Theory on transition and steer

[Guest]

I didn't explain myself very well in the other transition thread and I don't want to hi-jack it so here goes, here's a clearer example of what I meant this morning. Curious what you guys think and if you spot flaws of logic please do point them out.

If your rear alignment is perfect and you were to lift up on the nose of the car, your rear alignment would be slightly toed out. At least this was the consensus by some smart and fast builders years back in a long thread and it sure sounds plausible to me. It was stated that as the car traveled through the transition that the nose would in essence be raised in comparison to how the car sits when it is running on the straight section of the hill and the flat part of the track.

Here's where it gets tricky. If the rears are in fact toed out momentarily through the transition, then theoretically one or both of the rear wheels could have a slight steering effect and it would make sense that the heavier weighted rear wheel would have a higher authority on the direction the car is being steered as a result of having rear alignment that's not true through the transition, I believe they referred to it as rear axle frictional differentiation.

It doesn't make sense to me that equally weighting of the rears hasn't been proven to be faster than having more weight on the rear wheel opposite side of the DFW.

Could it be that the extra weight on the rear wheel opposite of the DFW is helping to steer the car through the transition to stay on the rail rather than a car that is equally weighted on the rears that doesn't have the same steering affect towards the rail? Might explain why some cars get wiggly through the transition and some don't.

 

[bracketracer]

Does the front end really "raise" in relation to the rears? With three wheels on the track it seems like the toe shouldn't really change. I think what you're seeing is a dynamic imbalance in the transition caused by offset weight loading in the car while it's going down the track. The heavier loaded rear wheel will become dominant and steer the rear. If the load shifts from one rear to the other and those two wheels aren't aligned exactly the same, then you get a wobble in the transition. If you have one wheel loaded heavy enough that it remains dominant all the way through the transition, then no wobble. I think that's why some cars like an equal static distribution of weight and some cars run better with a heavy offset. You can see this effect on a slow roll if you have a car with a slightly off drill. Take all the weight out and stack it on top next to one rear wheel. With a straight axle up front so the car has no steer, give it a slow roll on your tuning board. Note how much it drifts and which way. Now slide your weight over next to the other rear wheel. Roll it again and see what happens.

 

[Kinser Racing]

Does the front end really "raise" in relation to the rears?

It doesn't raise in relation to the rears but the angle of the track is not directly parallel with the plane of the car. As the car comes into the transition the track will be at lets say the 7 or 5 o'clock position, depending on the side of the cars you're referencing as apposed to the 6 o'clock position. So it will be briefly running at a toed out position

 

[Guest]

Thanks for reading through that guys, a bit long winded but an interesting topic and Kinser explained it really well.

BR, Ill give that a go to see firsthand the effects. It makes one wonder if using oil is more forgiving than graphite in regards to one wheel having more steer than other. It would seem that the higher the coefficient of friction of lube being used, the more drastic the outcome unless the added drag on the opposite wheel counter balances it. Ouch - my head hurts.

 

[Guest]

Hey Dog,
I don't know how I missed this topic because you know how I love your theories.

Those are interesting points BR and Kinser.

Thanks.

Personally I keep going back and forth on this topic.

The consensus seems to be lopsided weighting but I can't help but wonder.

Axle frictional differentiation!
That is awesome! Gotta watch the AFD fella!

PS.
Hey Dog,
Please check out the RR forum. I have a question for you there.
Thanks

 

[HMH Racing]

Interesting, but it only proves one point. I need a test track /images/boards/smilies/smile.gif

We ran open scout- graphite at MA this year. The 3 cars are prepped and built as close to identical as I can. we finished 6 , 9 and 14. I just got 3 digital scales so I could check the weighting. All 3 have a right DFW. Steer is very close on all 3. The fastest car had 3 grams more weight on the LEFT rear than the slowest. Our number 2 car had 1.9 gram difference. Do most of you try and weight the opposite rear wheel slightly heavier? Did I mention I need a track/images/boards/smilies/smile.gif

 

[Guest]

Hey Tom,

Those are great finishes for the MA!

I hear that there is some pretty stiff competition for that event.

Congrats!

