R/C car guy

I was just watching a video of a twin engine savage doing some monster wheelies, and it got me thinking. What causes a wheelie? I think I already know but i was just wondering if somebody can give a detailed explanation of what causes the front wheels to lift off of the ground.

What I think happens is that when the tires start to spin, it causes a shift in weight. It moves the weight mostly all to the back. Just like in a car. When the car accelerates hard from a stop, you get pushed back in your chair. From the weight mostly being in the rear of the truck, there is better traction in the rear and causes the rear end to try and get ahead of the front. This not only causes a wheelie to possibly happen but also, mroe commonly in street cars, it causes the vehicle to fish tail, or weave back and forth. It's like in model rockets, if the rocket is too light with an engine that is too powerful, it will cause it to tumble in the air. This happens becuase the bottom tries to get infront of the top and when it does so, the engine propels it towards the ground and causes a cycle of pointing up and down. Hence, the vertical spiral type of a tumble. I hope I explained that good enough(if it's even correct).

There was also another explanation for a wheelie, which seems more logical(cause it didn't come from me). When the truck accelerates the weight shifts to the back and causes the truck to squat. When this happens, the center of gravity is lowered in the back and as it goes forward, the rear goes under the front becuase its center of gravity is lower than the front. This explanation came from Skymaxx at rcnitrotalk.com. I think I understood and reworded it correctly.

These explanations could be a bunch of bull, or they could be perfectly correct. I'm just wondering if there is somebody, who maybe went to college and majored in some kind of physics or is an expert in this field, that can varify one of these explanations or give a detailed description of what actually happens.

And on more thing. If the theory that Skymaxx gave is correct, would a monster truck be able to wheelie if it had a rigid suspension that had no wheel travel so it couldn't squat and lower its center of gravity?

If i didn't explain something good enough, tell me. I'm not always very good at getting my point across.

lax195

My Feedback: (2)

where did you see the movie?

R/C car guy

[link=http://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=12831]http://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=12831[/link]

If I remember correctly, it took longer than expected to download.

Edit: Had to change the link, couldn't link dirrectly to rcpics.net for some reason.

vizaracer

i think they wheelie because when you accelerate, all the weight of the truck is on the rear end and there is none on the front. so the truck from accelerating so fast, pushs the front end up and it does a wheelie. and the rear has such good traction. also to do a wheelie you have to be accelerating the whole time. if you get to your top speed or stay at a speed, the front wheels will lower to the ground. like on a motorcycle or dirtbike.

ICrashThings

u also wheelie because once u get that wind to push up your truck it sticks up...and keep speeding up or u will lose the wheelie.

R/C car guy

The flow of air hitting the bottom of the truck when you start the wheelie would only have a very minor effect on the wheelie. The truck isn't moving fast enough and the truck is too heavy for the little bit if air that it would catch to do anything major. Once again this is ONLY MY THEORY, and is probably only true in certain situations. Like when someone has an abnormally heavy truck, has a narrow chassis, is moving really slow, or is at a high altitude where there is thin air.

And I'm not asking how to do a wheelie, I'm asking what forces actually cause it too happen, so you don't have to tell me to continue accelerating to keep the wheelie. Not only did I not ask about how to keep a wheelie going, but it was already stated.

paperclipracer

My Feedback: (3)

its rear driven, to press the trigger down casueing the two back wheels to spin at top speed, causeing tourqe to be forced to the ground.
thus razeing the two front wheels off the ground. and like vizaracer was saying everythings mostly in the back. but this is not true for a t-maxx its spread out more. I think thats all i know. im sure thats why it happens

BOOCAKE4U

interesting subject...here's the quick n dirty version

on acceleration, weight is transferred to the rear, the rear suspension compresses, and the front wheels come off the ground...the higher the center of gravity and the shorter the wheelbase, the easier a given vehicle will pull the front wheels (this is why you will never see a 1:8 buggy wheelie unless it hits a bump WFO)...it also helps to have the rear suspension set up stiff but that eliminates the "bounce factor" where you can blip-blip-blip-waaaaa the front wheels off the ground (with an underpowered vehicle, which marvin's truck definitely isn't...hehe)

newbie003

man that video is sooo cool i bet that truck hits 60 easaly. and the sound of the truck is roaring man thats a nice project

paperclipracer

My Feedback: (3)

that VIDeo was cool

jwren00

the stiffer your suspension is in the back, the easier it is to wheelie. When people want to make their real cars wheelie, they have to basically lock up the rear suspension. If it is too soft back there, the rear will just squat. if it is stiff, then the acceleration will cause the car to rotate backwards, instead of just squat down. so yah, stiffer rear suspension = better wheelies.

vizaracer

if its looser, does that mean more accel then??

popuptoaster

the main reason you wheelie a vehicle is due to the axle trying to rotate around the tyres.

As your axle is trying to turn the wheels forwards, there is an equal and opposite reaction, which tries to make the axle turn in the opposite direction. simple physics.

normally this opposing reaction is cancelled out by the wheels slipping against the ground (wheelspin) or the weight of the vehicles front end.

so, put simply, if the force turning the wheels is greater than the weight of the front of the truck, and the friction on the tyres is also greater than than the force turning the wheels, something has to give, and the front comes up.

This is further complicated by suspension geometry, weight transfer and various other factors.

BUGGIES_R_US

Actually.. while the torque on the wheels is a factor, it'd take TREMENDOUS torque to cause a wheelie just because of that.. Try it with a model car!

R/C cars are over power to hell but in a real car, the engine is in the front and weight * wheelbase = HUGE number.

