I just got my Konig's 17".

and first thing i noticed was that, car accelerates much slower (i think), and car just feels slow.

Is this normal? should i blame weight or grip?

my original wheels were 16", so i dunno

 

Big weight differential between the wheels? Better grip and the car should be faster.

 

Well my guess would be that your new wheels is alot heavier than your old ones. If in fact it is then this would explain your car being slower because now it requires more power to make those wheels turn.

 

Bear in mind that larger diameter wheels have a higher moment of inertia. The farther from the center, the more force is required to move it.

I noticed quite a bit of sluggishness going from 15" steel wheels (my winter wheels) to the 17" alloys. For one thing, the 15" weigh 35# each. The 17" weigh 47# each. I wont attempt to create the formulas involved (been too long since I took dynamics) but the point is that there is more weight further from the center of rotation.

So it will take a little more power right off the line. On the plus side though, I would assume you have tires with much better grip than stock, so you shouldn't have a problem applying the extra needed power!

 

I noticed it too, when I went from 15" to 17". It is now really hard to peel out, where I used to do it easily before. However, my 0-60 times are only .1 second off from where they used to be. I wouldn't give back the handling for the world though.

 

ok, i found the weight for these wheels: their only 19.2 lbs each.

arent the SE model 17" at least 20? i wish i knew someone who drives a SE so i can compare. =\

it might be a pyschological thing?

 

19.2? Not to shabby for 17's. I've compared my stock 17's to Jane's 17" Tantrums and mine weighed a ton. Mine were almost as heavy as CalsonicSE's 18" Concept 5's.

You should be happy because the new wheels are still pretty light.

 

Press the little button in the center of the long handle on your right side, this is called the parking brake. Once you do this you should be fine! Hope you like those new wheels now!

 

Check the tire weights also, I'll bet they are several lbs heavier also.

 

well even if they(tires) are not heavier, they are further from the axis of rotation... Big conceptual difference... same end result..

--> More torque required in order to get them spinning. = slower car


-Tom Z.

PS.. blame the universe... the creator was obviously prejudiced towards smaller wheels.... Perhaps 19" wheels were just never meant to be... :-(

**sigh** anyone want to start a petition?

 

ya, compare to the stock 16", those wheels are heavy, but compare to the stock 17", they are very good.

 

No! The new wider tires are heavier. They also have their extra mass at the edge of the tire also. Air does not weigh that much. The overall diameter of the wheel and tire has not changed much (maybe 2/10"). However the extra mass is at just about the farthest point from the axis of rotation. I ~ m x r^2 Becuase of the square law relationship, this is the worst place to put the extra mass. Therefore moment of inertia increases (bad). torque = I x alpha. Because I is bigger now, it takes more torque to attain a certain anglar acceleration, alpha. You were right about the less advantagous moment of inertia, but not why it increased.

 

Umm... you do realize that you just paraphrased what I said, and put two equations in to make it sound more legit...

Going for a physics major (actually, along with a comp-sci major, and math minor), so I did angular mechanics last semester... Touched a bit on moment of inertia in multi-var calc as well... And here I was, thinking that surface integrals would never be useful :-)


-Tom Z.

 

So who wants to do a surface integral for the 17" SE rims to find their moment of inertia? Can't be all that tough....there are only 6 spokes

 

So who wants to do a surface integral for the 17" SE rims to find their moment of inertia? Can't be all that tough....there are only 6 spokes

 

I don't want to integrate that. Besides we don't care about an explicit solution - an accurate numeric approximation should suffice. To do that, a piecewise linear approach makes sense. It would be nice to get an estimation and figure out how much of a change in the moment would be noticable to the driver. Everyone agrees that more weight is bad and you don't want the weight any farther from the axis of rotation as possible. No one has been able give a reasonable estimate as to how much a given wheel and tire combination would change perfromance. Maybe we can come up with something that the org can use???

 

heheh....I know, i know...it was just a joke Actually, if you assume that all the mass is at the edge furthest from the axis of rotations, you get kind of a worst case number. In reality, a rim does have weight that is close to the axis of rotation that will have less of an effect on the moment of inertia than if we assumed it were all at the edge.

 

Hmm... even arriving at an approximation frightens me...

think about it... even if you assume the density of the materials is uniform (which it should almost be in an aluminum wheel, and tire).. there's still a LOT of complicated calculations that have to go in before you get a number remotely close to the actual value..


However, it is possible to arrive at the FAIRLY CLOSE value for moment of inertia experimentally (we did this in a rotational dynamics lab)... if you apply a known amount of torque to the wheel, and measure the angular acceleration, it's as easy as dividing!!! If anyone's willing to start taking off their wheels in the name of science, lemme know, and i could give you the exact details of the experiment...

if we knew the moment of inertia for different wheel configurations, we would be able to put the performance hit you take in changing wheel sizes into better perspective...

-Tom Z.

 

You're right. That experiment will work. I don't have the equipment to do it. Maybe someone here does. However, the approximation is as difficult as you might think. I'm not saying that it is trivial, (If it was, someone would have already posted it.) but an approximation within 10% is not out of reach.

Assuming that we have baseline moments for the stock wheel and tire combinations, the question that still remains is how much of a change will make a noticeable performance difference? Can we relate a change in the moment to 0-60 mph, 1/4 mi or rolling start times? Until those are questions are answered, knowing the moments is a moot point and nothing more than an academic exercise.

 

My average stopwatch 0-60 times went up .1 second from 7.54 to 7.66 when I went from the 15s to the 17s. Quarters? I don't know. NOTE: I had the heavy early 4th gen GLE rims, which seemed as though were as heavy as the SE rims.

 

hey can u do me a big favor and find the weight of both of them?? becuz i have both of them.. 95GLE rims and the 2001 Se Rims.. just want to see the weight and how much it effects the times.

 

I still have the tires on both of them, give me about a day and I'll tell you.

 

Hmm... it's almost midnight, i've had a long day, and i might not be thinking straight.... so let's see if I make any sense..

If we hold the torque applied to the wheel constant, and simply vary the moment of inertia among wheel configurations, we could figure out the angular acceleration of the wheel... knowing the radius allows us to figure out the tangential acceleration and calculate 0-60 times with different rims/tires...

sounds good??? right?? well, umm... no.. not really... you see, that first statement in the above paragraph is not entirely true... the torque applied to the wheel is not constant... (proof : look at a dyno readout...) so while you would get an answer by doing the above, it would mean absolutely nothing in terms of real-world performance..


-Tom Z..

PS.. writing that got me to thinking... the torque applied to the wheel should not vary among wheel configurations, even if it is not constant... so now i'm thinking that even though you might not be able to get the ACTUAL 0-60 times, the numbers you get would be proportional to their real-world counterparts... (ie.. perhaps you could make the statement that a 19" xxx rim + yyyy tire is slower than a 17" xxxx rim + yyyy tire, on 0-60 by .1% or whatever the number would turn out to be...) That sounds like an awefully useful thing to know before buying wheels...