wider towards the wheel edges increases the (c.o.m from the axis to the edge) nearer the rim edge, hence drop in acc. Spokes that taper down at the the edges, (ie more mass in the centre) have c.o.m closer to the wheel axis and hence the acc will be better.

So, if I can find a 3 spoke wheel in 22" that tapers towards the edges (IE c.o.m close as possible to the axis) I will definitely buy them. Does one even exist?

Anyone know of any make/models that can meet these criteria?

Thanks.
 

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That's the real question I guess. After all the SRT folks decided that 20" wheels were worth whatever losses tehy might create in straight line performance. I suspect that running the quarter with your gas tank half empty and the garden implement removed from the back would make as much difference as 18" vs. 20" wheels.

Also, a lower profile tire will, to some degree improve handling in other areas, less sidewall give means better adhesion and a larger traction patch on the ground during cornering. you trae off one for another.

The difference (In my guesstimation) will be about the same as there is variation from engine to engine in the RTs. So if you have a "fast" engine/PCM combo then maybe you'll now ride like slow engine/pcm combo. You'll still take down most anything from a stop light. If you really like the look of 22's then go for it, you ain't racing this thing anway, right? If you are racing then get some cheapy 18" wheels and put slicks on them for the drag strip!

My math and insterest are not to the level that I'll be claculating the exact losses :)
 

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Isn't there also an issue associated with the wheels being "unspung" weight? Someone at some point -- a lot smarter than I am -- gave calculations and specifics on why weight on the 'bottom' side of the suspension was worse than weight on the 'top' side by a certain ugly multiplier.

As for speed, I've heard stories of guys running 18's whomping guys on 22's here. I did it once myself (I have chromed 18s, which are heavier than the 22 lb stock alloys but not by too much). Ran up a couple of car lengths over a fairly short distance. However for all I know the guy was an idgit and couldn't drive.
 

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Dan,
Didn't that make for this with gearing?
KK

dantodd said:
After all the SRT folks decided that 20" wheels were worth whatever losses tehy might create in straight line performance:)
 

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AWD is the right way
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Stock 18 rim is 23 lbs, stock Conti is 32 pounds. A Pirrelli 22" is 33 pounds. Good forged rims will be in the 25 pound range, cast wheels around 30 to 35. So the 22's could be be from 2 to 12 punds heavier and will indeed have a higher moment of inertia. But it is meaningless because you are not spinning the tires in a vacuum. You are launching 4400 pounds of car, driver and gas (more for some of you big guys). The pressure you run in your tires will have more effect than the weight on straght line performance.

The additional unsprung weight and skinny tires will give you stiffer ride, but so will running 40 lbs of air.

This discussion is much ado about nothing, I think.

But if you want to pursue it, take a look at:

http://online.cctt.org/physicslab/c...tes/angularmomentum/lessonangularmomentum.asp
 

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kstompaint
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I think this is being over thought a bit. After all, the SRT10 Ram has factory 22s and they run better than I can describe (I have driven one). If you are not drag racing and counting thousanths of a second, dont worry about it. I have 22s on my Turbo Diesel and it runs and tows the same as it did stock (only it looks way better). Also, you can do this wheel swap for WAY less than $5k. If you go cast chrome, you should be able to do it for $2500. If you go 2-piece billet polished it will be more like $4000. You cant go from retail prices because if you shop around, you can get a better deal.

If you're a performance junkie, consider the additional handling characteristics you will get with the larger wheel (did I mention it will look better?)

Tires... 300 guys seem to be using the 265-35-22 which is a 29.3 O.D. and thats what I ordered for my lowered Chevy Colorado. 265-40-22 is 30.3 O.D.
 
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done said:
This discussion is much ado about nothing, I think.
I respectfully disagree. I think it's a legitimate question. I noticed a difference in acceleration after installing my chrome 20's. Partly due to the added weight (which is rotational and unsprung), and also the taller tire diameter affecting the final drive ratio.

If there was nothing to it, racers would not have been using lightweight racing wheels all these years. And an inch difference in tire diameter can have the same effect as swapping a set of gears in the differential.

In answer to your question, Matrix, I noticed a slight difference in acceleration, but it was definitely worth the tradeoff for improved looks. My handling has improved also (I also lowered the car 1-1/2"). I hate to say it, but IMO the stock-wheeled Magnums look kinda boring now...
 

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my 20s add a good half second on a quarter mile run. 22s would add closer to a full second from the stock rims.
 

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No Loss of Power

I have added 22 inch DRIV wheels and Nitto tires...No Loss of Power!! The key is to make sure the wheels and tires weigh the same as or less than (hard to do) the stock package. Heavier wheels and rims will decrease powerto the ground although I am not sure anyone would notice much.... The look of the car is great with 22"s stay away from 20"s....Andy
 
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