Positive or Negative Camber on FDW?

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Nutty Pine
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Positive or Negative Camber on FDW?

Post by Nutty Pine »

Somebody please help me because I just don’t get it! In the six years that I built cars with my son and my two nephews, we built all our cars as 3 wheeler rail riders with negative camber on all 3 wheels including the FDW. Now that I have come out of retirement to help my other nephew with his car, my buddy Bill (Speedster) tells me (bless his heart) that I am doing it all wrong! He suggests that I put positive camber on the FDW for improved performance. He did not convince me so I read posts on this matter for two hours today and I am not yet convinced that positive camber on the FDW is better than negative camber.

I am not convinced because in that 6 year period with my son and two nephews, our cars won eight (8) pack championships and (5) district championships; all with negative camber on the FDW.

The Good Lord blessed me with an open mind and I am willing to change to positive camber on the FDW if it will improve performance. Has anyone actually tested a car both ways? I do not have a track so I can't do extensive testing and tuning but I hope that some of our seasoned Derby addicts can enlighten me on this matter because as I said when I started this post; I just don’t get it!
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Vitamin K
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Re: Positive or Negative Camber on FDW?

Post by Vitamin K »

I haven't done testing (this year will be our second year of Derby-ing, and our first building rail-riders), but the conventional wisdom is that you want positive camber on the DFW. The reasoning for this is that since the car is tuned so that the inside of the DFW is the only thing that contacts the rail, putting positive camber on it helps expose that small edge to the rail while allowing your rears (which have negative camber) to stay further from it.

Hoping that made some kind of sense. :thinking:
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FatSebastian
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Re: Positive or Negative Camber on FDW?

Post by FatSebastian »

Nutty Pine wrote:I read posts on this matter for two hours today and I am not yet convinced that positive camber on the FDW is better than negative camber.
Setting aside the empirical evidence of "that's just the way we've always done it," and after giving it several hours of your attention, do you have reason to think that negative camber would be better than positive camber?
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Stan Pope
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Re: Positive or Negative Camber on FDW?

Post by Stan Pope »

Hello, Nutty!

I'm not about to contradict your excellent experience! To help us put that experience in perspective, how does that experience fit, time-wise, into the timing of the recent growth in rail guiding. 10 or 12 years ago, good practice + DFW rail guiding would assure an excellent result in most district derbies.

That said, negative camber (axle head higher) places the DFW against the top edge of the rail and, as a result, it is in a poor position to react to a section alignment error. This is a non-issue if the tracks are in good shape and well assembled (as they should be)!

Negative camber also creates slightly more friction loss versus contact lower on the rail. Positive camber (axle head lower) orients the wheel so that it can roll over section misalignments rather than striking them head-on. Again, it is a small loss, and one that good practice can overcome against most competition.
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Re: Positive or Negative Camber on FDW?

Post by Speedster »

I'm disappointed Nutty Pine asked that question on Derby Talk. My demonstration will no longer work. Nutty Pine and I are going to race our cars this summer against the timer on my track. I was going to misalign two sections of my track . No matter which front wheel was dominant one of the misalignments would have gently directed his car into the cement blocks I have set up. I suppose now I can simply send an old car down the track for demonstration purposes. I'll be ready with the fire Extinguishers.
Nutty Pine
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Re: Positive or Negative Camber on FDW?

Post by Nutty Pine »

Thank you for your replies! What Viamin K says makes sense; with negative camber the inside of the wheel is bearing the load and when it makes contact with the rail, I can visualize increased friction taking place. Whereas, with positive camber, the outside of the wheel is bearing the load and is therefore not losing contact with the track when the wheel rides the rail.

In response to Mr. Sabastian, it’s not that I think negative camber on the FDW is better, it’s just that I am trying to understand why positive camber is better. The fog is beginning to clear but I am not yet there.

Mr. Stan Pope, I notice that you are a very active, and I might add, a productive member of this site. I lost count of the number of your posts I read the last two days and all I can say is “Keep Up The Good Work”!

Yes, we did our 1st car in 2007, it was a 3 wheeler straight runner pickup truck that won the pack and the districts. That is when I met Speedster and that is when I heard about rail riders and all our cars since then were 3 wheel rail riders but they all had negative camber on all three wheels.

We retired In 2011 when my son crossed over into Boy Scouts and I always thought we did the right thing until coming out of retirement last year to help my nephew. His car won the district last year and this year’s car won his pack race and recorded the best time of the day. Speedster looked at the car, noticed the negative camber, and then insisted that the car would be even faster with positive camber on the FDW. The districts are next and I am torn between leaving the car alone or change the camber and see what happens. We won the districts last year with a car set up exactly the same way but several of his races were really close so I don’t know what to do.

Alright Speedster, I accept your challenge!
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Re: Positive or Negative Camber on FDW?

Post by FatSebastian »

Stan Pope wrote:Positive camber (axle head lower) orients the wheel so that it can roll over section misalignments rather than striking them head-on.
I'll add that with positive camber, the wheel hub nominally rides against the body. With negative camber, the wheel hub nominally rides against the nail head, leaving no room for the wheel to slide outward without taking the body with it whenever a track irregularity is encountered. Thus positive camber has the potential benefit of acting like a shock absorber.
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Re: Positive or Negative Camber on FDW?

Post by Speedster »

Leave the car alone. You know the two tracks you'll be racing on and you're going to help set them up. If anyone beats your Team you'll know by how much and maybe there will be some adjustments next year. The High Tech, Commodore Perry Legal , car you are going to build to beat me can be raced against your nephew's car this summer to see how much faster you can build a car.
Good Luck at Districts.
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Stan Pope
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Re: Positive or Negative Camber on FDW?

Post by Stan Pope »

Nutty Pine wrote:Yes, we did our 1st car in 2007, it was a 3 wheeler straight runner pickup truck that won the pack and the districts. That is when I met Speedster and that is when I heard about rail riders and all our cars since then were 3 wheel rail riders but they all had negative camber on all three wheels.

We retired In 2011 when my son crossed over into Boy Scouts and I always thought we did the right thing until coming out of retirement last year to help my nephew. His car won the district last year and this year’s car won his pack race and recorded the best time of the day. Speedster looked at the car, noticed the negative camber, and then insisted that the car would be even faster with positive camber on the FDW.
Since Wiles "let the kitty out of the bag" ca. 2007-8 (prior to then the practice of guiding by rail was closely held by prior discoverers) the competition stiffened. With more cars applying the practice, more quality in other aspects of building was required for most of us!

So, what do you do? Do what you do best until you find the necessity (or good reason) to change!
Stan
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Re: Positive or Negative Camber on FDW?

Post by Noskills »

I am not a physicist or a engineer but I like to think of the philosophy of the positive camber. I see the toe-in and the rail riding as pushing the wheel to the axle head (ying) and the positive camber aa moving the wheel back towards the body (yang). We all need the ying and the yang.

Thats all I got.

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