r80 rear subframe

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alexxx
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r80 rear subframe

Postby alexxx » Mon Nov 11, 2019 2:02 pm

Hi Folks,
Has anyone modified or fitted a custom rear subframe to the twin shock R80?
I am wondering how narrow the top frame rails can go, I am thinking about how far inwards the shocks could be mounted/canted, maybe 1cm per side?
The frame rails are about 27 cm as standard, I could retain the width but would like to make it narrower.
Does anyone know the original tubing wall thickness etc
Regards,
Alex

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Rob Frankhamr
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Re: r80 rear subframe

Postby Rob Frankhamr » Wed Nov 13, 2019 11:16 am

I would be very reluctant to can't the shocks, even by a relatively small amount. I think it would cause considerable extra wear on the shock absorbers and on the mounting bushes. If you do decide to go down that route, remember that you have to factor in the dispacement with the rear suspension fully compressed.

Rob
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beachcomber550
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Re: r80 rear subframe

Postby beachcomber550 » Wed Nov 13, 2019 5:44 pm

sh1-1.jpg
Rob .... not so. I've been involved in the development and subsequent manufacture of speciality shox for over 15 years.

Absolutely NO reason to suspect additional wear.

You do have to factor in a LOSS of effective poundage of the springs due to increasing the angle.

Remember old Velos ? They had provision to alter the angle of the shock built in to the design. :cool:
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alexxx
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Re: r80 rear subframe

Postby alexxx » Thu Nov 14, 2019 2:31 pm

thanks folks,
Maybe I gave the wrong description of what I want to do. I want to have a slimmer top subframe, it is 27 cm at the shock mounting point. I would like it to be less. I don't want to change the fore/aft angle of the shocks just the "inward" lean.
I think the rubber mountings inside the shocks could take a bit of inwards lean or I could put rose joints there instead.

Regards,

Alex

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Re: r80 rear subframe

Postby Mjolinor » Thu Nov 14, 2019 2:38 pm

Why do you want to do this?

alexxx
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Re: r80 rear subframe

Postby alexxx » Thu Nov 14, 2019 4:21 pm

I want to make a slimmer, less bulky bike with a narrower lower seat, it will feel much better for me. I won't be doing any touring, just use it for country roads and bumbling around. Will be keeping all the original parts so any future owner can easily return it to an 80RT again.
I like the look of some custom made scrambler style airhead bikes, for my thinking I can try to make this damaged, tired old bike into a more interesting looking machine but still retain the main classic essence of an airhead.
My bike is likely at the bottom of any value range so no worries there.
The image below shows the idea...all I need now is money :)
DO-R80-1-700x463.jpg
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Last edited by alexxx on Thu Nov 14, 2019 4:35 pm, edited 2 times in total.

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Re: r80 rear subframe

Postby Mjolinor » Thu Nov 14, 2019 4:29 pm

Cheers. Makes my eyes water just thinking about it. Memories of those leather Brookes saddles one used to find on push bikes. :)

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beachcomber550
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Re: r80 rear subframe

Postby beachcomber550 » Fri Nov 15, 2019 1:33 pm

Alexxx ... OK I have it now.

That's a whole different can of worms.

A couple of options - IF there is room mount the lower eye of the shock to the inside of the existing mount ... I've done this with some Hondas. We [ RAMSHOX ] did then develop an offset mount, but there was no real call for these and the small volume made then non viable to have made.

If not, then I suggest you use rose / Heim jointed shock mounts. They WILL be more expensive, but will take up the misalignment without putting stress on the mounting studs / bolts or the bushes.
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Rob Frankhamr
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Re: r80 rear subframe

Postby Rob Frankhamr » Fri Nov 15, 2019 6:25 pm


A couple of options - IF there is room mount the lower eye of the shock to the inside of the existing mount ... I've done this with some Hondas. We [ RAMSHOX ] did then develop an offset mount, but there was no real call for these and the small volume made then non viable to have made.


Could be possible with the left hand mount but not the right. It's mounted on the outside of the final drive housing.

Rob
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george baker
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Re: r80 rear subframe

Postby george baker » Fri Nov 15, 2019 6:43 pm

Hi
how about a shock on lhs only? I am fairly sure I have seen pictures of that done

George

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beachcomber550
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Re: r80 rear subframe

Postby beachcomber550 » Sun Nov 17, 2019 10:40 am

George is this the set up ?

I wouldn't even consider using one of the original pair for this ! Noweher near strong enough.

We [ RAM ], supplied several shox for this set up about 6 years ago, but weren't popular enough to make the cost of investing in the special extensions viable. Might still be some kicking around in the experimental department - ie the back of the stores !!!
mounting-progressive-shock.jpg
img625.jpg
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Rob Frankhamr
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Re: r80 rear subframe

Postby Rob Frankhamr » Sun Nov 17, 2019 5:22 pm

I think, if you really want to make the sub frame narrower, this would be the way to go...

https://images.app.goo.gl/EpV1BcNBvFZDjEDx5

A lot of work though and not for the faint hearted.

Rob
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george baker
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Re: r80 rear subframe

Postby george baker » Mon Nov 18, 2019 11:22 am

Hi TJ
not sure, it was a while ago, and yes it would require "doubling up" if you just had the one.

George
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Re: r80 rear subframe

Postby beachcomber550 » Mon Nov 18, 2019 2:32 pm

We supplied several shox for this application ... 100% positive feedback but the investment cost in having the relevant parts made made it uneconomical for productionising. Minimum order for machined parts - 100 !!!
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Re: r80 rear subframe

Postby alexxx » Fri Nov 22, 2019 2:16 pm

Thanks for all the suggestions,looks like a lot of work has gone into those rear shock and frame designs, I will have to keep it all much simpler :) I think I will see how it mocks up with the shocks mounted outside the frame but with a narrower rear frame loop at the top. The bolt on rear subframe really helps as the original can be put back on at anytime. Thanks BMW :)


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