Lots of interesting thoughts here , thanks guys. I really don't have any intention of actually doing any testing, was just curious what your thoughts were on the claim.

One thing to consider that I don't think anyone has mentioned is the added weight of larger tires. Instead of running 255/40s on an 8.5in wheel, I'll be upgrading to a larger (and probably heavier) 275/40s. So the overall savings on the wheel will be slightly offset by the added weight of bigger tires.

 

It's exactly what we're after.

8 lbs that you can hold in your hands is easy to understand. What it's like to accelerate it in rotation is not. Every single correlation is attempting to link these two effects in an easily understandable manner. I have no problem with correlations, provided that they are somewhere near right. One lb of wheel to one point five lbs of added weight inside the car is probably pretty good for most wheels of reasonably normal size. One to ten (or twenty like mentioned earlier in this thread) is not. It's bad enough to be misleading and bad enough to coax people into making fairly costly purchase decisions that aren't sound, which is why I got involved.


Any of the simplified calculators that only use weight and HP - such as Speed = 225 * [HP/Weight]^1/3 - are only using the equations of curves that were fit to a lot of actual data back in the 1960's by some Chrysler folks (note to self - maybe ex-Ramcharger Billy Shope on a couple of other forums knows who was involved). They are not sufficiently accurate for any specific case for this particular purpose.

You need to go a whole lot deeper into the physics of it all, which is something that I've been tinkering off and on with since about 1968 (and been aware of for a few years longer than that). This is what I was working with earlier. Not this specific case, as that's on my work computer and I'm at home, but the same spreadsheet.





Sorry that I missed whatever joke was intended. And FWIW this is the third time I've typed this out, never mind why.


Norm

 

tinkering off and on with since about 1968 (and been aware of for a few years longer than that)

Norm...you are almost as old Newton himself

The point to be made here is that instead of power being generated by the relative motion of conductors and fluxes, it is produced by the modial interaction of magneto reluctance and redirected surveillance.

For the racecar, we use a malleable logarithmic casing in such a way that the two spurving bearings can run a direct line with the panametric fan. So using fluorescent square motioning, in conjunction with the drawn reciprocation dingle-plates of the lighter rims, it greatly diminishes sinusoidal depleneration.

 

The bolded reasons are why I posted a second time trying to elaborate without laying down the formulas. You come off pretty condescending when you assume your smarter or know more then someone (not necessarily how you feel, but your being mighty dismissive,) then keep implying that there the one going for the oversimplified route. I in fact was talking about going deep into the physics and projectile motion, to prove the theory through mathematics and develops a ratio, and not just throw weight in the car and call it the same. I think in actuality were talking about the same thing, your just acting like I don't understand and assume I am going for red neck math where I use something like the for mentioned .1sec = 100lbs, instead of coming up with my own equations that would only apply to our car due to the differences in drive train loss and weight distribution and transfer differences, etc, etc.

EDIT:
Thought on a side note it would be fun to mention, I was born 15 years after you started messing with this, physics just happens to be my strongest subject ;-)

EDIT AGAIN:
not going to be happy now unless I can show my work.

W= F x d
F= Force
d= distance
W= Work
Force in our case would be weight, and distance would be a 1/4 mile, wo would probably have to convert to newton meter to get joules.
-------------------------
we can then calucalte power

P=w/t

p=power (watts)
T= time
--------------------------
So if we did our first runs saying the car weighs x amount and did it in y time we can caluclate its work
W = X (Force is weight in lbs, we would convert to newtons) X D (distance, feet, we would convert to meters)
w= Z joules.

we would want power now so
P = w/t
P = z(from our eqation above) / t (the time it took to run quarter)
p = xx watts

----------------------------------
Now we would run the car again with lighter rims, we know the physical reduction in weight but are trying to solve this equation for a theoretical reduction in weight to equal the same gain. In this case, time would change, but we would want power to remain the same so that we can calculate back the theoretical weight change.

we need to now solve for work
W = PT
W = xx (from above) X t (the new time we got with the lighter rims)
W = yy ( new measure of work to be broken down into force and distance)

We are going for weight now (F)
F = w/d
F= yy / d (distance, feet, we would convert to meters)
F = XX (this will be the theortical weight in newtons it took to make the change in time. Convert newtons back to lbs)

We now then have what we need and it is simply take XX / actual weight difference and you end up with the ratio.


i just typed this in 5 minutes, have not checked for typos of if I put a formula wrong, but I know the math is dooable. It doesnt take into account that time can be changed by driver error or anything, but then again, were not trying to solve for that.

 

Sorry you took it that way.

I choose to let others have a glimpse into my train of thought up front. It's the approach that I've been procedurally required to follow for most of my professional life, where an engineering calculation is worthless if it does not provide enough explanation for a person "competent in the discipline to be able to follow without having to resort to the original preparer". Just saying "it can be calculated" or words to that effect has the possible translation "I know something that you don't, and you'll have to figure out what that is on your own because I'm keeping it to myself", which isn't very helpful.

