Dyno Day, Shocking Results!!!

[signit98]

Here is the formula:
MPH = (rpm x rolling radius of the driven tire in inches) ÷ by (168 x the overall gear ratio)

I can tell you the practical top speed, though... as I have previously mentioned. Maybe my speedo is just showing 10 MPH less that it should?

Sure it is...

[signit98]

...actually, there is one possible explanation for his reading:

The difference between nautical miles per hour and statute miles per hour at that speed would explain the difference, just about.

So, I wonder what his GPS was set to...

Also, as I said, I have seen 242, 247 and other values on my GPS on the GS... they are not always trustworthy...

[AZ-Twin]

Okay, let me see if I did this correctly, correct me if I am wrong, I am sure you all will. Forgive some rounding error, I used excel but am rounding below.


From my owner's manual
6 gear ratio .805:1
FD Ratio 2.62:1
Engine RPM 8500 RPM

At 8500 RPM the drive shaft is spinning 10559 RPM, and the rear wheel is spinning 4030.2 RPM.

With a 190 50 17 tire the overall tire height is 621.8mm tall * 3.14 = 1952.5mm circumference. /25.4mm = 76.9in traveled for 1 rotation of the rear wheel.

76.9in * 4030.2rpm = 309922.38 inches traveled per minute. This * 60, then devided by 12, then devided by 5280 should give miles/hour. I get approximately 293 mph as the theoretical top speed at 8500 RPM in 6th Gear.

After doing the math I decided to search the internet and found this, it agrees with my numbers.

http://www.catherineandken.co.uk/sti/tyres.html

Now, I know that speed is not obtainable, but I think 169 probably is with enough power. Not sure how much power it takes, that is another story.

[signit98]

Yeah, I found that website a long time ago and forgot it just as quickly... if that bike would have a theoretical top speed of 293 MPH in 6th gear at 8500 RPM, it would do 169 MPH at 5725 RPM... see what's wrong here?

Came to the same numbers... reality is, I cut out at the speed I stated... maybe I ran nautical miles... but I highly doubt it!

Take your bike, Rob... let Brian know you are coming and to have your back and then see what you get!

[AZ-Twin]

Originally Posted by signit98

Take your bike, Rob... let Brian know you are coming and to have your back and then see what you get!

Lol....yeah, I don't think so, I don't have the coals to run my bike all out. Mine is bone stock and still more than fast enough for me.

Where is Nate, he goes pretty fast on these things, he should know how fast they are capable of.

[signit98]

Nate does not run with a speedo... lap times are useless to determine top speed. Plus, you rarely top out at the track, not many of the tracks he runs at have straights long enough to top out...

Man, that brings me to an idea... if I can run at the local airport before they open and get one of the cops I know to meet me with a radar gun... that ought to do. Friends dad runs the show at Lindberg field... should be doable....

[chewie]

wonder if the straight at Phillip Island is long enough?...prolly not but I'll do my best...be there for a track day this Monday coming

[signit98]

Push it Jon, push it... and have fun!

[chewie]

I am excited but a bit worried too...

Hopefully there will be no red mist

[KMoore]

Originally Posted by chewie

wonder if the straight at Phillip Island is long enough?...prolly not but I'll do my best...be there for a track day this Monday coming

I think the straight is just under 900 mts long. The turn into the straight is very fast, as is the turn at the end. I would think you would be well in excess of 160 kph coming onto the straight on the 1200, but as you say, probably not enough room to top out. Let us know what speed you are able to come onto the straight at and what it gets to at the end.

[chewie]

righto

[RBMann]

Originally Posted by JonyRR

the long downhill straight on I-90 going east from wenatchee

....and that was a scary ride

I bet it was, since Wenatchee is not on I-90.

[Herb]

Originally Posted by AZ-Twin

Okay, let me see if I did this correctly, correct me if I am wrong, I am sure you all will. Forgive some rounding error, I used excel but am rounding below.


From my owner's manual
6 gear ratio .805:1
FD Ratio 2.62:1
Engine RPM 8500 RPM

At 8500 RPM the drive shaft is spinning 10559 RPM, and the rear wheel is spinning 4030.2 RPM.

With a 190 50 17 tire the overall tire height is 621.8mm tall * 3.14 = 1952.5mm circumference. /25.4mm = 76.9in traveled for 1 rotation of the rear wheel.

76.9in * 4030.2rpm = 309922.38 inches traveled per minute. This * 60, then devided by 12, then devided by 5280 should give miles/hour. I get approximately 293 mph as the theoretical top speed at 8500 RPM in 6th Gear.

After doing the math I decided to search the internet and found this, it agrees with my numbers.

http://www.catherineandken.co.uk/sti/tyres.html

Now, I know that speed is not obtainable, but I think 169 probably is with enough power. Not sure how much power it takes, that is another story.

You did not consider the primary drive ratio!

So in fact you have:

Primary drive: 1.824
6th: 0.805
Final drive: 2.62

With a 190/50 tyre that gives a top speed at the rev limiter (8800) of 166MPH or with a 180/55 top speed at the limiter is 168MPH (I knew mine was faster).

[Stampertje_35]

166 MPH = 267,26 KMH

Can you do the same thing for a ... HP2 Sport (tyre MPP 2ct 190/55) ???

I don't know the theoretical top speed ...

[Herb]

Originally Posted by Stampertje_35

166 MPH = 267,26 KMH

Can you do the same thing for a ... HP2 Sport (tyre MPP 2ct 190/55) ???

I don't know the theoretical top speed ...

I used this site for the gear ratios.

http://www.webbikeworld.com/BMW-motorcycles/hp-2-sport/

Gives a top speed at the rev limiter (9500?) with a 190/55 of 176 MPH.

This is not the theoretical top speed, which is more normally limited by other factors, but given enough power and the right conditions etc???

[AZ-Twin]

Originally Posted by Herb

You did not consider the primary drive ratio!

So in fact you have:

Primary drive: 1.824
6th: 0.805
Final drive: 2.62

With a 190/50 tyre that gives a top speed at the rev limiter (8800) of 166MPH or with a 180/55 top speed at the limiter is 168MPH (I knew mine was faster).

What is the Primary Drive? My owner's manual shows the "rear wheel drive gear ratio" as 2.72:1, and the transmission ratios for 1st-6th. I just chose 6th. Where does this other reduction of 1.824 occur?

[AZ-Twin]

Originally Posted by chewie

I am excited but a bit worried too...

Hopefully there will be no red mist

Jon, have fun at the track. We all look forward to the pictures and stories.

[Herb]

Originally Posted by AZ-Twin

What is the Primary Drive? My owner's manual shows the "rear wheel drive gear ratio" as 2.72:1, and the transmission ratios for 1st-6th. I just chose 6th. Where does this other reduction of 1.824 occur?

Its the first phase of the gearbox reduction, after the clutch, but before the input into the 6 gear ratio's, so 1.824:1 is applied to all 6 gears.

[JonyRR]

oops, I meant ellensburg

[shreddr]

I have the answers to all the velocity questions right here, enjoy!

http://www.youtube.com/watch?v=rzcLQRXW6B0