RPM vs. speed

[Incubus]

My God Incubus is running well. I think this might be the best running of all my bikes. And frankly, all of my bikes run well. But this one - wow. Rock solid smooth idle. Strong, consistent acceleration. This is the first time I have worked on a bike that I have come away with a measure of respect (bordering on admiration) for the PO. This bike was well cared for. When I took the clutch apart to examine it every thing was in very good shape. The springs measured 42.5mm and above, which is practically new spec. The steels were shiny and looked new. The tranny shifts so easily that it seems to grab the next gear. No issues with holding any gear under any torque. I suspect the dogs have been undercut. The PO even mounted a 16-inch Special rear wheel and either found or fashioned a very professional looking spacer for it. Incubus sat for more than a decade before I got it so the rings likely were stuck when it first started. But from the power this engine exhibits lately indicates they clearly have worked themselves loose and compression across all four cylinders is strong.

As you might have guessed, I am pretty pleased right now - and I am just wondering what is going to go wrong to shatter this nirvana. I am of Irish descent. We recognize genetically that the the beautiful rays of the rising sun exist only to create shadows so that doom may hide.

Enough. That really has nothing to do with my posting.

I've been reading a lot on the forum lately about the 850 FD conversion. My bike, the way it is now, does 60 mph at 4,000 rpm and 75 mph at 5,000 rpm. That is exactly the same gear ratio as all of my other 70s vintage rice burners. Is that stock? Does the 850 conversion lower that? If that is stock I am fine with it. I am just wondering, considering the other things PO did on the bike, whether he might have already messed with the FD.

Took a long time to get to that short question, didn't I. Again, Irish descent.

Thanks, y'all.

Patrick

[oseaghdha]

..........

<BLAH BLAH ..........

Irish(Been there done that) ..............etc>

I've been reading a lot on the forum lately about the 850 FD conversion. My bike, the way it is now, does 60 mph at 4,000 rpm and 75 mph at 5,000 rpm. That is exactly the same gear ratio as all of my other 70s vintage rice burners. Is that stock? Does the 850 conversion lower that? If that is stock I am fine with it. I am just wondering, considering the other things PO did on the bike, whether he might have already messed with the FD.

Took a long time to get to that short question, didn't I. Again, Irish descent.

Thanks, y'all.

Patrick

Sounds normal for the 16" wheel. That was the story on my Special. It would do 80 at 5K when the tire was new.

The 750/850 FD will drop it by about 500-600 RPM in 5th. I'm turning 4000 at about 68MPH per GPS with my gonna-have-to-get-a-new-one-soon rear tire.

[Incubus]

My back tire is new, but I wanted to lower the back end a little so I went with a 130/80-16 tire. Lowers it about 1/2 inch.

[fredintoon]

My back tire is new, but I wanted to lower the back end a little so I went with a 130/80-16 tire. Lowers it about 1/2 inch.

Hi Patrick,
switching from a 130/90-16 tire to a 130/80-16 tire reduces the the tire's outside diameter by 4%.
So the bike will rev 4% higher than with a 130-90-16 tire.

[XSokieSPECIAL]

I am just wondering, considering the other things PO did on the bike, whether he might have already messed with the FD.[Quote]

I just did the FD swap. My SG has the 130-90-16 and before the swap, allowing for differences from tach to tach,my RPMs were approxamatly the same as what your at.

I really like the lower cruising RPMs. Now at 5000 RPMs I'm running between 80 and 85. 70 is around 4200.

Greg

[XJOK2PLAY]

Greg,
Sounds to me like you're seeing the usual 600 or so RPM's drop compared to Succubus.

I'd say his is stock, from what he's saying his speeds / RPM's are.

[XSokieSPECIAL]

Greg,
Sounds to me like you're seeing the usual 600 or so RPM's drop compared to Succubus.

I'd say his is stock, from what he's saying his speeds / RPM's are.

Ya, that is what I was trying to say. Not to clear huh?

Seems like I'm closer to 800 though.

Maybe just wishful thinking.

Greg

[motoman]

Succubus, my 81 standard runs identical rpm/spd. as what you got, even though having the 17". Speedo and tach have been checked for accuracy, and both still "dead on" as they were 28+yrs.ago so yours is correct and stock for all practical purposes. Hope that helps.

[Incubus]

That helps. I am not unhappy with that gearing. It is exactly the same as my Honda 750s and other bikes I have owned. I don't mind the higher rpm at highway speeds. I think it keeps the engine happy to turn fast. That's what it was designed to do.

Patrick

[trbig]

That's what it was designed to do.

Depends on who you talk to. I have heard that the bike was originally designed to use the same final drive as the 750/850.. and that's why it feels so right to most. They only went to a higher gearing drive for the 11 to get it into the 11 second range for the quarter mile.

Can't prove it, but that's the story I hear. Not everybody is the same, so it's good we at least have options.


Tod