Scraping the Peg (The Physics)!!!

a7x3797

a7x3797

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Well, after a trip around my local round-about, I scraped the peg. This got me thinking, I wonder what lean angle I hit, and I wonder what the impact of removing the knob on the end of the peg would have on lean angle.

Note... these calculations reflect the max angle before scrape.
This is a static model. No suspension movement or weight distribution factored in

The following attached image is the calculations behind the results, but for those of you quick glancers...


Max Lean angle stock Pegs: 39.7*
Max Lean angle Peg knob Removed: 42.2*

As you can see, you can gain up to 2.5* more of a Lean angle from removing the Peg knob.

Measurements done with tape measure, Allow +/- 5% error on all values
 
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That's pretty cool to know. When I did my track day earlier this year, I took the scrapers off (at the insistence of an instructor after I ground half the ball off) and still scraped quite a bit of material off the foot peg itself. The foot rest was folding up a bit too. I took it as an indication that I need to work on my body position more.

A comment about the math: since the tire is both wide and round, wouldn't the contact point (vertical axis) move inward relative to the peg? It seems that this would decrease the lean angle slightly, right?

Sent from my Galaxy S3 using Tapatalk 4
 
Those are some pretty cool calculations.

Yeah, you might check your body position too. You want to lean off (your body) in the corner, while keeping the bike up so you can accelerate out of the corner exit. And that's at the track. ON the street, you really don't want to be that leaned over.

It's fun practice.

But scraping pegs (not good) tells you something, IMO. I did it some when I was figuring things out, trial and error.
 
How did your pegs not drop with a 1" lowering link?

There is an unaccounted factor in your math: proper vs improper throttle application. Closed throttle = compressed fork = less ground clearance.

And of course body position is the key player here. It's easy to scrape the peg if you're counter-weighing, even at a moderate speed.

With good body position, you can be pretty darn fast on the track (taking turns at good clip) and never come close to scraping.

The idea is to minimize lean angles, not maximize them.

I am curious though.. can you figure out the angles with compressed fork vs slightly extended fork (normal roll-on through the turn will likely extend the fork a bit past static sag).
 
It should tell you your bike is too far leaned over. Your contact patch of the tire loses points (out of 100, let's say) in the turn. So, something's gonna give, at some point.

Fix it with body position. Also, you can get adjustable rear sets.
 
Good use of trigonometry. But under dynamic conditions with suspension compression and road conditions (bumps and such) the numbers would be different, but the delta between the two calculated numbers would probably be pretty constant.
 
Clyde said:
That's pretty cool to know. When I did my track day earlier this year, I took the scrapers off (at the insistence of an instructor after I ground half the ball off) and still scraped quite a bit of material off the foot peg itself. The foot rest was folding up a bit too. I took it as an indication that I need to work on my body position more.

A comment about the math: since the tire is both wide and round, wouldn't the contact point (vertical axis) move inward relative to the peg? It seems that this would decrease the lean angle slightly, right?

Sent from my Galaxy S3 using Tapatalk 4
Click to expand...

You're right on that, I didn't apply that as I was unable to get 100% accurate measurements so the tire radius would fall within my acclaimed +\- 5%
 
Erci said:
How did your pegs not drop with a 1" lowering link?

There is an unaccounted factor in your math: proper vs improper throttle application. Closed throttle = compressed fork = less ground clearance.

And of course body position is the key player here. It's easy to scrape the peg if you're counter-weighing, even at a moderate speed.

With good body position, you can be pretty darn fast on the track (taking turns at good clip) and never come close to scraping.

The idea is to minimize lean angles, not maximize them.

I am curious though.. can you figure out the angles with compressed fork vs slightly extended fork (normal roll-on through the turn will likely extend the fork a bit past static sag).
Click to expand...

Peg height didn't drop because it's fixed based on the frame, not swing arm. I'd be curious to see the measurement from ground to peg on non lowered, but I don't think I would be much different, a far as suspension and all that nonsense... I measured with a tape measure in the garage, it took most of my cunning just to find the distance from the peg to the center of the tire. It is a factor, but I assumed Constant for calculations
 
This may sound simple but could you not have measured the distance from the bottom of the feeler to the ground then measured the distance from the bottom of the peg to the ground and then subtracted:confused:
 
Evitzee said:
Good use of trigonometry. But under dynamic conditions with suspension compression and road conditions (bumps and such) the numbers would be different, but the delta between the two calculated numbers would probably be pretty constant.
Click to expand...

