85mph speedo guys...how fast am I going??

[tkent02]

I dont think the HP curve is linear enough for that to work.

HP has nothing to do with it.
It would be absolutely correct except for tach and speedo errors.

[bonanzadave]

HP has nothing to do with it.

OK.....I guess. How about wind resistance ?

[tkent02]

OK.....I guess. How about wind resistance ?

So you open the throttle more, it does not effect RPM/Speed relationship.
It would in a motorboat or propeller driven airplane, or even in a car with a non-locking automatic transmission, but not a direct drive system like a bike with no slipping clutches.

[Baatfam]

Try using a Gps to see your speed.

A what??? GPS?? Wouldn't know what to do with one...
I still use a paper map and if really needed, a lensmatic compass...

Bob, do you get any speed wobbles at triple digits ? I guess youve gotten over that welded frame.

Smooth as if it was running on rails, Dave...(Still watching for a replacement frame, though)....

[Rudeman]

So you open the throttle more, it does not effect RPM/Speed relationship.
It would in a motorboat or propeller driven airplane, or even in a car with a non-locking automatic transmission, but not a direct drive system like a bike with no slipping clutches.

There might be some external influences from tire slippage. I would get a GPS unit that records the fastest attained speed for later retreival.

[tkent02]

There might be some external influences from tire slippage. I would get a GPS unit that records the fastest attained speed for later retreival.

You think a GPS can measure as precisely as tire slippage?
What, 1/20 of a mph or so?

That's a Hell of a tight GPS.

[Rudeman]

You think a GPS can measure as precisely as tire slippage?
What, 1/20 of a mph or so?

That's a Hell of a tight GPS.

GPS is very accurate. It is not tied to the engine or driveline; it does not matter if there is any aerodymanic drag or tire slippage or transmission slippage. All it needs is to acquire three satellites. If you want to know how fast you are TRAVELLING then GPS is the way to go.

[Guest]

There are a couple places that make a gear reduction for speedo's. Add that and then double the indicated speed.

[Baatfam]

There might be some external influences from tire slippage. I would get a GPS unit that records the fastest attained speed for later retreival.

You think a GPS can measure as precisely as tire slippage?
What, 1/20 of a mph or so?

That's a Hell of a tight GPS.

GPS is very accurate. It is not tied to the engine or driveline; it does not matter if there is any aerodymanic drag or tire slippage or transmission slippage. All it needs is to acquire three satellites. If you want to know how fast you are TRAVELLING then GPS is the way to go.

LOL you guys.....I was only looking for a rough idea....

[tkent02]

GPS is very accurate. It is not tied to the engine or driveline; it does not matter if there is any aerodymanic drag or tire slippage or transmission slippage. All it needs is to acquire three satellites. If you want to know how fast you are TRAVELLING then GPS is the way to go.

How many decimals does the speed readout go to?
Tire slippage is insignificant unless doing a burnout. It's really more tire squirm than real slippage, it's not much.
Clutch slipping? Then you are not going very fast at all.
Transmission slipping? What, broken gears or something? Again, it won't go very fast like that.

By the way, I use GPS all the time at work. Good stuff. With only three satellites the position is not all that accurate, the speed is an averaged estimation. With more satellites being received the position resolution gets much better, hence the speed readout becomes more accurate. But the GPS display does not tell you how many satellites it is receiving at the time unless you ask it, nor does it tell you how accurate the speed readout is at the moment.

It seems to me if he had a GPS he wouldn't have asked the question.

[tkent02]

LOL you guys.....I was only looking for a rough idea....

In my opinion, you were hauling ass. Good enough?

[Baatfam]

In my opinion, you were hauling ass. Good enough?

That's kind of what I figured.....

It was just a short blast on an isolated, empty road....just a test really, that's all...

[tkent02]

It was just a short blast on an isolated, empty road....just a test really, that's all...

I think "I was going to the hospital" would be a better line to use.

[headsbikesmopars]

Steve and Tkent02 are absolutley correct ! You DO have a mechanical 'link' between crank and rear wheel. NO fluid coupling . If you double speed...then rpm is doubled. And the reverse is also true. Try it for yourselves. Take it up to 40mph and note rpm..run it on up to 80mph and again note rpm, it will be exactly double rpm at 40 mph.

Terry

[Baatfam]

56-57mph at 4K in fifth....so X2 = 112-114....

OK...that leads to the next question...how accurate are the speedos on these things...