Hopefully the chart appears.

So I tried calculating MPH vs RPM for my bike using the spec sheet. To get the circumference for a 180/70B16 tire I used (180*70)/1270 to arrive at about 81.4 inchs. I double checked that by marking the wheel and the floor, rolling the bike until the mark returned to the same position and measuring it. I came up with 80 inchs so the calculated value seemed reasonable. That divided by 63360 inchs per mile gave miles per tire revolution.

So next was converting engine revolutions to tire revolutions. There I wasn't too sure what the "(overall)" meant. So I tried from the crank shaft to the tire. Since the numbers were getting smaller I figured that means it's engine revolutions per tire revolution so divided the engine RPM by the gear ratio to arrive at a tire RPM. That times the miles per tire revolution gave miles per minute and times 60 minutes per hour gave miles per hour.

So then came does this seem reasonable. No, not really. I came up that at 1.5k rpm I would be doing 12.4 mph in 1st and 41.5 in 6th. I've never taken 6th down that slow, but it's hard to imagine it would perform much like the bike at 12.4 mph in 1st would. So I figured overall meant crankshaft to driveshaft. So the numbers needed to be multiplied by about 1.35 for the 34/46 ratio. That produced the chart above. That gave a more reasonable 16.8 mph in 1st and 56.1 mph in 6th at 1.5k rpm.

The numbers seem more reasonable in that they are more inline with my experience. Still, they seem a bit off though. The bike certainly seems to be more responsive at 90 mph in 5th than 6th and the numbers seem reasonable there. 1st though is redlining at over 60 mph. The manuals shifting recommendations are rather sedate, but still they are reasonable.

Using the shifting recommendations from the manual versus my numbers seem a bit off. What I have is: 15 - 1.4k to <1k; 25 - 1.5k to 1.1k; 35 - 1.6k to 1.3k; 45 - 1.7k to 1.4k; 55 - 1.7k to 1.5k. I don't know what the lower end of the operating range of the engine is, but under 1k seems a bit low to be running the engine. So I'm wondering, what did I do wrong?

Anyone see a mistake in this? Anyone know enough, like maybe someone with a tach, to say if these numbers are reasonable? Seperately, but sort of related, is there a OBD port on a motorcycle? I figure not but I have a logger that will plug into one. Also what do you get with a dyno? Just a print out or do you get an actual dataset? If you get an actual dataset does anyone has a stock twin cam 96 dataset, perhaps as a before?

[IMG]local://upfiles/55839/E55B568023994A079C052EDD157FE176.jpg[/IMG]

 

Why did you need all this? Just buy a tach if you really need to know what RPM your at. I just shift when it feels like I need to, and don't lug the engine. Your numbers for 6th gear are pretty good, I usually shift into that above 60mph and it seems to pull pretty good. It's for cruising not accelerating. Any overdrive type gear doesn't have alot of torque. All in all... good work with all the math. I don't think I could have figured any of it out.

 

Because it costs a lot less than a tach

 

Any overdriver gear has LESS torque than a 1:1 drive ratio. 4th is 1:1 5th and 6th are overdrive.

Shift when she sounds like she wants to shift.

 

you have waaaaaaaaaaaaaay too much time on your hands.

And your figures are totally wrong.

 

I don't get it and I even have a tach. If I run my bike at 56 mph in sixth the engine would fall outon to the highway.

 

Can I watch you go 60 in 1st?

 

My rev limiters kick in at 45 mph in 1st. gear. and 2nd gear rev limiters kick in at 75 mph. That is 5500 to 5600rpm's the rev limits will kick in. Redo your Math.

 

+1 Way off in the low range, for sure ....... try this, it was posted earlier for reference.

 

Ok, so looks like "(overall)" means it includes the primary. That puts the rev limiter at 45 mph in 1st and 66 in 2nd. It also puts you just under 4k rpms in 6th at 100 mph. I would use the actual measurement of the tire, but I figure the speedometer ismeasuring RPM's for the tire and reporting it in MPH by the spec's of the tire. It might be interesting to get the GPS out and check the speed against the speedometer.