R80 G/S upper triple clamp

Dr. Evil

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Any recommendations or experience?

I'm planning to refurb the forks soon and was thinking while at it to put a triple-clamp ontop. I'm planning on keeping the stock 36mm forks and indicator brackets and pods as I'd like to keep it discreet/OEM'ish.

I have a suspicion that the fork spacing on the early G/S is carried over from the same era airheads, which looks to be spaced 184mm and offset of 38mm (not having taken it off yet to be 100% sure), so I wonder if any triple fitting a dual shock r75 would fit.
 
Dr. Evil said:
Any recommendations or experience?

I'm planning to refurb the forks soon and was thinking while at it to put a triple-clamp ontop. I'm planning on keeping the stock 36mm forks and indicator brackets and pods as I'd like to keep it discreet/OEM'ish.

I have a suspicion that the fork spacing on the early G/S is carried over from the same era airheads, which looks to be spaced 184mm and offset of 38mm (not having taken it off yet to be 100% sure), so I wonder if any triple fitting a dual shock r75 would fit.
Click to expand...

Spacing are same. As far as fitting, depending on the particular ‘design’, you may have to change other items.
 
Some have used a lower triple clamp, once the lock stops are milled off… as an upper clamp on a ST or G/S.
I have a lower triple if you want to go down this route….
 
It may surprise some, to see just how much abuse the OEM top yoke will take!
:aidan
 

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If anyone is interested, I contacted cognito moto and asked if they can adapt one of their designs to have the same profile as the original flat plate. Being CNC, I guess if they have more than one order, the price might be more interesting. What I like about their design is the hidden clamp mechanism means the original indicator brackets etc would fit, and the machining has a robust bridge on the underside between forks.

I just need to send them my upper yolk, which I'll most likely do over the winter. I'll probably have an opportunity to go to their VA shop as well.

https://cognitomoto.com/collections...clamp-bmw-r50-r60-r75-r90?variant=39686467725
 
update - Cognito has taken my original upper clamp and 3d modeled it:

https://photos.app.goo.gl/JGJV24ektTBoEBq99

Same silhouette as the original so I'm expecting the instrument cluster, turn signals and pods to fit without modification, and the whole setup to look nice and nearly original.

it will be CNC'd and I'll pick it up on my next trip to US. If anyone is interested, let me know.

BTW, my original top-plate turned out to be bent around the riser holes from the handlebars, so just as well time for an upgrade.
 
Dr. Evil said:
update - Cognito has taken my original upper clamp and 3d modeled it:

https://photos.app.goo.gl/JGJV24ektTBoEBq99



BTW, my original top-plate turned out to be bent around the riser holes from the handlebars, so just as well time for an upgrade.
Click to expand...

Thinking about fatigue and structural strength of the replacements. The original (on my /6 bikes) is a flat plate of mild steel. This is 3x stiffer than the equivalent size aluminium. So looking at where the top plate/yoke bolts onto the bike (the central large hole) you have about the same thickness in aluminium (presumably) as the original steel. True, the stanchion holes have beefy clamps so you should get improved bounce response from the forks, but when it comes to forces that twist the forks it could be argued that you are weakening the whole thing. The thick web that runs around the front helps the twist but the actual place the force is resisted is where it bolts to the bike. Worth a thought, especially as your original top plate was bent in this area.

Avoid sharp 90 degree corners, which will act as stress raisers. The larger the radius the better.

After saying all this I have a bike with a milled bottom yoke, done by a member of this parish. We modified the lock nut (the one with the hole for the damper rod on the /6) so that it worked with a thicker yoke. They are the same dimensions as the G/S.
 
Good points. The clamp will be made of 6061-T6. The flat plate section is 5.77mm thick vs. the 4mm mild steel original plate. So with this additional thickness is should be as strong and stiff, all things being equal as the original 4mm mild steel plate. With thick webbing underneath it should be significantly stronger and stiffer than the original.
 
scooter paul said:
Or ‘Triple tree’ as the Americans call it. I’ve always assumed, possibly wrongly that the top yoke had one clamping screw and the bottom yoke, two.
Click to expand...

Clamping 3 tubes together? 2 forks + the steering tube, hence triple?
 
Dr. Evil said:
Good points. The clamp will be made of 6061-T6. The flat plate section is 5.77mm thick vs. the 4mm mild steel original plate. So with this additional thickness is should be as strong and stiff, all things being equal as the original 4mm mild steel plate. With thick webbing underneath it should be significantly stronger and stiffer than the original.
Click to expand...

I did a quick search for 6061-T6 and the propaganda says it is stiffer than mild steel for the same weight (or a component of equivalent strength weighs 34% of the mild steel equivalent). I don't doubt that. But here we have a space issue, so the weight of material where it counts is less, so the strength is less. It's a case of just stepping back and looking at the materials in and around the area where they need to perform. The actual strength can only be established by some stress program fed with the CAD model your mate has produced, and done by an experienced stress engineer (which I am not). I guess it will be fine for you; keep your eye on it though.
 
Gelandestrasse said:
I did a quick search for 6061-T6 and the propaganda says it is stiffer than mild steel for the same weight (or a component of equivalent strength weighs 34% of the mild steel equivalent). I don't doubt that. But here we have a space issue, so the weight of material where it counts is less, so the strength is less. It's a case of just stepping back and looking at the materials in and around the area where they need to perform. The actual strength can only be established by some stress program fed with the CAD model your mate has produced, and done by an experienced stress engineer (which I am not). I guess it will be fine for you; keep your eye on it though.
Click to expand...



All good points, also worth bearing in mind that steel doesn’t suffer from fatigue fractures to anything like the extent that aluminium alloys do……
 
This part is being made by an engineering firm that makes aftermarket motorcycle triples including BMW airheads. being a clamp design it is substantially thicker and stronger than the original top plate enough to where it should be a fair bit stronger. I'm confident it will be fit for purpose, but I'll keep an eye out.

From inspection of the original part, it looks like the biggest forces are on the risers - i would suggest you check your original top plates aren't bent as mine was.
 
Dr. Evil said:
This part is being made by an engineering firm that makes aftermarket motorcycle triples including BMW airheads. being a clamp design it is substantially thicker and stronger than the original top plate enough to where it should be a fair bit stronger. I'm confident it will be fit for purpose, but I'll keep an eye out.

From inspection of the original part, it looks like the biggest forces are on the risers - i would suggest you check your original top plates aren't bent as mine was.
Click to expand...

So the original BMW design was flawed ?
 
I would not say it is flawed, people have gone around the world on them after all, but it is not as strong as the cast aluminum upper triple which they introduced in the '87 R80/R100 GS. I've gone this way because I want to keep the original G/S 36mm front end and look of the bike, but with an improved part.
 
Hey folks, update on this front-end rebuild. Scott at Cognito CAD/CAM'd my upper triple (a little greasy in the picture). I got a very nice SS steering nut and fork-nut spacers from ToasterTan who was very helpful and also make a nice triple. New 36mm forks from moto-point.pl (old ones were 1mm out of straightness) New seals on the damper rods, new steering stem bearings (significantly brinelled), new SS fork brace (old OEM one bent). Carefully put together, this feels like a huge improvement over a badly worn out front-end. Nice to have it back on the road!

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