COM - vs- Weight in ounces on front wheel

Nov 25, 2011
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COM - vs- Weight in ounces on front wheel for two different wheelbases.

Car weight 5.000 ounces

5 3/4 wheelbase

COM Weight Ounces
1.25 1.0870
1.20 1.0435
1.15 1.0000
1.10 0.9565
1.05 0.9130
1.00 0.8696
0.95 0.8261
0.90 0.7826
0.85 0.7391
0.80 0.6957
0.75 0.6522
0.70 0.6087
0.65 0.5652
0.60 0.5217
0.55 0.4783
0.50 0.4348
0.45 0.3913
0.40 0.3478
0.35 0.3043
0.30 0.2609
0.25 0.2174
0.20 0.1739

4 3/8 wheelbase (Pure Stock)

COM Weight Ounces
1.25 1.4286
1.20 1.3714
1.15 1.3143
1.10 1.2571
1.05 1.2000
1.00 1.1429
0.95 1.0857
0.90 1.0286
0.85 0.9714
0.80 0.9143
0.75 0.8571
0.70 0.8000
0.65 0.7429
0.60 0.6857
0.55 0.6286
0.50 0.5714
0.45 0.5143
0.40 0.4571
0.35 0.4000
0.30 0.3429
0.25 0.2857
0.20 0.2286
 
This is a fantastic chart. I appreciate you taking the time to share this with us. I am sure it took some time to make this and it will be a huge help for some.

Ian
 
This is new to me. Is this chart saying if the wheel base is 5 3/4 and the COM is 1.25oz's the weight on the front wheels is 1.0870? As you add more weight and move the COM back the amount of weight on the front wheels would be lighter. Is there a perfect front end weight to shoot for which give you best control without being to light?
 
Great info W!!

Air, Com to very important. That being said is there a perfect COM? Yes. But it is different on every car. That's is why the hobby can be so frustrating. What worked on the last car doesn't always work on a new one.
rolleyes.gif
 
This is a great chart W, On my pure stocker the lightest weight I was able to achieve was a .6xx on my DFW with the body style I have. My car runs the best at .78 oz so that should be at about a 5/8 com. that sounds about right, that is the COM I have always had my best luck at. What kind of wheels where you using for the tests? Will lighter wheels such as a mod wheel v/s a purestock wheel effect the weights enough to compensate for? Thanks W you always have great info.
 
AC- This shows for a given COM the weight pressing on the track from the DFW. Weight at COM is always 5oz.

DF - Thanks!

This looks at weight of DFW pressing on track and is constant for all wheel weights if you determine COM with wheels on car. However I also make a chart which shows weight of the axle on DFW wheels bore. And in fact all wheel bores...

To do this I subtract the weight of the touching wheels from the car. I keep the weight of the raised wheel and axles / pin.

From this I can design a car as pure stocker. Then design a second car with lightened wheels and change the COM to give the same weight on the DFW wheel bore as the pure stocker.

I like to run 5/8"-3/4" on Pure Stock and I run 1/2" on MODs. The lighter wheel of the MOD allows a more agressive COM. Of course there are other factors allowing the more agressive COM as well..
 
Weight (ounces)Wheelbase
5.0495.000
COMWeight DFW
0.1250.126
0.18750.189
0.250.252
0.31250.316
0.3750.379
0.43750.442
0.50.505
0.56250.568
0.6250.631
0.68750.694
0.750.757
0.81250.820
0.8750.884
0.93750.947
11.010
1.06251.073
1.1251.136
1.18751.199
 
Weight (ounces)Wheelbase
5.0495.250
COMWeight DFW
0.1250.120
0.18750.180
0.250.240
0.31250.301
0.3750.361
0.43750.421
0.50.481
0.56250.541
0.6250.601
0.68750.661
0.750.721
0.81250.781
0.8750.842
0.93750.902
10.962
1.06251.022
1.1251.082
1.18751.142
 
W, thanks for the cool charts, I should have searched a lot harder from the get go. Pardon me for assuming the info was not already available. I would have skipped the "wheelbase considerations" question and comments. This provides all info needed for a good start. Thanks again J.
 
Front Wheel Weight ounces = (COM from rear axle") x (Total Weight ounces) / (Wheel base")

COM From Rear Axle = (Wheel base") x (Front Wheel Weight ounces) / (Total Weight ounces)
 
I see so much written about COM, but I wonder. I almost never check the COM, except occasionally out of curiosity.
When I do check, I am always less than 3/4" and often sneak close to 1/2", but I depend solely on Veer adjustments after test runs.
E.g. On SS, I start with 12", then move up or down based upon test times and stop at best time, which varies some with different cars.
AM I MISSING SOMETHING?
Or is this a lot to "to do" about an insignivicant factor?
Or maybe my method is just a different way of determining the correct COM without realizing it.
Or is checking the COM a good substitute when you don't have access to a timed test track.

I think I have read the same opinion from both Kinser and DD4H, two of the past bests.
 
I am not a regular league racing guy, but will be sending in two cars next month. These two are the fastest I have built. Faster than the two I sent in last year. I shoot for a certain weight on the front wheel, but not even sure that is the correct weight. I did calculate the com on these cars to be around 5/8" only because everyone is referring to com. I had no idea what is was until today.
 
CDB Racing said:
I am not a regular league racing guy, but will be sending in two cars next month. These two are the fastest I have built. Faster than the two I sent in last year. I shoot for a certain weight on the front wheel, but not even sure that is the correct weight. I did calculate the com on these cars to be around 5/8" only because everyone is referring to com. I had no idea what is was until today.

I also pay absolutely not attention to the weight on the front wheel. In fact, I do everything possible to reduce all body weight from rear axle to front point (except that weight required just in front or the rear axle necessary to bring it up to 5 oz). Maybe shift several of the front cubes (i.e. just in front of the rear axle)over to the dominant side.

Believe me, Use an 8 foot test board and a timed track to set the fastest veer. The COM will take care of its self once you find the fastest veer.
 
Yes,

The weight on the front wheel comes from the COM of the car itself which (hopefully) is very far away form the front wheel.