What caused this roundabout lowside?

[akima]

Link to original page on YouTube.

It looked like he was only going ~30mph.

I heard his engine loose revs as he was going down. His bike may have lost a little bit of traction and he then tightened up on the bars and chopped the throttle making it worse.

Maybe his tyres were not heated up to their required temp.

Maybe both.

Thoughts?

[RacinNinja]

Max lean, cold tires, cold road, applied throttle, lots or torque in the FZ07.

[Triple Jim]

It did seem unexpected, but then with a body/helmet mounted camera, it's hard to tell just how big the lean angle was. I think RacinNinja has the answer.

[allanoue]

sounded like he geared down a second before crash and right after getting back on the throttle.

Too much throttle.

cold tires are normal for the street

[Alex]

Gravity?

[VaFish]

Originally Posted by Alex

Gravity?

I think it was because he was driving on the wrong side of the road.

[akima]

Originally Posted by VaFish

I think it was because he was driving on the wrong side of the road.

That's not a problem here because we have all agreed to drive on the wrong side of the road

[1uglybastard]

Originally Posted by VaFish

I think it was because he was driving on the wrong side of the road.

Gravity is stronger on the wrong side.

What a pretty bike. I wish they offered all those extra neon parts on the u.s. model.

[RacinNinja]

Originally Posted by 1uglybastard

Gravity is stronger on the wrong side.

What a pretty bike. I wish they offered all those extra neon parts on the u.s. model.

It's a Yamaha FZ07. The FZ07, FZ09 and FZ10 for 2016 are all available in those colors.

[Motofool]

Originally Posted by akima

.......His bike may have lost a little bit of traction and he then tightened up on the bars and chopped the throttle making it worse.

Maybe his tyres were not heated up to their required temp......

All of the above: too fast for conditions, including tire's condition.

Assuming a 185 lb rider and a 40/60 weight distribution, at max lean of 45 degrees, the rear tire's contact patch was feeling around 350 lb of lateral force.
The torque of this bike can reach 50 ft·lb (68 N·m) @ 6,500 rpm, which means that the rear tire's contact patch could feel a max. additional load of around 46 lb of longitudinal force (it seems that it was less in this case).

Both magnitudes, when combined, could overwhelm the traction capability of the rubber for those specific conditions.
Just for reference:
https://www.ninjette.org/forums/showthread.php?t=172628

[Triple Jim]

Originally Posted by Motofool

The torque of this bike can reach 50 ft·lb (68 N·m) @ 6,500 rpm, which means that the rear tire's contact patch could feel a max. additional load of around 46 lb of longitudinal force (it seems that it was less in this case).

Multiplying the engine's torque by the primary ratio of 1.925 and the final drive ratio of 2.688, you get 5.174. Even with the 6th gear ratio of .964, you still have 5 times the torque at the rear wheel that you have at the engine. Assuming you lost 10% of that to friction, you have about 225 lb-ft at the wheel. With a tire radius of about 1.13 feet, you get a maximum of 199 lbs of driving force at the tire in 6th gear, and a lot more in lower gears.

This means it's pretty easy to overcome tire friction with throttle when leaned over in a turn!

[akima]

Originally Posted by Triple Jim

This means it's pretty easy to overcome tire friction with throttle when leaned over in a turn!

... at 45 degrees right?

I like that circular char motofool posted. It's a nice way of visualizing it.

[Snake]

Too much speed into the second turn.

[Triple Jim]

Originally Posted by akima

... at 45 degrees right?

Well, with the kind of driving force that the FZ-07 can produce, you wouldn't have to be anywhere near 45 degrees to break the rear tire loose, especially in lower gears.

In 1st gear, the bike has 2.9 times the overall drive ratio that it has in 6th, so the approx. 200 lb. force available in 6th becomes 580 lbs, meaning if you could keep the front wheel on the ground, you'd almost certainly be spinning the rear wheel while going straight. (No lean required to slide the rear tire.) That point would be out the top center of the grey circle.

[shift957]

"your ambition outweighed your talent."

--Casey Stoner

[Mohawk]

Originally Posted by Triple Jim

Well, with the kind of driving force that the FZ-07 can produce, you wouldn't have to be anywhere near 45 degrees to break the rear tire loose, especially in lower gears.

