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Discussion Starter #41
So I got a response from one of the guys I consult with for topics that are beyond my depth of understanding. Below is his response. I made it clear that I wanted a "quick and dirty" response understanding that there are many variables to consider.

"So as you can imagine I had to make some assumptions. The best number I can find for drag coefficient for a good racing motorcycle with rider fully tucked is .6 I could find no numbers for when the rider comes out of the tuck and is intentionally aerobraking with his body, so I just used an intermediate number between a race bike and a touring bike on which you sit upright. I used .75 could be higher or lower based on rider/bike combo.

I know the GP guys' bikes are insanely light, but I just shaved a few pounds off an S1000rr with rider ( since the velocity is the the dominant term at high speeds anyway). Assumed 600 lbs total bike/rider weight.

I also had to guess on the cross-sectional area of bike/rider when they’re out of the tuck and I decided to use .75 square meters just using a rough guess based on a frontal photo of a GP rider on braking and average height of motorcycles, etc.

I also assumed sea level for air density.

At 210 mph, just wind resistance would be generating .51 G’s
at 200 mph it would be .466 Gs
at 180 mph it would be .375 Gs
at 160 mph it would be .299 Gs
at 140 mph it would be .228 Gs
at 120 mph it would be .168 Gs
at 100 mph it would be .117 Gs
at 80 mph it would be .076 Gs

Notice that it falls off quickly as speed decreases (the drag force is proportional to the velocity squared so halving the speed cuts the force to 1/4 it’s original value).

So the big takeaway from this and it definitely makes your point is that a 180 mph turn has 3.5 times as much braking force being applied by the wind before you even grab the brake lever as a 100mph corner. And the GP guys have 10 times the braking force from aerodrag on the front straight as they might have on a slower 60 mph turn. It’s definitely something that has to be taken into account.

For the starting at 180 mph I’ll be going X speed after 1 second, I can try to get you a more comprehensive answer to that another time, but fortunately you’re asking for a short time interval, so even though the drag force is changing with time, I’ll assume it is constant over that 1 second. My rough estimate is that in 1 second you will have slowed down to around 170 mph. Assuming a -.375 Gs and a starting velocity of 180 mph (80 meters per second), after 1 second you’ll have slowed down by about 3.7 meters per second. 76.4 meters per second comes out to around 170 mph. 10 mph in 1 second is pretty significant."
 

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So I got a response from one of the guys I consult with for topics that are beyond my depth of understanding. Below is his response. I made it clear that I wanted a "quick and dirty" response understanding that there are many variables to consider.

"So as you can imagine I had to make some assumptions. The best number I can find for drag coefficient for a good racing motorcycle with rider fully tucked is .6 I could find no numbers for when the rider comes out of the tuck and is intentionally aerobraking with his body, so I just used an intermediate number between a race bike and a touring bike on which you sit upright. I used .75 could be higher or lower based on rider/bike combo.

I know the GP guys' bikes are insanely light, but I just shaved a few pounds off an S1000rr with rider ( since the velocity is the the dominant term at high speeds anyway). Assumed 600 lbs total bike/rider weight.

I also had to guess on the cross-sectional area of bike/rider when they’re out of the tuck and I decided to use .75 square meters just using a rough guess based on a frontal photo of a GP rider on braking and average height of motorcycles, etc.

I also assumed sea level for air density.

At 210 mph, just wind resistance would be generating .51 G’s
at 200 mph it would be .466 Gs
at 180 mph it would be .375 Gs
at 160 mph it would be .299 Gs
at 140 mph it would be .228 Gs
at 120 mph it would be .168 Gs
at 100 mph it would be .117 Gs
at 80 mph it would be .076 Gs

Notice that it falls off quickly as speed decreases (the drag force is proportional to the velocity squared so halving the speed cuts the force to 1/4 it’s original value).

So the big takeaway from this and it definitely makes your point is that a 180 mph turn has 3.5 times as much braking force being applied by the wind before you even grab the brake lever as a 100mph corner. And the GP guys have 10 times the braking force from aerodrag on the front straight as they might have on a slower 60 mph turn. It’s definitely something that has to be taken into account.

For the starting at 180 mph I’ll be going X speed after 1 second, I can try to get you a more comprehensive answer to that another time, but fortunately you’re asking for a short time interval, so even though the drag force is changing with time, I’ll assume it is constant over that 1 second. My rough estimate is that in 1 second you will have slowed down to around 170 mph. Assuming a -.375 Gs and a starting velocity of 180 mph (80 meters per second), after 1 second you’ll have slowed down by about 3.7 meters per second. 76.4 meters per second comes out to around 170 mph. 10 mph in 1 second is pretty significant."
That's interesting. Top speeds at COTA and Mugello are about 225mph. If a rider really opens himself up for more drag, maybe with some webbing in the armpit area that only spreads when up braking, they can achieve a significant braking advantage and right at the spot where it makes the most difference: at the beginning of the braking zone at the end of a long straight. Obviously the aerodynamics would need to be well tested to preclude any lift. Downforce for better brake efficiency would be another plus.
 

