SP370 Tracker ish build

here is the last great twin shock motorcycle
it was the best twin shock lashup ever done then or since .fact
one reason was the ohlins built husky/ohlins designed itc shocks (ITC internal travel control )they were the only production shocks ever used with a sophisticated position/travel active/sensitive damping and were on par with mono shocks in action however monoshocks did and still do have many advantages
husky was the last holdout on twinshocks and at the time they were focusing on off road racing something i witnessed first hand racing with champions like ama national enduro champion dave bertram who always used the husky automatic
the 1984 husky 500 auto a masterpiece
husky%20500%20ae%20001.JPG.crop_display.jpg
 
Thanks X
The swinger bearings are still originals but will definitely get some new modern replacements

What is SLR and abbreviation of ?

And yes fun is being had, and picking up on the learning, hope to get some brackets tacked up in the new year and see where that goes, also halfway through a making a DIY shock press so should have that sorted pretty soon


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stock swingarm bushing type are ok if in good shape and well greased you cant easily swich over to precision stuf
its not something to be grteatly concerned with its just that the extra loading if on shitty old bushings will defo cause sticky action ,just keep it in mind, the can of worms you are flailing about with ;D
 
Kipper,
I'm transforming my SP370 into a cafe racer, but instantly felt good looking at your progress and ideas. Mono shock looks great, totally transforming the original SP370 into something that's up to date. The swing arm construction can easily be made stronger by changing into an aluminum box construction - the modern kind. It will improve the looks even more and at the same time be strong enough to stand alone without the extra supporting construction. Maybe have your welder adapting (if necessary) a swing arm that with certainty is taking the extra load. This kind of bike looks great with the motto - Less is better. That is, less tubing and less weight.
 
Hello gents
I scored a new shock from a ktm duke ( roughly same dry weight as my SP give or take a few kg's) and lashed up the brackets. Whipped the spring off the shock and measured the travel to bumper which is 6 inches. Then measured each inch of travel and got the below table
1738aa42204815ea67cdc477a2e708d6.jpg

If I understand correctly I have a consistent ratio of 2:1
the second column is the distance left on the shock for each inch of travel on the rear wheel and the 3rd column is how the shock moved in relation to the rear wheel travel.


Unless of course I have my arse and elbow confused again !

Cheers



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kipper said:
Hello gents
I scored a new shock from a ktm duke ( roughly same dry weight as my SP give or take a few kg's) and lashed up the brackets. Whipped the spring off the shock and measured the travel to bumper which is 6 inches. Then measured each inch of travel and got the below table
1738aa42204815ea67cdc477a2e708d6.jpg

If I understand correctly I have a consistent ratio of 2:1
the second column is the distance left on the shock for each inch of travel on the rear wheel and the 3rd column is how the shock moved in relation to the rear wheel travel.


Unless of course I have my arse and elbow confused again !

Cheers



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Click to expand...

hey you are doing great excelllent work and testing
yes a consistent straight rate if you can alter to get the shock travel to start inceasing it would be best scenaruio
did you use a ratchet strap to pull into the bumper as well this is part of the wheel travel and really should go into the calcs as well
also the wheel travel of a duke do you know what it is ?
post up some pics of the bike with springless shock ;) it would be the first time i have ever seen anybody doing the work correctly on this sight !!! ;D ;D
 
Ah bollocks didn't realise I had to pull right into the bumper, I stopped as soon as I hit it, oh well I can test that out when I tack in the top bracket before finalising the bottom end.

No pictures as when I stood back and looked at it, it was like looking at a Heath Robinson cartoon and was slightly ashamed, I only have a small garden shed and need to take everything apart to get it back in which is a right ball ache. And as I live in the uk can't leave stuff outside as it rains all the time, unless it wanted that rusted to death look everywhere.

The ktm duke rear travel is listed as 135mm which is 5.3 inches. So reckon the 6 inches I have planned is good enough but will figure that out before final welding. Then it's into the swinger brace which I have mocked up and cut ready for weld when the suspension is done.




