[svb]

Hello and Namaste All ,

This is my first post on the forum and for starters I would like to thank all admins , moderators and members for making this forum such a wonderful source of information . A double thumbs up from me !

I have been riding a stock standard 350 for 8years and recently decided to give it the bobber treatment .So i Stretched the stock swingarm by 3 inches ,chopped the fenders(rear /front) and got a solo seat made from the friendly neighbourhood garage .The bike feels much more planted now at speeds of 70 -85 kph in a straightline , though the ride at  low speeds (25-35 kph )  is bouncy to a point that my wrists ache from holding on to the 'english' style handle bar . This is making me refrain from riding the bike for extended periods ,So hoping to remedy the handling bugt I made sure that both the wheels are true ,tyres are running the recommed pressures and still the bug persists . Right now my perception is that the forks are causing all the discomfort since as i have a slight ache  in my forearms after a ride and my  bottom seems to cope well  

I do not have knowledge regarding a bikes geometry so I ought to ask you people if  this problem related to the increase in wheelbase ?

REgards

[1Blackwolf1]

  How did you re-do the rear suspension?  If you left the shocks in their original location the swing arm is prone to flexing a bit.  You may end up moving the mounts out board of the standard location to compensate for the added length.

  And how much longer is the swingarm opposed to stock?  Believe me you can feel a lot of vibration when you do any mods to a rear suspension.  I hard tailed a Triumph years ago and it made a dramatic handling difference at low speed..cruising speed handling was basically unaffected.

  Pictures would be helpful in this situation..

 Will.
 

[svb]

The shock absorbers are mounted at the same location and the have been lengthened . This was done because of the additional 3 inches added to the stock length of the swingarm and the angle of the shock absorbers (made with the swingarm) is now more acute . I will try to post pics here as soon as click some later today

[1Blackwolf1]

  Pics are good to have in this situation.  Believe you have started figuring out the problem.  Raer suspension mods can have a definite impact on handling.  Trail angle can make for an unruly ride if it is not correct.

  See what I think after I see pics.  Just may have to move the top mount back a little to make the geometry correct.  I also had to add a wider rear tire when I chopped the Triumph I had.  Adding the wider tire also calmed down some low speed vibration issues.

  Will. 

[svb]

Thanks for your inputs Will .
Here's a pic of the modified rear suspension setup . I will post some more if required later.
The rear tyre i am using is stock 19 inch (3.50 x 19) its done 20,000 km and is due for replacement .I intend to replace  it  one having a 110 or 120 section and will update this post as soon as I have done so .

[Vince]

     That picture helps. The modification you made puts the shock at a more acute angle. This will lower the rear end, changing front end geometry. It would be a little more stable at high speed but at low speeds steering would be heavier and require more effort. The change in geometry puts more load on the fork tubes, causing them to bind. At low speeds there may not be enough load to overcome the binding. The forks will lock up and not work. There is your bounce. Additionally, the greater shock angle puts more leverage on the shock. This has the effect of softening shock action.  The softer shock sags more, thus exacerbating front end geometry changes. At the more acute angle stress on the shock are greater. This can cause the shock to break off at the eyelet.
      The wheel base change is the smallest part of your problem.
     You have ruined the ride and the handling. To get it back you will either have to do some real actual engineering or go back to stock.

[1Blackwolf1]

  Welll a worn out/nearly worn tire will certainly make the problem seem worse.  Especially if the tire has a broken belt.  And looking at the angle of the shock makes me wonder if in reality it is actually doing any real shock absorborbing duties.  Angle may be to great so all it's doing is being a link in the suspension, sort of like a bolt on hardtail.

  I can't see how well it compresses of course, but I'd try and see how far it compresses while at rest.  Measuring the difference compressed and realeased may give some insight as to how well the rear suspension is working.  And try setting the shocks to the highest spring rate (highest setting) and see if there is a marked difference.  If not try try the opposing end of the scale (lowest setting).

