Conering During The Power Band Of A Motorcycle, Will It Slip?

[bloodrun]

Hi,

 

I'm riding a Fireblade and have been riding on the track for a couple of months already. Really love the power delivery of the machine. Due to to it's smooth power delivery i've manage to increase entry engine rpm at a higher rate.

 

In the mean while, i;ve wonder if the bike riding at higher rpm near to it's maximum torque rpm, will the tyres still be able to hold traction?

 

Say for instance, the rpm at 11,000 rpms pulls 82ft of torque, will these torque knock the tyre out of traction when the bike is lean over? Or during riding, we should always place our rpm at a lower rpm range and open the throttle slowly & smoothly toward maximum torque? i've seeing racers in the 600 super sport class conering near maximum torque limit not sure if it's applicable in the 1000 cc class catergory.

 

 

Look fowrard to hear the floor.

[tmckeen]

I'd say that really depends on the tires your using, while I doubt you'd be able to overpower a full on race slick I'm sure you can overpower a sport touring tire

 

Tyler

[csmith12]

So many factors here....

 

In the wet a ninja 250 with 27hp can break loose the rear. Under perfect conditions, there is not enough power to spin it up. So yea, depending on your tire compound, tire temp, lean angle, speed, track surface and so on... a rider could loose traction due to throttle inputs. Some even spin it up on purpose, as it's their "style". One must alter their riding for the conditions their riding in, even if it's just "take it easy the first lap until your tires warm up".

 

It's common for me to be just under the rev limiter at corner exit. So yea, I enter a lot of corners at or near max torque. Just gotta try to leave yourself some roll-on room because shifting mid corner is not preferred but it does happen depending on the rider, line through the corner and so on, think long sweepers.

 

Having put some time in on an older fireblade, I completely understand why you want to keep the revs up. Even though she was smooth all the way through, at least for me the bike felt so much better at a higher rpm. Maybe because I normally ride an r6.

 

What makes you ask? Just curious? Have you experienced slipping mid corner?

[Cobie Fair]

As CS pointed out, a few factors here.

 

Have you had a look at the Twist of the Wrist 2 book or DVD yet? Or been to the Superbike School? I'm assuming not, but like to check. Balancing the bike tires, suspension, engine is a pretty broad subject, and the Twist 2 materials give a great guideline. Just let us know if you have had a look at that, then we can go from there.

 

CF

[bloodrun]

Yes Cobie, i've watch twist of the throttle 2 as well as been to lesson 1 of the super bike school at philip island australia. Understand that we have to roll on the throttle smooth towards the exist of the turn.

 

Couple of days ago, my friend who also rides a fireblade on Sepang international race circuit had a suffer a major high side. He broke his pevis bone on a long left hand corner.

I met him a couple of day ago after his recovery also to understand the reason behind his mistake to his crash. He explain of his process with an entry at a higher rpm range (which is about 9-10 rpm which he could remember). If it is on the fireblade, the torque curve than is close to maximum torques range of that in-line 4 engine. The next time he knew, his ride rear slip than his front wobble and he got sprung out of his ride into mid air.

 

Listening from his explanation, it sounds like he had a slip on this rear tyres, than shut off the throttle and than his front just gave way. (correct me if i'm wrong) That enables me to re-think corner entry near max torque.

 

How much affect will it cause?

[YellowDuck]

Maybe I'm missing something, but I think the question doesn't make total sense. The engine output is a function of rpm *and* throttle position. In a certain rpm band you are going to have max torque at wide open throttle (WOT), but the *range* of torque available at that rpm, depending on throttle position, is anything between zero and that WOT max torque. Actually, the range of torque available is between the max and some fairly negative number because with closed throttle your will have negative torque (engine braking) - the max negative torque will be greater at high rpm, unless you have a slipper clutch which limits back torque.

 

I don't think the real danger is cornering in an rpm band where you have max torque. The more dangerous scenario is opening the throttle while cornering in an rpm band where the torque curve rises very sharply. That can become difficult to control, and lots of inline 4 bikes have a part of the torque curve where there is a large and sudden step.

 

Kevin Cameron once wrote an article in Cycle World speculating as to the technical reason why V-twins were dominating superbike racing at the time. His idea was that, since the V-twins of the era generally had declining torque curves at high rpm, when a rider broke the rear loose on cornering and spun up the engine, the torque would naturally decline, making the spin easier to control, whereas on an inline 4 you would get the opposite effect. This was in the era before electronic traction control.

[YellowDuck]

 

 

Listening from his explanation, it sounds like he had a slip on this rear tyres, than shut off the throttle and than his front just gave way. (correct me if i'm wrong) That enables me to re-think corner entry near max torque.

 

How much affect will it cause?

 

Actually sounds like a classic high-side. Rear spins up and steps out to the side, rider closes throttle suddenly, rear regains traction and the bike snaps back into line violently, standing up and tossing the rider out of the seat. The error (other than applying too much throttle and causing the rear slide in the first place), is closing the throttle suddenly when the slide is detected.

[Lnewqban]

......Listening from his explanation, it sounds like he had a slip on this rear tyres, than shut off the throttle and than his front just gave way.....

 

It didn't have to end up that way:

 

 

The available torque translates into additional longitudinal force on the rear tire's contact patch.

 

The acceleration that the bike is experiencing during a turn is the best thermometer of the magnitude of that additional force.

 

In order to put invisible forces in perspective:

 

- The recommended 0.1g ~ 0.2g acceleration (gain of 2.2 ~ 4.4 mph per each second on the turn) is the result of an additional longitudinal force on the rear patch which is equivalent to 10 ~ 20% of the bike-rider combined weight.

