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?
Where are the reactions for a longitudinal engine ?
Rider sidewise lean?





RE: Longitudinal motorcycle engine - torque effects
RE: Longitudinal motorcycle engine - torque effects
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
RE: Longitudinal motorcycle engine - torque effects
RE: Longitudinal motorcycle engine - torque effects
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
Kinda fun after you got used to it.
RE: Longitudinal motorcycle engine - torque effects
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
RE: Longitudinal motorcycle engine - torque effects
RE: Longitudinal motorcycle engine - torque effects
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
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
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
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
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
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
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
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
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RE: Longitudinal motorcycle engine - torque effects
RE: Longitudinal motorcycle engine - torque effects
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
Rod
RE: Longitudinal motorcycle engine - torque effects
Please post more videos.
- Steve
RE: Longitudinal motorcycle engine - torque effects
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
RE: Longitudinal motorcycle engine - torque effects
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
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
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
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
- Steve
RE: Longitudinal motorcycle engine - torque effects
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
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
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
So... was that air-time on the Beemer the impetus to start you on an aeronautical career?
RE: Longitudinal motorcycle engine - torque effects
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
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!
Rod
RE: Longitudinal motorcycle engine - torque effects
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.
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
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
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
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
RE: Longitudinal motorcycle engine - torque effects
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
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RE: Longitudinal motorcycle engine - torque effects
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
RE: Longitudinal motorcycle engine - torque effects
RE: Longitudinal motorcycle engine - torque effects