I have no way to measure the suspension, so I left constant
 
Well there is a bit more to that. The lean angle required for a given speed in any given corner depends on the weigth distribution (body posiiton) but as well on suspension state (compression of the suspension). That said I often scraped pegs, a lean angle of 45 deg is no problem on the street as long as road surface is good and clean. I installed aftermarket rearsets and the first thing now hitting the ground is the brake and shiftlever and my foot. With more hanging off I would get the knee slightly earlier to the ground but usually I am to lazy. That said on the road I would not do this by purpose but sometimes you need to make a tighter line and then you can not avoid it.

The Fz1 hits very early the pavement with the pegs. I guess Yamaha meant it to good with warning the driver about getting to much leaned over.
 
Dreamdemon said:
Well there is a bit more to that. The lean angle required for a given speed in any given corner depends on the weigth distribution (body posiiton) but as well on suspension state (compression of the suspension). That said I often scraped pegs, a lean angle of 45 deg is no problem on the street as long as road surface is good and clean. I installed aftermarket rearsets and the first thing now hitting the ground is the brake and shiftlever and my foot. With more hanging off I would get the knee slightly earlier to the ground but usually I am to lazy. That said on the road I would not do this by purpose but sometimes you need to make a tighter line and then you can not avoid it.

The Fz1 hits very early the pavement with the pegs. I guess Yamaha meant it to good with warning the driver about getting to much leaned over.
Click to expand...

Nothing to do with speed, it's bike lean angle based on peg height. No weight involved either. Simple model of a static rigid body
 
a7x3797 said:
Peg height didn't drop because it's fixed based on the frame, not swing arm. I'd be curious to see the measurement from ground to peg on non lowered, but I don't think I would be much different, a far as suspension and all that nonsense... I measured with a tape measure in the garage, it took most of my cunning just to find the distance from the peg to the center of the tire. It is a factor, but I assumed Constant for calculations
Click to expand...

Don't get me wrong, it's a pretty cool calculation! Do fix it with better body position though. There is no benefit to scraping and there is potential for trouble.
 
Erci said:
The idea is to minimize lean angles, not maximize them.
Click to expand...

And this is the point that I laugh at when people tell me not to hang off the bike or call me out for chicken strips. When you hang off, you can use the shift in the center of gravity on the bike to keep the bike more upright, thus maintaining a max contact patch with even more lean available if necessary for any correction. I have chicken strips, I will probably always have chicken strips till I get a race bike that I can thrash by pushing it to the very limit of the tires lean.
 
Lonney said:
I don't agree with lowering the bike doesn't lower the pegs. I raised my bike up 3/4" and now my kickstand needs to be longer.
Click to expand...

We'll it doesn't lower the pegs, it lifts the rear wheel. As for a one inch drop at the swing arm, the pegs distance to the ground will change at a ratio to the amount you dropped it, if you think of a triangle where the front wheel is the point and the bases are the swing arm and another base at the pegs, you could find the delta value. Without measuring, I would guess somewhere between 1/2 and 3/4 if an inch, and since my calculations deemed one inch at the pegs to be ~2.5* angle, it would only affect the angle by up to 2* which is 5%. And that falls within my set tolerance.
 
a7x3797 said:
Nothing to do with speed, it's bike lean angle based on peg height. No weight involved either. Simple model of a static rigid body
Click to expand...

You calculation is fine, however the lean angle you need is influenced by the other stuff. Removing the feeler is a good idea and body position will help a lot in situations were you need more lean angle.
 
a7x3797 said:
Nothing to do with speed, it's bike lean angle based on peg height. No weight involved either. Simple model of a static rigid body
Click to expand...

Suspension characteristics (weight) absolutely have to do with your clearance. If you've got really soft suspension, your bike might be an inch or two lower in a corner than someone with really stiff suspension. Corner speed creates lateral g-force which, on a leaned-over bike, compresses the suspension.

That said, I scrape my pegs all the time at the track (even with the knobs removed) and the rear is still pretty stable. If you've got a 190/55 tire, you've still got a lot of rubber on the ground at a 43 degree lean angle. From what I've heard, your max (safe) lean angle is about 5 degrees less than your tire height number. So on even on a stock 190/50, you can go to 45 degrees and still be in pretty good shape. I wouldn't go wide open on the throttle, but you should be able to hold a constant corner speed.
 
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