extending a swingarm

45disco

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i am in the middle of a rally build and i have two options for the swingarm, i have a double sided and i have a mono. the mono final drive is off a rt so it has a 4 bolt and a mag wheel which i can change to a g/s final drive and wheel later when the cash flow increases. the double sided yelds a plethora of final drives that can be had easily.
my question is which should i spend my time on? i want it to be as stable(rugged) as possible for travel and i am trying to keep it as much as "off the shelf" as possible for future fixing. a

any thought on this....

cheers
jim
 
There's not much wrong with the standard gearing on the mono so I'd stick with that and extend your existing swingarm. Just out of interest though - why do you need to extend it at all? The standard setup is well proven and rugged.
 
i have both options sitting on my work bench, and i am building a rally/adv bike out of a 79 r100. i have a wp inverted front end so i need to extend for balance and ground clearance (10-12in.) which is +2 on my standard g/s . i want to extend 70mm or 100mm. i have a spare g/s shock so that is why i am considering the monolever idea even though i don't have the optimal drive for it yet. i have yet to get a dual swing final drive and wheel.

is there a company that sells the extension block for the swing arm? i think i have seen a few in the 70mm length, this would be the simplest way to extend it.

cheers
 
I don't remember where but in germany someone sold the extenssion.
But this is an easy billet work. The most difficult is the extended drive shaft.
 
what is the consensus on length of the swing arm. i have heard and read both 70mm and 100mm. which is better.
 
Mick13 said:
I don't remember where but in germany someone sold the extenssion.
But this is an easy billet work. The most difficult is the extended drive shaft.
Click to expand...

The drive shaft extension is the easiest part !!!!!
When you buy a swingarm extension piece you also buy a driveshaft extended section at the same time. It has male and female splines at each end and just slots in :augie
 
and who sells this??? i have heard that some are extending the spline cup but only for the 70mm ones. this would make it a bit easier, except for the tire clearance.
 
Steptoe said:
The drive shaft extension is the easiest part !!!!!
When you buy a swingarm extension piece you also buy a driveshaft extended section at the same time. It has male and female splines at each end and just slots in :augie
Click to expand...

Ok, the only one I've seen (maybe HPN) were lenghtened ones in one piece, like for race cars (maybe stiffer)
 
45disco said:
what is the consensus on length of the swing arm. i have heard and read both 70mm and 100mm. which is better.
Click to expand...

The more length, the pore the bike is stable at speed and worst on small turns.
An other reason to lengthen is to gain in rear travel suspenssion
 
45disco said:
i am in the middle of a rally build and i have two options for the swingarm, i have a double sided and i have a mono. the mono final drive is off a rt so it has a 4 bolt and a mag wheel which i can change to a g/s final drive and wheel later when the cash flow increases. the double sided yelds a plethora of final drives that can be had easily.
my question is which should i spend my time on? i want it to be as stable(rugged) as possible for travel and i am trying to keep it as much as "off the shelf" as possible for future fixing. a

any thought on this....

cheers
jim
Click to expand...

Jim

HPN use both - the extended single, by 100mm, (they weld in a 100 mm tube), and the double for a substantial increase in stability.
I am sure if you look at their site you will find more information and if you search their Forum it will probably give you the details that you are after

Photos always help - and here is one, (not mine), that I must have got from the web, I think that it was bought from HPN
You can see that they strengthen the swing arm as well as extending it

hpn_swing_arm.jpg
 
thanks for all the posts, i have decided to go with the double sided, due to the fact that u can get many different final drives for different riding, i found a guy to extend both the arm and shaft, it would take me for ever to make a jig, unless any one on here would like to share a picture of theirs. i am working on a jig.

i am going to extend it 70mm instead of the 100mm, i think from a usable shaft angle the 100mm is a waste, unless u raise the motor up a bit. the 70mm should give me 9.5-10in of travel. i should have a rolling chassis in about a month with re-enforced frame.:D


cheers
 
The 100mm extension was done for several reasons; increased suspension travel, lessening shaft jacking and keeping the bikes geometry correct. If you raise the front end or the back by itself you change the rake on the front end and get a bike that does tank slappers at a certain speed or one that has a "heavy" front end, since HPN wanted to lift the bike for suspension travel and clearance and keep the geometry the same they needed to extend the swing arm to keep the geometry the same as well as lessening the shaft jacking effect, this, they later reduced with the paralever.

When putting a longer front end (WP KTM extreme) on the math shows that 100mm is the proper extension. Be careful of the shock mount as well moving it back changes the shocks behavior so you will want to consider this before doing any monolever modification.
 
the 100mm extension only increases travel by a fraction of an inch over the 70mm. due to the maximum pivot angles of the drive shaft (+0-). it also lengthens the wheel base which is good for tracking in a strait line(sand). changing the motor slant by raising the engine mount in the front to the top of the frame increases the usable pivot angle of the shaft in relation to the pivot point of the swing arm. so in a real life scenario the 100mm has no advantage over the 70mm except the wheel base and a fraction of an inch of travel + & -. and maybe a slight decrease in rake (steeper head angle).0? of a degree.

the hpn remouting the shock bracket back further for a flatter action was due to the rebound stress on a drive shaft machine. the higher the bike the more downward force is present thus the need for a stiffer pre load resulting in a quicker rebound which super seeds the shocks ability to control it(due primarily to length) and resulting in shaft breakage. also increasing the mount also reduces the angle of the shaft which really means that u are not using all the angle and not getting the full travel replacing it with a longer wheel base. the older twin shock models had a steeper angle shock and more travel (100mm extended) because the two shocks could keep the rebound under control. the newer oilhead swingarms are a whole different geometry..

so i could go with a 100mm b/c of the twin shocks, but i want the shortest wheel base i can reasonable get. where an inch make a big different in handling doesn't mean much is susp travel (9.5-10" to 10.5-11"). to me
 
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