My son and i built our first pinewood derby car this year. We got 2nd in weblos I den and fifth overall and going to districts. My question is - I think we did everyting humally possible to this car and still got outrun. It is a standard wheel base car. Found out that we could extend wheel base. COG is at a little over 1/2" from rear axle. poslished axles to 3000 grit sandpaper. Trued wheels and polished them in every angle. Cut a center groove in axles or less friction. Used a low sleek wedge body design. It wasn't the fasted off the start line but always pulled through at the end of the track and won all four races. We had to hog out just about all the underneath of the car to achieve 1/2" COG and made moveable weights so that COG could be moved. We made a test track and worked on the car wheels staying centered on axles and tracking straight. It does carry one wheel up. Any IDEAS on making it Faster. It seems like it slow out of the starting line and I think that is where it is losing time but at practice it would post faster time the more I moved the COG towards 1/2" HELP!!!!!!!!
We have learned that in order to be very competitive we have to add at least 3.5 to 3.75 oz of tungsten. This is with the new standard 2.6 g wheel. A little more weight is added there with epoxy, body filler etc. So at the end of the day it is more like 3.6-3.8 oz.
Seems 3.75oz with 3/4 COM and RR (rail rider) should help you get that extra few inches and/or car length.
You can also move .3 from the rear of the car and put on front- this moves the weight further back in the car without sacrificing stability.
Lastly, might consider canting wheels 2.5 and 1.5 front.
But if adding more weight then previous years and working with RR is a bit new for next year, then don't do too many new things or changes as previously mentioned, as it may negatively impact perfection on the other fronts. You may want to hold off on canting for next year for example.
The key/basic things that work for my son is- at least 3.5 oz tungsten at 3/4 com, polished axles- no grooves, but deburred etc, lightly sanded wheels- even on the lettering, hob e lube works great for him, three wheeler, wheel to body distance at 1/32, dead on alignment- due to type of track he runs on, however you may consider rail rider.
**PS- son won district last year by a car length..
Again, you may consider moving .3 to front, baking the block to lighten it up front, (His bodies weigh about .5 oz typically)
**If you can extend the wheel base= faster car all else same**
Did your car shake/shimmy at all and what type of track was it? Was the car aligned to go straight? How much did your son's car get beat by? Did his wheels touch the car body at any time? Did you use standard 2.6 g wheels or colored?
We did add about 3 ounces of lead not tugnsten. It won all of its races but how they set race up was that we race against everyone elses average four races run time. The car that won ran a 2.60 we ran a 2.66 for fastest times. We ran against him once and his car pulled away in the middle of the downhill part of the track. The car is aligned to go straight and it does do that. It does not shimmy on the track. We did use the standard wheels that came in the kit. We did sand and polish them polished all bores and edges. The wheels touched the body very little and we did grafite the body where we thought the wheels would touch. One thing that I dont know about is that two of the wheels when i spin them by hand as fast as i can, they wobble, is there any cure for that?
well it did not look like bounced of the rails. It ran a 2.66 in lane #4 2.67 in lane #3 2.68 in lane #2 and 2.66 in Lane #1 I looked the rules over really good and other than moving the wheel base what else is there? I am a little confused as to why when i free spin the wheels by hand they wobble. Does that mean anything? the car tracks straight and does wobble on the track. Any ideas?
Regarding the wobble of the wheels- yes they should be dead on- no wobble at all. Ideally, as we all try, we need to get the wheels typically to spin on/against the axle head. The wobble you had was most likely due to too much work on your bore/inside of the wheel- something was just off enough for wobble.
The wobble definitely had an impact on your times, but from our experience and without seeing how much wobble, was most likely minor if it ran mostly against the axle head. My quess is that the wobble of your wheel was due to bore work and/or the axle groove you put in and this had a minimal affect on your times.
Next year- see if you and your son can get the weight up to 3.5 tungsten at 5/8 to 3/4 COM and make a RR. If you do what you've done this year and keep the wheels from any wobble and use RR for your steering- youll run with the best of em..!!!
Net net- increase the tungsten wt to 3.5 oz, RR steering, smooth running wheels with no wobble- and you should see a faster car by at least 4-8 inches.
** Also- next year, if you can extend the wheel base- please do.
Oh- one other note- if I understand correctly, you are saying that your son's car did shake/shimmy a bit- correct?