  Chopping/bobbing a bike are fun..but the resulting follow up work is sometimes a bit tedious.  Believe me I've chopped/bobbed a couple bikes in the past.  Pretty sure the problems can be remedied with low buck fixes.

  Will.

[Vince]

     These kind of modifications were very common when I entered the industry. A lot of these bikes are still around. Next time you see one, look at the front fork. You will see the wear on the inner fork tube at the beginning of the stroke, in front. This is where it is binding as the forks flex from the unnatural angle they are at. A lot of people just got extended tubes for the same effect, and got the same resulting excess wear and bad ride and handling.
     Since I started riding in 1969, I have never seen a bike with these modifications that rode or handled anywhere near as well as it did before. Can it be made "workable" or "acceptable"? Sure, depending on your definition of these words. But I wouldn't ride a bike like this.

[Geirskogul]

It doesn't help that the front forks are rubber-mounted.

[500KsGerry]

did you turn down  your shock preload?.  move your seat back a couple inches if ya can too. Y a got more body weight on the front fork. move seat back OR progressive spring kit in forks if your a shorter rider. Looks nice Gerry

[1Blackwolf1]

  Gerry makes a good point moving seat location back may help handling a lot.  Of course this may also require handle bar adjustments/replacement.  Being in the Enfield mother country helps..you'll be able to find parts quickly if needed. 

  Will.

[svb]

Thought of bumping up this thread to post some updates .

.... so eventually i did move the shock absorbers forth to the original mounting position  , Got the seat shifted wee bit  as suggested (many thanks to all members for their valuable insights).having done that on the weekend , earlier this evening i took her out for a spin to the other side of town (~ 50 km)  and yep things have improved dramatically !  On one or two occasions hitting a pothole made her lose composure a wee bit but i could wrestle back into line with a slight effort. would be  changing to a sprung solo seat and wider rear rubber shortly in bid to improve it further

[1Blackwolf1]

  Could also try a fork brace/steering stabalizer to cut down the shimmy from the front end.  Worth a try.

  Will.

[cyrusb]

So you made the bike ride better at 70 to 85 kph, and worse at lower speeds?How often do you ride that 350 at those high speeds? 

[svb]

So you made the bike ride better at 70 to 85 kph, and worse at lower speeds?How often do you ride that 350 at those high speeds? 

Most of my riding is in 55-65 kph as the traffic situation here will not allow much more .At these speeds the bike feels no different than before. The pain area is riding  Lower speeds (25 -35 kph) over uneven / broken tarmac , i am trying to remedy this by trial and error and of course also with the valuable inputs of good folks over here . So far my efforts have made the ride go from a pain in ass to very nice .Not perfect yet mind you , so i'll keep trying some more

[basanti]

  Could also try a fork brace/steering stabalizer to cut down the shimmy from the front end.  Worth a try.

  Will.

What's a fork brace?

By "steering stabilizer" do you mean what they use on high end sports bikes?

[svb]

found this on the interweb  while searching for a fork brace , good demo
 
http://www.superbrace.com/simulation.html

 

[500KsGerry]

found this on the interweb  while searching for a fork brace , good demo
 
http://www.superbrace.com/simulation.html

 

very sensible and simple bolt on,  modified bike or not.

[1Blackwolf1]

  The guys hit it on the head, but since no one probably makes one for our bikes you may be able to use one from a different bike.  This link gives dimensions and may allow you to use one from a different bike.  There used to be a universal brace that was available here in the states in the 60's-70's but I believe they went out of business.

  I'll see what else I can find if this doesn't help.

http://www.fastfromthepast.com/PDF/fork_brace_dimensions.pdf

[luoma]

Another thing you might want to look at whenever changing a swingarm geometry, is compatible angles. Using a compass (the drawing type, not the magnetic type), draw a depiction of your rear suspension in scale and look at the motion of the rear end from the pivot point. Does your rear spring/shock move at about the same angle of attack? If not, it's going to feel funky. I've seen people move their suspension mounts on race cars, thinking they were geniuses, only to find out that they totally messed up their handling.