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Longitudinal motorcycle engine - torque effects

Longitudinal motorcycle engine - torque effects

(OP)
Lateral engine torque reactions are produced at the wheels.
Where are the reactions for a longitudinal engine ?
Rider sidewise lean?  

RE: Longitudinal motorcycle engine - torque effects

Draw a FBD

RE: Longitudinal motorcycle engine - torque effects

In steady state conditions, the torque generated at the engine/transmission is opposed at the 90-degree gear drive in the final drive.

During acceleration conditions, the rider has to oppose the torque that it takes to accelerate the flywheel and crankshaft and everything else. When riding, the rider does have to lean slightly, although the effect is so small when riding that it's hardly noticeable.

Go to a BMW dealer, test-ride an R1200GS. Or even test-sit with the engine running. Give the throttle a big handful in neutral and tell us what you feel.

RE: Longitudinal motorcycle engine - torque effects

Don't know about motorcycle engines, but I am told that when you blip a longitudinal V8 car engine in a bike, the block tries to rotate around the crank and flywheel mass. That could get interesting.........

RE: Longitudinal motorcycle engine - torque effects

The situation is exactly the same. 'Course, the BMW bike engines have nowhere near as much inertia, so the magnitude of the torque reaction is a lot smaller.

RE: Longitudinal motorcycle engine - torque effects

The torque reaction is not _that_ small.  
You can see it while driving behind a BMW or MotoGuzzi or GoldWing or whatever.  
Whenever the rider grabs a good handful of throttle, or closes the throttle quickly, the whole bike rolls around a longitudinal axis.
I assume the riders learn to ignore it.




 

Mike Halloran
Pembroke Pines, FL, USA

RE: Longitudinal motorcycle engine - torque effects

My "classic" 1275S Mini Cooper would change lanes under power
Kinda fun after you got used to it.

RE: Longitudinal motorcycle engine - torque effects

I rode a new Moto Guzzi in 1967, a 700cc touring bike. Having gear drive in place of a chain was nice, but the torque reaction to angular acceleration of (mainly) the flywheel/clutch was annoying. I noticed that during every spirited up- or down-shift, the resulting track of the bike had a little 'S' curve in it. So, for about forty years, I put up with chain drive. Then, a few years ago I sat on a Guzzi V50III (500cc, 49 HP) and observed only slight reaction to engine acceleration in neutral. The V50 apparently has a flywheel/clutch with a severely-reduced polar moment of inertia. I've been quite happy riding it for many thousands of miles.

Incidentally, the mention in an above post of the torque reaction to the driveshaft torque has no bearing on this discussion, as it is totally resolved within the machine.

For whatever it's worth: to experience practically zero torque reaction with a longitudinal engine, find yourself an antique (fifties and earlier) BMW R25- traditional boxer layout with a 250cc single! [I borrowed one to ride for my European bike license test (a LONG time ago)- figure-eights were a piece of cake!]

RE: Longitudinal motorcycle engine - torque effects

Yeah, okay... it's difficult for a single cylinder to be a "boxer". But ya' all know what I meant...

RE: Longitudinal motorcycle engine - torque effects

At low rpm and heavy throttle the torque variation from the individual firing strokes are very noticeable on an R60/7 BMW

RE: Longitudinal motorcycle engine - torque effects

I rode a Goldwing for years.  Honda has the torque reaction tuned out to a fair degree, mtr mounts, whatever.  Correct in that after you ride for a while, engine tq is just not noticeable to any drastic degree, very low CG for a bike.  I guess you just get used to it.  The most difficult thing for me was adjusting to the width of the Honda.
BMW, very noticeable and I dislike the exhaust note.
Moto G...not too bad, I disliked the 'linked' braking system.

I race a 150hp Mini...You have no idea what 'torque steer' is until you put your foot down hard in a tight turn with limited slip diff...

Rod

RE: Longitudinal motorcycle engine - torque effects


  A 150hp Mini might have a mind of its own but a normal road Mini should not change lanes etc. - possible cause is steering or suspension ball wear.    

RE: Longitudinal motorcycle engine - torque effects

I had a small Japanese FWD hatch with a twincharged engine.
Under acceleration it would rock from side to side, and weave under acceleration, classic torque steer.

Converting the same car to four wheel drive with a 60R/40F torque split fixed the problem.