 

[HMH Racing]

Thanks, It was our first time running. The boys and other families are hooked. They are already planning on next year. I am working on sending in a couple of cars to NPWDRL. I just ordered the proxxon mill, should be here Thursday. I just had knee surgery so progress has been slow in the workshop. I know there are so many variables with these "little blocks of wood" but the main difference between the 3 is the amount of weight on the left rear. Man, there is so much I want to try.

 

[Guest]

Thanks, It was our first time running. The boys and other families are hooked. They are already planning on next year. I am working on sending in a couple of cars to NPWDRL. I just ordered the proxxon mill, should be here Thursday. I just had knee surgery so progress has been slow in the workshop. I know there are so many variables with these "little blocks of wood" but the main difference between the 3 is the amount of weight on the left rear. Man, there is so much I want to try.

Man, I hear that!

Kinda wacky that your fastest is overweighted on the left of the car with a right DFW.

Sorry to hear about the knee. I sure hope it wasn't an ACL because I had that one done and it hurt like a mother.

Take it slow.

That Proxxon mill looks cool.

 

[ngyoung]

So far it seems that there isn't a clear cut answer. From what I read combing the forums the guys that have a track and tune the weight it varies from one car to the next. Some have more success with the weight biased to one side where others have better results on the other side or evenly balanced.

Interesting, but it only proves one point. I need a test track /images/boards/smilies/smile.gif

We ran open scout- graphite at MA this year. The 3 cars are prepped and built as close to identical as I can. we finished 6 , 9 and 14. I just got 3 digital scales so I could check the weighting. All 3 have a right DFW. Steer is very close on all 3. The fastest car had 3 grams more weight on the LEFT rear than the slowest. Our number 2 car had 1.9 gram difference. Do most of you try and weight the opposite rear wheel slightly heavier? Did I mention I need a track/images/boards/smilies/smile.gif

 

[HMH Racing]

Thanks, It was our first time running. The boys and other families are hooked. They are already planning on next year. I am working on sending in a couple of cars to NPWDRL. I just ordered the proxxon mill, should be here Thursday. I just had knee surgery so progress has been slow in the workshop. I know there are so many variables with these "little blocks of wood" but the main difference between the 3 is the amount of weight on the left rear. Man, there is so much I want to try.

Man, I hear that!

Kinda wacky that your fastest is overweighted on the left of the car with a right DFW.

Sorry to hear about the knee. I sure hope it wasn't an ACL because I had that one done and it hurt like a mother.

Take it slow.

That Proxxon mill looks cool.

wacky is right. I did not have a way to check the weight distribution before the race. I just set the com at about 3/4". When I got the 3 new scales all 3 cars are weighted the heaviest on the opposite rear wheel. So was this a freak thing or should I shoot for the same weighting? Does the lubrication make diff? In setting up a car to run BASX and SS for the league, should the weight be equal in the rear, opposite rear weighted more or rear dominate weighted more?

Gotta love it

No ACL but surgery #3. I do have slight ACL tear but not fixing it. Local Dr's wanted to replace the knee, STL Dr said no replacement needed just few repairs and clean out.

 

[Kinser Racing]

Weight is an extremely touchy thing on many cars. I think I've said this before but on my Unlimited "No Denial" it ran about a gram under weight, so I decided to add the weight to try to get more speed. It slowed it down and I wend back to the previous weight.

 

[bracketracer]

wacky is right. I did not have a way to check the weight distribution before the race. I just set the com at about 3/4". When I got the 3 new scales all 3 cars are weighted the heaviest on the opposite rear wheel. So was this a freak thing or should I shoot for the same weighting? Does the lubrication make diff? In setting up a car to run BASX and SS for the league, should the weight be equal in the rear, opposite rear weighted more or rear dominate weighted more?

If you draw a line from the contact point (on the track) of the non-dominant rear wheel diagonally to the contact point of the DFW, everything from that line up to the tip of the non-dominant front corner of the car is cantilevered weight. It counterbalances the weight resting on the dominant side rear wheel. So if you load the cubes evenly into the car the dominant side rear wheel will show less weight than the non-dominant side rear wheel will. Some guys load the cubes asymmetrically with a bias towards the dominant side to make the reading on the scales more even.

