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Old 01-09-2015, 10:02 AM   #1
russbryant OP
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Adding Lightness - R100 GS aND GSPD

There are a lot of posts scattered throughout the Airheads forum concerning the weight of the BMW R100GS PD. Specifically...what a heavy pig it is. So the question that comes up is how can it be made lighter?

I have a 1990 R100GS PD that is being stripped down and I have been weighing the parts as they come off. I also have an 1989 GS that has been lightened a bit and I hope to get it weighed soon to see where it is compared to the stock weight. In the meantime, maybe you can find some useful info here to apply to your own GS's weight loss program.

The goal is roughly...strip off any unnecessary weight and to replace heavy parts with lighter ones as long as reliability isn't compromised of course.

Here is a pic of my 1990 R100 GSPD that will be the donor of the parts that I will weigh for reference in this thread.




In case you're wondering why I would tear apart a perfectly good GSPD, well...it's not exactly "perfectly good" anymore thanks to a left turning cage.




The scale I am using is a Berkley 50 lb Digital Fish Scale, model # BTDFS50-1

The BMW published curb weight with full tank of gas:

BMW 1990 R100GS PD 236 kg = 519 lbs
BMW 1990 R100GS 210 kg = 462 lbs
57 lb. difference

The first thing to be mindful of is the amount of gas in the fuel tank itself.
There is a mind boggling 56 pounds of fuel in a full 9.25 gal. GSPD tank!!
That's not an issue when slabbing down the highway, but for riding off pavement it can really make a difference in the feel of the bike.

Gas weighs 6.073 lbs per gallon and listed below is the weight of just the gas for various GS tanks.

The R100 PD 9.25 Gallon (35 liter) tank = 56.2 lbs of gas.
The R80 G/S PD 8.45 Gallon (32 liter) tank = 51.3 lbs of gas.
The R100 GS 6.34 Gallon (24 liter) tank = 38.5 lbs of gas.
The R80 G/S 5.15 Gallon (19.5 liter) tank = 31.3 lbs of gas.

The empty gas tanks weigh:
GSPD 9.25 gal. tank w/petcocks & no cap 21 lbs. 2 oz.
GS 6.34 gallon tank TBD
G/S 5.15 gallon tank w/o petcock or cap 10 lbs. 3 oz.
G/S PD 8.45 gallon tank TBD

The heaviest combo of tank and fuel is 76 lbs 5 oz for the GSPD tank.
The lightest is 41 lbs 8 oz for the R80 GS tank

Largest GSPD tank with full tank
GSPD tank = 21 lbs 2 oz
9.25 gallons of gas = 56 lbs 3 oz
Front faring, Instruments, etc. = 18 lbs 4 oz
total = 95 lbs 9 oz

or

Smallest Tank with 3 gallons of fuel
3.00 gallons of gas = 18 lb 3.5 oz
G/S tank = 10 lb 3 oz
Front faring, etc. = 18 lb 4 oz
Total = 46 lb 10.5 oz

===> 95.5 - 46.7 = 48.8 lbs to play with!!!


Here are some of the parts I've weighed so far:

Items on the front end:
Windsheild w/no hardware (OEM) 1 lbs 2 oz
Insrtument fairing bracket 1 lbs 4 oz
Insrtument fairing, w/headlight, no instruments 4 lbs 15 oz
Speedo, tach, clock, small bracket, and screws 2 lbs 4 oz
Roo Bar w/headlight guard 6 lbs 7 oz
Handguards (both) 0 lbs 8 oz
Front left fairing cheek 0 lbs 14 oz
Front right fairing cheek 0 lbs 14 oz
Front Fender (Acerbis) 1 lbs 5 oz

Front fairing/headlight/roo bar etc. (forgot front turn signals) = 18 lbs 4 ozs

Left Side Cover 0 lbs 14 oz
Right Side Cover 0 lbs 6 oz
Rear Fender w/turn signals, tailight, etc. 4 lbs 4 oz
Rear Subframe w/dual seat rack 10 lbs 5 oz
Lower Engine Fairing w/clamps 1 lbs 9 oz
Seat (Dual) (no rack - included on subframe) 5 lbs 8 oz
Seat (Solo) 3 lbs 8 oz
Rack for Solo Seat 2 lbs 8 oz
Seat (Solo, Q-Tech) 3 lbs 4 oz
Rear Shock (Wilbers) 8 lbs ?
Exhaust OEM Stainless Steel 9 lbs 12 oz

More to follow...


Russ
Tucson
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Old 01-09-2015, 10:16 AM   #2
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in...and glad you're O.K., I hope...
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Old 01-09-2015, 10:20 AM   #3
patrkbukly
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Weights & measures

Wow, now this will be an intersting process. I see these mountain bicyclers that have those cycles down to the ounce.

