Passing Gear?

[BA80]

[IanDMacDonald]

TR, too funny! I was referring to the fact that a fixed gear system can't change rpm based on carburetion(!) and if guys continued to debate that it does, was going to "give them a helmet and put them on the short bus". Purely coincidental about your helmet stuff!

CZ has the FD swap on his 80G, what rpm are you turning at highway speeds, CZ?

Hey Bonz/Trbig- Maybe I have faulty memory or something, and I'm wrong. But, I coulda sworn that when I had 137.5's in, with mixture screws not dialed-in, I was seeing mid to high 70's @ 5k rpm, and 80 mph @ 5200 k rpm. But, pretty sure with the 140's, and dialed mixture screws, I see 70's much sooner, and 80 rpm much sooner than 5200 rpm's.

[TopCatGr58]

Hey Bonz/Trbig- Maybe I have faulty memory or something, and I'm wrong. But, I coulda sworn that when I had 137.5's in, with mixture screws not dialed-in, I was seeing mid to high 70's @ 5k rpm, and 80 mph @ 5200 k rpm. But, pretty sure with the 140's, and dialed mixture screws, I see 70's much sooner, and 80 rpm much sooner than 5200 rpm's.

Hey Ian,

Not trying to be a Smarta$$, but was that before or after you installed the BARNETT clutch springs?? As was stated, carburation itself won't affect the rpms/vs road speed, but clutch slippage will.

T.C.

[CaptonZap]

CZ has the FD swap on his 80G, what rpm are you turning at highway speeds, CZ?

Geeze, I hate to get in the middle of this, since it shows a lot of the various mechanical comprehension levels of the various protagonists.
But in the interest of furthering the debate, I will make a note of RPM versus MPH next time I go for a ride.
Just to muddy the waters, I replaced the speedo a few miles back, and have no idea how accurate IT is.
I need to ask Diver Ray if there are any electronic components inside that are a common failure point. (Yes, I did take the bezel and glass off, just to see what is in there)
I heard that he is our resident guru on speedo repair.

Carry on, CZ

[motoman]

Just came from a short ride. About 4 years ago I checked my speedometer with GPS. When the speedometer said 65 GPS said 60 and 100 vs 94 respectively. So today, no video because I don't have anything that well take a video. Anyway, when the speedo said 75 (which should be 70) my tach said 3600 in 5th, standard with 750/850 FD, 17" rear wheel. And I can hit 100+ in 3rd. Don't know why I have lower RPM's than most. YMMV.

Gearing is the same as others, so don't waste your time with wild dreams.

[IanDMacDonald]

Hey Ian,

Not trying to be a Smarta$$, but was that before or after you installed the BARNETT clutch springs?? As was stated, carburation itself won't affect the rpms/vs road speed, but clutch slippage will.

T.C.

That's a good question T.C. I had to think about it. Here's the facts: pre-Barnett's (last riding season), I always rode 80 mph @ 5200 rpm on the highway. This riding season (post-Barnetts), I ride 74 mph on the highway. So, not much attention to rpm's and speeds higher than 74 mph.

Now, the "dreamy" part on my end that I guess you guys are shaking my faith in:

Over the past month I changed-up carb jets from 140 to 137.5 to conserve on gas. Had the opposite effect, and I used more gas. I did not pay attention to top-end rpm. Going back to 140's, and plug-chop tuning my carbs, I instantly noticed that my rpm's were lower at highway speeds. Like, u ride the bike enough, u know where the rpm's were, compared to now. So, now I believe 80 mph is below 5200 rpm?

[Bigfoot]

Hey Bonz/Trbig- Maybe I have faulty memory or something, and I'm wrong. But, I coulda sworn that when I had 137.5's in, with mixture screws not dialed-in, I was seeing mid to high 70's @ 5k rpm, and 80 mph @ 5200 k rpm. But, pretty sure with the 140's, and dialed mixture screws, I see 70's much sooner, and 80 rpm much sooner than 5200 rpm's.

79 standard, stock FD, 17" wheel. i see 80 at right around 5K as indicated on the tach. But.... i am just relying on the stock tach and speedo which i have checked against a gps and seems fairly accurate.

[IanDMacDonald]

79 standard, stock FD, 17" wheel. i see 80 at right around 5K as indicated on the tach. But.... i am just relying on the stock tach and speedo which i have checked against a gps and seems fairly accurate.

So, maybe T.C. is onto something with the springs? As what Harry confirms what I see now (80 mph below 5200 rpm's), I saw 80 mph @ 5200 rpm's last year.

[CaptonZap]

OK, after some close observation, here are my numbers, with a high mileage 17 inch Dunlop 491 on the rear.
All numbers are approximate, since my tach lacks a vernier scale.
40mph = 2300 ratio 57.5
45 = 2650 58.8
50 = 3100 62
60 = 3600+ 60
65 =3750 57.7
70 =4000 57.1

The center numbers are suspect, given the ratios don't fall in with the others. Or it could be that parallax in the reading while at speed leads to rounding errors. Who knows.
Any way, there it is, make of it what you will.

CZ

[IanDMacDonald]

Wow. 4K @ 70. I woulda like to have seen what 80 was.

[red bandit]

OK, after some close observation, here are my numbers, with a high mileage 17 inch Dunlop 491 on the rear.
All numbers are approximate, since my tach lacks a vernier scale.
40mph = 2300 ratio 57.5
45 = 2650 58.8
50 = 3100 62
60 = 3600+ 60
65 =3750 57.7
70 =4000 57.1

.

CZ

Same numbers I had with stock FD.

[CaptonZap]

Wow. 4K @ 70. I woulda like to have seen what 80 was.

If the ratios hold true, using 58 as a median, we could say that at 80 mph, we would be turning ( 80 X 58 ) 4640, and we would be doing about 85 at 5 grand.
Hooo boy, are we having fun yet?

CZ

[IanDMacDonald]

Hmm. Those revs just seem a little low. Maybe my tach is off?

[red bandit]

I have 2 spare tachs + the one on the bike. All 3 give the same reading. just sayin.

[ViperRon]

There would also be a difference if the 750 or 850 final drive was installed of like 700 RPM also at this speed. So who is running what rear end is very important too.