Official Rant thread.

[wytbishop]

...if someone on a bike was stupid enough to screw with me first I would slow down and let them get ahead then if that didn't deter their interest a lane change would be in order and a life lesson learned by them.

Absolutely. And that is from a lifetime street rider. If I tried that on my bike I would expect to be killed...which is why I would never try that on my bike.

[Daninski]

So just what would you try that on

[Ryan]

New rant:

Was at an indoor cart racing place, they had a sign:

"track times are unaffected by driver weight. lighter drivers accelerate more and heavier drivers have more traction".


Someone missed out on grade 12 physics.

F=ma. That is, literally, the best known math equation. Think about what it means. F is the force resulted from the product of your mass and the acceleration you are subject to.

Apply this to a cart.

Straight line acceleration, the lighter driver wins.
F is constant (the cart produces x power)
m is the variable (fat and skinny driver)
So if m is less, a must be higher to be equal to F.
therefore, a lighter driver will accelerate at a greater rate.

Now, lets examine traction.

Traction has to do with the friction between your tires and the ground. The friction force is described as
f = uF, where u is some constant that desribes how grippy your situation is. It is always less than 1. F is the normal force you feel. In the case of a level go cart track, this is your mass, times gravity.

I'm assuming in their argument that they refer to "traction" for use in corners.

A corner is simply an acceleration. If you don't believe me, go read elsewhere, but I'm telling you it is. From the first example, you can see already that a lighter cart can take a faster corner, since all we're talking about is an acceleration that is changing direction.

Now, if you say a heavier driver provides more traction, you are correct, but you also require more force to accelerate that driver in an arc. The problem now, is that the heavier the driver gets, it is a 1:1 ratio for the amount of force required to accelerate them at the same rate. (double mass of driver, require double force to accelerate them at the same rate)

now in a corner, friction is your limiting factor (or you slide, which is slow) The issue is that teh friction your fatness produces is not a 1:1 ratio, it is less, its a u:1 ratio, where u is that number (less than 1) that describes the grippyness.

So if you weigh 2x as much, you need 2x the force, but your friction is only providing 2*(number less than 1) extra force.

So a fat driver will always be slower, a heavy car will always be slower, twisties or straight.

This applies to you winter drivers too, who put salt bags in your trunk or bales in the back of your pickup. Sure, you have more friction, but you are also upping the mass that you need to accelerate to come to a stop. Adding weight to a vehicle does not help the acceleration on snow or ice. The only place this might help is when adding more weight changes how the tire interacts with the surface.


/rant.

[ethand]

This rant has received the Ethan seal of approval. He speaks truth.
Haha... what a weird sign to show, hey?!

[Daninski]

Engineers applying math to explain things is not a perfect science, we all know this (one example, the bumble bees ability to fly). I owned a pick up truck (more than one) and found with an empty box my back tires got no traction what so ever. I added two patio stones over the rear axel and experienced a noticable improvement in traction on both snow and ice. I attribute part of this to the fact that my tires were being forced into the snow rather than floating on top of it. Ryan, is grippiness not referred to a coefficient of friction?

[Ryan]

I did mention your anomaly at the end there. Adding more weight can change how the tire interacts with the surface (forcing it into the grooves of your tires, compacting it, making it interact with the snow on the ground)

But as a rule, this is untrue.

[Daninski]

I did mention your anomaly at the end there. Adding more weight can change how the tire interacts with the surface (forcing it into the grooves of your tires, compacting it, making it interact with the snow on the ground)

But as a rule, this is untrue.

My apologies, I failed to read your post thoroughly enough.

[wytbishop]

The reason we are able to turn corners at all is because the reaction force between the tire and the road causes the vehicle to accelerate towards the center of the corner's radius. The unbalanced force which causes that inward acceleration results directly from the normal force of the mass of the car and driver. Therefore by basic physics a heavier object is capable of generating higher cornering acceleration.

Do a free body diagram of a car going around a curve. Assuming constant velocity, what are the forces? Acceleration due to friction points toward the center of the turn and the force due to the car's mass points away from the center of the turn. As long as the force of the mass of the car is not greater than the force of friction the car will continue on the line it is steered on.

So if the ability to corner is essentially the balance between the inward acceleration generated by the friction between the tire and road and the outward force of the mass of the vehicle, which is proportionate to velocity in the case of a car going through a turn, it is clear that an identicle car with a heavier driver will be capable of carrying greater speed through the corners than a lighter driver would...i.e. a lighter driver will spin out at a lower speed than a heavier one in an identicle gocart.

