Best speed/rpm for fuel economy? GS850

[Grimly]

So anyways, at what highway speed have you guys noticed the best fuel economy on an 850? 55, 65, 75 mph?

A long time ago I was accompanying a friend on a small bike that could only really cruise at 60mph on the motorway (freeway). That was the longest most boring 100 mile journey I've ever had on that 850.
When I refilled the tank and worked out the fuel consumption, I was surprised to find it had done 60+mpg. Which means, on the European tank, it could have done 300 miles. It was never anywhere near that on any journey since.

Would it hurt the engine to do 75mph which is likely closer to 5,500 rpm for an extended period of of time? Please forgive my ignorance.

When the bikes were working for a living, my normal motorway cruising speed was in the mid-80s. More than that was counter-productive, as it just used more fuel and made no difference to journey times, unless I was willing to risk life, limb and licence by doing 120.

[Grimly]

We did not do this all day long, but here is what your engine speed would be when going just a bit faster.



Rest assured, I had BOTH hands on the grips. My wife leaned over my shoulder to get the picture.

The engine will be quite happy at anything less than redline. Gas mileage will suck over 5k RPM, but it will do it.

.

Of course, the normal speedo and rev counter will have both needles pointing straight ahead at that speed in gear, which is a fairly useful symmetry.

[93Bandit]

A long time ago I was accompanying a friend on a small bike that could only really cruise at 60mph on the motorway (freeway). That was the longest most boring 100 mile journey I've ever had on that 850.
When I refilled the tank and worked out the fuel consumption, I was surprised to find it had done 60+mpg. Which means, on the European tank, it could have done 300 miles. It was never anywhere near that on any journey since.


When the bikes were working for a living, my normal motorway cruising speed was in the mid-80s. More than that was counter-productive, as it just used more fuel and made no difference to journey times, unless I was willing to risk life, limb and licence by doing 120.

Interesting. That's quite the range. How confident in your math are you? lol! Just kidding. How does the European tank differ from the US tank? Fuel tank, not war tank in case someone is feeling witty...

Of course, the normal speedo and rev counter will have both needles pointing straight ahead at that speed in gear, which is a fairly useful symmetry.

Oooo, I like how you think Grimly! In my car, when the speedo, tach, fuel gauge and temp gauge are all point north it makes me a little too excited. I don't run it long like that though because straight north on the tach is close to redline lol.

[Admiral Beez]

On my 82 GS650G I get less than 200 km (125 miles) before reserve is needed. Though it’s a smaller motor hauling my 220 lb ATGATT frame around, so sprinted throttle is often used.

[Grimly]

How does the European tank differ from the US tank?

The book says it's 22L, but on more than one occasion I've put in 24L when it was running on reserve for a while and I'd hoped to find a petrol station soon.
I suspect the book is being conservative, but that 22L figure is repeated all over the various spec pages on the web and even in the Haynes manual.
Whether Suzuki ever made the tanks a couple of litres larger for the EU market - I doubt if it was worth their while to go to all that extra hassle just for us, so nah.
Otoh, in the early days of having both bikes, the first thing I did was to enlarge the stupidly small breather hole at the top of the filler neck, and that allows a bit extra fuel in with a rapid fill, so perhaps that's it. I suspect the 22L figure is to allow sufficient headspace for expansion in the desert, etc. Not a problem for me, as there are no deserts here, and I always have a journey after filling, even if it's just the journey home, so the bike is never parked up with a totally full tank, there's always a little headspace in it.

[Burque73]

Speaking of tank volume, I'll never forget this post by 2BRacing showing a massive 28L tank on a GS1000

https://www.thegsresources.com/_forum/showthread.php?250880-Suzuki-s-in-the-family&highlight=

[Gorminrider]

Now THAT ^^^ is a cruising bike!

[zuluwiz]

My 850 is as stock as I can make it, and on a 140-mile(each way) trip 1.5 years ago, I was usually running 4k rpm and getting 43 mpg. That gives me 60 mph. That's loafing for the 850, but I'm not the speed demon I was 40 years ago.

[93Bandit]

The book says it's 22L, but on more than one occasion I've put in 24L when it was running on reserve for a while and I'd hoped to find a petrol station soon.
I suspect the book is being conservative, but that 22L figure is repeated all over the various spec pages on the web and even in the Haynes manual.
Whether Suzuki ever made the tanks a couple of litres larger for the EU market - I doubt if it was worth their while to go to all that extra hassle just for us, so nah.
Otoh, in the early days of having both bikes, the first thing I did was to enlarge the stupidly small breather hole at the top of the filler neck, and that allows a bit extra fuel in with a rapid fill, so perhaps that's it. I suspect the 22L figure is to allow sufficient headspace for expansion in the desert, etc. Not a problem for me, as there are no deserts here, and I always have a journey after filling, even if it's just the journey home, so the bike is never parked up with a totally full tank, there's always a little headspace in it.

22L? That's 5.8 gallons. That's a lot bigger than mine. Is the GL tank smaller than the G tank? Honestly I don't understand all the differences. The GL tank is more tear drop shaped, and the G tank is more rectangular. I assume the G tank is bigger? Can someone clarify? If you include pictures too, you'd be extra cool.