There is a huge amount of simplified (redneck?) math out there, so unless you describe in enough detail to separate your approach from the simplified rules of thumb there is no way to know that that approach is in fact different. I certainly couldn't tell that yours was, and I even looked at your profile page at least twice. Three times, counting the fact that it's open right now.


When you finally did get around to explaining your train of thought it gets a lot clearer. Sure, it'll probably work - as long as you can test in a manner where everything remains essentially linear.

Wheelspin is one nonlinearity (which I think affects ET more than it does trap speed), and wheelspin is slightly easier to encounter specifically with lightweight wheels. There are at least a couple others. Don't lose sight of the fact that we're looking for at most only a few hundredths of a second out of 13 or 14, so it doesn't take much "noise" to make it difficult to separate out the "signal" that you're looking for. You might want to somehow work with the differences between results at 330' and the full 1320. Or use instrumented runs in (say) 3rd gear only to avoid wheelspin and upshifting effects entirely.

Power is also a measure of force * velocity, which you can use directly for theoretical top speed estimates. For better or worse, that's the way I tend to view it. Crudely as a first cut,
[TheoreticalTopSpeed] ≈ [SomeConstant] * CUBEROOT( [EngineHP] ÷ [DragAt100mph] )
And time as a measured quantity is not involved.

But all that aside, if you're looking at estimating the effect of lighter wheels beyond the simple fact that they remove weight, what you're really after is the comparison between the combined mass and rotational inertia effects. Even though the effect on acceleration performance is the ultimate practical goal, that's actually a "downstream consequence". It is not an inherent requrement that time be involved in order to establish this correlation, and from an engineering point of view doing so introduces its own uncertainties.


I guess at this point that means that you and I represent the difference between science and engineering. The difference between me and somebody like Sam Strano is the difference between engineering and test driver, just to extend the spectrum the other way.

Physics classes were too long ago (1966) for me to remember where I stood, either then or after a few years out of school. But it couldn't have been a really weak area, otherwise I doubt that I'd have ended up with a career in a field of engineering that includes both structural and mechanical engineering topics. There are times when I wish I were a little stronger on theory, but at other times I fear that if I were that I might make too many assumptions without even realizing what I had done.

That said, I'm open to learning from any source, from you or anybody else here once I can follow the train of thought.


Norm

 

JD, when you enter the real world, you will learn some of the things that Norm knows. Using newtonian physics is great for simple problems and getting a ballpark answer. However, there are many things in the real world that simple projectile motion does not account for. These little things like norm said cause "noise" in your calculations. This might not be a big deal if you were comparing 100 lb wheels to 20 lb wheels, but a 5 lb difference will be hard to filter out from the "noise." In college they don't teach you this stuff. Believe me, I just graduated in May and started working full time as an engineer. I learn more every day at work than I ever learned in school. Not trying to beat you down, but just keep an open mind, especially to people with lots of real world experience.

 

Jeez guys, I am pretty good at math and physics... as I'm one of the minority who actually finds it interesting. But you guys have really gone beyond my level here. I'm trying to follow some of the more complex calculations but this branding/marketing manager is certainly outclassed here. :-)

Based on what you all have here in this thread, I'm very interested to see what Enkei have used to base their claims off of.

Now if you want to learn about brand positioning, market segmentation and messaging delivery strategies... I'm your guy! :-)

 

To Norm: i was a little harsh in my words, sorry, but glad you see what I was talking about now that I elaborated. It was a while séance i had looked at those formulas myself, thats why I said it could be calculated the first two times, the third post I got off my *** so to speak and googled the equations I needed and re worked them to solve for what i wanted :-)

jahudso: Is Iraq real world enough for you? I mean seriously I'm trained in Electro-Mechanical engineering, served in the marines as a Electro-Optical ordnance repair tech (missile guidance systems, thermal imagery devices, etc.) Now I work on fully automated clinical chemistry analyzers. I'm not some college kid, I actually use these skills most days of my life.

On a side note, yes, if we wanted to we COULD tear into every variable, temperature, track conditions, tires, driver, etc, etc. I was actually expecting norm to call that one but he left it at, "if we could keep everything else the same" or something close to that.

Likely what they did was take a car with stock rims and tires, run it. Then put in lighter tires with some drag radials or something, then plug that into a formula like what I said. If a company wants to sell rims based off that claim, my math would support them if they were to gain a few extra 10ths of a second because of a superior tire and not factor it out.


The math could be perfect, but the results of the runs can be intentionally misrepresented.

 

Guys, great responses, but aren't we missing the point of the question? It seems like the responses are addressing rotational weight compared to static weight and the effect on acceleration.

I'd be more in the engineering types digging into the unsprung weight issue and the real impact on handling and grip dynamics. I noticed I had to tweak my shock settings when I upgraded to the Brembo brakes (along with heavier discs and 18" wheels...).

 

handling and grip would seem to be more effected by the chassis weight distribution, stiffness, and exact suspension composition.the wheels being on the ground and under the suspension would seem to not be effected near as much as other weight loss in the car.

All though I suppose they also have a gyro like effect and rebound could be effected also by the shift of weight on the hub... but any more and my head is gonna explode.