Yep, I got your answers, John.
I am not convinced that adding a heavier weight than the engine normally has doens't skew
the results, even if you run all the tests with the same weight.
The pulling power increase from the tire is the product of the weight and stickiness of
the tape. i.e. You get a higher and higher coefficient of friction as you increase the weight.
If you add 5g of weight, a stickier tape will cause your pulling power to increase
more than a slipperier tape that has that same 5g weight on it. Put another way...
Let's say a stock engine with no weight could pull 10 cars.
You put traction tire 1 on it, and it pulls 20 cars.
You put traction tire 2 on it, and it pulls 25 cars.
If you then double the weight of the engine, I'm not convinced that the two
traction tires will increase the pulling power in a linear way. In other words, if the pulling
went up to 40 and 50 cars, respectively (both doubled), then we could say that
the weight doesn't matter as long as it's the same in all cases. But I suspect
that the stickier tape might pull, say, 55 cars, and the slipperier tape might pull only 40, or 37.
I am not so sure that the pull increases the same for all the tape types as you add weight.
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Whew...
Now, having gone through all that, what I'm getting at is that if you weigh the engine down
more than the standard Berk weighs, you might see more dramatic increases in pulling from
sticky tapes that won't really happen with the real engine. For 4 different types of tape,
you might see increases of 10, 20, 30, and 40% respectively, whereas with the real
Berk weight, you might see increases of 10, 18, 25 and 28... or... something.
I don't think the two factors are independent.
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And at this point... I doubt any of this long winded winging makes any difference. The
2-sided tape worked for you and it pulls the train, so who cares?
Oh... and about needing the tools to cut that groove properly...
yeah, I don't have them either. That's why I cut mine IMproperly, and I just got lucky that
it worked.