[kjs]

Draw a rectangle around the frontal area of the motorcycle (including rider). The dimensions of this rectangle (L X W) equals total frontal area, which is one of the variables required for accuracy (and a very important one!)

The red rectangle illustrated in the attached picture is an illustration of this...

This is the main obstacle in achieving higher speeds, as the speed increases it takes exponentially more HP to "punch a hole" through the air.

The point of that is to calculate the surface area encountering friction at the front end of the bike? Using the rectangle that measures the highest point to the lowest on the bike and the widest points of the bike seems almost arbitrary. There has to be an accurate way to calculate the actual surface area.

To clarify, that picture you posted has a lot of blank/white space. It seems like that area is being counted as surface area.

 

[tonyjuliano]

The point of that is to calculate the surface area encountering friction at the front end of the bike? Using the rectangle that measures the highest point to the lowest on the bike and the widest points of the bike seems almost arbitrary. There has to be an accurate way to calculate the actual surface area.

To clarify, that picture you posted has a lot of blank/white space. It seems like that area is being counted as surface area.

Without a wind tunnel, and corresponding flow analysis, this is actually the way it should be estimated.

It may appear that there is a a lot of dead space that is free doing it this way, but there is serious turbulence present in those areas at high speeds, rendering them much less "transparent". The airflow over a normal motorcycle and rider is MUCH less free-flowing than air passing around a much more aerodynamic car.

It's an estimate - to be sure - but a surprisingly accurate one.

 

[kjs]

That makes sense, it just seems like kind of a crude calculation with significant margin of error.

 

[tonyjuliano]

That makes sense, it just seems like kind of a crude calculation with significant margin of error.

All of the variables have some margin for error, but in my calculation they were very optimistically chosen.

The first, CD (coefficient of drag), was given a value of .7 - this is wildly optimistic for a naked bake, as the norm is usually .9

The second is the "frontal area" we are currently debating. 10 SQ FT, the number I used, is less than actual.

The third (HP) was chosen as "75" - I don't think there are ANY Scramblers (in stock form) that are capable of this number measured at the rear wheel.

But, this is why they are called "variables".

I'm still standing behind my calculated estimate of top speed being somewhere between 115 and 120 mph (without modifications from stock, of course), but thanks to our friend here - we will soon see.

 

[tonyjuliano]

Plug in your own numbers and tell me if you get something different.

CalcTool: Terminal velocity calculator

OMG...

I just reread this whole thread, and I don't know how I missed this particular one of Ralphs intelligent rebuttals (quoted above).

Hey Ralph (if you're still watching), the "calculator" you posted a link to is for determining the terminal velocity of a FALLING OBJECT!!

There is no rolling resistance accounted for - an absolutely critical element in determining a motor vehicles top speed as it travels ALONG THE GROUND.

So yes, my numbers do yield a top speed of 160 MPH...

If you drop a scrambler out of an airplane!!

 

[SQLDude]

My $0.02...and no science to back it up...

In 1991, I owned a 400cc Suzuki Bandit. I remember topping it out somewhere between 105-110 mph. The body stylings of the Bandit and Scrambler are very similar, but with twice the displacement and half again as much HP (50/75)...I would hope the Scrambler could muster more the 115.

-Jason

 

[tonyjuliano]

My $0.02...and no science to back it up...

In 1991, I owned a 400cc Suzuki Bandit. I remember topping it out somewhere between 105-110 mph. The body stylings of the Bandit and Scrambler are very similar, but with twice the displacement and half again as much HP (50/75)...I would hope the Scrambler could muster more the 115.

-Jason

Hi Jason,

It only takes around 53 hp to hit 105 mph (assuming the same variables).

The HP requirement rises pretty dramatically as speeds increase. Plus, the speedo on your GSF400 was also optimistic (they all are), and it weighs over 30 lbs less than a Scrambler.

 

[ralph]

I'm still standing behind my calculated estimate of top speed being somewhere between 115 and 120 mph (without modifications from stock, of course), but thanks to our friend here - we will soon see.

