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Weight transfer due to drive torque!

  1. Nov 10, 2009 #1
    hi guys
    I read something interesting yesterday(atleast to me) that weight transfer can occur in a car due to drive torque from driveshaft to axle which causes axle to rotate. I found it strange that why drive torque in differential will rotate the whole axle(a small angle however).Can u tell me how it occurs?
     
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  3. Nov 10, 2009 #2

    Mech_Engineer

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    Here's a good example of some significant weight transfer due to drive torque and acceleration:

    http://img87.imageshack.us/img87/4149/mustangtorquedemotivaticg2.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  4. Nov 10, 2009 #3
    I love demotivational posters.

    R Power, simple mechanics casues this. Draw a free body diagram of a car and put on the forces and moments.

    All should become clear.
     
  5. Nov 11, 2009 #4
    I am talking about lateral weight transfer due to drive torque on axle. The weight transfer in the given poster in longitudnal which i can easily understand. But i am talking about lateral weight transfer due to drive torque. Plz explain.
     
  6. Nov 11, 2009 #5

    Ranger Mike

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    great poster..me being a dumb country boy..pls explain what you mean by lateral? becasue their is drive shaft weight transfer from left front to right front and left rear that takes place when you step on it ...
     
    Last edited: Nov 11, 2009
  7. Nov 11, 2009 #6
    By lateral i meant from from one side of wheels to other. e.g left to right. I mean to say about lateral axis of car.
     
  8. Nov 11, 2009 #7

    Ranger Mike

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    the engines firing order (american V8) rotates in a counter closewise direction. this means the left side of the engine will lift. ( i broke motor mounts and had to CHAIN the left side to prevent this). Efforts have been made in the past to make a reverse rotation engine but this requires a trick crankshaft, cam shaft and ignition.

    what you have is a high torque engine, trying to rotate in a counter closewise direction thru the clutch , transmission. this counter closewise direction is converted to a 90 degree direction by the differential. This counter closewise direction torque continues to the wheels and tires. if the tires are really hooked up to the asphalt, little or no tire spin occurs and the twisting effect has to go some where...so the tires spin or the clutch slips or engine motor mounts break. some times drive shaft U joints shear, some times transmissions break.
     
    Last edited: Nov 11, 2009
  9. Nov 11, 2009 #8
    Please tell clearly how the torque which rotates the axle and thus wheels through the differential, tends to transfer lateral loads.
     
  10. Nov 11, 2009 #9

    Danger

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    I had this problem with the Roadrunner. In fact, it's why I had to park it.
    The engine & tranny twisted over so far during acceleration that the torque tube for the clutch popped off of the pivots. I chained the intake manifold down to the shock tower to eliminate that, and the stupid thing started pulling the left front wheel off of the ground. After I switched to radial tires, it did both.
    Some idiot teenaged girl in a turbo 'Vette started harassing me when I was peacefully heading home from lunch. I tried to ignore her all across the mall parking lot, but when we got to the lights that turned onto the main street, she got really aggressive with burping the throttle and glaring at me. I figured that it was time to tune her in. We were on a dual left-turn intersection, with her in the right lane.
    When the light changed, she smoked around the corner. I eased out until I was straight, then romped on it. So far, so good. I went past her pretty quickly. A block later, just passing through the first set of lights, I power-shifted into 2nd at 65 mph. Much to my delight (not!) the clutch pedal stayed on the floor. The irritation of that was offset by seeing the 'Vette slink off onto the cross-street.
    (For anyone who knows Calgary, this was coming out of Sunridge Mall onto northbound 36th.)
    Anyhow, I couldn't afford to fix it. That was over 25 years ago, and it's been sitting in my yard ever since. :frown:
     
  11. Nov 11, 2009 #10

    Ranger Mike

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    I know what you mean...i bought my Roadrunner because some zitty faced pencil neck geek in a 1992 Buick with NO FEAR decal in the rear window bugged me at a traffic light..
    funny how once you race you always hanker to race!
    bottom line is torque is real! chain that puppy down!
     
  12. Nov 11, 2009 #11

    Danger

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    Take a closer look at the picture. Notice that the left front wheel is about twice as high off of the ground as the right one. That is the result of driveline torque acting upon the chassis and body. Given how much that body is twisted, think about what the effect upon the rear wheels is.