In 1st gear, the bike has 2.9 times the overall drive ratio that it has in 6th, so the approx. 200 lb. force available in 6th becomes 580 lbs, meaning if you could keep the front wheel on the ground, you'd almost certainly be spinning the rear wheel while going straight. (No lean required to slide the rear tire.) That point would be out the top center of the grey circle.

??????
The FZ07 makes about 45 lb/ft, which is about what a 600 4 puts out, not sure where you got 200 from. And instead of multiplying, the force goes down with higher gearing, lower gears multiply the force available from the motor. This is why dyno runs are usually done in 4th or 5th gear, depends which is closest to a 1-1 drive ratio between crank & output shaft.

YMMV

[Triple Jim]

Mohawk, check my first post above. The increase comes from the primary reduction gear and the final drive (sprocket ratio). Gears lower than 6th make it even higher.

[Mohawk]

I think you got your numbers mixed up. The engine makes 45ft/lb at the wheel in 4th gear, even in first gear at the same 6500rpm point the torque will be no more than 2.5 times this maximum & usually closer to 2x. Check out some dyno charts of bike torque through the gears. Mechanical losses compound the issue, when you add gearing. So this bike will make a maximum of about 100ft/lbs.

[Triple Jim]

The engine makes 45 lb-ft of torque. This is at the crankshaft. If you're seeing a dyno run that was made in 4th gear, the torque measured was adjusted to crankshaft torque by taking into account the transmission ratio, primary drive ratio, and final drive ratios. Dyno torque values are normally adjusted to crankshaft torque, or it would be meaningless to compare torque values of different motorcycles when trying to describe the engine characteristics.

The primary gear ratio is 1.925, so the available torque going into the transmission is 45x1.925=86.625 lb-ft. The final drive ratio (sprockets) is 2.688, so if the transmission were in a 1:1 gear, the overall torque at the rear wheel would be 86.625x2.688=233 lb-ft.

Since 6th gear's ratio is .964, in that gear, the torque at the rear wheel is 233x.964=224.lb-ft. If you were to use 1st gear, you get 2.9 times the mechanical advantage that you have in 6th, so the available rear wheel torque becomes 651 lb-ft, resulting in a possible driving force of 580 lbs at the rear tire. As you said, there are significant losses, so that number when actually measured may be more like 500 lbs, and this is in 1st gear, of course.

This checks out when you consider that the motorcycle and rider probably weigh around 600 lbs. The resulting maximum acceleration would then be about 5/6 of a g, which is near the limit of tire spin, and about like you'll experience in 1st gear on an FZ-07.

[JohnnyBravo]

I heard all thar scrapping; I knew just what happened.

[Mohawk]

Well if that's how YOU believe a dyno works, then good luck with those numbers.

The manufacturer specifies power figures at the crank normally, so NO drive ratios involved, nor the clutch, nor any parasitic loses. NO dyno I have ever used, has a database obike gear ratios, even if they did it would be meaningless if you changed the wheels, tyres or final drive ratio. All dynojet dyno's, just measure power at the rear wheel. They only measure torque & use a calculation to estimate horse power from that.

And that is why, every bike ever tested fails to generate the power figures the manufacturers quote, because of the parasitic losses from the gear train.

YMMV

[akima]

Originally Posted by Triple Jim

Dyno torque values are normally adjusted to crankshaft torque, or it would be meaningless to compare torque values of different motorcycles when trying to describe the engine characteristics.

If you are comparing the performance of 2 complete bikes (not just their engines), then surely it makes a lot of sense to look at torque values at the wheel instead of the real or calculated values of torque values at the crankshaft. Once you collect up that data, then to fairly compare the acceleration performance of the bikes you only need to additionally factor in their weights.

I'm a noob when it comes to this stuff, so I've probably missed something obvious.

[Triple Jim]

Originally Posted by akima

If you are comparing the performance of 2 complete bikes (not just their engines), then surely it makes a lot of sense to look at torque values at the wheel instead of the real or calculated values of torque values at the crankshaft. Once you collect up that data, then to fairly compare the acceleration performance of the bikes you only need to additionally factor in their weights.

I'm a noob when it comes to this stuff, so I've probably missed something obvious.

No, you're right. The only confusion here is how the engine torque numbers are calculated when measured on a chassis dynamometer.

Mohawk, without using any of the drive ratios, an inertia dyno like a Dynojet can measure power by measuring the acceleration and RPM of its huge flywheel/drum. Once HP is known, it can divide by the engine RPM to calculate crankshaft torque. This is the torque number displayed on that type of dyno. The key is that it divided by engine RPM before displaying the torque value, so that value is crankshaft torque, not the rear wheel torque.

