How fast would you say...

[hikermikem]

...I was going on my "81 1100EX - saw the tach needle hit 8K in 5th gear.

Stock sprockets. Just wondering, I know it was a bit quicker than 85MPH

Mike

[Steve]

87?

.

[Nessism]

You're an engineer Mike, calculate it. I'm feeling lazy or I'd do it for you. Only hard part is coming up with the wheel radius. Might be easier to measure circumference.

[jbs80106]

well, 8k in 5th on my 750 is 100+...

[Curly]

speed=(rpm/primary reduction/fifth gear ratio/final reduction)*wheel circumference/12/5280*60

On my bike that's 105 mph, with a 170/60-17 tire size.

with a 110/90-17 (I think that's roughly your size) it's 103mph, but again that's with my primary, final, and 5th gear reductions. Your results will vary.

[Steve]

On my 850, 4k = 56 mph, so 8k = 112 mph.

Your 1100 would be geared a bit taller.

.

[Smokinapankake]

You were going fast enough to lose your license.
I've done this a time or two as well, and it feels like about 300 MPH on my 82 Katana. But oh the sound is so sweet.

[Nessism]

It's easy enough to calculate, only getting the wheel circumference is tricky since the radius will shorten with weight on the bike. A dot of paint on the tire helps, then sit on the bike and move it for two rotations or three maybe if you can still see the paint mark. Measure the distance between the marks and you have circumference.

[Dogma]

It's easy enough to calculate, only getting the wheel circumference is tricky since the radius will shorten with weight on the bike. A dot of paint on the tire helps, then sit on the bike and move it for two rotations or three maybe if you can still see the paint mark. Measure the distance between the marks and you have circumference.

Wouldn't it be easier just to double the reported speed at 4k in 5th?

[trippivot]

put a stopwatch on your dash. Get on the highway where there are mile markers.

Go 60 Mph and check the time at every marker. You'll get good at it and see that your speedo is really off.

Go your 8.5K and test it this way then it is super easy to calculate.

60sec/60mph = 45sec/90mph = 30sec/120mph

[Nessism]

Wouldn't it be easier just to double the reported speed at 4k in 5th?

No. The tach is not accurate.

[Dogma]

No. The tach is not accurate.

But if you're calculating from the revs, you're still relying on the inaccurate tachometer. On top of that, the measurement error of several dozen inches multiplied over several hundred revolutions in a mile. Probably still more accurate. The method I describe does add the errors of the tach and speedo, then double them (assuming error scales linearly).

OK, so my way is probably less accurate, but I still contend it's far easier.

Speaking of errors in the tach and speedo... I recently installed a gizmo (SportVue MC-1, always wanted to try one) that allows me to monitor speed based on a magnetic wheel sensor and digital electronics. The mechanical gages not only have nonlinear error, there is also hysteresis. I saw as much as 4mph change in the mechanical speedo vs the digital, and a few hundred revs difference in the tach at the same speed. This was done with fairly new cables, and the gages operating smoothly. Something to keep in mind when trying not to get busted.

[chef1366]

With stock sprockets I'd say around 115. Possibly faster since 9.5 is redline.

[1948man]

Wouldn't it be easier just to double the reported speed at 4k in 5th?

Yes.........

[ddaniels]

Does it really matter anyway? I know it would be nice to know, but anything over 85 is too fast anyway on these old bikes.