Topic: MPH vs RPM question?

[Skyguyz]

My 76 K6 has both aftermarket gauges. *Came with the bike.....

Edit: Bike has a standard 17/48 tooth sprockets.

I know these are not accurate as I have tested the MPH vs a GPS speedo and it reads 6-7 MPH high than actual speed, (Typical of these things.)

My question is at what RPM should you see 50 MPH, 60 MPH & 70 MPH?

The bike seems to be reving higher than what the aftermarket tach gauge is showing.

On the inaccurate MPH gauge - 50 MPH, (actual 43 MPH) = 3000 RPM   60 MPH, (actual 54 MPH) = 3800 RPM 

70 MPH, (actual 63 MPH)  = 4200 RPM  *I am sure the engine is spinning faster than what the RPM is showing?  Yes/no ?


Thanks in advance,

Sky

[david 750f]

http://forums.sohc4.net/index.php/topic,157062.msg2010023.html#msg2010023

That for the 17/48 sprockets. Your results may differ with gearing changes  and non-stock tire sizes,

[Skyguyz]

Thanks, I meant to include that info. Post has been edit to reflect a 17/48 tooth sprocket combo.

[TwoTired]

What is your front tire size?

[PeWe]

You can change sprocket sizes and rear wheel - tire diameter on that Excel sheet to get your calculated speed.

I have edited that file which I got on this forum around 8 years ago.  Added Kmh and later gearbox where 4 and 5 differ.

My K6 with 3.25-19 tire did not differ much when comparing speedo and laser/radar sign beside road complaining on peoples speed
I think speedo showed +2.5%, absolutely below 5% too much which is good.

Important to find that laser/radar sign without any frantic braking i_iot in front  of you so you can test much faster which makes reading more accurate.
Streets with such sign has usually speed limit well below a good testing speed.