This won't change the numbers in my examples above. To get the driving force at the rear tire, you can start with crankshaft torque, multiply by the overall drive ratio, and then divide by the tire radius. I did take off about almost 15% for losses.

[sharky nrk]

Graphical example from a Sport Rider comparison test. Thrust is essentially driving torque at the rear wheel. Each set of lines is a gear.

[Zaph42]

Roundabouts are where cars leak oil more heavily. Never trust traction in a roundabout.

Originally Posted by Motofool

Neat chart. The circle becomes smaller when the asphalt tilts to the outside like some roundabouts. Then it gets smaller when cars leak oil on it. Pretty soon your bike just flies out from under you unless you limp through it almost upright.

I think my question is why do cars leak more oil in a roundabout. I think it's the quick transition from braking to throttle combined with the chassis roll...

[Triple Jim]

Originally Posted by sharky nrk

Graphical example from a Sport Rider comparison test. Thrust is essentially driving torque at the rear wheel. Each set of lines is a gear.

Yes, my '72 H2's manual has similar curves. It's really thrust, as labeled. The driving torque at the rear wheel is thrust multiplied by wheel radius.

[Mohawk]

Triple Jim, I think you got that backwards. Dyno's measure torque NOT HP. You can calculate HP from a known torque & rate of work which is why dynojet & every other dyno measures the rpm. HP is acalculation of force overtime. Thus HP=Torque X RPM / 5252. The figure is at the wheel, as no gearing, primary or secondary ratios are known or applied.

It's impossible to measure HP, it's purely a calculated figured as above. it's also impossible to calculate torque from a HP figure, unless you know the rpm. This is why a 2.0L turbo, can deliver 500HP at 6krpm, same as a V8 5.0L can produce the same power at less than half the rpm.

As per graph above about 5 bikes & 6 gears each, look at the 4th & 5th gear values & then at the first gear values, all are approximately 2-2.5 times the MAX.

But I digress, the guy fell off by simply confusion his intentions with his abilities Same as most folk who can't pin it on an external force outside their control.

YMMV

[Triple Jim]

I understand how HP is calculated very well, being that I studied that sort of thing to get my degree in mechanical engineering. Yes, one formula is the one you gave. HP is the time rate of doing work, as in ft-lbs per minute, the ft-lbs being a force over a distance (as opposed to lb-ft, which by convention refers to a torque). It takes one HP to lift a one lb weight 550 feet in one second, for example. Also 1 HP to lift a 1 lb weight 33,000 feet in one minute.

One lb-ft (torque) making one rotation, does 2π ft-lbs of work, which is where the 5252 comes from: 33,000/2π=5252.11

When I said the dynamometer measures power, I was referring to it using its computer to calculate power from the information it gets from the acceleration of the drum and the RPM of that drum.

You can check my arithmetic in my posts above, I believe it's correct. I understand some of the points you're making as well, but some were based on incorrect assumptions like the torque readout of a Dynojet being rear wheel torque, when it's actually torque measured at the rear wheel, corrected to crankshaft torque, knowing the RPM of the engine. It's definitely true that people refer to "rear wheel torque" when it's really engine torque as measured at the rear wheel after losses, and that's confusing.

I'm tired of your "I think you got that backwards", "I think you got your numbers mixed up", and "if that's how YOU believe a dyno works, then good luck with those numbers" type comments. I tried to stick to simple statements of physics, and I certainly didn't mean to start a peeing contest, but you did ask where I got my numbers. Peace.

[akima]

Originally Posted by Triple Jim

When I said the dynamometer measures power, I was referring to it using its computer to calculate power from the information it gets from the acceleration of the drum and the RPM of that drum.

That's an important distinction right? Measuring vs calculating. I can't measure the average height of my family members, but I can measure their height and calculate the average height. That could be, partly, why Mohawk didn't comprehend your post.

I got some value out of the discussion you guys had, so thanks

[Triple Jim]

You're sort of right, Akima. There are direct and indirect measurements. Measurements made by measuring something different from the thing you'd like to measure are indirect measurements. Measuring your family members and averaging is an indirect measurement of their average height. A dynamometer makes an indirect measurement of horsepower. That doesn't mean it can't measure HP, just that it indirectly measures HP.