my car feels a lot lighter. Takes off a lot easier and more smoothly, but brake distance increased slightly. old set up : Rota SDR 17x7.5 w/ Falken FK451 225/45/17 --> 18 lb + 25.8 lb = 43.8 lb current set up : OEM 16x7 w/ RE92 205/55/16 --> 16.5 lb + 22 lb = 38.5 lb Difference of 5.3 lb at each corner is pretty significant. this adds upto 21.2 lb of unsprung weight. This equals to almost 100 lb worth of sand bags in trunk. I bet dat I have more whp than before. :banana: :banana:
I noticed a difference in my stock wheels vs. my volk wheels on the evo. Without tires, the stock 17x8 weigh about 21lbs and the Volk CE28N 17x9 wheels weigh 15lbs. With the wider 255/40-17 tires on the Volks, I measured a 5lb difference on the scale. Great way to improve the handling and performance of the car. -- Brian
In rotational motion it is not mass alone that counts but mass times the square of the distance from the point (or line) about which the rotation is taking place. The body (wheel and tire) has an AVERAGE mass (m) to radius squared (r^2). This average mr^2 is a point called the 'moment of inertia'. The torque required to stop (or start) the rotating object in a given period of time depends not upon the mass of the object but its moment of inertia. The value of the moment of inertia depends on the distribution of the mass and can be changed without altering the total mass. Practical application: The figure skater spins slowly with arms extended, yet speeds up when their arms are brought close to the body. The rotational energy is the same, yet the moment of Inertia is increased and decreased. Whats it mean? Smaller wheel = better acceleration....
yup~ gotta love physics. It really does apply in everyday life. 225/45/17 and 205/55/16 have very close overall radius. That's not where i picked up more acceleration. This is my theory about founding few more whp after swapping to 16". AWD has higher drivetrain loss due to more frictions and more mass to move = work. Let's assume that I'll do dyno at DynoJet (The one TopSpeed has). With heavier wheel/tire, the engine has to crank out more torque to overcome extra mass --> more power loss/waste. This can be calculated as another drivetrain loss since that's where wheels are connected. That's why I said I gained HP @ wheel instead of HP @ crank.
yes if ur trying to compare crank power which i usually never do... heavier wheels or not, a roller dyno like topspeed's will give u an estimate of the numbers u r putting down at the wheels... ive been curious how much difference there would be if ur overall diameter was larger than stock... that would definitely affect correction factors
Damn... wat's up with weather these days?? Today's high was 69F. Seems like this winter will be abnormally warm. hopefully this will bring down gasoline price little bit. newayzz.. I used this warm weather as the excuse to swap back my with Summer tires. wow~ big difference!! taking corners hard is now doable under firmer control & authority. Those RE92s were really suck @ braking & turning!! After the swap, body roll cut down pretty significantly, and my confidence in my car soared up high. :bigthumb: