doodad

you might not feel it but it does hurt your performance.. do physic or ask someone who knows physic and they will tell you the truth..

bomb79

isnt the overall circumference of the tire about the same on an 18 in rim and 20 in rim depending on on the sidewall height?if you get 18s with 50s i think the cicrumference is about the same as 20s with 35s.

mygt500

Or a 17inch with 55's is equal to 20 with 30's

CrazyAl

Yes, in these examples the circumferance of the tire tread is about the same (or so close it doesn't matter).

That's not the issue at hand here. The issue is at what radius is the main weight of the WHEEL being carried.

Let's imagine that a rim is made of two parts: A solid "disc",representing the part of the rim that you see (With the spokes and all that), that bolts to the axle. The second part is a hollow "tube" or ring--this is the part that the tire is fit over.

Now, compare a 20 and an 18. The 20 has a 20" diameter disc. The 18 has an 18" diameter disc. The 20 has a ring that is just under 20" in diameter. The 18 has a ring that is slightly under 18".

Inertia equals the summation ofradius times mass. If our two wheels weigh the same (same mass), the 20" still has more inertia becasue its radius is larger. It has the same mass, but that mass is located (on average) farther away from the centerline of the wheel.

This is stuff from high school physics, people.

lonny2

i have th ruff's like stowestang and weighed them on a ups scale 28lbs on the rears 24 on the fronts and my tires are falken, my 17's weighed with tires 46lbs each!!!! i dont feel a drag or lost of anything i can tell you it corners better due to shorter side walls. and s197 stangs just look bada** with certain 20"s.

06GT4RAD

Al is correct the rotational mass of the 20's is greater than with the 17,18' therefore performance is effected how much depends again on the weight of the wheel and tore combo but it will be effected. I run 20's and there was a small drop in acceleration. I noticed it right away. However it is nothing that a few mods cannot overcome. Will you still have the same performance as a car with 17's and the exact same mods NO due to rotational mass.

Richard

05SDI

OMG! Why do I let myself get dragged into these!

CrazyAL, your point of moving weight further out from the center and trying to change the inertia is quite valid and can be calculated to show there is a measurable difference! This is 100% correct and anyone who disputes this is either uneducated or just pulling chains to get a rise out of others.

NOW THAT BEING SAID:

IF the two sets of rim/tire combos (smaller rim/tire vs. larger rim/tire) (and YES you have to compare the combos as rims alone will not work on modern cars) Now IF a combo of 18” and 20” rim with tires weighed the exact same. (oh this is great!) Using the theory the 20” rims are heavier and also places this weight further away from the center….. Hmmm…. So if overall weight is the same, one will have to conclude therefore the 20” tire HAS to be lighter. So now the 20”s have less weight even further out from center than said smaller rim tire combo and thus reducing the force of inertia because the tire itself has to be lighter, since the two different size rims weigh different from each other but overall weight of each combos is the same. Now we have less weight at the furthest point away from center!!
Now let me say this loud and clear; IF THE TWO DIFFERENT SIZE RIM/TIRE COMBOS WEIGH THE SAME THERE IS NO MEASUREABLE DIFFERECE IN PERFORMANCE FROM INSIDE THE CAR!
One can NOT break down the equation and say ‘ok but’ the rim moves the weight further out AND THEN completely ignore that the tire evens this weight back out because it has to be lighter or better yet it moves lighter mass further away from center theoretically improving said force of inertia!
Now I’ll go out on a limb here and say something like for the average performance minded driver’s ‘butt dyno’ would not feel the difference between rim/tire combos weighing within 5-7 lbs. Yes it can be measured but it would NOT be felt to most.

Bottom line is some people like 20” and others don’t. I stand by the FACT that all 20” rim/tire combos do not ‘rob’ performance and in most cases improve cornering performance when comparing a good aftermarket 20” set vs. stock Mustang rim/tire combo.

05SDI

StowesStang

Just curious, when you weighed your Ruffs was that wheels and tires or just wheels? That sounds high for just the wheel.

MY6SRB

anyone know what these 20" Cobra-R's weigh?

https://mustangforums.com/albumtn.as...h758150417.jpg

jay0heavenly

^I clicked on the link, but no wheels came up