Weight Distribution

[Vitamin K]

So I see that TxChemist tried to even out the weight on the rear wheels by moving it closer the the DFW side. This natural condition, as explained by Vitamin K, of one rear side weighing more than the other, should be mitigated by placing more weight on the other side. (?) Is it possible to achieve a perfect balance?

Also, is it your experience that with all other items being equal, a balanced rear will run faster than a non-balanced rear?

So when it comes to "balance" you can have (assuming the car runs on 3 wheels) one of two possibilities: The weight on both rears can be the same, or the car can be balanced laterally. For a three wheeler, you won't achieve both (though I guess you could achieve neither!)

I can't speak from experience regarding what is best. Stuff I have heard seems to indicate that the fast guys do end up with a car that is close to being laterally balanced, but there are a ton of other factors. I suspect a lot of guys have a per-wheel weight that works for them, and they use those numbers, not really worrying about balance points.

 

[txchemist]

So I see that TxChemist tried to even out the weight on the rear wheels by moving it closer the the DFW side. This natural condition, as explained by Vitamin K, of one rear side weighing more than the other, should be mitigated by placing more weight on the other side. (?) Is it possible to achieve a perfect balance?

Also, is it your experience that with all other items being equal, a balanced rear will run faster than a non-balanced rear?

Complex question. Always trade offs. In the old days, the only tungsten available was 95% at best (cubes) Optimizing speed with cubes ended up with most putting 12 behind and 13 to 14 in front of axle with the lightest bodies. Most really fast racers would not put all cubes as close as possible to the back axle, but would stack them on up the DFW side to get some better balance. But as you do this, you start to move the COG forward and DFW gets heavier. Individuals could still see a speed gain so this became common. Most would see a speed drop off if they moved so many cubes to the side to get back axles equal, so a little imbalance became the "optimum". Now enter the age of 99.95% tungsten bars and you have the flexibility to offset the back bar easily and get a head start on balance. It is possible to get the back perfect and have a COG better than a total cube car that still had an imbalance., You can also have a slight imbalance and a super low COG. At least you can see what works for you much easier with better materials.

 

[txchemist]

Another trick is to obviously have your best 2 wheels on the back. But if one still had a longer spin time, less wobble, what ever you grade on, put your absolute best wheel on the DFW side. The slight difference in performance is magnified when you go through the curve. You want any slower wheel to pull the DFW into the rail, not away from the rail. So if you see a bit of a wiggle where your DFW pulls off the rail at the bottom of the hill ( might even be enough to touch the NDBW onto the rail), swap back axles and see if that has some improvement. If both set ups still give that bottom of the hill wiggle, You are a candidate for improving the balance.

 

[cmoney atrain]

That is some great info txchemist. Thank you!!

 

[FDM]

Another trick is to obviously have your best 2 wheels on the back. But if one still had a longer spin time, less wobble, what ever you grade on, put your absolute best wheel on the DFW side. The slight difference in performance is magnified when you go through the curve. You want any slower wheel to pull the DFW into the rail, not away from the rail. So if you see a bit of a wiggle where your DFW pulls off the rail at the bottom of the hill ( might even be enough to touch the NDBW onto the rail), swap back axles and see if that has some improvement. If both set ups still give that bottom of the hill wiggle, You are a candidate for improving the balance.

I am glad you mentioned this, I always thought that having a bit more weight on the NDRW would make that wheel rotate less freely than the DRW resulting in a steer assist from the back giving the car a more stable ride and even let you get away with slightly less steer (or even weight) on the DFW.

 

[txchemist]

Strange things happen with oil under load, friction drops.
Also, steel against polystyrene friction drops with increasing load in Pinewood speeds and weight. This is not normal at all for most materials so will go against your usual experiance.

 

[FDM]

Strange things happen with oil under load, friction drops.
Also, steel against polystyrene friction drops with increasing load in Pinewood speeds and weight. This is not normal at all for most materials so will go against your usual experiance.

Thanks for the explanation, I was wondering if something like that might happen since a free wheel spin of an unweighted oil wheel will be shorter than an unweighted graphite wheel. But for graphite the friction would increase with increased weight? All of our graphite cars (3 wheelers) have the standard weight bias and are not balance corrected. Same as our oil car, but based on this it could pay off to play around with the balance on the oil car.

 

[txchemist]

So because the plastic wheel can drop in friction with increased load, Graphite or oil will have lower friction with increased load, but oil at low load is usually higher than Graphite at a low load, we have the case where for many years the fastest Pros ran oil in the back and graphite on the DFW. But even then, messing around with the individual wheel loading on each car could produce interesting speed changes. No one answer fits every racer because they may not have anywhere near the same COF. You may gain some speed by going to graphite on the DFW. You might gain even more speed with a better oil process.

 

[M Tull]

I really enjoyed this thread and learned a lot. Thank you all. I believe earlier in this thread and other threads it was mentioned the ideal weight on the FDW being in the vicinity of .5 oz. What if we were talking about a car with four wheels touching? Many have stated the goal is for the NDFW to touch as little as possible but it still adds to the overall weight distribution. I haven't actually set a car on four scales but I imaging the weight is naturally a little more centered? Is the goal still around .5 oz. for said type of car? In our case we use the SBP to drill the axle holes but still have to use stock BSA out-of-round wheels and axles ... so even with a perfect drill and passing the lightnin boy alignment test I can see where a bad wheel may complicate an aggressive COM?

 

[txchemist]

Get on the Premium list and look at Johns 4 wheel touching video. You will learn much.
I am working on pushing the limits a bit with my new build.

 

[M Tull]

txchemist,
Very impressive weight distribution ... thank you for ALL the advice. I purchased the premium content last year and have indeed watched the four wheel touching video four or five times now ... maybe more. If I remember correctly I purchased the premium content specifically for said video.