Bikes are fun, but rain, not being able to carry anything bulky, and seeing the scenery upside down a few times converted me to four wheels.

RE: Longitudinal motorcycle engine - torque effects


  The usual reason given to explain torque steering (in a FWD car) is that the drive shafts are of unequal lengths. This may be correct but I have to say that I cannot see why this would effect the torque applied to each wheel. Generally speaking, the length of a shaft does not effect the amount of torque transmitted.
 
 One thing I do know (and have had experience of) is changing the scrub radius of a tyre - this certainly will change the torque steer effects.      

 

RE: Longitudinal motorcycle engine - torque effects

Torque reactions in the steering of front-drive cars are obviously way off the original topic, but anyhow ...

The trouble with unequal half-shafts is that the centerline of the diff is not aligned with the centerline of the hubs - partly because ride height is never exact and partly by design, because universal joints don't like running absolutely straight - usually the diff is a little forward or aft of the hub centerline and a little higher than nominal ride height.

If the halfshafts are unequal lengths then the angle of the halfshafts is also unequal.

A universal joint that is not straight, exerts forces on its mountings.

Since the steering axis is not absolutely perpendicular to the drive shafts (it is always inclined inwards and there is always positive caster) there is a component of the reaction forces around the outer CV joint that is aligned with the steering, and because the angles are unequal left to right, it's different between left and right.

If the steering is not aimed straight ahead, then that introduces a whole bunch more reasons for torque reactions.

Regarding U-joints not wanting to run absolutely straight ... even in rear-drive cars with prop shafts, some measures are generally taken to ensure that the drive shaft is never completely straight. Sometimes the entire driveline is shifted slightly to one side (Mopars). Sometimes the input shaft to the axle is offset slightly to one side.

RE: Longitudinal motorcycle engine - torque effects

Te effects of torque steer I was seeing on my own car were most likely due to positive caster and large scrub radius.
 
As we all know, positive caster adds stability in a straight line, and even more so during heavy braking. But positive caster also has the exact opposite effect when tractive effort is applied at the front wheels. The contact patch being behind the steering axis. If there is also a significant scrub radius (either way), this can lead to trouble if the front wheel wights change from side to side.

In low powered FWD cars it is not that serious, but with a lot of power, the tractive forces are much greater.

What I was getting was the car started to gently rock gently from side to side under acceleration, creating a slow cyclic body roll. The weight being transferred from side to side at the front,  causing the car to weave.
The front was also much raised in height during this acceleration.

This weaving and rocking would be self reinforcing, gaining in amplitude. that, and the very light steering, becoming quite disconcerting.
Trying to correct for it only made it far worse.
Best to just hang on grimly and back off a bit....

I believe the cause was the combination of caster and excessive scrub radius, the lateral weight transfer and tractive effort combining to self steer the front wheels. This steering causing more body roll, which created more self steering.

The drive shafts on this particular car are of identical length, but I have never understood the often quoted theory that unequal driveshaft lengths can somehow steer the car.

I am working on the design of a four wheel drive hot rod right now, and plan to run zero front scrub, and only about three degrees of caster.
All quite interesting.

RE: Longitudinal motorcycle engine - torque effects

Weaving and rocking like that happens in RWDs with Posi.
I have the impression that Torsens are less quirky, or at least don't have that quirk.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Longitudinal motorcycle engine - torque effects

Thanks warpspeed for the info.

I only ever did suspension mods on RWD cars before and developed a taste for lots of castor. I had not considered the issue of lots of castor on FWD.

I am always inclined toward pretty much neutral or slightly negative scrub after having to wrestle with kick back on Toranas with 7" rim widths.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: Longitudinal motorcycle engine - torque effects

Pat, I much prefer rear wheel drive, but these days most smaller cars do not offer much choice.  FWD works pretty well, until you start to push the limits.

RE: Longitudinal motorcycle engine - torque effects

"I race a 150hp Mini...You have no idea what 'torque steer' is until you put your foot down hard in a tight turn with limited slip diff."

Man, I wish I still had the thing, a victim of a divorce. Rod, have you seen the Honda Conversions for the "classic minis"? I bet that would be a hoot!

