For a 3 wheel rail rider car, people are saying to have the front drivers wheel (DFW) downward canted (bottom of the wheel closer to the car) as that would have the least amount of drag, and then also have the axle turned slightly inward so the car steers toward the rail slightly to prevent any bouncing around on the track.
What angle should that DFW be canted downward? Should it be about 3 degrees like the rear wheels, but obviously it is the opposite direction of the rear?
What angle inward should the DFW be to have it turn in just enough? I am planning to experiment with this as many people suggest. But looking at ranges or approx people have had most success/fastest car/least bouncing. I have read testing a car on a slightly slanted board going about 4 feet and the car moving about 1", but I have also read like 6" which just seems like it would be a lot of drag wouldn't it? Again, wondering what should be a goal here.
Thanks for any help!
Couple of notes. Until recently there was no real way to measure axle bend. So, even though 7 degrees is the recommendation - what exactly is 7 degrees seems to depend on who is doing the bending.
You have to understand the greater the angle the tougher it is to set the steer. The slightest little turn of the axle makes a bigger difference in steer.
And, even with a bending groove the greater the angle the harder it is to get the wheel bore over the bend without damage.
Greater downward axle bend creates "firmer" wheel-hub contact with the body, correct? And it ought to consider the condition of your track's lane guides; ideally the front wheel should be able to react to guide imperfections without changing the direction of motion. Imagine an extreme downward bend: if the front wheel gets bumped and slides outward along a downward axle, the nose of the car must rise (rapidly, but slightly). The lightweight front is now rotating upward, with the cantilevering car pivoting on its rear axles. That up-and-down motion (pitch) seems potentially unstable, but no bend in the front axle means that the front is more able to slide side to side (yaw)... so where's the sweet spot?
However, I am not sure that performance is highly sensitive to "downward angle", especially on a well-maintained track. In our past experience with kids' races, we used the same bending processes (employing a bending tool) for all bent axles, then slightly rotated the dominant front axle to get the targeted amount of drift on a test ramp / tuning board as you suggest. The logic was that, if 3 degrees on the rear is necessary to direct the rear wheels to the axle ends, then why not use the same amount to direct the front wheel toward the body? So IIRC the kids usually started with about 3 degrees on the front axle (because we had a tool that bent that amount), and increased that amount only when testing dictated otherwise. Was that optimal? They won their races on tracks that were assembled well. As Eagle notes, the slight steering / large turning radius is more difficult to perfectly adjust with a heavily bent axle, which is why we usually worked with 3 degrees or so... but if the experts say 7 degrees is optimal via experimentation, then certainly try that! It gives you a lot more steering capacity than 3 degree should you need it.
(BTW, as they improved, the rear axle holes were drilled at an angle; only the DFW axle was significantly bent.)
Aft CoM is de-stabilizing, and the steer-in stabilizes the directionality of the car as it meets imperfections in the track. So the desired amount of drift depends on the smoothness of the track, and the aggressiveness of the CoM placement. Opinions will vary, but if memory serves, I think a safe starting recommendation might be a couple of inches of drift (rather mild) over four feet with the CoM 1" to 7/8" ahead of the rear wheels (also mild). More aggressive configurations and/or rougher racing surfaces likely require more aggressive steer.
That seems like a bizarre (and unenforceable) rule - at least, I don't recall ever hearing of such. If a car is dropped, or encounters a hard stop at the end of the race, or some other incident accidentally bends one of the axles, is the car disqualified?
(I've lost count of how many times I've seen a little kid take his freshly assembled car and immediately fling it across the floor to "test how fast" it is, only for it to hit an obstacle and badly bend a front axle...)
Here are two more ideas...
- If you are using nail-based axles (BSA-like, as opposed to "hinge-pin" axles that come with some higher quality kits), some axles could have more natural bend than others. Employing the "most bent" axle on the DFW may give you some additional ability to adjust steering.
- Search for "wax paper shim" method for aligning axles. It was an advocated practice (before rail-riding) to get the axles perfectly parallel with each other, but in your case you could use paper shims to introduce needed DFW toe and camber adjustments... but you would need to completely trim the excess shim material away to not interfere with the DFW against the body.
So I attempted a mathematical analysis of how the drift over a 4-foot tuning board relates to toe-in angle, assuming a wheel base of 5-1/2" (maximum extended wheelbase). The relationship was effectively linear when the drift is less than 6 inches. The equation I got (which may or may not be correct) is:
Code: Select all
steering_angle_in_degrees = 0.37 x drift_in_inches drift_in_inches = 2.7 x steering_angle_in_degrees
Eagle when you say 7 degrees.. are you saying to bend the axle to 7 degrees.. or are you talking about the tilt angle ( camber) of the DFW wheel in relation to the track running surface ?