    Hey, Mike. Yeah, it do get into your blood. I can't stand the way kids do it nowadays, though. That's just stupid and deadly, to themselves and innocent bystanders. My friends and I were always very careful that we had unobstructed good pavement in a straight line, with lots of deceleration room. In the episode that I outlined, for instance, we were the only 2 cars within a couple of blocks. I knew the synchronization of the lights, so there was no worry of the first intersection going red on me. Just the same, if a car had been approaching on that side-street within half a block, I would have backed off in case it didn't stop. (That was a T-street, by the way, so I had only to watch one way on it.) These guys who chase each other through the streets like rats on bennies are a disgrace.
     
    Last edited: Nov 11, 2009
  13. Nov 11, 2009 #12

    Ranger Mike

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    Yeah I know..earlier this year i was pretty bummed out about this younger generation..until i had my toys for tots volleyball tournament on labor day..it was raining very heavy but about 30 kids 20 to 30 years old showed up to play in the rain, on their day off work just to get a cheap plastic trophy ..after the final game and after the award cerimony ..they ALL stayed around to continue to play..in the rain and in the mud...so there is hope !
     
    Last edited: Nov 11, 2009
  14. Nov 11, 2009 #13

    Danger

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    I can't speak toward their common-sense, as to not coming in out of the rain, but it certainly beats what they could have been doing instead.
    By the bye, was that a typo? Did you mean toys for tots? I've heard of that, and think that it's a great cause. The way you typed it, it sounds like a kindergarten dating service. :tongue:
     
  15. Nov 11, 2009 #14

    Ranger Mike

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    good catch Danger..
     

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  16. Nov 11, 2009 #15
    OK I can see the left wheel is twice high. But why?
    I mean can u explain me physics of this??
     
  17. Nov 11, 2009 #16

    Ranger Mike

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    the engines firing order (american V8) rotates in a counter closewise direction.
    this means the left side of the engine will lift.

    what you have is a high torque engine, trying to rotate in a counter closewise direction.
    this rotating force goes thru the clutch , transmission.
    this counter closewise force changes direction by 90 degrees by the differential. This counter closewise torque continues to the wheels and tires. if the tires are really hooked up to the asphalt, little or no tire spin occurs and the twisting effect has to go some where

    the result is the twist you see in the photo
    either the tires spin or the clutch slips or engine motor mounts break. some times drive shaft U joints shear, some times transmissions break.
     
  18. Nov 11, 2009 #17

    Danger

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    I'm not sure why, Mike, but after looking at that picture I have a sudden urge to go out and pick a couple of lemons.

    R Power... I am going to assume that you know how a car engine works. (I don't mean that insultingly... some people don't know.) In North America, at least, the working bits rotate counter-clockwise as viewed from the driver's seat. Whatever amount of torque is applied to the crankshaft, flywheel, clutch, transmission etc. is countered by an opposite torque applied to the engine block, motor mounts, K-member, rear suspension... (action/reaction, in obedience to Newtonian law). The whole vehicle tries to twist in the opposite direction to that of the crankshaft, which sets a pre-load condition upon the round rubber bits that connect it to the road.

    edit: I see that you beat me to it, Mike. Good post.
     
  19. Nov 11, 2009 #18
    It's comedy how honkin great V8's can twist the chassis up like a corkscrew.
     
  20. Nov 11, 2009 #19

    Danger

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    Only until you have to shell out a few thousand bucks to alleviate the problem.
     
  21. Nov 11, 2009 #20

    Ranger Mike

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    teachable moment- this into compact unibody cars..e funny car scene hit in the early 1960s. was NHRA class A/FX which was Factory eXperimantal. this was Detroit stuffing huge 400 plus cid V8s into comapct unibody cars...these unibody desighns did not have the heavy full channle frames on which the body was bolted. unibody deign used a stamped sheetmetal floorpan and relied on the windshield and sheetmetal roof / pillars to tie the body together...anyway..when you nailed the throttle the twist would crack the windshield so we have to tie the front and rear sheet metal channels together to reinforce the body...NHRA mandated a full roll cage that took care of this problem, we welded in tubing to connect the rear spring mount points to the main roll cage hoop and ran tubing to the front end to tie in the whole pan. this reinforced the floor pan and assisted in weight retransfer to the rear. we still had twist but could control this with traction bar setting or pinion snubber setting , springs and shocks..
     
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