RPM's at speed

[waldo877]

I have an '81 GS850GL, and at around 50-55mph, the RPM's sit at about 4,250 in 5th gear. Does this sound about right?

[Nessism]

[1948man]

Seems like if the ratio stays the same throughout 5th gear you would expect about 3940 rpms at 55mph.

[duaneage]

Depends on the tire

[TheCafeKid]

Hey Ed, you have one of these for the chain drive bikes? I know it would obviously change if you've changed the sprockets, or a 530 set up (tho you can get REALLY close to stock with a 530 set up as well) Id be curious to see exactly how far off my electronic tach on my 1100ES really is...

[Steve]

On my wife's 82 850L, I have checked the speed with a GPS and found the speedo surprisingly accurate. 55 indicated is actually about 54.2 on the GPS, and it's just under 4,000 rpm. I figured out that it's real close to 14 miles per 1000 rpm, so 4,000 should be 56 mph, 5,000 rpm should be 70 mph.

.

[Nessism]

Depends on the tire

The tire size can make a difference. For example, going from a 120/90 to a 130/90 will drop the freeway rpm by about 150 rpm at 70 mph.

[Nessism]

Hey Ed, you have one of these for the chain drive bikes? I know it would obviously change if you've changed the sprockets, or a 530 set up (tho you can get REALLY close to stock with a 530 set up as well) Id be curious to see exactly how far off my electronic tach on my 1100ES really is...

Hey Josh,

To perform the calculation we need...

- primary reduction ratio though the clutch hub gear
- reduction though the transmission gears
- final reduction through sprockets
- total wheel + tire height = radius

Gather this info and I can make some calculations.

[DanTheMan]

On my '80 850L, I have a 17" rear, always have had, the specs on the fender and the sticker on the head tube show the same size. My rpm at 55 (on GPS, speedo reads 59) is 44k-45k it's the first time I've seen the chart, the '80 850 GLT w/a 16" rear tire. I'm running a 130, but my new tire is a 120, I couldn't find anyone with a Perelli Scorpion M/T in the 130 size for some reason.

[bwringer]

Just to get ahead of your next question... these engines are incredibly durable and designed to SPIN. So grab that funny handle on the right and twist it hard and often.

6,000 RPM and 80mph all day are no problem. In fact, the fun on a GS850 doesn't really begin until 6,000 rpm. Run it up to redline regularly -- it won't hurt a thing and you'll have more fun.

[waldo877]

I guess you cleared up my concern Bwringer. Since I have a loud 4-1 setup, I got concerned that it was being wrung out too much for too long. I haven't even HIT 80 on it yet, but I guess I shouldn't worry about it now.

[bwringer]

The top speed of an unfaired GS850 is about 115-120. In case you were wondering...

They will happily drone along the interstate at 85mph for several hundred miles, too.

Twist it up!

[Dogma]

On my '80 850L, I have a 17" rear, always have had, the specs on the fender and the sticker on the head tube show the same size
....

Same on mine. Faulty chart?

[DanTheMan]

Just to get ahead of your next question... these engines are incredibly durable and designed to SPIN. So grab that funny handle on the right and twist it hard and often.

6,000 RPM and 80mph all day are no problem. In fact, the fun on a GS850 doesn't really begin until 6,000 rpm. Run it up to redline regularly -- it won't hurt a thing and you'll have more fun.

True. I redline mine in 1st and 2nd, sometimes 3rd, but then I'm exceeding the speed limit by quite a bit so I have to shift up and back off.......

[Nessism]

Same on mine. Faulty chart?

Sounds like a faulty chart. I know the guy who made it and it's not the first mistake he's made around here...

EDIT: Should be fixed now.