Whie it is certainly true that a heavier vehicle will accelerate forward less quickly than a lighter one, in the confines of a gocart track and with the power available from the gocart engine which is still adequate to bring all but the heaviest drivers up to a significant speed, the added cornering speed could definitely make up for the slower acceleration for a reasonable range of driver masses.

[Ryan]

Wyt, I agree, but the magnitude of this normal force is 1:1 with weight, whereas the friction force is less than 1:1.

If you weight 2x as much (2m), you can only apply u*2m times more friction force.

Fn = mg
f = uFn, f = umg

2Fn = 2mg
2f = 2umg

Since these balance out in a corner just before you spin out, you see that you're going to be at a disadvantage due to u<1.

Example...

75kg cart
A)25kg driver (100kg total)
B)125kg driver (200kg total)
u= 0.8

A)Fn = 981
B)Fn = 1962

A)f = 784.8
B)f = 1569.6

assuming constant velocity, A = v^2/p where v is the velocity and p is the radius of curvature.

assume p = 10m, thats a pretty tight corner.

f = ma, a = f/m. a =v^2/2

f/m = v^2/p

v = (pf/m)^1/2

A) (10*1569.6/200)^1/2 = 8.859m/s

B) (10*784/100)^1/2 = 8.854 m/s





Damn.

Its all linear and everything cancels... aaahhh!

I feel like I am missing something.... lol. Tomorrow.

inertia.... versus centripetal force....

[ethand]

Main thing is that the karting track is not snow or other such extreme surfaces where traction is difficult to get, and the main mass of a kart is generally roughly over the middle of the kart, not over one set of tyres more so than the other. This means that adding weight to the kart doesn't force the 'end' of the kart with lesser weight to gain better traction, it mainly just adds weight, which slows accelleration (and therefore the ability to punch out of corners). The reason adding weight to the back of a ute (pickup truck) aids traction is that there is very little weight over the rear wheels (which, on Australian utes at least, are the driving wheels). Pressing extra weight over the DRIVING wheels when most of the mass is over the non-driving wheels is what aids traction in such extreme cases... Which doesn't apply to karts, at least, not from my karting experiences, anyway...

[SuperK]

But the biggest issue is that no one wants to oogle at a fat chick driving the go cart, it's the skinny one with the itsy bitsy teensy weensy polka dotty bikini! Screw you guy's math, SuperK knows what's important!

[MrMazda92]

But the biggest issue is that no one wants to oogle at a fat chick driving the go cart, it's the skinny one with the itsy bitsy teensy weensy polka dotty bikini! Screw you guy's math, SuperK knows what's important!

This.

[ethand]

Another rant: Some twat-face hit my car and hasn't owned up to it...
I just found 2 reasonably large dents on the driver's side rear fender, along with scratches/chips down the panel, rear bumper & mudflap. GRRRR!!!! SO gay
I think it might've been my neighbour/their friends that were over on the weekend. On Saturday avo I cleaned it & there was nothing wrong with it, so I rate it was Saturday night, when I parked across the road from my neighbours driveway on the street. Judging from the angle of it, it looks like that could be right. Same thing happened to my housemates car a while back, only the person fronted up & got it fixed under insurance...
It SO bugs me when people damage stuff & just don't front up

[RobMinhas]

Another rant: Some twat-face hit my car and hasn't owned up to it...
I just found 2 reasonably large dents on the driver's side rear fender, along with scratches/chips down the panel, rear bumper & mudflap. GRRRR!!!! SO gay
I think it might've been my neighbour/their friends that were over on the weekend. On Saturday avo I cleaned it & there was nothing wrong with it, so I rate it was Saturday night, when I parked across the road from my neighbours driveway on the street. Judging from the angle of it, it looks like that could be right. Same thing happened to my housemates car a while back, only the person fronted up & got it fixed under insurance...
It SO bugs me when people damage stuff & just don't front up

No!! Not your beautiful MX3! I've had it happen like three times and it sucks sooo much man. I can feel the pain.

[ethand]

Ya, it makes the car look like a junker! I so hate it! And I'lll have to leave it until I do my student exchange and return again (in 18 months' time) as right now, I need every $ I get to go towards this exchange...