Derby Talk is a forum for Pinewood Derby, Awana Grand Prix, Kub Kar Rally, Shape N Race Derby, Space Derby, Raingutter Regatta and other similar races where a child and an adult work together to create a race vehicle and a lot of fun and memories
pwrd by tungsten wrote:The track record at PDDR for standard BSA wheel base and unlightned wheels was just set by a car with rear fenders.
Is this the car?
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There are very many interesting aspects to this design, especially the rear wheels with the sidewalls facing inward (presumably to deal with new double-step recess on the outer hub?). The windshield behind the (presumably non-dominant) black tire is also interesting.
The nice thing about the tire windshield and fenders in this design is that they allow for a certain level of streamlining around the wheels without increasing the cross-sectional area of the body in the direction of motion (which seems to have been minimized already).
pwrd by tungsten wrote:I think fenders will change the sport for league racing next year and BSA racing soon as well...
Sporty, can you attach some rear fenders like this on one of your thin test bodies and report back on how many milliseconds are gained?
The wheels running on this car are not the new style BSA wheels. They are the 3.3 g Jewkes old style wheel. The outer hub has been turned down/reduced in length to allow for them to be ran this way. I should have a car ready to test this way by the weekend. The fenders are shaped, primed and ready to paint. I'm very curious how it's going to do.
Grubartez wrote:The wheels running on this car are not the new style BSA wheels. They are the 3.3 g Jewkes old style wheel. The outer hub has been turned down/reduced in length to allow for them to be ran this way.
Thanks much for the clarification. So then, what is the supposed advantage of turning the sidewalls inward?
Grubartez wrote: I should have a car ready to test this way by the weekend. The fenders are shaped, primed and ready to paint. I'm very curious how it's going to do.
Can you do some "before and after" runs with and without fenders and report back some numbers?
I like the idea of running the wheels with the inner hub out. That would eliminate having to modify the countersink on the outer side of the bore (against our rules). Does the open profile cause any extra turbulence?? I still need confirmation the new wheels will be allowed in our District.
I also like the idea of the fenders on the rear tires but I'd be afraid of them accidentally touching the rail due to some possible rear end wiggle going over rough track joints.
Grubartez wrote:The wheels running on this car are not the new style BSA wheels. They are the 3.3 g Jewkes old style wheel. The outer hub has been turned down/reduced in length to allow for them to be ran this way.
Thanks much for the clarification. So then, what is the supposed advantage of turning the sidewalls inward?
Grubartez wrote: I should have a car ready to test this way by the weekend. The fenders are shaped, primed and ready to paint. I'm very curious how it's going to do.
Can you do some "before and after" runs with and without fenders and report back some numbers?
What I can tell you is I sent out a car with basically the same design and shape and wheels. The front raised wheel had the wind deflector and it also had the rear fenders with the rear wheels running in the normal position. Now, on my 42' ft Best track it ran a 2.948 avg with a 2.942 fast pass. During shipment, the right rear fender was damaged and had to be repaired the best it could at the event. The car ran a 2.963 avg with a 2.959 fast pass. When the car arrived home, I ran it again to see and again it ran a 2.963 avg with a 2.960 fast pass. After I looked over the repaired fender, it was ever so slightly touching the wheel. I adjusted it and ran the car 6 more times and it ran a 2.950 avg with a 2.948 fast pass. The car has been taken apart and rear cones added. A new set of 91 SGA's will go on along with a new set of modified wheels to allow the wheels to be turned around along with a new fresh set of fenders. Hopefully, I'll be able to test it by early next week.
Grubartez wrote:What I can tell you is I sent out a car with basically the same design and shape and wheels. ...
Thanks much for the data, Grubartez. Another question is whether adding fenders to an already fast car offers any advantage on final times. Sporty claims to "have tried this in the past and had no real gains," and based on your testimony there seems to be some risk associated with their use. So how does one know that fenders are providing measurable improvement? I suppose the only way to test this is to run a control car with and without fenders?
psycaz wrote:Would you care to share any info on the wind deflector for the raised wheel?
Yes, psycaz is not the only one who is curious about that.
Grubartez wrote:What I can tell you is I sent out a car with basically the same design and shape and wheels. ...
Thanks much for the data, Grubartez. Another question is whether adding fenders to an already fast car offers any advantage on final times. Sporty claims to "have tried this in the past and had no real gains," and based on your testimony there seems to be some risk associated with their use. So how does one know that fenders are providing measurable improvement? I suppose the only way to test this is to run a control car with and without fenders.
psycaz wrote:Would you care to share any info on the wind deflector for the raised wheel?
Yes, psycaz is not the only one who is curious about that.
Without the fenders, the car is about 0.01 seconds slower.
As for the wind deflector, I turned the front raised wheel around and covered the open area with clear packing tape. I don't know what LA used on his wheel.
When looking at this car (and it does look really neat ), I am reminded of one simple question - Why do many of the cars with fenders have only rear fenders ? Aren't the front wheels causing more air to be displaced ? Aren't the rears protected by the fronts some ?