RE: Longitudinal motorcycle engine - torque effects

A friend and fellow Mini racer does these conversions.  Some are quite nice, some are a bit over the top.  I saw a Clubman conversion with a 1600 VTEC that was quite nice. Street ready at <1500 lbs with 150+ hp.  Tractable, good fuel mileage and not a handfull to drive.  My race car is the antithesis of this...

Rod

RE: Longitudinal motorcycle engine - torque effects

Rod,

Please post more videos.

- Steve

RE: Longitudinal motorcycle engine - torque effects

I post them all on YouTube (eventually) under "evelrod's videos"

http://www.youtube.com/my_videos

I'm not too good at editing...wow, that's an understatement...If I can get my son to edit the raw footage from Chuckwalla I'll add it.

This is one from a BMW 2002 that shows my very wounded white #130 Mini being lapped.  It was posted to add to my campaign to have the dangerous pit wall changed before someone gets killed.

http://www.youtube.com/watch?v=NgVvi5LgqVA

Sorry for the hijack, amorrison.  This really should be in the Pub, Steve.

Rod

RE: Longitudinal motorcycle engine - torque effects

I believe both Ford and GM have come out with a new front end design that moves the upper pivot point to the top of the spindle (from the top of the McPherson strut), reducing the scrub radius and resultant torque steer.

RE: Longitudinal motorcycle engine - torque effects

BrianPetersen - you wrote above "A universal joint that is not straight, exerts force on its mountings"
 Is this another way of saying that a CV joint operating under load at an angle will attempt to straighten itself out?

 When a car is accelerating in a straight line (when most people notice torque steer) the difference in CV operating angles from each side of the car must be very small - a few degrees at most - surely not enough to cause torque steering effects?

RE: Longitudinal motorcycle engine - torque effects

I really don't think the tq-steer problem has much to do with u joints, cv joints or, even unequal length axles, all being in top condition.  From my observation, it is much more prevalent under traction conditions that are not equal, side to side.  Under acceleration should one tire get more traction than the other (FWD) the car is likely to pull to that side.  This phenom is observable under braking as well. A limited slip diff could possibly mitigate this but, limited slips on FWD's are not viable without some power assist on street cars.  Electronic traction control has made great strides but, again in my experience, has not completely cured the so called tq-steer of FWD under limited traction conditions.

Also, pertaining to broken axle in a RWD race car...obviously I would not drive a street car with a broken axle...tq-steer is very evident. I did not break an axle to find out, it sorta found me.

Rod

RE: Longitudinal motorcycle engine - torque effects

Certainly unequal grip will give torque steer, but I've driven a few very old-design front-drive cars that torque steered during acceleration at well below the traction limit on dry pavement while driving straight ahead on level ground. I've owned a front-drive car with unequal half-shafts (first-generation Honda Civic) in which the steering wheel moved visibly (if you didn't manually stop it from happening) on every gear change! It's not a grip issue. I test-drove a Suzuki Swift once upon a time which did this even worse than my Civic did.

Back then, you just got used to the way the car drove, and dealt with it.

It's very true that the angle of the half-shafts is small, and there is a big mechanical disadvantage of that torque reaction back to the steering wheel - but the drive force at the wheels is vastly higher than the torque the driver applies to the steering wheel (these cars were all manual steering - no power steering mechanism to cover it up).

RE: Longitudinal motorcycle engine - torque effects

It is not normally very easy to do a back to back test on the same car with similar versus different front driveshaft lengths !
But I have had the opportunity to do exactly that.

In Australia the Mazda 323/ Ford Laser comes normally aspirated with unequal driveshafts, turbo with a different gearbox and equal front driveshafts, and 4WD turbo, also with equal length driveshafts.

The normally aspirated (with only 55Kw stock) did not torque steer, but it sure did when a turbo was fitted.
Upgrading to the turbo transmission with equal length driveshafts, and the same identical car and turbo engine, it still torque steered just as badly.

Upgrading again to 4WD, with the same car and engine, there was no evidence of any torque steer whatsoever. It just went where it was pointed.

I might suggest that very high front tractive effort, along with less than ideal suspension geometry is what causes torque steer.  
Feeding less power through the front makes it pretty benign, no matter what it is.
But the problems of directional stability multiply rapidly as front tractive effort is increased.

RE: Longitudinal motorcycle engine - torque effects

I created a full model of a Fiat Tipo powertrain many years ago (in ADAMS).  It had unequal length half-shafts.  It was driven through an engine model, with throttle angle being the only dynamic input.  I was very amused/impressed when it exhibited torque steer.