If so, I attribute to wheel wobble in some regard, but typically this is usually a result of a too aggressive com. Put your weight as low as possible in the car and stay above 5/8 but no more then 1 inch.
If the weight is VERY low and you stay above 5/8, our findings are that any shake, shimmy etc dissapear and the car becomes more stable. My son's sweet spot to avoid this in his cars is always safe at 3/4 inch com.....just my two cents.
At 1/2 com, you are on a very thin line and this actually slows your sons car times down due to any wobble. If I misinterpreted your issues, please disregard...
thanks for the info. We just found out that our distric race is April 2nd. and we can build a new car if we would like. I am thinking o doing just that. I have heard about toe in and out on the rear wheels. I raced cars for ten years and know the wheel alignments and what they do but on this little car and no gauges to check it - how would i check to see if i toe in or out on the rear wheels? I heard that could our car to be slow starting too.
This is canting your wheels your referring to.....
There are tools/tips on this site that can assist you in measuring and configuring canting degrees for your tires.
I will leave it up to the experts that have tested two identical cars with canted and uncanted wheels for their opion. My opinion is that we have done this in the past with VERY simlar and the same cars and canting was very minor in speed gain- ie .002. I would actually focus on the other items that will provide your sons car a greater speed return as related to the issues you mentioned.
This is just one mans opinion, but considering the fact that you still have a wheel wobble item to address, I wouldn't introduce new things to your build.
IF however, you and your son decide to build a new car, then I would focus on improving weight, RR, extending the wheel base/slots, COM and ensuring no wheel wobble. IF you do these things, you will have a very fast car!
The big speed return items will be creating a RR. Increased weight at 5/8 com, extending the base and ensuring wheels have no wobble.
Moving wood from back to front, canting, etc, perhaps take these new things on next year;)
Glad to help, and remember - just my humble opinions...
Cutting off the back of your car and putting .3 of an inch to the front of your car. This essentially allows you to move your weight back further in your car without sacrificing stability. The car length is still the same and the axles slots have not moved (if required).
Post by derbydominator on Feb 4, 2011 13:37:36 GMT -6
First of all, excellent advise TKP!!!
AGC, a couple of other questions please. How did you go about grooving your axles and what pattern did you use, i.e. one wide groove, several narrow grooves, etc.? If you were using the standard wheel base, were you using the slots or drilled axle holes? Did you polish the wheel bores? Wooden or aluminum track? TKP is right on regarding the COM suggestions. With a rail rider and a well aligned and balanced car, we can get away with 5/8" COM. With a car set to go straight and not rail ride, we would recommend no more aggressive than 3/4 to 7/8" COM. At 1/2" and with some suspected play in the axle/wheel combination, I would be surprised if you weren't getting speed wobbles at the bottom of the ramp as you head into the flat stretch. They happen quickly and are not always obvious to the naked eye but video shows them well. If your car was aligned properly, an aggressive COM such as the 1/2 you mention would allow your car to do the passing on the flat stretch, not be passed. If other cars are passing you there, it is because your car has been slowed down and the likely culprit would be the speed wobbles which are hard, quick contacts between the weight bearing rear wheels and the center guide rail. The advantage of the rail rider is to reduce the likelihood of those impacts and give you a smoother, faster ride down the track. If you can build a new car for districts, set it up for a rail rider, cut in 1/16" on the dominant front wheel side of the block, extend the wheelbase, cant the rear wheels with negative camber, front dom with positive camber and the non dom front straight and up off the track. Shoot for 3/4" to 7/8" COM on your car if you have a wooden track and cannot test the car before the race. If you have a smooth aluminum track and can test beforehand, you can practice with 5/8" COM but we still recommend 3/4 with a rail rider.
thanks for the help. We grooved the axles with one wide groove. and polished to 3000 grtit paper. The car had slots for wheel base . I did polish the wheel bores. The car did pass the other cars on the flat part of the track. I couldnt see any wobble with it on the track. We did not run against the car that had the fastest time overall. We did win our four heat races. But on friday night practice- we ran twice with the car that won overall and that car would beat us going the slope part of the track and the distance would never increase on the flat part of the track. Would the change in COM help with a quicker start? Would railriding or camber help with that too? We raced on a wooden track I was told it was 32 feet.