The forward acceleration working with the suspension.. in other words.. the sin of the acceleration is the major factor.
The bigger the difference in CG, the more likely you are to lift. You want HIGH acceleration in the beginning. This causes the front to lighten up due to weight transfer (increases the sine angle).
As you guessed, the responses are nowhere close to being linear..

popuptoaster

the twisting effect of the axle IS the major cause of a wheelie, if you set up stay bars from your axle to the chassis at the right points, you can actually force the rear of the car to rise under acceleration instead of the front, and a motor cycle with shaft drive will do the same as the pinion tries to climb around the crown wheel if its mounted on the right.

both of these effects can almost completly cancel out weight transfer and use the force of the twist to firmly plant the front. if this effect was so minor it wouldnt make any difference would it?

and before you say "why dont drag racers use this technique then? the answer is that they do to an extent, but its so good at cancelling weight transfer, you actually end up with less traction, and therefore less acceleration.

Also look at cars with leaf sprung suspension on the back, without anti tramp bars fitted, the axle will twist enough to actually wind up the spring if enough power is applied, until it releases very suddenly and causes the axle to hop from the ground. and thats with all the weight transfering onto it..

fantomracer

My Feedback: (1)

rongo!!!!!!!! did nobody pay any atention in physical science class or is it im taking that class now and its freash in my mind.........
any who

when a car is not in motion it has potential energy is changed to kinetic energy at a great rate pulling the car up causing it to wheelie.

thats probably not true but thats what my science teacher told me!!!!!!

popuptoaster

weight transfer does contribute to a wheelie, but its not as vital as the "wind up" effect. test it out yourself, if you got something driven by a reaction engine, and its mounted flat and level along the axle centre line, viola! MUCH less chance of a wheelie than from a wheel driven vehicle.

d16z6

Common people listen to popuptoaster. He right on in the simplicity of explaing the physics of a wheelie. Yes it maybe a combination of other variables, but when it comes down to it, it's the equal and opposite reaction of the torque applied to the axles.

Think about it, when you gun the throttle in the air and there is obviously no ground friction to counter act the torque force what does the car do? Most likely 9/10 times the nose pitches up while the wheels spins faster. Same goes for when it's on the ground and you actually have enough traction to keep the rear tires planted while there is still an extra amount of torque causing the "less weighted" front end to be lifted. If the front end was any heavier that it exceeds the moment (twisting force) around the rear axle then it wouldn't be doing a wheelie period.

This torque can also causes cars with inline shaft trannies to experience moment about the center shaft depending on which way the motor/engine spins. This is why some shaft driven cars will experience a "pull" to the left or right when accelerating. I bet if you put a motor with enough torque and a narrow wheel base you'd be able to make the car ski or start side tumbling on it's own. Now that would be [X(]

d16z6

One more thing as for those real 1:1 modified home build drag cars that have gobs and gobs of power at their disposal, when you see them launch you will notice that in some cars the frame twists and it will twist to a point where a front wheel will lift off the ground. This is another example of an equal and opposite reaction where the moment is exceeding the frame of the car which is supposed to counter act the engine's movements.

Of course this applies to RWD setups and possibly 4WD's too.

popuptoaster

i dont know any of the posh words or theoretical physics, but i built my first petrol powered go kart at the age of 7 from bits of machinery my dad had laying around (he was an agricultural engineer).

I dont remember too much about it, but my dad took it away from me when he saw my older next door neighbour doing 40moh up the hill outside our house on it.!!!!

30 years later im still a petrol head [8D]

PornstaR16L

I didnt want to read all of the posts on this thread but Im thinkin the best way for you to understand what is actually happening is to strap the wheels to the ground so that the power is not lost to slippage of the wheel. Now when the motor turns the drive train the axles but the wheels wont spin causing the chassis to rotate in a opposite revolution as the tire does on that side of the vehicle. Pretty simple to see it all in motion when this is done

Dekz

popuptoaster is the one that correctly explained it.

PornstaR16L has the best way of demonstrating it.

Hold the back tires of a car with your hands and hit the throttle, the tires can't spin so the car does instead. This is exactly whats happening on the ground. With enough power, and traction the car does a wheelie, not because of weight being transferred to the back, but because the car is trying to spin around the axel.

The weight transfer WILL help a little bit, both because of the force going backwards, and because it will push down on the back creating more traction.

All this stuff about lowering the center of gravity and the back end trying to go under the front end is garbage. The wheelie is caused by the torque.

gubbs3

My Feedback: (1)

The two biggest factors in a wheelie are CG and torque. Torque has been mentioned and yes it is a big factor. If you held the rear wheels and floored it the front end would want to lift up but there usually is just too much weight. That same vehicle may be able to wheelie even if the previous test didn't work because the center of gravity is above the rear axles. All the forward force is coming from the rear wheels, on a 2wd, so if the CG is above the axles it will want to tip backward as you accelerate. Its a combination of both that will produce a wheelie.

Spudnik

[X(][sm=spinnyeyes.gif] gubbs3 that is wrong (for the smilies, i just wanted to use the second on e fo r the first time). if you held the rear tires and give it wot then you would be pushing the tire into the ground, not lifting. as for how a wheelie is caused, i belive that it is the fact the truck is still and then it moves. the truck wants to stay still so the front end does so by lifting up.(when it lifts up it stays where it was). as for the cg is lower to the ground, that is wrong for a fact. the higher a cg is the more easiliy a truck will wheelie. aas for being pushed back in a car when it acleartes, that is because of one of the Newtos three laws....inersha (sound it out letter by letter(sorry about the spelling))an object at rest will stay at rest. that is the reason for a wheeloe to happen. the front whats to stay at rest so it lifts up to stay in the position it was at.

sorry if i made fun of anyone i didn't mean to.

newbie003

i was just wondering if a 1/10 nitro touring car can pop a whelie?