Maximum Radius for Wall of Death

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Discussion Overview

The discussion revolves around the mechanics and limitations of the "wall of death," a motorcycle stunt involving riding along a vertical circular wall. Participants explore the forces at play, such as centripetal force, G-forces, and the implications of wall radius on speed and safety. The conversation touches on theoretical aspects, practical considerations, and the relationship between speed, radius, and rider experience.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the G-force acting on the rider is a limiting factor for speed on the wall of death, with smaller radii resulting in higher G-forces.
  • Others propose that theoretically, there is no maximum limit to the size of the wall, as increasing the radius allows for higher speeds with lower G-forces.
  • A participant mentions that practical constraints, such as cost and the physical limits of motorcycle performance, may impose limits on wall size and speed.
  • Some contributions discuss the torque effect and the need for the rider to lean into the wall, which varies with speed and radius.
  • One participant provides a formula relating speed, diameter, and G-forces, suggesting that higher speeds require larger diameters to maintain lower G-forces.
  • Another participant raises the question of whether there is a fundamental maximum radius that would invalidate the wall of death concept due to increasing lean angles or G-forces.
  • Concerns are expressed regarding the physical limits of both the rider and the motorcycle under extreme conditions, including the effects of G-forces on stability and control.

Areas of Agreement / Disagreement

Participants express a range of views on the limitations of the wall of death, with some arguing that practical factors like cost and motorcycle capabilities are significant, while others maintain that theoretical limits are less clear. The discussion remains unresolved regarding the maximum radius and its implications.

Contextual Notes

Participants note that the relationship between speed, radius, and G-forces is complex and may depend on various assumptions, including rider tolerance to G-forces and the physical characteristics of the motorcycle. The discussion does not reach a consensus on these points.

  • #31
minilandrover said:
see you can work it out, although you got the wrong G force, Just don't go asking for a job at nasa
You might want to crack back the attitude. You're embarrassing yourself.
 
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  • #32
Quote: 187.5 mph squared over 3 equals 5468.75

I think your math is wrong, please feel free to correct me if my numbers don't add up.

upload_2016-4-5_11-32-58.png


upload_2016-4-5_11-32-58.png
Quote: 187.5 mph squared equals 35156.25 divided by your 231 meters ! will be 35156.25 over 25 x 231 this equals 6.087 G not 3 g !
who taught you maths ?
mfb stated the radius was 231m

Radius is half the diameter, is it not?

upload_2016-4-5_10-23-39.png


If 300 kph = 186.411 mph then the G forces would be;

upload_2016-4-5_10-23-39.png


Which brings us back to what mfb started with, 3 G's or be it a couple of decimal places out. Hehe,

Hi mfb, can you expand on your formula please, I'm trying to learn this for fun and I'm not particularly good at math.

I can see part of your workings out with regards to velocity which is measured in m/s:


upload_2016-4-5_11-13-25.png
upload_2016-4-5_11-13-25.png


Using your formula I found:

upload_2016-4-5_11-14-19.png


But when I bash these numbers into the abacus, I get:

upload_2016-4-5_11-22-8.png


upload_2016-4-5_11-22-8.png
What have I done wrong?
 
  • #33
Jimbo54321 said:
Using your formula I found:

upload_2016-4-5_11-14-19-png.98583.png
The acceleration is 3g, not 3. (g = 9.8 m/s^2)
 
  • #34
Hi Doc, I thought that was the case but when I used (rightly or wrongly) 83•33332 / (3 x 9•81) I got 235•964m
Which isn't what mfb got (231m), so I assumed I had done it wrong.
 
  • #35
Jimbo54321 said:
Hi Doc, I thought that was the case but when I used (rightly or wrongly) 83•33332 / (3 x 9•81) I got 235•964m
Which isn't what mfb got (231m), so I assumed I had done it wrong.
Close enough. The method is correct.
 
  • #36
I used ##g \approx 10 ms^{-2}##. The difference is just 2 %.
 
  • #37
Just as a side note, ##a = v^2/r## is just the centripetal acceleration. If you want to find the total acceleration experienced by the rider, use Pythagoras' theorem to find that
$$
a_{\rm tot}^2 = g^2 + \frac{v^4}{r^2}.
$$
For a total acceleration of ##Ng## this would give a velocity
$$
v = \sqrt[4]{N^2 - 1}\, \sqrt{gr},
$$
indicating that for a fixed target acceleration, ##v## needs to grow as ##\sqrt{r}## (this was true already for the centripetal acceleration and follows directly from basic dimensional analysis). The angle is always the same for a given acceleration, ##\cos(\theta) = 1/N##, where ##\theta## is the angle of the rider from the vertical position.
 
Last edited:
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  • #38
I am the first to admit that I am not good at mathematics and have struggled all my life, but I do try, and I will persevere in improving my understanding.
I can see from other threads that this forum is used by Ladies and Gentleman that are so far above me in the league tables, that when it comes to understanding mathematics, physics and science, you guys leave me feeling like a Bum at a banquet. LOL.

Anyway, the only reason I questioned my math was to answer a nagging thought of how many G's Patch would be pulling at 48mph (as stated in the program), but when I worked out that there is no way he could do 48mph, I had to question (1) my math, or (2) the programs statement.

I'd like to thank you guys for helping me, mfb, Doc Al and Orodruin you three have given me a lot of self homework, (trying to decipher the formulas you used) PMSL.
But I will strive to understand this math. Oh the late nights.
Thanks again.
 
Last edited by a moderator:
  • #39
What is to be said on the topic has been said and several posts have already been deleted. It is time to close this thread.
 

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