wheel base/weight behind axle

[plhiatt]

If your stuck with a 4 3/8 wheel base, but can slide it back to to the rear, is it still faster
with 2oz behind? Or would it still be faster with a little less for stability-like 10 cubes instead of 12?
I know 12 cubes are fastest when extending wheel base a bit.

 

[Guest]

I would have the rear wheels 5/8 from the back and put 12 behind and the rest right in front of rear axle. If you have a good drill job and tuned good it should be fine.

 

[plhiatt]

Thanks, that is what I have always done with the 4 3/8 wheel base 5/8 from back and 12 cubes behind.
Just wondered if any one had tried less behind for more stability, and maybe faster times.

 

[IAE Racing]

I believe 4 3/8 all the way back used to be a div back in the day of another league. You'll be fine. built a couple cars this way this year.

 

[RichZ]

I had 3 rows of 6 behind the rear wheel on my last car with a COM of 3/4" on a 42' Best track. I won the Outlaw Class but was disappointed in my time - didn't brake 3 sec. It did run faster with only 2 rows of 6 but I thought I would give it a try, now I know.

 

[Obsessedderbydad]

Rich your theory does make sense. Higher the COM the more potential energy. The problem is with 3rows behind the rear axle that means your rears are almost 1" from the rear where most are 5/8". So the people with the 5/8" wheels have their car on the down slope longer which = more potential energy

 

[Dr. T]

I have build 3 cars with the standard wheelbase with the rears at 5/8th from the end. All with 12 cubes in the rear and 10-11 in front (all I could get with heavy stock wheels). One did great with 3.5 in of drift over 4 ft. The other two wiggled (had the same drift). I have read in this site and others that 10 in the rear might be best. Am currently trying a district car built just like that, 10 in the back and 12-14 in the front (however much I can get). Am aiming for a COM of 5/8th.

So you could do either but play it safe with the drift if you don't have a test track (I dont). I am going for 4.5 in over 4 ft now with this set up.

Hope that helps.

Dr. T

 

[plhiatt]

Dr. T, I have found the same thing to be true. With 12cubes stock wheelbase 5/8 back, most cars need at least 4" if not 4.5 to be sure to keep the wiggles away.
Some times 3.5 on my track is okay but then it wiggles on the scout track some.
I wonder if 10 cubes and 3" of steer will be faster, I guess no way to know but try....

 

[Obsessedderbydad]

Don't forget if your car has the shimmy even a little bit, if it runs by a car with the shakes it'll make yours shake worse

 

[HurriCrane Racing]

One of my fastest 4 3/8" Wheel base cars had three rows of 5 behind the rear axel and 8 cubes in front.
The drill must be dead on or it will wiggle.

 

[Guest]

I believe 4 3/8 all the way back used to be a div back in the day of another league. You'll be fine. built a couple cars this way this year.

I agree. This is the way the block is made with the slots.

Somebody figured out at some point that this was a good number.

From there the track and wheels and everything else was "built around" in a sense.

 

[Obsessedderbydad]

Dont make me get TxChemist to hit you with some truth!

 

[Obsessedderbydad]

bottom line, the longer your wheels remain on the slope, the faster the car will be. At least from all the cars I've seen.

 

[Guest]

bottom line, the longer your wheels remain on the slope, the faster the car will be. At least from all the cars I've seen.

Yes. This makes sense. It has to be correct.

Well. I guess it doesn't have to but just about.

Don't be hitting me with that street knowledge Mike.

I feel that the MOI at the transition will be the next big thing.

Or maybe two big things from now.

The major factors have been studied by the best for years.

Now it will be the less obvious things that will add up to the car that is superior.

 

[OPARENNEN]

You can get the same rear weight result using two rows of five cubes each behind the rear axle.
In addition to the 10 cubes, just glue two pieces of the slab tungsten on the bottom rear of the car (or sheet lead).

One of my best UNLM's uses this method. I checked the COG, and it is exactly the same as another car with two rows of 6 cubes, but with no weight added to the bottom. The two bodies came from two different GoatBoy laser cut bodies. In fact one of the advantages of the GB 10 cube bodies, is that the width of the car is narrower by 1/4 inch.

Another less expensive way (for bottom weight) is to buy a square foot of "sheet lead" (either 1/64" or 1/32"). You can cut it to size with scissors. On the internet, look for "sheet lead suppliers".

Using this bottom weight method, you can easily adjust the weight placement on a finished car, by just cutting the bottom weight in different patterns, and/or moving it side to side, or back and forth during testing, without screwing up the paint on a finished car.