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Discussion Starter #44 (Edited)
We know that if the tires are gripping, the limiting factor is the rear wheel coming off the ground, but the rider's body, at high speeds, will act as a lever and keep the rear wheel from coming up. So, some other things come into play. I'm wondering what the peak G's would be at very high speeds e.g. 215mph but I reckon it could be briefly slightly over 2G's for example at Philip Island and Mugello.
 

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Discussion Starter #46
I just received this correction to the last post from my source:

"Dylan,

Sorry, this is what I get for doing those calculations when I was sick and half asleep. I messed up on a unit conversion, so the G numbers are actually much higher. I forgot to convert lbs to kgs when I was doing Gs.

210 mph (1.31 Gs)
180 mph (.82 Gs)
160 mph (.65 Gs)
140 mph (.50 Gs)
120 mph (.36 Gs)
100 mph (.25 Gs)

And rolling off at 180 mph, after 1 second you would be doing 161 mph. Nearly 20 mph loss. That sounds more like it.

I’m sorry for that error"
 

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Had a great time riding the HP4R today
When grow up I want to be just like you. :grin2:

I'm still kicking myself for not going to a special HP4R invitation event at VIR. I scored an invite from Bob's BMW but then a hurricane visited the area and I concluded that we'd be out at the track taking selfies all day and watching it rain. They actually got in a few track sessions on it and I would have been able to ride it if I'd gone. I keep hearing great things about it.
 

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I just received this correction to the last post from my source:

"Dylan,

Sorry, this is what I get for doing those calculations when I was sick and half asleep. I messed up on a unit conversion, so the G numbers are actually much higher. I forgot to convert lbs to kgs when I was doing Gs.

210 mph (1.31 Gs)
180 mph (.82 Gs)
160 mph (.65 Gs)
140 mph (.50 Gs)
120 mph (.36 Gs)
100 mph (.25 Gs)

And rolling off at 180 mph, after 1 second you would be doing 161 mph. Nearly 20 mph loss. That sounds more like it.

I’m sorry for that error"
This significantly larger than posted before and gives even more reason for enhancing and exploiting it as much as possible.
 

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@PittsDriver Don't be a stranger just because you are riding a Super Duke that puts an S eating grin on your face every time you ride. :laugh: You'll be back once you ride a properly flashed, full exhaust 2020. :wink2:

Completely O/T... Why do call yourself a Driver? Isn't that some sort of put down for pilots? You have posted videos of your aerobatics. Hardly "driving." Google search was no help. While not a reputable source of reference even some episodes of JAG refereed to pilots driving F14s. :rolleyes: Shed some light please.
It's all an illusion. We make it look hard but it's just like driving around a patch of sky. :wink2:

Any yes, the 1290R is still giving me a woody every time I ride it. Not the track bike that the S1000RR is but for the other 99% of my riding, there's nothing else out there like it.
 

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It's all an illusion. We make it look hard but it's just like driving around a patch of sky. :wink2:

Any yes, the 1290R is still giving me a woody every time I ride it. Not the track bike that the S1000RR is but for the other 99% of my riding, there's nothing else out there like it.
Many of us have a second (or more) bike for practical purposes. Mine is a K1300S, which is a great sport-tourer, but it will eventually be replaced. Leading candidates include the upcoming new-generation XR (BMW S1000XR) and the (rumored) upcoming Ducati Multistrada V4. I rented the XR last summer for 9 days on a phenomenal trip through the Alps of five countries. The XR is a very comfortable, fast and sporty bike. Loved it.

I haven't tried the SuperDuke, but have been on a friend's 1290 adventure bike (forget the model name). It was good, but didn't get me nearly as hard as the XR or my K1300S. I might not be a twin guy, though did like a friend's 1260 Multistrada.
 

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Many of us have a second (or more) bike for practical purposes. Mine is a K1300S, which is a great sport-tourer, but it will eventually be replaced. Leading candidates include the upcoming new-generation XR (BMW S1000XR) and the (rumored) upcoming Ducati Multistrada V4. I rented the XR last summer for 9 days on a phenomenal trip through the Alps of five countries. The XR is a very comfortable, fast and sporty bike. Loved it.

