Oh my do I remember this discussion not too very long ago. It got a bit ugly. Check out the previous thread and see if it helps you any. There is much to read but trust me, its all good!!! lol

https://mustangforums.com/m_2149636/tm.htm

One other thing, it doesnt start off talking about the 20's but it certainly changes gears and gets heavy into 20's.

 

OH! Thanks Stowes for rescuing that thread as it was trying to die a peaceful death! lol
I’m guessing this one will end with the same people arguing the same points and ending with the same conclusions!
I think some know how I stand on this issue! lol!!!!

To be continued I’m sure…..

 

Were in the heck did you pull those numbers from?

SO your saying someone with a good CAI & tune wearing 20" will be even in RWHP as a 100% stock GT?

I THINK NOT!

All you guys saying larger rims hurt performance; Here is your perfect example:
Do you have any proof that the GT’s with 18" rims are slower then the GT’s with 17" rims......

I THINK NOT!

Oh and the saga continues....

 

Awww man, Im sorry Ya gotta admit, it was good reading material though!! LOL BTW, you held your own very well so let the arguing begin!! LOL LOL (its all good)

 

ok well, heres the thing, i dont have the GT, so the power loss would be even more noticable for me wouldnt it? 20s look really really nice on the s197, but will the power loss be worth it (if any?) or shoulod i just look for nice 18s or 17s?

 

A good CAI + Tune is worth 25 or so HP on average. I'd say a 10 HP loss is about right for the average set of 20's. Thus, the modded car with the 20's would still be better off than a stock GT, but by less of a margin than he otherwise would.

Go to the "other forum" (m o d u l a r f o r d s). There are numerous firsthand dyno experiences described there. The proof of the power loss is EMPIRICAL.

By the way, I HAVE weighed the OEM wheels, and they only differ by about half a pound each between 17" and 18". That's not enough to see a significant change in performance. However, I have handled and weighed some 20" wheels that were 18 lbs HEAVIER than the oem wheels. Ouch!!!!

The issue is the WEIGHT of the wheel-tire combo. Of course, there are heavy wheels in all sizes. However, the logic goes like this: The TYPICAL 20" wheel, or "Dub" if you prefer that term, is not made with performance in mind. It is designed for style. As such, weight is a very minor concern, if it is a concern at all. Thus the AVERAGE 20" wheel is significantly heavier than the OEM 17" and 18" wheels. Think about it, the average person cares about what their wheels look like. You might ask your buddies or your fellow forum members "what do you think about these wheels for my car" and then point to a picture. You see guys like Chip Foose design wheels on TV. He gets out a sketch pad and draws what he thinks looks good. That's shopping based on LOOKS. How often do you see someone shop around for wheels by asking for weights? Or even better, moment of inertia? That information is difficult to find becasue the average customer doesn't care about those specs. Consequently they are also less important for the wheel makers.

A 20" wheel is not a performance wheel, at least not on these cars. The 20 will leave you with a very thin sidewall, which in addition to making your ride uncomfortable, also greatly reduces the torsional sidewall give in the tires--and that is key to getting a good hookup on the drag strip. Take a look at what the serious drag racers are doing: They ditch the OEM wheels and they go through a lot of effort to modify the rear end so they can put on 16" or 15" wheels in the back. That lets them put some serious wrinkle-wall tires on there.

Sure, you could get your 20's with some nice, wide, grippy tires. And that might be better than stock for traction (Due to the tires and the extra width). But getting the same type of tire on 18" or 17" rims would be even better. Then you'd have the added contact area and the sticky rubber but less of the weight. The serious racers known this. That's why they run 15" Bogarts that weight half what the OEM wheels do, and give them a nice fat wrinkewall sidewall.

BUT, a lot of people don't do that becasue 20" wheels are the hot style these days. And there's nothing wrong with that. Just about everything on these cars is a compromise of one sort or another. If you like your 20's, great! More power to you. But understand that if your wheels are particularly heavy (which most 20s are) then you will loose some power becasue of it.

 

UCF you would be wise to pay close attention to the actual weight of any 20" rims you are looking at. We added the same rim/tire set up as my car to my wife’s V6 convertible and I assume because she drives as one might consider "normal" that acceration was not something she complained about with the new 20" rims. Having to dodge pot holes was! I will add that acceleration, or lack there of, was one of the 3 things she did mention when she drove it home the first day we got the car a few months back. But she had gotten used to driving our GT with over 500hp so there was quite a step to the new V6! If you are coming from 16's or 17's I think the biggest thing you'll notice (OVER THE LOSS OF PERFORMANCE sorry I had to throw that in lol) is the ride. Now we lowered her car by installing Eibach pro spring kit and Tokico D-Spec (same as mine) when we went to the 20" so there was a very noticeable ride difference! I had to run here D-Specs about a half a turn out to get the same ride she liked on my car.
Please don't think I feel I'm some guru on rims and tires and I'm far from it! I just don't appreciate broad statements from people that have never had any first hand experience with actually using these but yet they claiming that just because we bolt on a set of 20" rims our cars can't perform anymore! Yes there are better rims out there for all out performance but Stock Mustang rims and tires are NOT them!
To any of the nay sayers:
Did I claim that 20's made my wife’s car quicker? NO As a matter of fact every time I drive her car and go and punch out in it, right about the time the RPM get close to 5300 or so I get the impression in my mind of the little engine cowering down hands up screaming NO! NO! Please stop, what did I do to you! LOL! So I don't drive her car hard at all! It's just not any fun! More then once I have forgotten which car I was in and started to ease into the throttle to pass and though what the heck! Then just laugh because I realize I left those extra 300+ ponies back in the garage. Funny thing, I don't thing I have ever though I was in her car while actually having been in mine!

 

CrazyAl

And that is the true argument! It is weight that robs horsepower NOT necessarily rims size!

I could confuse the issue by saying even in drag racing if I showed up with either of our cars and ran passes where the only thing I changed was rear tires, for example 215/65/16 (stock on some V6 Mustangs) and made passes with a set of 285/30/20 that the traction I would gain at the launch would never be over came by the hp I would be robbing as the car accelerates down the track!
Now this IS speculation on my part and next summer because my wife’s car isn’t banned from the track (lol) I will practice this theory!

Again my point isn’t that 20’s are the best, my point is and always has been some 20’s are NOT as bad as some people claim!

 

moment of inertia of a 17in rim @ 20lb = 5.0173 lb ft^2
moment of inertia of a 20in rim @ 20lb = 6.9444 lb ft^2

the 20in rim will require 38.4% more power to accelerate at the same rate.
now increase the actual mass of the larger rim to 25lb (only fair that the 20 weighs just 5lbs more)...
I= 8.68 lb ft^2...requiring 73% more torque to turn
now add the fact that the rubber is centered further out, so lets just round to 85% more.

that tiny little increase in diameter suddenly made that wheel twice as hard to turn (requiring twice as much torque), and since horsepower and torque are directly proportional at a given rpm, you also need twice as much horsepower to accelerate the rate at which the wheel spins.

you will lose 10-20rwhp depending on teh bolded variables



crazyal--while weight does have an large affect on power loss, the moment of inertia of the wheel is mass * radius^2...so the radius has an exponentially greater effect on power loss. granted, however, radii do not change much (a couple inches max), while weight might increase 2-fold with big rims.

 

I think you're probably right. All else being equal, if you have good tires on those 20's you would probably see that it would do better than the other car with the stock tires.

HOWEVER, let's say that instead of 20's with 285/30-20, you had something like 18s with 285/40-18. That would most likely be even better.