- Steve

RE: Longitudinal motorcycle engine - torque effects

The issue with torque steer is that you are dealing with controlling torques of the order of 300 Nm via a sensing system that can resolve 0.3 Nm, regards 25 Nm as a maximum, AND has a 17:1 mechanical advantage. Almost any errors in cancellation will be sensed.
 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Longitudinal motorcycle engine - torque effects

In 1977 I was loaned one of the first BMW R100RS Boxer twins in the UK for the afternoon.

I got a bit carried away trying to see how fast it was (about 125mph) and it got airborne over a bump on the A19 near Thirsk in Yorkshire. I snapped the throttle shut and it rolled to one side in mid air. Very frightening at the time because it landed back on its wheels leaning the wrong way for the next bend which I was rapidly approaching....

Didn't do that again.

RE: Longitudinal motorcycle engine - torque effects


  Warpspeed - I was interested to see your comments on the non-turbo and turbo Mazda 323.
 I wonder if some torque steer in a powerful FWD car can be just due to the various rubber bushes in the suspension deforming/deflecting under the increased load and allowing the wheels to move about and do a bit of unasked-for steering.    

RE: Longitudinal motorcycle engine - torque effects

As you know the 323/Laser uses a typical strut type front suspension.

While high lateral cornering forces will certainly create some definite compliance steer, pure tractive effort should not.
The front wheels may move forwards slightly due to rubber compliance, but there is nothing there to cause the front wheels to steer.

Put another way, the steering arms, and lower control arms remain unloaded from tractive effort, and it is the relationship between these two that provides the normal steering input to the front wheels.

Torque steer either has to come from the drive shafts or the contact patches.

My money is on the contact patches not being directly centered on the steering axis.  But others here seem to feel very strongly that unequal drive shaft length can steer the wheels.

Question.
If you have a long drive shaft, and a short drive shaft, which way will the vehicle torque steer.  Will it ALWAYS pull the same way ?  It absolutely must if that is the root cause.

So why does the vehicle weave instead of just pulling strongly one way if drive shaft length difference is the true cause of torque steer.

Not trying to be difficult, just trying to get my head around the unequal drive shaft length causing torque steer theory.

RE: Longitudinal motorcycle engine - torque effects

PEW- thanks for sharing that episode with the BMW boxer. That's something I never experienced (and don't want to). I'm curious whether you also detected a pitching moment while airborne? If so, was it an up- or down-pitch (I have trouble remembering/applying the rule of gyroscopic torques!)?

So... was that air-time on the Beemer the impetus to start you on an aeronautical career?

RE: Longitudinal motorcycle engine - torque effects

Warpy - if the lower arms remain unloaded from tractive effort - what does transfer the tractive effort from the wheels to the chassis?

 I am inclined to agree about the contact patches not being centered being likely culprits.

 One reason that I think the unequal shafts may be the cause (although, like you, I still can't see why) is that a lot of car companies have spent a lot of money to arrange equal length drive shafts - surely their testing showed them that it reduced (at least) torque steer.  
    

RE: Longitudinal motorcycle engine - torque effects

HEHtex---

 

Quote:

One reason that I think the unequal shafts may be the cause (although, like you, I still can't see why) is that a lot of car companies have spent a lot of money to arrange equal length drive shafts - surely their testing showed them that it reduced (at least) torque steer.

Hmmmmm.  Seems I heard that particular line of reasoning once or twice...

pontiacjac---

Jumping on a dirt bike, I revved the engine to pull the front up, chopped the throttle to drop the front wheel. When I was younger, had a lot of practice at that.  Kinda miss it, too.

Warpspeed---

I agree with the others here that some anomaly in the suspension certainly can cause tq steer but I maintain that it is caused primarily by traction issues.  My little car has lots of power, unequal length axles and soft, fat tires.  It tends to steer if one wheel has a bit less traction, never the same way each and every time, more prevalent at low speeds and, very difficult to control with any steering input at low speeds.  I've posted several videos where you can see all this in action.  A racing Mini Cooper is just not a car you can, as my dad put it, "loose heard" down the road.