I haven't tried the SuperDuke, but have been on a friend's 1290 adventure bike (forget the model name). It was good, but didn't get me nearly as hard as the XR or my K1300S. I might not be a twin guy, though did like a friend's 1260 Multistrada.
It's a short wheelbase, very torquey high performance v-twin. In other words, a hooligan bike. The effortless way it sends the front lofting is a real kick. I looked really hard at the S1000R before I pulled the trigger on the KTM but it felt too much like my S1000RR and everyone should own a high performance twin once in their motorcycling life.

Dylan, sorry for the thread hijack and it sounds like you got pointed to some good information. It kinda begs the question about rider suit design if it could incorporate some drag inducing feature that is effective when sitting upright but is eliminated in a racing tuck. That would provide more levering force as you described it for keeping the back tire on the track. It would probably also be pretty fatiguing for the rider!
 

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Discussion Starter #53
Dylan, sorry for the thread hijack and it sounds like you got pointed to some good information. It kinda begs the question about rider suit design if it could incorporate some drag inducing feature that is effective when sitting upright but is eliminated in a racing tuck. That would provide more levering force as you described it for keeping the back tire on the track. It would probably also be pretty fatiguing for the rider!
Sure I bet a poor fitting suit would add to the drag. The main thing I was trying to see was how the drag increased with mph and be able to give riders a ballpark on wind resistance slowing the bike at high speeds. Knowing the top speed at the end of the front straght at Philip Island and seeing how relatively short the braking duration is to get into turn one was the thing that got me wondering initially.
 

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Sure I bet a poor fitting suit would add to the drag. The main thing I was trying to see was how the drag increased with mph and be able to give riders a ballpark on wind resistance slowing the bike at high speeds. Knowing the top speed at the end of the front straght at Philip Island and seeing how relatively short the braking duration is to get into turn one was the thing that got me wondering initially.
The problem with adding more drag from the rider are the immense forces involved at high speed. The bike and rider weigh around 450 lbs. Thus there is 45 lbs of force put on the rider for every .1 G of additional drag.
 

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Discussion Starter #55
Picking this back up because I got some fresh data from a MotoGP engineer from a recent MotoGP race at a track that had a high speed approach to a hard braking zone.

1st second 200mph to 160mph---1.82G
2nd second 160mph to 126mph---1.55G
3rd second 126mph to 102mph---1.09G
4th second 102mph to 80mph----1.0G
 

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If TLDR, then go to end to see the graph.

For anyone who wants to measure real life air drag and deceleration (flat, straight line, clutch pulled in), and then make a equation out of it:

(wiki-copy-paste) In fluid dynamics, the drag equation is a formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid. The equation is:
Fd = 0.5 * p * u^2 * A * Cd

Where p (mass density of the fluid), A (reference area) and Cd (drag coefficient) are constants and you can kind of "skip" them and use one constant which replaces them all.
u is speed, unit m/s.

And you can also "skip" mass and force (F=ma), because you are only interested about measured deceleration, and also mass is constant in that case.

So, a modified equation for this purpose (your measurements/data -> your bike&body position equation) is very simple:
Deceleration = 0.5 * speed^2 * constant

And because you measure speed (datalogger) and deceleration (datalogger), the only unknown is the constant (all-in-one constant).
You can also use for example Anroid phone with RaceChrono and external 10Hz GPS. Phone and internal 1Hz GPS is too inaccurate.

You need to have only one speed and deceleration value to be able to calculate the constant, because:
constant = deceleration/(0.5 *speed^2)

But it is better, if you plot out multiple measurement points to a graph, and add the equation, and fine tune the constant a little bit. From the graph it is easy to see what kind of constant is close to the real life values. And/or just calculate a average constant value from those measurement points.

There is always some error margin in your speed and deceleration (datalogger) values, and that is why your constant will have too much error in it if you use only one speed and deceleration value. And measurements are more accurate if they are done at 100+ mph. Below 100 mph air drag starts to get too small and that is why error margin rises.

And when you have your constant, you can use it to find out deceleration at any given speed with your bike and your body position.

For example, if measured real life data points are:
Braking body position (head up, knee on the side), clutch pulled in, no brakes
190 kmh -0,400 G
180 kmh -0,350 G
170 kmh -0,315 G
160 kmh -0,275 G
150 kmh -0,225 G
140 kmh -0,215 G
130 kmh -0,205 G
120 kmh -0,175 G
Calculated constant is about -0,0002872022, and with that value you can extrapolate and make some graphs.

In graphs:
Measured G = Measured Air Drag & Rolling Recistance
Calculated G = Calculated Air Drag & Rolling Recistance
Total G = Calculated Air Drag & Rolling Recistance & -1.2G Brake

 
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