thanks for clearing that up russ...its good to finally know someone around here takes the time to figure things like that out!

Good info, and definitely sounds more realistic than the crap i constantly read elsewhere!

 

Believe 2.5 if you want to, but the simple answer is that there is no simple answer. If you'd really spent 3 years on this Russ, I have a hard time believing you'd flush all that hard work away and post something so simplistic. Not to mention utterly wrong if somebody tried testing it out in first or sixth gears.

I don't think we ever got to see that article...
http://forums.s2ki.com/forums/showthread.p...25&pagenumber=2

 

Instead of spending 3 years discussing theories did anyone ever just test the effects of different wheel weights on a dyno? Should be pretty simple to weigh a couple of rear wheels, do a couple of dyno runs, swap wheels and do another couple runs.....to reduce the complications that would arise from polar inertia (eg Rim X may weigh less than stock but have more weight at the farthest point from the axis when compared to stock) you could add a couple of pounds of lead wheel weights to the identical rims....

Something tells me that if it was that simple someone would have done it by now. What am I missing?

 

The mag article I mentioned earlier did just that. I will try to dig it out this weekend. I have a track event Sat. but maybe I can do it Sunday.

But more importantly than simple dyno numbers the reduced weight improved the ability of the shocks and suspension to follow the road and there was a noticeble difference in lap times that was mostly due to increased handling limits.

They made note of one rough corner that was "smoothed out" by lighter wheel/tire weights. On the streets rough roads had less skitter as well.

Also, remember that lighter tires have more impact than lighter rims because they are further out. Rims weights are easy to come by but tire weights are tough to find!!

 

Also don't forget that most of the weight of a wheel is on the outside. However, it's closer to the center than the weight/mass of the tire...

 

I've got more than enough Tazzo runs to vouch for my 2.5x factor. When you have the ability to measure time between rpm points in a given gear, it pretty much is easy to decipher decreased (or increased) unsprung weight
differences to performance.
My formula is based on well over 75 runs with several vehicles using different tire wheel combos.
Anyone is free to believe whatever they want but I'm quite comfortable with my real world results. Think of this way guys, if the weight was 10x the amount, my earlier 18-inch wheels weighed 24-lbs. My new wheels weigh 13.8-lbs. Are you telling me I dropped 408-lbs from my car?
BWHAHAHAHA That's nearly a full second's worth of performance off the 1/4-mile! To date, I haven't run in the 12's but I have run in the 13.6x's which is more indicative of the weight drop (2.5x) factor.
Believe 2.5x guys and you'll be happy with your results or you can get lost in formulas based on inertia in all six gears and end up spending more time with your Texas Instruments scientific calculator than you will with your car.
Hell, I once raced Bianchis in Italy with a local cycling club. This was many years ago long before technology took over the sport. (See link below). If you want to start there and work your way up to automobile wheels be my quest. This link will put you to sleep for sure.
The choice is yours.

http://www.analyticcycling.com/WheelsConcept_Page.html

or you can read this for a bit more relevance, though not entirely biblical.
http://www.clubcivic.com/showthread/t-944.html

 

Based on my background, i think the 2.5 is about right - as far as it goes.

But that is for linear motion, and hard to translate into a meaningful real-world benefit. Lowering wheel weight 2 pounds does not guarantee an improvement in performance, except perhaps in a straight line.

People sometimes forget that when the wheel turns, the suspension starts to factor in; changes in wheel weight, tire patch, etc become important factors in the total handling mix. I have seen countless test reports of "tuner" cars where they slapped on superlight Plus-2 wheels and super low sidewall tires, and ended up with worse slalom times! I tend to stick with the factory setups because they have the engineering savvy and the telemetric equipment to assess the total effect of changes of the types we are discussing. One has to look at these things as a whole system rather than a bunch of individual elements. I am not saying that it is impossible for us amateurs to get a great result, but it is a crap shoot.

 

RR brings up good points. There should be more considerations to any tire/wheel combo than simply weight. Straight roads eventually curve.
Good topic.

 

I yell about this all the time but it seems no one listens. At least I now know of one person who does...

 

According to helms manual, There is a conversion factor to be used in case somebody does not have a Wheel balance machine tu measure how much weight do you have to add in order to balance the wheel.

Front wheel conversion factor is 2,9
Rear wheel conversion factor is 2,5

For example if the unbalance at the front wheel is 15gr, it is calculated as 15x2,9=43.5gr.
Therefore the unbalance amount is 43,5 grams.


According to this Russ estimate is not so far.


Juan