[fergy]

Been that way since day one. I have seen threads here where others get the same readings.

If all gears/tires are the same size, that's practically impossible. I'm not saying yours doesn't say that, I'm just saying there has to be something different. From 4500 to 5000 rpms on my bike in 5th gear, we're talking a large increase in speed. Sounds like a bad tach or something.

 

[cegodsey]

Maybe our clutches are slipping? Hey Newell, what kind of oil you using?

 

[Woody]

I can see front tire diameter effecting the speedometer since the sender is mechanically tied to that but I'm with Fergy about the back tire as it turns independant from the front and there is no link from the speedo to the tranny so tranny rpm's should have no effect on the readings. Slipping/worn clutch makes the most sense to me.

 

[El_Taco]

I like what I see. Been wanting to build a bigger bike for some time now. At 70mph my 1971 CB500 is pushing 6500. Keep in mind that's with wide open megaphones.

 

[cegodsey]

OK Woody, imagine if you will, a matchbox wheel and a bulldozer wheel. If our engine drives both wheels, which one will go the furthest with a driveshaft speed of 1 rps? So, take it a step further, and put a larger tire on the bike, perhaps a bulldozer wheel. At the same rpms, won't the bike have gone further, thus faster? So the speedo is tied to the bike tire (thus the tranny) by the common denominator - that being the ground. A bigger tire (like the 180/90) will lower the rpms by about 500. This isn't theory - there are some here and on Yahoo that have gone to the larger diameter rear in order to lower the engine speed.

...the back tire as it turns independant from the front and there is no link from the speedo to the tranny so tranny rpm's should have no effect on the readings.

So you must think that the bike will go 70 even if you have no back tire, huh?

 

[Woody]

Son of a! I'm the only person in America that lost the same arguement twice!

:rockon:

Yep, but I'm only one behind you.:BLAM:

 

[cegodsey]

Sorry if I came across terse. I seem to have developed a pet peeve that has to do with speedometers and tire sizes. The "peeve" started in high school, with a friend that insisted that if a speedometer was off by 5 mph at 60, then it was always off by 5 mph. He couldn't explain exactly why the speedometer didn't register 5 mph when parked, but insisted that he was right. Arrgghh!

 

[Dan]

When my speedometer reads 70MPH, which is actually 64-65 according to my GPS, my tach reads 4700RPM.

 

[cegodsey]

That's semi-reasonable.

 

[cegodsey]

Hey guess what? I'm an IDIOT. I *thought* I knew what the rpms were, but I was really wrong!

At 5000 rpms, my speedometer reads 75
At ~4700 rpms, my speedometer reads 70

So rnewell, although I'm never wrong, I was WRONG! Your rpms are about right.

 

[racohoon]

Can't tell you off hand about other speeds, but I travel @ 60mph all the time and am reading 4,000-4,100 RPM. I only pay attention to the 60 mph tach reading so I can remember it in the event my speedo fails so I know I'm not speeding to the point I'll get a ticket.
Tires are stock front and rear.

 

[rnewell]

Hey guess what? I'm an IDIOT. I *thought* I knew what the rpms were, but I was really wrong!

At 5000 rpms, my speedometer reads 75
At ~4700 rpms, my speedometer reads 70

So rnewell, although I'm never wrong, I was WRONG! Your rpms are about right.

Right or wrong thats what my tach says.

 

[Hizzo3]

i guess if your spedo fails, u can always use the tach as a refference

 

[hyperbuzzin]

I usually look at the tach more than the speedo when riding. That way I don't try for that missing 6th gear too often.

 

[Hizzo3]

I usually look at the tach more than the speedo when riding. That way I don't try for that missing 6th gear too often.

you do that too? lol, cause i do it all the time, esp in city driving cause i for some reason think it should be slower

 

[cegodsey]

Yeah, I too have to look at the tach before shifting into 6th.

 

[rnewell]

We have a 6th gear ?

 

[cegodsey]

Yeah. You didn't know that? Funny thing is, the rpms stay the same as 5th, so you don't gain much. If you're on the highway, and you're in 5th, try shifting into 6th. There won't be an obvious clunk like the other gears. When you release the clutch, you'll see that the rippims are the same. One good feature of 6th is the fact that when downshifting, the next gear down will be 4th, so you won't have to go through 5th.

 

[rnewell]

Actually I wish we had reverse. I have to back the bike up to get it out of the garage. I'd like to have one of those Batman thingies where the car rotates in the bat cave.

 

[cegodsey]

Build one! All you need is one of those lazy susan thingies that can support 700 lbs, and a big slab of plywood.