 

[B_Regal Racing]

Another very interesting discussion.

While weighting seems to be a touchy subject, I truly believe there is no secret formula. What is more interesting to me is not how a car is weighted in the end state, but how you come to that weight placement for that car. I absolutely believe every car is different, and even if you had the weight on the wheels of a winning car, it probably would not translate as well as one would hope for.

To determine the weight placement, I have a basic setup I choose to start with. I leave one cube out of the car and tape it to the top. I test the car on the track and try to dial in the steer, not to the extreme edge, but so it is comfortably stable and getting fairly good times. In the next set of runs, I'll move the weight around on the top of the car looking to improve my time. Next, I'll move the weight to the bottom of the car and try to duplicate the times. Lastly, I'll try to absolutely dial in the steer. This is all time permitting.

I'm curious what procedures others follow to set their weight.

 

[Guest]

wacky is right. I did not have a way to check the weight distribution before the race. I just set the com at about 3/4". When I got the 3 new scales all 3 cars are weighted the heaviest on the opposite rear wheel. So was this a freak thing or should I shoot for the same weighting? Does the lubrication make diff? In setting up a car to run BASX and SS for the league, should the weight be equal in the rear, opposite rear weighted more or rear dominate weighted more?

If you draw a line from the contact point (on the track) of the non-dominant rear wheel diagonally to the contact point of the DFW, everything from that line up to the tip of the non-dominant front corner of the car is cantilevered weight. It counterbalances the weight resting on the dominant side rear wheel. So if you load the cubes evenly into the car the dominant side rear wheel will show less weight than the non-dominant side rear wheel will. Some guys load the cubes asymmetrically with a bias towards the dominant side to make the reading on the scales more even.

Hey BR,
I like the way you described that and it makes perfect sense.
There is little doubt that the shifting of weight has been studied to within an inch of its life and lopsided weighting keeps proving to be the preferred method.
Perhaps I have some part of me from the show me state because I am still not convinced.
In a static position the weight should be biased off center. My feelings are that static stability should translate to kinetic stability 99% of the time.
This just might fall into the 1% though.
I can't explain it but it is more of a sense I get.
If anyone on this forum has skated half pipe before then they might get the same gut feeling.
This is kinda what I am basing it on. In essence this is a way to really feel what the car is going thru at the transition.

 

[bracketracer]

Try breathing through your eyelids, like a Lava lizard.

 

[ngyoung]

Hey BR, I like the way you described that and it makes perfect sense. There is little doubt that the shifting of weight has been studied to within an inch of its life and lopsided weighting keeps proving to be the preferred method. Perhaps I have some part of me from the show me state because I am still not convinced. In a static position the weight should be biased off center. My feelings are that static stability should translate to kinetic stability 99% of the time. This just might fall into the 1% though. I can't explain it but it is more of a sense I get. If anyone on this forum has skated half pipe before then they might get the same gut feeling. This is kinda what I am basing it on. In essence this is a way to really feel what the car is going thru at the transition.

I think for the most part keeping the weight in the triangle is a safe approach. In a vacuum it is likely the best approach. Since there are so many other factors that are going on all at once I think that moving the weight around can lessen or exacerbate flaws in the build. That is why for those that actually have a track to tune there weight usually have inconsistent weight placement. I think when a car finds more speed by changing the weight differential it is being gained because the weight is being taken away from a wheel that may have more friction then the other or is aligned better with the DFW. There is always a more dominant rear wheel which is usually the one with the most weight on it. If shifting the weight to the opposite wheel gains more speed it may be that wheel is tracking better with the DFW or has less friction then the other one.

 

[Guest]

What would be helpful is a PWD related glossary where one can get quickly get familiarized with commonly used abbreviations and their variations.. Maybe pin it at the top of the tools page or somewhere handy and easy to find..

AFD- Axle frictional differentiation (good one Joe!)

MVD- Micro vibrational detail

DFW - ....

COM/COB- ...

NDFW/floater- ...

RR-(rail runner)

K-House

etc.

 

[Guest]

Try breathing through your eyelids, like a Lava lizard.

Lol!!
Now you are finally speaking my language BR.
I was wondering when you would come around.