Handlebar vibration modifications

[jlparsons]

Thought I'd post this here in case it's of use to anyone. I have a 2023 BMW S1000XR which wasn't bad for handlebar vibration but there was more than I liked so I thought I'd do something about it. I added Ecotech hand guard protectors which adds significantly to the weight at the ends, both with heavier bar weights and the thick metal protector bars themselves. I have also now injected two-part shore 40 silicone rubber into the handlebars as well and tested again. Results of vibration tests so far;

Stock weights- Max 6.9 Mean 3.7
Evotech hand guard protectors - Max 5.0 Mean 3.5
Evotech & shore 40 silicone injected - Max 3.6 Mean 2.9

So quite a reduction again for the silicone, in fact more proportionally than the Evotech hand guard protectors which I didn't anticipate. Not perfect test conditions however, these measurements were made with a vibration app using my phone's internal accelerometer while holding the phone in the vertical position with the bottom pressed against the end weight on the right, engine started cold and waiting till the revs settle down to take the measurement for each test, so far from all variables accounted for but about the best I could do with the equipment I have (bugger all) and I think this should give a valid comparison. I went with shore 40 two part silicone (Smooth-On Mold Max 40) as I figured a denser and more firm silicone would dampen vibration more and should last effectively forever. I couldn't find much data comparing silicone grades for this purpose unfortunately. This silicone has a 45 minute pot life and in this case (18 degrees C ambient) stayed easily workable for about twice that time, which did make me worry something was wrong and it was not curing!

To inject it I put the bike on the side stand with the bars in full left lock to give as much of a slant as I could, took out both bar end bolts and used a large 300ml syringe to force it through until it started dripping out of the other end, which took a while and a lot of pressure. I then installed the left bar end bolt first to push the mixture further up, then put in the right bolt and tightened both finger tight. I think the viscosity of this mixed silicone was a about right, any more and it would have been difficult to push through, any less and I suspect you'd have a greater likelihood of air gaps. I vacuum-treated the mix first using the syringe and pushing out the resulting air before injecting.

One point of note however, turns out there is a hole in the handlebars within the left hand control cluster, and when you screw in the handlebar end bolts the pressure inside the bar increases and forces a dribble of silicone out of this hole. I didn't expect there to be a hole as there is no internal cable routing so I suspect this is a hole for a pin to secure the controls in place. Fortunately this was a minor dribble out the bottom of the control wheel assembly and I was able to clear this up as it dripped and I wound back the bolts a tad once I realised it was happening - as soon as the pressure was lowered the drip stopped so I think the gap must be tiny and the quite thick silicone mix only came out when under pressure. Methylated spirits and kitchen roll cleans up the silicone very effectively so I'm left with no residue and the control wheel function is not affected. ideally though if you're going to do this you should take off the left controls (or undo and slide them if possible to reveal the hole) and tape this before you proceed. Make sure to cover the bike where the silicone will drip out the right end of the bar when the bar is full too, but the meths and kitchen roll will clear up any drips perfectly and any missed will peel off easily once cured. Also take some silicone lubricant spray (or silicone grease or just oil would suffice) and make sure the bar end bolts are lightly coated before you insert them to seal the bars after injecting the silicone otherwise the silicone will lock them in.

One possibility I considered but rejected was to suspend powdered tungsten in the silicone once mixed. I think if you went with a low viscosity silicone you could end up with a tungsten-silicone mixture which was still injectible but this would likely have to be tested multiple silicone grades, plus 500g of powdered tungsten can be found for about £50 so I expect you'd have to spend several hundred pounds on experiments before you got a recipe for an injectible mix. However I calculated that mixed tungsten powder and silicone should have a density about equal to lead (tungsten is about twice as dense as lead) as opposed to a density slightly higher than water for the plain silicone, so much more weight and I suspect much greater internal damping as the tungsten would be suspended weight. Maybe someone braver or richer than me can give it a try![/i]

[stinkwheel]

The old way was to fill the bar with lead shot. Has the advantage you can remove it if you want to.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jlparsons]

[stinkwheel]

The other way if you were getting intrusive vibrations was to try repositioning the engine. There's always a degree of slop on the engine mounts. You loosen all the engine mounts then either jack up under the engine or give it a few kicks and re-tighten. Or nip them up again while the engine is running. This will alter the frequency of vibrations transmitted to the frame.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jlparsons]