Let me dig out my Protractor and put up a few pic's.
the protractor is set 7 degrees off of 90. to show tilt angle of DFW.
Back wheels 3 degrees ( sorry the pic not the best .. very hard to hold every thing and snap a photo on the I phone.)
The side view of car.. shows that my front end is running a little bit high in relation to the rear looking at it from the top side of the body.
like FS point out.. how it was done back then with a bent axle.
Now or days some drill the axle hole a little bit higher up to lower the front end. (air flow drag plays a roll in slowing a car if the front is catching air.)
Stan Pope & VK has a axle bending reference chart.. that can be found at.
drew_351 ( The only rule set I've ever seen that doesn't allow for bent axles.drew_351 wrote: ↑Tue Jan 24, 2023 5:28 pm I am actually not allowed to bend any axles. So I am working with trying to drill the hole at the axle point at a specific angle. I have figured out how to do that, but it makes it not very adjustable. One block has one angle for both cant and steer. That is why I am asking my questions!
Is the Pinewood Derby World Championship In NYC.. allows for canting of the axles but.. does not allow bending of the axles.
There is a topic about rail riding with out bent axles.
Good info, Whoda -- thanks! I found a copy of the Greater New York Councils (GNYC) rules here (which also require the use of factory slots and four-wheels touching). An internet search for phrases like "Axles may not be bent" discovers a few derby-related hits across the entirety of cyberspace. I would venture to guess that it remains a relatively uncommon restriction, yet it is more common that I would have believed...
Don’t quote me on this..
But I think the Gulf Stream Council
has a no bent axle in there rule set as well.
https://www.gulfstreamcouncil.org/files ... erby-Rules
I combed the rules and worked really hard o build a car to their rules. I sent it to him hoping to see how it compared to his fastest and maybe the fastest Scout's. Unfortunately car was returned without being raced. So, I don't know if it is fast, but it is definitely different.
"No obvious angle" is slightly different aspect to a restriction of "no axle bending". Because of the subjectivity of the qualifier "obvious", I suppose that a slight (non-obvious) angle might pass inspection and provide some slight benefit? I'd assume that the OP is not constrained by a requirement to "positioned squarely" since this topic about drilling at compound angles ...
Yeah, the rule I saw there was "The axle nail may not be bent in a way to cause the wheel to not make contact with the track." It seems like that rule is not against "axle bending" per se, but rather against angling so much that a wheel becomes raised because they have a four-on-the-floor requirement.
It appears that the OP stopped visiting DerbyTalk less than 48 hours after joining. He apparently posed the same question simultaneously on another forum. There, Loud2ns suggested 4-6 degrees downward and 4" of steer over 4 feet, but then discussion petered out after a vendor / forum-sponsor marketed a block pre-drilled to optimally-determined angles...
I would be grateful if Drew shares on DT the amount of steer he ends up using...
Yeah seen his posting there as well FS, and it would be nice if he Chimes back in.FatSebastian wrote: ↑Wed Feb 01, 2023 9:53 am It appears that the OP stopped visiting DerbyTalk less than 48 hours after joining. He apparently posed the same question simultaneously on another forum. There, Loud2ns suggested 4-6 degrees downward and 4" of steer over 4 feet, but then discussion petered out after a vendor / forum-sponsor marketed a block pre-drilled to optimally-determined angles...
I would be grateful if Drew shares on DT the amount of steer he ends up using...
I used to think that 3'' of steer in 4 ft was a good drift angle to start out with.. but like they say it's better to have enough steer to hold the car to the rail then not enough.
And like Eagle said to much bend or camber makes the car hard to adjust.. re minds me of an older posting..
Seth aka.. Noskills did sometime way back while over bending a DFW axle and what Murph from shining light had to say about his camber angle of the DFW.
Randy Davis (aka MaxV) did an interesting analysis back in 2008, when riding the rail was first gaining popularity. He made a test car with a steerable front axle, then tried different steering angles to illustrate the benefit.
Although the analysis wasn't thorough due to the constraints of his test hardware, the limited data seemed to imply the possibility of waning benefits with larger steer angle (the curve flattens to the right).
I have conjectured that the optimal steering angle ought to be a function of track condition, center-of-mass (CoM) placement, and possibly track shape. This is partly out of theory, and partly because recommendations of heavier steer tends to come from upper-echelon racers who routinely operate with the most aggressive (aft) CoM location. So it would be really keen to try to repeat Randy's experiment with more extreme steering angles and a few different CoM placements to explore the limits of the performance envelope... it would be especially interesting to know at what extreme steering angle the same car might begin to slow down relative to its CoM placement. Randy declared most of the parameters used in his experiment, but the CoM location of his test rig was not one of them.
And who knows... maybe this has already been done and posted by someone, but I am just ignorant of it...