Contour Enthusiasts Group Archives Forums Modifications Wheels & Tires Lightweight 18's

Originally posted by DemonSVT:

---

Originally posted by SteedaSVTââ??¢:

---

ya 15 pound wheels def preformace robbing!

---

They are actually and you just don't know it.

Stock E1 = 19.5lbs
225/50 Falkien = 22lbs
Total = 41.5lbs

Your 18" rims = 15lbs
235/35/18 XXX = 25lbs
Total = 40lbs

However the bulk of the weight is where? Exactly, it is at the furthest point out radially from the center. This increases it's moment of inertia exponentially.


The E1 Falkien combo requires 14.48 lb/ft of torque (per tire) to rotate and stop rotating.

The 18" combo requires 16.41 lb/ft of torque (per tire) to rotate and stop rotating.

That is a 13.3% increase in torque required even though the "combo" weighs 1.5lbs less. That will be directly tied to the car's acceleration and braking ability.

How does this apply to acceleration and braking? The car's ability to accelerate & brake (rate of speed change) is a factor in how much difference the change in torque required makes.

For instance using 0-60mph times (in seconds) and comparing it to changes in the total chassis weight.

7 sec = 70lb heavier chassis
6 sec = 80lb heavier chassis
5 sec = 100lb heavier chassis

Now for braking times 60-0.

Stock 132 feet (3 sec) = 165lbs heavier
124 feet (2.8 sec) = 180lbs heavier
116 feet (2.6 sec) = 200lbs heavier

So if I were to run those same "light weight" 18's my car would perform "roughly" as if it were 100lbs heavier when accelerating and 200lbs heavier when it was braking.

So just being lighter means next to nothing at all unless you do the math behind your changes. I stand by my first statement.
This is also the main reason I never went to 17" rims. In order for a 17" rim combo to not hurt my performance the combo would have to weigh about 35lbs.

I used 3150lbs as the vehicle weight (with driver) for all my calculations. A heavier car would slightly raise those results and a lighter one would slightly lower them.

---