Between 115 and 120? What happened to 116.25. Can't show your math like any grammar school kid would be required to so you make up new numbers....pathetic.

 

[kjs]

It's a discussion about physics. All parties involved, lighten up and let's stop the name-calling and silly arguing.

 

[stavely]

The point of that is to calculate the surface area encountering friction at the front end of the bike? Using the rectangle that measures the highest point to the lowest on the bike and the widest points of the bike seems almost arbitrary. There has to be an accurate way to calculate the actual surface area.

To clarify, that picture you posted has a lot of blank/white space. It seems like that area is being counted as surface area.

I'm with Kjs on this one. The Scrambler is a "thin" bike anyway but you missed applying this bit of the calculation Tony...
Calculation of Frontal Area

Frontal area (farea) represents the front projection area of the vehicle. If one takes a picture of a vehicle, it is the area included in the outline. Use the following to calculate:
1. Calculate the area of a rectangle which would encompass the front of the vehicle (multiply width by the height). For motorcycles, use the handlebar width (to a maximum width of 30 inches) and a height consisting of seat height plus an estimated "seat to helmet" height.

2. Adjust the figure obtained above for areas not included, such as top rounded corners, etc. Typical adjusting values are 85 percent for cars, 70 percent for motorcycles, and 100 percent for trucks.

I think a little guy/gal might even get inside my 8 squ. ft.

 

[Scrambler 69]

Scrambler speed

127mph on rev limiter speedo reads a little fast reckon 122mph a little bird tells me
Reckons more if up geared

 

[[email protected]]

Well aside from all the math on here, and speedo accuracy, I know for a fact that its not that hard to get the Scrambler up to 200kph.
It screams pretty good, but I know 200+ when it reads on the speedo.

Throw a better highway set of gears on there and I think you could see 210, but probably not much more.

Besides, who cares about the math and the arguing. If you are not willing to take your bike out some where and see what it will do, why post here on a top speed forum.
For those who are, you know the bike can hit 200+

Nuf said.

 

[YankeeDoodle]

facts are facts, primary knowledge or cited notes... encourage this socratic dialogue, peasy ala lemonade

 

[Rob Thomson]

Classic top speed

With tank bag full of gear and sleeping bag, matress and tools on the back, I wound it out on the Hay plains in Australia....2 runs; 198kmh the first attempt with nothing left then 200kmh the second try. No idea what revs the engine was doing because I was too busy watching the road and hanging on.:laugh:
Here is a picture loaded with gear.
The bike was totally stock.

 

[Bunio]

On my Urban Enduro I got 183kmh with 8000RPMs.
Got a small Piug windshield on front and a back topcase at the back.

Side bags were removed.
Basically no red blink about MAX RPM but over 180 km/h reached. Ended with loosing rear licence plate and unstable bike with over 180 km/h.

I would not recommend such high speeds on Urban Enduro.

 

[MotoChief]

I hit 118mph(189kph( on a long straight the other day, on the speedometer.

 

[jazzndre]

With tank bag full of gear and sleeping bag, matress and tools on the back, I wound it out on the Hay plains in Australia....2 runs; 198kmh the first attempt with nothing left then 200kmh the second try. No idea what revs the engine was doing because I was too busy watching the road and hanging on.:laugh:
Here is a picture loaded with gear.
The bike was totally stock.

What tank bag is that?

 

[MarkTravaglini]

My Zumo GPS recorded a top speed of 116 mph. I can't say how fast the speedo said I was going. I had my eyes closed. . . . .

Made my day! LOL

 

[MarkTravaglini]

On my Urban Enduro I got 183kmh with 8000RPMs.
Got a small Piug windshield on front and a back topcase at the back.

Side bags were removed.
Basically no red blink about MAX RPM but over 180 km/h reached. Ended with loosing rear licence plate and unstable bike with over 180 km/h.

I would not recommend such high speeds on Urban Enduro.

Hey Bunio! Would you post some pics of the back trunk? Also, those saddlebags are the rigid Ducati ones? thanks!

Cheers!

 

[Karlo]

Today I hit 182kmp or 113mph