Also, as I said before...I've only driven a few FWD cars and I never felt any difference from any other cars I've owned.  Of course, most all my driving is in sunny, dry SoCal.  Also I'm not the greatest driver on the street so I don't push the issue.  My few times racing in the rain, I'll take a FWD over a RWD, any day!  clown

Rod
 

RE: Longitudinal motorcycle engine - torque effects

Tex, the lower lateral link is not as heavily loaded during braking and acceleration as it is in cornering.
It is the radius link that suffers most of the pushing and pulling, during braking and acceleration.
I know it is not really all that clear cut and simple, but you can probably see what I am trying to get at.
Side to side compliance movement of the lower ball joint will steer the wheel. Fore and aft compliance movement of the lower ball joint should not.  

Quote:

My little car has lots of power, unequal length axles and soft, fat tires.  It tends to steer if one wheel has a bit less traction, never the same way each and every time, more prevalent at low speeds and, very difficult to control with any steering input at low speeds.

That is precisely what I am seeing too Rod.
The key words being never the same way each time.
But the short drive shaft is always on the same side ?
If drive shaft length was the the true fundamental cause, it surely must show a preference to always pull one way ?
 

RE: Longitudinal motorcycle engine - torque effects

Some cars definitely torque steer predictably. Some cars 'squirm'  or dart under acceleration. I'm not convinced they are exactly the same thing. I can easily believe that darting is caused by a positive feedback mechanism at the contact patch.

Incidentally a CV joint at an angle behaves as a force amplifier, generating various reaction forces proportional to the torque it is transmitting.

The Rev O Knuckle and the like are a good shot at removing most of the geometry errors and so on (I had to say that the guy at the next desk is one of the patentees), yet if you stick enough torque through them even with equal length driveshafts you get some sort of torque steer again.

It seems to me that if you have equal length driveshafts and no silly errors, you don't get too much torque steer up to about 200 hp.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Longitudinal motorcycle engine - torque effects

Thanks Greg.
There are probably several potential causes of torque steer, and as you say, more torque and tractive effort multiplies whatever is going on.

RE: Longitudinal motorcycle engine - torque effects

Quote:

Fore and aft compliance movement of the lower ball joint should not.

Wouldn't that imply zero Ackermann correction / true parallel steer?

There would still be vertical effects and bumpsteer.


Norm

RE: Longitudinal motorcycle engine - torque effects

If the steering tie-rod is not absolutely parallel with the main lateral lower suspension link (not the trailing link) then fore/aft compliance movement certainly could have some steering implications.

RE: Longitudinal motorcycle engine - torque effects

Unless the tie rod and lower link are very seriously out of parallel, it would take a substantial fore and aft movement to create a very small toe change. I have never seen one that is more than a few degrees off parallel.

It also depends on the upper lateral arm and how the steering arm is positioned relative to both arms as they are often out of parallel in both plains to control camber and anti dive.  

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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for site rules
 

RE: Longitudinal motorcycle engine - torque effects

I don't notice the torque reaction much on my '87 BMW R65,it's only when starting and taking off that I notice it,otherwise it rides just like a normal motorcycle.The R65 has a lighter flywheel and shorter stroke than the bigger BMW's,but I don't even notice on them.

I have noticed it much more on Moto Guzzi's - they actually require opposite lock under hard acceleration at low speeds (1st gear),and will pull the bike down under power exiting right hand corners,and are self righting exiting left hand corners.Even though the effect is noticeable,there is no problem riding the bikes,you just adapt.

RE: Longitudinal motorcycle engine - torque effects

Lada- Please don't lump all Guzzis together. I've done a one-on-one comparison with a friend's R65, and my Guzzi V50 has less polar inertia of flywheel/clutch.

RE: Longitudinal motorcycle engine - torque effects

I have noticed that my BMW's give you an interesting torque reaction if you have backed up to a curb, then go to start up and leave. The rear wheel being pinned increases the reaction to the machine that can be somewhat disconcerting if you're not expecting it.

RE: Longitudinal motorcycle engine - torque effects

I didn't mention the V50 - because people tend to lump all Guzzi's together.I have a Stornello 160 - even Guzzi riders don't know what I'm talking about.I've ridden the V50,and it has almost no torque reaction at all...I just notice squat when backing off in corners,but that's more a shaft drive thing.The V50 has a different engine package to the bigger bikes,the R65 is basically a short stroke 750,particularly my mono which has the same frame as the bigger engines.  

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