New Wheel Times Vs. Old Wheels

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PWD_addict
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New Wheel Times Vs. Old Wheels

Post by PWD_addict »

I should have done more research on this with our own Derbies but I'm wondering who found that the new wheels were significantly faster than the old wheels?

I am not totally convinced based on our results that I recall. We did not remove the step on the outer hub. Wheel prep involved reaming the bores to 0.098 and rounding them off with the Pro-XT Shaver II. So much easier than previous years but we didn't see that much difference in speeds. Old track record (from two years ago--old wheels) fell during District races but only one car (my son's) two times. Record went from 4.0674 to 4.0516s. I don't think average times were that much better than last year. I really thought that we'd break the 4.0s glass ceiling with the new wheels.

I'll have to double check the times when I get to my laptop. I have this year and last year's numbers on it.

I'm just curious if anyone has some hard and fast numbers that show significant improvement with the new wheels.

Thanks!
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pwrd by tungsten
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Re: New Wheel Times Vs. Old Wheels

Post by pwrd by tungsten »

The new wheels are 0.01 to 0.02 faster...
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sporty
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Re: New Wheel Times Vs. Old Wheels

Post by sporty »

I did some testing and comparison awhile back, if you are interested in checking it out.


http://www.derbytalk.com/viewtopic.php? ... &start=105" target="_blank


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Re: New Wheel Times Vs. Old Wheels

Post by Kenny »

All else being equal, the lighter wheel wins on standad length PWD track and a 5 oz car. Physics says it's so, and empirical data says so too. The difference is substantial as stated above.

This year many of the wheels were so good - out of well made and fresh molds - that you probably should have left out the Shaver and just polished the bores, which also have been very good. Some mold numbers were definitely better than others, but overall they all are a marked improvement over previous generations.

I suppose it's possible that you got a bad wheel or two in your batch too.

K
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Re: New Wheel Times Vs. Old Wheels

Post by FatSebastian »

PWD_addict wrote:Record went from 4.0674 to 4.0516s. [...] I really thought that we'd break the 4.0s glass ceiling with the new wheels.
Perhaps your expectations were too high? Doc Jobe has a lecture that sets expectations on a 42-foot Best Track to be less than a 0.02-second advantage due to wheel MOI reduction - I believe that's about 1/2 car length. That seems fairly consistent with the change to your track record.
PWD_addict wrote:I'll have to double check the times when I get to my laptop. I have this year and last year's numbers on it.
Please let us know what your data indicate. I am just as curious to know whether the new wheels seem to narrow the spread in the distribution of times.
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Re: New Wheel Times Vs. Old Wheels

Post by rpcarpe »

One point for consideration:
Light vs. Heavy wheels will give you steadily changing results as you increase track length.
Light wheels show better on short tracks, heavy wheels do better on longer tracks.
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Re: New Wheel Times Vs. Old Wheels

Post by Stan Pope »

rpcarpe wrote:One point for consideration:
Light vs. Heavy wheels will give you steadily changing results as you increase track length.
Light wheels show better on short tracks, heavy wheels do better on longer tracks.
Yes, and the crossover point at which heavier wheels begin to be superior is out around 64', IIRC, for tracks with a 48" high starting gate.
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Re: New Wheel Times Vs. Old Wheels

Post by FatSebastian »

rpcarpe wrote:Light wheels show better on short tracks, heavy wheels do better on longer tracks.
Stan Pope wrote:Yes, and the crossover point at which heavier wheels begin to be superior is out around 64', IIRC, for tracks with a 48" high starting gate.
The topic of crossover point comes up from time to time on DT, and the ~64' value has been reported before (e.g., here, and here). However, its origin seems uncertain; the value is attributed to Michael Lastufka, but I have yet to find it on his site (instead this is what I found). Teeeman has suggested +150' using Michael's software?

I once suggested that the crossover point might be closer to 100' based on sims using VRII - of course any estimate is highly dependent on a lot of assumptions.
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Re: New Wheel Times Vs. Old Wheels

Post by Stan Pope »

FatSebastian wrote:
rpcarpe wrote:Light wheels show better on short tracks, heavy wheels do better on longer tracks.
Stan Pope wrote:Yes, and the crossover point at which heavier wheels begin to be superior is out around 64', IIRC, for tracks with a 48" high starting gate.
The topic of crossover point comes up from time to time on DT, and the ~64' value has been reported before (e.g., here, and here). However, its origin seems uncertain; the value is attributed to Michael Lastufka, but I have yet to find it on his site (instead this is what I found). Teeeman has suggested +150' using Michael's software?

I once suggested that the crossover point might be closer to 100' based on sims using VRII - of course any estimate is highly dependent on a lot of assumptions.
Sadly, I am quoting Michael L. from memory of his writings from about the same time he released his pinewood car simulation program. It included a linear relationship to the starting pin height. I don't find the reference on Michael's current web site so perhaps I am remembering incorrectly or perhaps he decided to remove the information for his own reasons. His current writing at http://www.lastufka.net/lab/cars/why/qwtwhl.htm disputes my recall! Guess I need to go absorb those differential equations and see just what the logic is! :)
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Re: New Wheel Times Vs. Old Wheels

Post by PWD_addict »

OK...I ran some quick numbers!

This year, we ran trucks and a couple of extra fun races and I didn't have the time to pull them out of the averages but here are the numbers for
the last two years.
2009 Pack avg speed 4.4379
2009 Districts avg speed 4.4415
2010 Pack avg speed 4.5933
2010 District avg speed 4.4029

0.04 quicker speed at Districts with new wheels compared to old. The difference in Pack speed this year included some slow trucks and cars so it's tough to include that.

Comparing this years District speed in the Grand Finals round only (smaller sample), we have 2009 Dist avg speed of 4.2893. 2010 avg speed of 4.3204 :O :O :O That means that this year's Grand Finalists were 0.03 SLOWER than last years.

I guess the smaller sample size messed things up a bit--only 14-15 cars in the District Grand Finals both years. My son's car really flew down the track and there weren't any that were even close in the Grand Finals.

So, I guess there is a modest improvement with the new wheels.

Thanks for all of the input.
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Re: New Wheel Times Vs. Old Wheels

Post by Kenny »

One thing that may account for some people experiencing slower times with the newer wheels could have been performing legacy wheel and axle treatments. When using methods used on pre 2009 wheel/axle combo for example removing step, rounding the head, strong neg camber may negatively impact performance if overdone versus the old wheel styles.

K
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