From tonight's SRT Chat Session at http://www.srtforums.com/:

Originally Posted by jlandbl
In your opinion, would 22" wheels negatively impact 0-60 times on the Jeep SRT8?

"Yes, even if they are the same weight as the 20's they will have more rotational inertia since they are larger diameter. This will affect braking as well as acceleration. Of concern is also the load carrying capability of the short sidewall tires. And the ride. And the shocks' ability to hold the tires on the ground...."

A non-winable argument from my limited personal research, coupled with reading, and talking to many many informed sources. I have a friend who is a professional race car driver, and he slaps everything from 17s to 23s on porsches that he races, just to try things out. I've seen him do this, and according to his research, it all depends on the entire vehicle setup, the weight of the wheels, the tires, the conditions etc. Our vehicles braking systems and suspensions systems are more than adequate to support wheel upsizing, if done in moderation. Without increasing the overall diamter of the wheel and tire combo, say going from a 20 to 22, and even with the weight of the barrel being further from the hub, it's not going to present a noticeable difference from stock. The walls of the run flat tires add considerable weight outside the barrel of the stock 20s, which is greatly reduced when going to a non-runflat 22. So even though the barrel is an inch farther from center on a 22, the weight distribution is not necessarily detrimental.

I've never done an 1/8 or a 1/4 on a strip, and don't intend to, but I am willing to bet that IF I did a run with my stockers, then swapped on my 22s, the difference, if not increased, would be decreased by thousanths of a second. And though that isn't a big enough difference to concern me, those of you that are performance and race junkies would probably care.

Yeah, I second the neglible effect of 22s on performance as long as you try and keep the overall circumference the same.

Well, considering our vehicles were tuned and tested with the stock rims/tires it stands to reason that the BEST performance option is the stock wheels and tires. Logically speaking.

However, if one were to modify the suspension, etc. it would all need to be retuned once wheels and tires were modified.

Well, considering our vehicles were tuned and tested with the stock rims/tires it stands to reason that the BEST performance option is the stock wheels and tires. Logically speaking.

That's a stretch. Our vehicles aren't some Formula1 car prepped for a track.

So let me ask an honest question. Just play along. If there were some 30 inch ultra high tech composite wheels, that improved our 0-60, yet cost $10000 each, do you think Jeep would have put those on instead?

There is a fine line between the way a vehicle is engineered, and the money they spend on it. Our vehicles are tuned and setup to run as produced. That doesn't mean that any modification will hurt it's performance. Quite the contrary, really. Otherwise you wouldn't see people adding headers, cams, intakes, exhaust, etc (yes, I'm aware that not all of these mods always help performance, and some *can* hurt it, as we've seen with a few of the exhaust systems).

And don't you think that the engineers will ALWAYS tell you that what they built is the perfect specimine, and any changes you make to their creation will hurt it?

if the diameter of the tire/wheel combo is larger than stock then it will affect acceleration performance as the larger combination will increase your differential gear ratio.

as far as suspension & braking performance, i don't know.

That's a stretch. Our vehicles aren't some Formula1 car prepped for a track.


It's a stretch? Huh? Call me crazy but I generally side with the individuals whose jobs it is to ENGINEER and BUILD our vehicles. I could be one of those guys and ask how many years you've spent in engineering school, and how many automotive engineering certifications you hold, etc. But I won't do that.


Regarding ge2's comments about $10,000 ultra rims/tires. Well I'm no engineer and do not attempt to sound like one, instead I'll stand by my initial assessment that logically speaking, it would stand to reason that our vehicles should technically perform the best with the wheels/tires that they were initially calibrated to run on.

It's simple logic. If you were to change said variables, it would have an effect on anything after the initial change. However, whether or not that change is enough to dramatically alter other systems is beyond my perspective.

Also, don't confuse my posts with somehow being AGAINST changing rims/tires. It seems many are far too sensative of this subject. I never once said that.

I'm a huge fan of ge2's rims and plan to get a set on my black truck. :D

Here's my take.

No way that our cars are engineered solely for top performance. Everything is a compromise to some extent.

Take the wheels and tires. If you cared only about performance, we'd have lighter wheels and stickier tires. And the average consumer would be *****ing about bent rims and poor tire wear.

I agree that a 22" wheel should perform similarly assuming that the overall diameter with tires doesn't get larger. If it does, you're changing the effective gearing.

Alex

These are really my favorite topics. There is no way aside from one driver, with one car, and two sets of wheels, to go to the track and just do it. So until one of us does it with video, we will always debate :) It's good. Give us something to do ;)

Here's my take.

No way that our cars are engineered solely for top performance. Everything is a compromise to some extent.

Take the wheels and tires. If you cared only about performance, we'd have lighter wheels and stickier tires. And the average consumer would be *****ing about bent rims and poor tire wear.

I agree that a 22" wheel should perform similarly assuming that the overall diameter with tires doesn't get larger. If it does, you're changing the effective gearing.

Alex

Watch out, the moment of inertia change is VERY significant when moving up to a larger wheel but maintaining the same overall diameter.

I remember with GM trucks that going from a 17" to a 20" wheel would add 20 - 40 feet to your braking distance.

These are really my favorite topics. There is no way aside from one driver, with one car, and two sets of wheels, to go to the track and just do it. So until one of us does it with video, we will always debate :) It's good. Give us something to do ;)

Well, I haven't done it with the Jeep or at a dragstrip, but I did it all last year with my autocross car. 2 sets of lightweight wheels, same brand of tires, the only difference being an inch in wheel diameter and almost an extra inch in outside tire diameter. I ran both on the same course at a test and tune and ran slightly better times with the shorter tire. In my case, I was dealing with a horsepower starved BMW so the taller tire negatively impacted acceleration.

But in the end, you're right. There's no controlled environment, so we're all our own experts. :D

Alex

Watch out, the moment of inertia change is VERY significant when moving up to a larger wheel but maintaining the same overall diameter.

I remember with GM trucks that going from a 17" to a 20" wheel would add 20 - 40 feet to your braking distance.

I agree, but the debate has been with 22's that were lighter then stock. Or at least I thought so.

Alex

17s to 20s and talking about braking is a horse of a whole different color. Not even close to the same thing. For starters, stock pickup brakes are not close to those on the SRT. Next, growing 3 inches, and most likely staying with a cast wheel in the 20, you're weight increased significantly.

It's simple logic. If you were to change said variables, it would have an effect on anything after the initial change. However, whether or not that change is enough to dramatically alter other systems is beyond my perspective.

Which is exactly what ge2 and I said, it's not going to dramatically alter other systems.

And asking me about my engineering background is a poor argument. Experience and a general knowledge about cars can answer this question.

Larger rims = usually more metal = usually more weight X 4

My past experience even with just moving up 2" in size had a dramatic negative effect on acceleration and braking performance. The tire/rim combo's I used still had the same overall diameter as stock. I found even the ABS was affected. I am sure there are some exotic lightweight alloy rims out there that this rule does not apply to.

I like the look of the bigger rims but I have always gone back to stock for the performance.

Just my 2cents

While what you said is true, most aftermarket wheels tend to be lighter than stock cast wheels.

Mine are right around 6 pounds lighter up front, and 7 in the rear each.

don't forget the stock wheels are forged, if someone were to get some knockoff cast 22" wheels then I'd bet it would make a significant difference.
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Exactly right Ideal. That is very true. Going to a cast knockoff, or just about any cast wheel will increase the weight.