Interesting approach to a never ending frame cracks issue maybe. Lighter parts on same frame maybe will fix that.

Cool.
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Old 01-09-2015, 10:29 AM   #4
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I believe TAG sells carbon-fiber fuel tanks... both small and large.

Airhead Wrangler documented the weight reduction process for his R80ST that he built into an HPN... check there for great data.
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your bike is suitably dirty. Well done.
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So I sold my GS and went shopping for a G/S!
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Old 01-09-2015, 10:54 AM   #5
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Old 01-09-2015, 10:55 AM   #6
neil p
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Interesting project.

I swapped out the PD set-up for a regular GS tank and big headlight a few years ago.

I miss the fairing/screen on faster runs but not the extra weight in daily local use.

The whole roo-bar fairing has a significant bulk that really loads up the front end.

I still have the PD kit, and like the tank.

Definitely don´t miss the crappy PD headlight.

Looking forward to seeing which direction you go in.
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Old 01-09-2015, 11:48 AM   #7
ianboydsnr
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I lightened my R80Gs,
I actually took the roo bar and fairing off to refurbish, which I did, but it seemed so heavy that I decided to leave off!

Here it is before I finished it!

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Old 01-09-2015, 01:22 PM   #8
russbryant OP
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Quote:
Originally Posted by Rapid Dog View Post
in...and glad you're O.K., I hope...
Thanks, I'm OK now...it was in Nov 2010

Russ
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Old 01-09-2015, 01:32 PM   #9
russbryant OP
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Originally Posted by SOLO LOBO View Post
I believe TAG sells carbon-fiber fuel tanks... both small and large.

Airhead Wrangler documented the weight reduction process for his R80ST that he built into an HPN... check there for great data.
Yep, I've read his thread and will likely need to use some of his data or at least use it for comparison.


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Old 01-09-2015, 01:39 PM   #10
russbryant OP
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Quote:
Originally Posted by ianboydsnr View Post
I lightened my R80Gs,
I actually took the roo bar and fairing off to refurbish, which I did, but it seemed so heavy that I decided to leave off!
My roo bar, instrument panel, and instruments, etc was over 18 lbs and the Trailtech Vapor and Trailech X2 headlight I'm using on my 1989 GS is under 2 lbs.

Russ
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Old 01-09-2015, 01:43 PM   #11
russbryant OP
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Quote:
Originally Posted by neil p View Post
Interesting project.

I swapped out the PD set-up for a regular GS tank and big headlight a few years ago.

I miss the fairing/screen on faster runs but not the extra weight in daily local use.

The whole roo-bar fairing has a significant bulk that really loads up the front end.

I still have the PD kit, and like the tank.

Definitely don´t miss the crappy PD headlight.

Looking forward to seeing which direction you go in.
I'm right there with ya brother!!! I'm going to keep the tank and some other bits so that I can swap em around as needed.

Russ
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Old 01-09-2015, 01:51 PM   #12
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The best way to reduce the weight of the GS and GSPD is to get a DR650.
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Old 01-09-2015, 01:52 PM   #13
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there's all sorts of places, but among the easiest below. My R80G/S is about 350lb dry with these two changes .. about 375lb stripped trail weight w/3 gal fuel. sooo .. assuming you want to ride an airhead, easiest way to drop weight is to switch bikes to G/S

1. install an EarthX ETX 36 (14AH) about 3lb 12oz .. tested down to 15f on test mule R80G/S .. totally bombproof if your charging system is working correctly and putting out about 14.2v. weight saved depends on what's installed. Odyssey PC925 is about 28lb .. so that would save 24lb.

drawback is costs $$$ .. there's an electric bike 20AH actual LiFePO4, weight about 7lb, tested down to 20f and cost about $135. it's important to realize our carb airheads have much higher AH requirements vs modern bike with fuel inj.

all sorts of test data on my battery testing thread .. link in sig

2. change out stock muffler .. my preference is super trap. best of all it's tunable by adding or removing discs.


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Old 01-09-2015, 02:15 PM   #14
russbryant OP
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Originally Posted by MotorcycleWriter View Post
The best way to reduce the weight of the GS and GSPD is to get a DR650.
So why stop there ?? Why not get a 317 lb KTM 690 and be done with it??

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Old 01-09-2015, 02:30 PM   #15
chollo9
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Why stop there, get an XL100.

But wait, bicycles are really light.

Shoes weigh almost nothing.

Barefoot does weigh nothing.

Now a hunger strike, that's the way to go!
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