[Steve]

22L? That's 5.8 gallons. That's a lot bigger than mine. Is the GL tank smaller than the G tank? Honestly I don't understand all the differences. The GL tank is more tear drop shaped, and the G tank is more rectangular. I assume the G tank is bigger? Can someone clarify? If you include pictures too, you'd be extra cool.

Yes, the GL tank is smaller. It is 4.5 gallons. It will be the same as my wife's '82 850L.

Your '81 850G does have a 5.8 gallon tank. The two tanks are NOT interchangeable.

This is one of the better pictures I have of her tank:


I don't have a decent picture that shows my 850 tank, but this is my son's 1000G, which is the same tank.


.

[93Bandit]

Thanks Steve, that's perfect. OK, so my suspicions were correct.

I wish the tanks were interchangeable. Is it just due to GL tank is two bolts, G is one? Or are there other differences as well?

[Rob S.]

Rest assured, I had BOTH hands on the grips. My wife leaned over my shoulder to get the picture.

.

I love your wife. I love you. But it goes without saying I hate the 85 mph speedo. I was only too glad to replace mine with the 140.

I remember when the KAW Z1 came out, it had a 160 speedo. I recall some dufus who thought it would go that fast. Darn near broke my heart to break the truth to him.

[Steve]

I wish the tanks were interchangeable. Is it just due to GL tank is two bolts, G is one? Or are there other differences as well?

The '79-'81G models and the '80 L have a single horizontal bolt at the back. The '82/'82 G and the '81-'83 L have two vertical bolts at the rear.

Besides that, the L tanks are shorter from front to rear, so the front mounting points on the frame are a couple of inches farther back and there are plastic covers to hide the exposed frame. The reason the tank is shorter is because of the forks. To give that extended "chopper-esque" look, Suzuki straightened out the angle on the triple clamps and moved the forks behind the axle (this left the axle just about exactly where it was before). Now that the forks were behind the axle, they could extend them for "the look". Now that the fork tubes are farther back, they would hit the tank when the forks were turned to full lock. Shortening the tank gave them the room to do that. It also allowed the opportunity to do their version of a "peanut" tank that was popular on choppers. The stepped seat, chrome fenders and the shorter, megaphone mufflers completed the "chopper" look.

Mechancially, the Ls are virtually the same as the Gs, but ergonomically, they SUCK.
Unless you happen to be that ONE individual that happens to fit.

.

[bwringer]

I just dropped in to say that generally, if you're worried about fuel economy on a motorcycle, you're doing it wrong...



Anyway, you can happily flog an 850 at 6,000+ RPM for hours and hours on end. I've done it many times because I live a long way from the mountains. These engines love to rev, they need to rev. Grip it and rip it. It won't hurt a thing. Learn to love that groovy rush between 6,000 rpm and redline. You wanna putt around like an old lady, buy a Harley or a lawn tractor. Spin to win.

However, a motorcycle with a rider on top is an aerodynamic disaster, with stuff sticking out all over and a coefficient of drag resembling a brick. Worse, probably.

So fuel economy on a motorcycle mostly varies with average airspeed. Other factors like RPM and acceleration rates make very little real-world difference. Drag varies with the square of speed (it's not linear), so there's a big difference between, say, 70mph and 80mph.

To put it another way, drag at 85mph is about double the drag at 60mph.

[93Bandit]

The '79-'81G models and the '80 L have a single horizontal bolt at the back. The '82/'82 G and the '81-'83 L have two vertical bolts at the rear.

Besides that, the L tanks are shorter from front to rear, so the front mounting points on the frame are a couple of inches farther back and there are plastic covers to hide the exposed frame. The reason the tank is shorter is because of the forks. To give that extended "chopper-esque" look, Suzuki straightened out the angle on the triple clamps and moved the forks behind the axle (this left the axle just about exactly where it was before). Now that the forks were behind the axle, they could extend them for "the look". Now that the fork tubes are farther back, they would hit the tank when the forks were turned to full lock. Shortening the tank gave them the room to do that. It also allowed the opportunity to do their version of a "peanut" tank that was popular on choppers. The stepped seat, chrome fenders and the shorter, megaphone mufflers completed the "chopper" look.

Mechancially, the Ls are virtually the same as the Gs, but ergonomically, they SUCK.
Unless you happen to be that ONE individual that happens to fit.

.

So based off of this information and some other info I've gathered, I'm doing this all backwards... I should use my G as my crusier and L as a cafe racer. The problem with that is my L is in far better condition than my G and I'd hate to ruin it. My G is so far gone it'll either remain a parts bike and soon decay into rust and uselessness, or I can attempt to revive it into something I would enjoy. If only I could put a larger tank on my L.

Do you think with some ingenuity and a welder the G tank could be retrofitted to my L and turn out half way decent?
Using the front mounting point to avoid fork contact? Although I suspect I'd have seat problems then since the tank is longer... Hmm....

I haven't ridden many bikes so I don't really have a good perspective on what good ergonomical bike feels like vs. what a bad bike feels like. So I don't really have any issues with my L. I've never ridden for more than an hour though so I haven't truly tested it yet.