 

- At 45-degree lean angle and under the recommended acceleration, that rear patch will be stressed with a lateral force equivalent to 60% of the bike-rider combined weight.

 

The above forces combined result in an actual lateral load on the rear patch of 61% ~ 63% of the bike-rider combined weight.

 

- Heavy braking while upright can stress the front contact patch longitudinally as much as 85 ~ 100% of the bike-rider combined weight.

 

- During the extreme case of a burn-out, the longitudinal force on the rear patch overcomes the traction of it, which in that case is around 50% of the weight of the bike (the rider usually stands up on the pavement to reduce tire traction).

 

As Acceleration = Torque / Combined weight, the acceleration that your body feels is proportional to the torque that the rear tire feels.

[khp]

The engine output is a function of rpm *and* throttle position. In a certain rpm band you are going to have max torque at wide open throttle (WOT), but the *range* of torque available at that rpm, depending on throttle position, is anything between zero and that WOT max torque.

This seems quite confused to me. Last time I checked, the torque was ONLY decided by the RPMs., not your throttle position.

How would the maximum (ie peak) torque change with RPM - there is only one point with the peak torque.

[bloodrun]

Pardon me, but according to keith code, the throttle has to be open the as soon as possible to stable the bike and than gradually roll on the throttle as bike proceed to the exit of the turn. Cracking 1/3 of the throttle in the turn than only the bike will start to accelerate.

 

My question is, if we enter a corner by choosing a lower gear, or by gradually roll off, assume that as soon as we open the throttle, the rpm rise 200 rpm and it hits maximum torque of the bike machine. Will it be safe? will the torque knock out the tyre under minimum acceleration or should i say the right way of riding is to drop the rpm further and accelerate slowly out of the corner? This question has float in my mind for a certain time as i'm asking my self i could roll on the throttle a little sooner just to accelerate out of the corner as soon as possible.

 

For a V-twin, all the torque of bike is on the low and mid rev. Recently i had a friend that got a little greedy over the throttle during his hang off position and he got thrown out of the bike. But surprisingly his bike rear tyre sill manage to hold onto the ground

[Lnewqban]

.......My question is, if we enter a corner by choosing a lower gear, or by gradually roll off, assume that as soon as we open the throttle, the rpm rise 200 rpm and it hits maximum torque of the bike machine. Will it be safe? will the torque knock out the tyre under minimum acceleration or should i say the right way of riding is to drop the rpm further and accelerate slowly out of the corner? This question has float in my mind for a certain time as i'm asking my self i could roll on the throttle a little sooner just to accelerate out of the corner as soon as possible.

 

Since the rear tire and the crankshaft are solidly connected, opening the throttle will increase the torque delivered by the engine, but the crankshaft will not rise 200 rpm immediately; the rpm's will increase only after the rear tire overcomes the inertia of the bike and increases its speed (acceleration), which will increase the rpms' of the rear tire.

 

Many riders purposely enter turns with high gear and the engine working on the weakest portion of the torque curve (very low rpms') in order to minimize the chance of loosing grip due to accidental over-torque (due to "being too "greedy" with the throttle at roll-on").

However, that is just a crutch to compensate for poor throttle management.

 

Again, the throttle is your supplier of torque; learn to manipulate it with micrometric precision, on and off.

The gear you choose only gives your engine more (lower gears) or less (higher gears) leverage over the rear tire.

 

From Twist of the Wrist II:

 

"By the numbers, we want to transfer 10 to 20% of the weight rearwards, using the throttle.

Technically, this is 0.1 to 0.2 G of acceleration.

Simply put, it's the force generated by a smooth fifth-gear roll-on in the 4,000 to 6,000 rpm range on pretty much anything over 600 cc.

That's not much acceleration, but it does the job.

It seems riders often have difficulty sorting out this small amount of traction-maintaining-throttle through turns, instead trying for more dramatic acceleration.

This is most easily seen in the common error of being too "greedy" with the throttle at roll-on, which will make the bike run wide or slide and lead to a roll-off."

 

Note that the book doesn't mention brutal torque or HPs', it refers to fine and sustained input (throttle) from the rider, and consistent output (smooth acceleration and bike-suspension stability).

 

High lean angles are less forgiving of any errors regarding "being too "greedy" with the throttle at roll-on", simply because all the traction available is dedicated to resist the high lateral forces.

Moderated lean angles will allow certain margin for such errors.

[YellowDuck]

The engine output is a function of rpm *and* throttle position. In a certain rpm band you are going to have max torque at wide open throttle (WOT), but the *range* of torque available at that rpm, depending on throttle position, is anything between zero and that WOT max torque.

This seems quite confused to me. Last time I checked, the torque was ONLY decided by the RPMs., not your throttle position.

How would the maximum (ie peak) torque change with RPM - there is only one point with the peak torque.

 

Torque curves you see from dyno measurements are for WOT. Torque is the rotational force the engine is applying to the drive train, or, if measured at the wheel, that the tire is applying to the pavement in the backward direction. If you are neither accelerating nor decelerating (neutral throttle), that torque is very low, regardless of the engine rpm. The torque is just enough to overcome the forces of aerodynamic and rolling resistance, and that's it. Crack open the throttle and begin to accelerate, and torque has increased greatly. The torque increase happens even before engine rpm has changed.

 

Gear selection has a proportional effect on rear wheel torque. The lower the gear, the higher the torque at the wheel, given the same rpm and throttle position.

 

If you don't like that explanation, think of it this way...even if you are at high rpm, if the throttle is closed there is very little fuel / air reaching the combustion chamber. How does an engine generate torque without fuel?

 

One other way to think about it: acceleration is determined by torque at the rear wheel. Do you always accelerate at the same rate when the engine is at a given rpm, regardless of throttle position?