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cool the bumper is probably going to add 1/2" of shock travel easily,yuou see it really isnt much resistance at first especially when you consider how much force is being used to overcome the spring. if the bike is sprung correctly there will be times when it starts into the bumper when it is that o"oh shit hold on " type of situation the bumper comes into play more.this is all said with the thing set up with the correct spring
you did set it up with the rear wheel at a ride height you were shooting for right?
it looks like you will have closer to 7" + rear wheel travel
how much fork travel do you have ?
dont weld it yet, you have come this far i think you should let us study a bit more
 
7inches on the front
Gonna be a while before I get to welding so will run another lash up session and take photos for review


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kipper said:
7inches on the front
Gonna be a while before I get to welding so will run another lash up session and take photos for review


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Click to expand...
excellent !! what i am getting at is the final lash the position of the rear wheel in full drop is the most important thing that is hard to jigger with once welded
if the shock then needs to be retsicted on trave this is very easy to do with a simple spacer under the bumper no need to take apart the shock itself
the damping in the shock may be ok on full soft klicker settings but is likely to be over damped on high speed hits.this would be an easy thing for a shock service shop to refigure

the spring is probably going to be too stiff,but maybe not your bike is lighter but your leverage ratio is higher as well
 
xb33bsa said:
excellent !! what i am getting at is the final lash the position of the rear wheel in full drop is the most important thing that is hard to jigger with once welded
if the shock then needs to be retsicted on trave this is very easy to do with a simple spacer under the bumper no need to take apart the shock itself
the damping in the shock may be ok on full soft klicker settings but is likely to be over damped on high speed hits.this would be an easy thing for a shock service shop to refigure

the spring is probably going to be too stiff,but maybe not your bike is lighter but your leverage ratio is higher as well
Click to expand...
the higher leverage ratio may overcome the oversprung shock.

Keep at it, this suspension design project of your build is really interesting

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dualero said:
the higher leverage ratio may overcome the oversprung shock.

Keep at it, this suspension design project of your build is really interesting

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Click to expand...
i have thought this too
you may be right it is a bit of a head twister but i really dont understand as much as i think i know about it
like i said i get a headache trying to work this bit out :-\
you got a higher leverage ratio with a certain % less weight ,it may cancel out
if i could get it out of my brain thinking you see on this i have reached my limit :mad:
and work the physics with the math ....so simple........


............well that gonna happen :-X :-\ ::) dont be watchin me for a pure math answer
 
because the higher levratio creates slower piston speeds the fluid is always flows at a lower volume per second this througfh the valving which is specifically designed to be speed sensitve which boils down to sensitive to great changes in flow rate, modern valving,matched to a use and machine, will flow a nice correct amount,a restricted flow so that on easy bumps basically at lower roads speeds all bumps are easier hence the term high speed damping which also not coincidentilly means higher pist/valving speed
so that the easier more smoothy rollers are not real squishy
OK then this valving must also be able to get outta the way (compresion damping) cant be high hittin a sharp bump at high speed nobody got time fo dat,itll send you over the bars
so it releaves at higher speed but we gotta lighter machine with slower always piston speed per inch of wheel travel
where's the aspirin :mad:
 
Kipper, would you take a measurement of the shock's shaft as if the bumper wasn't there?

Have you investigated the rear wheel travel of the KTM Duke the shock is coming from?

This numbers would really help out mathematically. I think I can do some help

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dualero said:
Kipper, would you take a measurement of the shock's shaft as if the bumper wasn't there?

Have you investigated the rear wheel travel of the KTM Duke the shock is coming from?

This numbers would really help out mathematically. I think I can do some help

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Click to expand...

The ktm duke rear travel is listed as 135mm which is 5.3 inches.

And the shock shaft without the bumper is 4 1/8 inch

Might be worth mentioning that as this shock is bigger than the Ducati I am moving the top mount to the seat stay rather than the position in the previous set up - I don't have a photo so will draw you a pretty picture
0cacf79efa917265b9b9d069f973db42.jpg


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xb33bsa said:
because the higher levratio creates slower piston speeds the fluid is always flows at a lower volume per second this througfh the valving which is specifically designed to be speed sensitve which boils down to sensitive to great changes in flow rate, modern valving,matched to a use and machine, will flow a nice correct amount,a restricted flow so that on easy bumps basically at lower roads speeds all bumps are easier hence the term high speed damping which also not coincidentilly means higher pist/valving speed
so that the easier more smoothy rollers are not real squishy
OK then this valving must also be able to get outta the way (compresion damping) cant be high hittin a sharp bump at high speed nobody got time fo dat,itll send you over the bars
so it releaves at higher speed but we gotta lighter machine with slower always piston speed per inch of wheel travel
where's the aspirin :mad:
Click to expand...

Lash up number 2 with pictures this time
6f63a8b9c967cfe9fe61943542d3d0a9.jpg
36c7eaaf2466ec98ce2f8489e72e95af.jpg


With this set up I have 7' of travel as suspected and the rear wheel hits the seat rail before pulling into the bumper full on

Here it is with the spring on for reference
7f2077edc41d42e4dea7afbb9f7c5768.jpg


The ride height is 33' which feels right for my height and looks about the same as the original sp370 stance

Let rip on the feedback



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Hello chaps

Assume my plans stand up to review and should move on to tacking brackets and running the shock with Spring on and ratchet up to the bumper

Cheers


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