RPM to speed

[Tom M]

I sometimes wonder how fast I'm really going during my highway commute. I do know that my "vague-lia" speedo is pretty optimistic, but I still really don't look forward to the day that a state trooper answers this question for me.

 

Since I didn't find anything here after a quick search I plugged some info from the owners manual into a gear-speed calculator that I found and came up with these numbers for 6th gear with a 180/55-17 rear tire. The numbers for my 170/60 are slightly higher.

 

RPM = MPH

8000 = 141.39

7500 = 132.55

7000 = 123.72

6500 = 114.88

6000 = 106.04

5500 = 97.21

5000 = 88.37

4500 = 79.53

4000 = 70.7

3500 = 61.86

3000 = 53.02

2500 = 44.18

[Paul Minnaert]

Looks almost to what I have, mine are slightly less, 139,1 @ 8000 rpm, might be the tyre size calculation.

 

Mine does 9000 in 6th so that gives 156,5 in my calculation.

[raz]

I sometimes wonder how fast I'm really going during my highway commute. I do know that my "vague-lia" speedo is pretty optimistic

What does your speedo indicate at some of those speeds? Of the motorcycles I have tried, my Sporti actually has the most accurate speedo. Pretty much like my car. At 90 km/h indicated, I have a GPS speed of about 87 km/h.

[Tom M]

My speedo is not as far off as I thought. With my 170/60 rear tire at 5000 rpm I should be going 89.21mph according to the calculator. My speedo showed about 92mph.

[mdude]

this was fun. I'm obviously going a lot quicker than I thought! No wonder I drive alone....

[rocker59]

 

 

 

 

sixth gear. 180/55-17 Dunlop Roadsmart.

[dlaing]

The numbers for my 170/60 are slightly higher.

I think you got that backwards.

Actual speed per RPM for a smaller tire will be lower.

Veglia speed per RPM will be the same regardless of tire size.

Otherwise, nice work. If my speedo dies, using your numbers I could index the tach.

As it is, using a 160 tire, my actual speed is off by about 6% at the Veglia speedo and distance covered seems to be off by about 3%.

So when I calculate 30MPG it should really be about 29MPG

[Tom M]

I think you got that backwards.

Actual speed per RPM for a smaller tire will be lower.

Veglia speed per RPM will be the same regardless of tire size.

Otherwise, nice work. If my speedo dies, using your numbers I could index the tach.

As it is, using a 160 tire, my actual speed is off by about 6% at the Veglia speedo and distance covered seems to be off by about 3%.

So when I calculate 30MPG it should really be about 29MPG

 

I think I got it right. 180/55 = 99mm sidewall height, 170/60 = 102mm sidewall, so the 170/60 has a larger diameter than stock 180/55.

 

FWIW here's the final drive ratio (engine to rear wheel) for each gear according to the owners manual in case anyone wants to check speed vs rpm in other gears.

1st gear = 11.7589 to 1

2nd = 8.7103

3rd = 6.6812

4th = 5.4439

5th = 4.7306

6th = 4.1737

 

Since these are engine to rear wheel ratios I entered 4.1737 (6th gear) into the transmission gear ratio field and 1 into the differtial ratio field into the calculator referenced above to get my numbers. The calculator I used is at http://www.kabamus.com/garage/gears.html

 

Rocker, either my numbers are off or your ITI gauges are Do you have GPS and if so how does it compare to your speedo?

[docc]

Ya'll make me dizzy with your math. Watching the Veglia, and compensating for its fluctuation, the Garmin shows almost-exactly 5 mph less even up into the higher ranges (90 mph indicated is 85 by the satellites). It could be 4%, but I try not to look down much at those speeds. Not that I've ever actually gone that fast; you know: yesterday or otherwise . . .

[dlaing]

4000 = 70.7

3500 = 61.86

3000 = 53.02

2500 = 44.18

FWIW

on my 2000 V11 with Pirelli 160/60

in sixth gear comparing tach to speed in Vague-lias

3500 = 68

3000 = 58

2500 = 48

2000 = 38 (going down hill, you bloody anti-lug nazis)

I would not be surprised if others get very different readings.

Will try to get more readings.

Also, FWIW, I regularly ride by a road side radar that tells you how fast you are going, and when I am going 50 Veglias, it says I am going 45MPH. Unfortunately the radar only registers from 40 to 50MPH, but I think it is accurate as long as there is no traffic around, and also unfortunately, it does not work late at night, maybe it is solar powered????

 

PS belated thanks, Tom, for the correction regarding tire size and diameter, and thanks for posting the numbers...