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Old 08-17-2013, 11:29 AM   #1
Dmaster OP
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Another dirtbike build "BMWsaBERG"

After a few years of abusing the R65GS i came to a conclusion: Its a awesome bike but it needs less weight and more suspension travel (and some other details.)

I have a R100R cafe racer project waiting not to be finished so this will be the base.

This is the plan:
- 280mm or more suspension travel front and back.
- less then 150 kg (with gas, oil battery and starter.)
- paralever (i don't want the jacking like a non paralever)
- a wheelbase less then 1500mm (that could (will) be a hard one)
- reinforced frame
- small engine (short stroke R65 maybe with 1000cc cylinders)
- rear drum brake
- small main gas tank
- and a 1000 things to over think before putting them on this list.

Dmaster screwed with this post 08-18-2013 at 04:16 AM
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Old 08-17-2013, 11:33 AM   #2
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This thread is worthles without pictures:

Current status:

Max travel on the rear now is: 285 mm.

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Old 08-17-2013, 12:23 PM   #3
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HOLY SH#@!!!!! That's gonna be a MONSTER.
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Old 08-17-2013, 12:40 PM   #4
Ras Thurlo
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Quote:
Originally Posted by Dmaster View Post
This is the plan:
- 280mm or more suspension travel front and back.
- less then 150 kg (with gas, oil battery and starter.)
- paralever (i don't want the jacking like a non paralever)
- a wheelbase less then 1500mm (that could be a hard one)


esp interested to see how the 1100 paralever vs wheelbase thing works out

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Originally Posted by hardwaregrrl View Post
HOLY SH#@!!!!! That's gonna be a MONSTER.
+1

Ras Thurlo screwed with this post 08-18-2013 at 05:45 AM
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Old 08-17-2013, 12:41 PM   #5
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This could be a fun build. Why use a r65 with a 1000 bore. When you could use a r100 motor? It my be a stupid question.
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Old 08-17-2013, 01:59 PM   #6
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short stroke, big bore, quick rev's
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Old 08-17-2013, 06:21 PM   #7
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What type of u-joints will you be using? I found the restriction in travel to be the u-joint and/or clearance between u-joint and swingarm.BTW...Love your videos. The Berg plastics and seat looks great on the airhead.
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Old 08-17-2013, 06:44 PM   #8
AntonLargiader
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A stock R100GS is over 1500mm wheelbase. According to some calcs I did a few years ago, an 1100 swingarm and 265mm front travel puts you well over 1600mm (like the HP2). You will have to shorten the frame, engine and transmission to get under 1500 with 285mm travel F&R. The Airhead drivetrain is the big limitation: you have front wheel (at full compression) touching engine bolted to transmission adjacent to swingarm pivot plus swingarm length determining where the final drive is. Without surgery, that stack-up is fixed. Measure it yourself; you need to know it.

Your wish list is admirable. :) But it's roughly the same wish list that I've seen here over and over, and only the very talented fabricators get close to realizing it. Most attempts simply die off and the threads roll off the page into oblivion. Who knows what happens to the cut-up bikes.

My point isn't to squash your dreams, it's to suggest that you develop meaningful and reasonable goals. Do you really want a heavy bike with 285mm travel front and rear, when every centimeter of travel adds to the wheelbase and height? I'm glad my XR400 has that kind of travel but I'd never use it on my GS. If I rode in the desert things might be different. The KTM SuperEnduro is about 250 and it's probably a great bike to emulate. There's a reason KTM didn't give it 300mm travel.

Lighter than an R80G/S? Again, you're into major surgery.

Have you seen this thread? It should be your inspiration:
http://www.advrider.com/forums/showthread.php?t=30044

But he still didn't get under 1500mm wheelbase.

