Swing arm angle 1

[enfield]

Hi there
Can anyone help What effects on the bikes handling/traction does the change in Swing arm angle have

Kind regards

Stephen

 

[mburgess]

On its own hard to say, but in relationship to the chain pull moment and rear wheel force curve quite alot. you will need to be more specific, it is a bit of a pandora's box.
Regards,
MB

 

[enfield]

As the suspension ( prolink honda) goes through its motions the swingarm goes through the arc of say -6 to 15 deg what effect does this angle have on traction
The wheel base effectively gets shorter, So the wieght would I assume tend towards the rear and the front would lift

If I made the link arm shorter,( altering the swingarm angle) assume this would have the effect of making the wheelbase/swingarm shorter and make the front tend to come up more

Stephen

 

[mburgess]

What exactly are you trying to achieve. Shortening the swing arm will also cause the bike greater pitch under accelleration & braking unsettling the balance of the bike. while not improving traction. If you are trying to get out of turns harder I would look at spring & dampner settings first, maybe consult with a reputable suspension tuner in your area. Have you measured your linkage ratio & rear wheel force curve. This will help you optimise the spring settings, it is not uncommon to change the rear spring to suit your weight & riding. If it is a late model bike (less than 10 years old) I would suggest that not alot can be gained from altering the swing arm in anle or length.
All this being said unfortunatly some 12 year old with his brains in the tool box will get on it and go faster anyway.
Regards,
MB

 

[enfield]

Yes I have done that, I Have the Tony foale Soft ware ( very convienient )
I an trying to reduce the spring preload as much as possible while using the softest spring I can get away with

If I shorten the Linkage arm ( NOT) the swingarm ,,the swingarm altitude changes from -4.3 to -6.9 I dont know what effects this swing arm angle change will produce .. ( I drew the bike on Cad then ran it through the motions and hence noted the wheel base change ) ]
Other than that I would like to know more about the effects the swing arm angle change produces

Stephen

 

[mburgess]

Sorry,
I didnt correctly read your comment with regards to the change in swing arm angle.
You have to look at the situations where power is applied and the position of the suspension at that time. Commonly when you apply power the chain pull moment will attempt to cause the bike to rise on its rear suspension (top out), or another way of thinking is the wheel will push itself into the ground. This is opposed by the wight transfer to the rear under accelleration (pitch). The engineers will try to optimise the position of the swing arm pivot to the countershaft to achive a good balace between the chain pull moment & pitch for best comfort, control & traction. You will find that the bike will sit at a position of 30%-50% of available travel when under accelleration. The change in angle thus length will be a minimal factor in traction.
Hope this helps.
MB

 

[mburgess]

When trying to use the softest spring possible remember that you have to account for g-outs of jumps & ruts. Altering the linkage arms can affect the rising rate of the rear wheel force curve, pro teams may alter between a straighter rate & a more rising rate. You need to find a balance between preload & spring weight. Remeber there is no perfect setting everything is a compromise. As a guide I would set the shock to have a wheel force of approx 30kg at top out to approx 320kg at bottom out & a smooth rising curve between.
Regards,
MB

 

[enfield]

Thanks
That was a very good answer So, if under accel ( throttle pinned ) I am about 30 to 50 % of aval wheel travel
Then with that set up I can have a look at the rising rate ,,,My local track is tight and twisty with only 2 big jumps with a g out before both ,,
So may need more of a rising rate will have a play and see

Stephen

 

[mburgess]

You dont really need a rising rate set up. Chances being you may already have one. The 1st stop in setting up suspension is getting the springs correct for you, someone elses preferences may be different. Remember that a stiffer spring with less pre load will be initially softer and have more bottoming resistance than a softer spring with more preload. Have you done your basic sag measurements yet, these are a good way to get started.
Regards
MB

 

[R1100S]

Not to hijack your thread, but tell us more about Tony Foale's software. I've read his books and learned a lot, and would be interested in the software if it is worthwhile.

Good luck with the suspension settup, I'll try and avoid giving you advice. As mburgess said it can be a pandora's box.

 

[enfield]

The Toney foale software is good...it gives all the info you need from pivot forces wheel rates and spring calcs for front and rear
go to Tony foales Web site and download the users manual PDf the software itself was very cheap

I am an Engineer and can work all this stuff out from first principles ..but I am flat out...and this software and the help from MB has saved me lots of time...and as a result I have been able to test and make changes on the computer ( I use acad as well) ..then I machine /change the bike ..so far this has given me a resonable machine in a very short time

An example would have been Spring rates ...Stock is 4,2 kg/mm I need 5.4 at 17mm preload ...( have another spring so may go harder based on fresh evidence ,,thanks MB ) that was done on T/F software ,,,I cut the spring to the required stiffness ,,,,( havent tested the spring yet maybe in the weekend if I get a chance )

in conclusion worth the money .... ( the only prob is understanding what the changes do and the effects are ....for which the book is needed

Stephen

 

[mburgess]

Check the race tech web site. Under Student Seminar Downloads,

http://www.racetech.com/SubMenu.asp?cMenu=4&c=Yes&cSubMenu=8&cSSMenu=51&showPage=street

They have some excel templates for working out spring & leverage charts.
Regards,
MB