I have a couple of bikes in the garage... among them two Fatboys and lately a relatively new 2016 Sportster Forty Eight 1200 with only 4200 km on the clock (mag wheel fat front tire). So far combined the Harleys I had and have did over 120000 km. I only changed tires and replaced batteries. So it is safe to say that in my case I have/had reliable bikes. The Fatboys are the choice for longer trips and the Sportster for trips up to 150km or so. I also had a 2013 Breakout which was not bad at all. The worst Harley so far was the Rocker C which just had a horrible, hard suspension....

Back to the issue of instability.... and here the 2016 Forty Eight is the culprit. From day one the bike had a strange feeling of being unsure on the road. Hard to describe but it feels like a subtle unseen hand constantly pushing it slightly left, then right and then corrects itself... it follows uneven road that is not there! It feels as if the back is momentarily going over a slippery part of the road which is not there quite so often - like wind turbulence or something affecting the bike. I have had two other Sportsters in the past (883 and 1200 Custom) that never did this.

Today I went to the HD dealer 120km South of me and took the same bike (demo 2018 Forty Eight) for a ride. Light wind, good even road - exactly the same unsureness and movement I experience! Tire pressures are correct, bike has 3200km on clock. The bike is OK up to around 75 km/h ... thereafter the instability creeps in. I did not go over 120 km/h.

The dealer said that he also felt the issue on the "new" Sportsters and thinks the fat front / rim size may have to do with it. This is ruining a very nice little bike - for me at least! I have changed the rear shocks and completely rebuilt the front ones in search of a cure... Neck bearings and rear swing arm bearings all checked!

Am I alone in this or do others find the same issue with the "newer" Sportsters? Can it be the rim size (16" up front with high profile tire)? Will it help by fitting another fatter rim & tire at the back? I have sorted so many other little issues on this bike... and yes I like the Forty Eight - but I hate the unsure on the road feeling.

Any suggestions?? Can this be cured?? I need help here please....

 

You can try playing with the preload on your neck bearings. Set them up as per the manual- and then loosen the preload off -say 1/2 a turn- ride it- loosen it up another 1/2 turn- ride it- etc. Goes the same way on tightening the preload- 1/2 turn at a time. You know what im getting at. Helps to write your adjustments down so you dont lose track. Its free and worth a try!

 

For sure - I will try this.... Thanks!

 

I would also look at your tires. Could be a tire issue of some sort including balancing, and alignment.

 

Ummm….. the dealer's demo bike has the same handling characteristics?
My first thought was also steering head bearing adjustment...but...see first sentence.

OP seems like they are "ruled out" loose bolts, alignment etc.

IMO I don't think changing to wider rear tire and of course this may require a front tire too to keep a matched set.
I would check wheel balances, play with air pressure, play with steering head bearing tension.
Maybe add a steering dampener and/or a fork brace.
Perhaps play with both compression and rebound front fork dampening with oil weights or level.

I ride a 1200N so I have not experienced what the OP is describing.

Good luck.

 

Loosen up the steering head bearings just a bit.

 

Thanks! Note that the demo bike and mine are doing the same thing so I assume this is a Harley Forty Eight issue... We must find a common denominator. That brings me to the changes from the older Sportsters and specific the 16" fat front....

 

Thanks! The alignment is in spec and the wheels balanced.... maybe a different brand of tire (rubber composition) is part of the answer....

 

Note the only real difference is the front wheel....

 

Hi JWCFatboy your not alone on this one!!! I too have the feeling of my 2018 48 Special being slightly unstable at speed, seems fine at cruising speed but like you I can't pinpoint the cause. In your case you have changed out most things that could possibly cause the problem, whereas mine still has the standard shocks etc in place.
I too have been wondering if a steering damper may cure it, but not totally convinced on that one because the front end seems to be stable enough, I sort of get the feeling it's the back end that's actually unstable, and to be honest although unpleasant it never ever feels like it's going to get out of control.
A few years back I had a Dyna which scared the s**t out of me a few times due to getting into near tank slappers, but I found the cause to be the handlebars which were too wide.
Anyhow I will keep an eye on this thread to see if either your good self or someone else comes up with the answer........if there is one.