Measure twice, cut once.
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Old 08-18-2013, 04:01 AM   #9
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Quote:
Originally Posted by AntonLargiader View Post
A stock R100GS is over 1500mm wheelbase. According to some calcs I did a few years ago, an 1100 swingarm and 265mm front travel puts you well over 1600mm (like the HP2). You will have to shorten the frame, engine and transmission to get under 1500 with 285mm travel F&R. The Airhead drivetrain is the big limitation: you have front wheel (at full compression) touching engine bolted to transmission adjacent to swingarm pivot plus swingarm length determining where the final drive is. Without surgery, that stack-up is fixed. Measure it yourself; you need to know it.
A R100GS should be 1516mm in wheelbase the swing arm = 285mm
a 1100 swing arm = 355mm a difference of 70mm
A longer fork will add some wheelbase but I probably use triple clamps with less offset then the stock R100GS triples so i don't think this will add much to worry about.
In your link (i did see the picture before) he said the frame was shortened 62mm that would be enough to get it back to 1525mm, close enough.
It would be pretty damn hard to shorten the frame that amount but i'll see what i can get.

Quote:
Originally Posted by AntonLargiader View Post
My point isn't to squash your dreams, it's to suggest that you develop meaningful and reasonable goals. Do you really want a heavy bike with 285mm travel front and rear, when every centimeter of travel adds to the wheelbase and height? I'm glad my XR400 has that kind of travel but I'd never use it on my GS.
I know its a stupid idea but i think i can build one. I use my R65GS as a dirtbike know and use all the travel in there (255mm front +/-230mm in the back) so my goal is less wight more travel and it could be even more fun than i already got.
Quote:
Originally Posted by AntonLargiader View Post
If I rode in the desert things might be different. The KTM SuperEnduro is about 250 and it's probably a great bike to emulate. There's a reason KTM didn't give it 300mm travel.
The KTM is still over 180kg and top heavy, thats not what I'm after....
Quote:
Originally Posted by AntonLargiader View Post
Lighter than an R80G/S? Again, you're into major surgery.
That would't be to hard, tank is heavy, as also the wheels and exhaust are.
Lighter than a R80G/S is easy (if you don't mount more parts) going under 150kg will be hard.
But again, i'll go for it and try to go as far as i can get.

Have you seen this thread? It should be your inspiration:
http://www.advrider.com/forums/showthread.php?t=30044

But he still didn't get under 1500mm wheelbase.

Measure twice, cut once.[/QUOTE]
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Old 08-18-2013, 04:07 AM   #10
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Originally Posted by bromax.ca View Post
What type of u-joints will you be using? I found the restriction in travel to be the u-joint and/or clearance between u-joint and swingarm.BTW...Love your videos. The Berg plastics and seat looks great on the airhead.
I'll use the stock driveshaft for now. I found the travel i want already.
Thanx for the compliment on the videos i'll keep making them
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Old 08-18-2013, 04:10 AM   #11
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Originally Posted by orangebear View Post


This could be a fun build. Why use a r65 with a 1000 bore. When you could use a r100 motor? It my be a stupid question.
The R65 engine has the short stroke, it will make the engine smaller, putting the carbs closer to the engine leaving more space for my legs end feet.
If i get on a 100GS i immediately notice the difference. Imo its worth the hassle.
If your doing wide open tracks its no problem, but i like to short stuff all the time thats why i don't want the insane wheelbase.
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Old 08-18-2013, 04:27 AM   #12
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Quote:
Originally Posted by Dmaster View Post

The KTM is still over 180kg and top heavy, thats not what I'm after....
Hmmm, sounds like an RS is out of the question then.
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Old 08-18-2013, 08:47 AM   #13
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150kg might not be doable without getting seriously savage. Custom frame, drill holes in all your gears, carve extra metal off your final drive crown gear, no starter, etc. Take a look at some of the stuff SWT has done to reduce weight. A LOT of work and he's down to 157 kg with oil.
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Old 08-18-2013, 09:22 AM   #14
Ras Thurlo
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Quote:
Originally Posted by Airhead Wrangler View Post
150kg might not be doable without getting seriously savage.
what approx weight can you get these bikes down to, before getting medieval?

what is the basic laundry list of items that give you big savings, before you start getting to diminishing returns?


Quote:
Originally Posted by Dmaster View Post

That would't be to hard, tank is heavy, as also the wheels and exhaust are.
Lighter than a R80G/S is easy (if you don't mount more parts) going under 150kg will be hard.

Ras Thurlo screwed with this post 08-18-2013 at 09:35 AM
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Old 08-18-2013, 12:58 PM   #15
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WHOA.

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