rpm vs. mph

I have this old 1980 KZ1000 and the speedometer doesn't work. I believe the sprockets and chain are stock size.
So until I get another drive unit for the wheel, I have no idea how fast I'm going.
As far as blending in with normal traffic, it's turning between 4000 and 4500 rpm's.
Any of you gearheads know about how fast I'm flying with it fifth gear, turning 8 grand?

really fast!

JEEBUS! Yeah, I'd estimate that you're pushing 125?
See, my tach is broken, so I don't know how fast my motor is spinning...but 8K in fifth? WOW

Accoring to my gearing table, my stock 900 will do 114mph at 8000rpm in 5th gear.
Your 1000 will probably do a tad better.

Yeah, I'm insane. But it was on a long smooth stretch with zero traffic, so I just tucked down and let her rip. Didn't take long to get there either. This is by far, THE fastest machine I've ever ridden. My old Honda 750F would start this real nasty wobbling crap when I got up around ninety or so. But this bike is just smooth as silk. And it it doesn't even sound like it's working hard at 8 grand.
I think if it ever comes down to choosing between my wife and this bike, well, I'm gonna miss her.

River ,that old 1000 only doin about 97 mph , they won't go any faster than that . Not enough cc dude !! Don't let these guys BS you . :whistle:








































Wonder what kida shit i'll get started outta this comment !! :woohoo: :silly: :woohoo: :silly: :woohoo: :silly:

geerbanger:
I just plugged rpm into my gear ratio spreadsheet. I got it from a site that was posted here on KZr.
Just put in your gear ratios, front/rear sprockets, & wheel/tire size.

I'm going on record to say that my speedo is pretty accurate. I've timed the miles on my odometer, and I'm within one or two mph at 80. I know my odo is accruate, because I've clocked the mileage to work (CA doesn't use mile markers on the freeways).
And the speed vs rpm chart seems about right to me.

wireman wrote:

really fast!

Interesting question.

The best answer is somewhere between Wireman's and LTD's.

There are book/table answers, there are bar stool answers, and then there's the *right* answer.

The trouble is that there's too many variables to get a handle on with the info available - like actual gearing, condition of the motor, and err... how much *freight* the 'ole gal is being asked to pull at a given rpm...

LTD's answer is good for a textbook case. Wireman's is the *best* - most honest - bar stool/real world answer available.

Given unknowns, a good SWAG (Scientific Wild-Assed Guess) is somewhere between 100 and 110mph...

Post edited by: Pterosaur, at: 2006/10/25 18:03

Yeah, but if the gearing is true, then then the wheel has no choice but to spin at a certain speed at a certain engine rpm. And that translates to vehicle speed.
If your tach isn't accurate (and I don't know how to test one on the bike), then all bets are off.
So if you can't make 114 mph on a 900, you shouldn't see 8000rpn on the tach. Right?

Edit:
I should say that I've never seen 114 on my speedo. I did see about 108 (my personal best) during our California Ride about a month ago, and I think the bike had plenty left.

Post edited by: ltdrider, at: 2006/10/25 19:26

I was just being a shithead stirring the pot a little ltd .

ltdrider wrote:

Yeah, but if the gearing is true, then then the wheel has no choice but to spin at a certain speed at a certain engine rpm. And that translates to vehicle speed.

Utterly true.

If your tach isn't accurate (and I don't know how to test one on the bike), then all bets are off.
So if you can't make 114 mph on a 900, you shouldn't see 8000rpn on the tach. Right?

Also true, and the dangerous part of firing off *quick* answers to nebulous questions.

A factor I didn't put in there was accuracy losses due to condition of the tach/tach cable.

The old Kaw analog speedos were famous for being from mildly to *wildly* optimistic when gauging indicated vs. actual speeds. With that margin for error in the speedos, I'd expect no less from the tachs.

A worn/shot inner cable sheath will also have a big effect on readings - most discernable as "needle bounce" between a hi-low varience, with the most accurate reading being the average of the two.

A cable core acts essentially as a long, spinning coil spring within the sheath. If everything's in good shape, the energy applied on one end reaches the other with negligible losses. But if there's a lot of drag on the cable core due to odd bends, worn housing. lack-'o-lube and a collection of rust dust inside the sheath, energy applied on one end of the cable will not make it to the other end, and it will actually read low.

It wouldn't be too hard to build a test rig to gauge a calibrated vs. indicated RPM reading, but a cheaper option would probably be to pick up one of those new-fangled digital jobs...

Edit:
I should say that I've never seen 114 on my speedo. I did see about 108 (my personal best) during our California Ride about a month ago, and I think the bike had plenty left.

Some, but in reality probably not all that much.

Remember - there's a *logarithmic* relationship between gains in horsepower vs. increase in speed, all else being equal...