Why tire design can cause Head Shake

[Sir Price]

What a pussy.

My $0.02 worth

All the FJ owners that I have spoken to in Australia have the same problem no matter which tyre . The only one that doesnt shake its head has taper roller bearings fitted to the head stem.

Most will do it at around 70KPH whatever that equates to in the old money (around 35 to 40mph I spose ) with hands off the bars which also usually ( unless you have cruise control ) means the bike is slowing and therfore the front end is slighty loaded

 

[spineman]

PRIIs you get what you pay for.

So is it my oem Metzelers or you really shouldn't be riding at 100+ with the bags on? or both!

 

[Bobcattoo]

I've never seen, in 37 yrs of riding, a front tire wear out like that Azaro. It looked like I had ridden 7K on a Nascar Track. Left side tread gone! Tread remaining in center and right side.

Replaced with Michelin PR about 7,000 miles ago and very satisfied with that decision.

 

[Wee Willy]

I am an "enjineer", and was in charge of the Space Shuttle wheel and tire shop for many years. My personal opinion, regarding motorcycle tires is that you get what you pay for! The visible tread pattern is just a small part of the handling equation. What really affects the handling is the tire carcass structure and how well it is constructed. A more expensive name brand tire will have better balance and quality control built into it and thus will usually give a better ride.
Caveat:

Of course this assumes that your bike's steering head and front forks are not all outa whack from hitting deer and driving down redneck driveways and such!

+1. I'm an enjuneer too. This sort of dynamic response is a coupled reaction that relies on many variables besides the tread. Some big hitters are tire wall compliance, tire pressure, shock settings, CG location, speed, road surface roughness, just to name a few.

Getting the compliance (rubberiness) out of the system should go a long way to tightening the system up. I agree with Jack when he points you to top shelf tires and I would add that you should always keep your pressures where they belong. Next place to look would be shock settings. if all else fails, install a damper. Do they even have these for FJR's?

Cheers,

W2

 

[spineman]

I had a mechanic/friend test drive it at 100mph and he doesn't think its the tires or head causing the shake. He thinks its the windshield and fairing design. No one else can feel this?

 

[03HiYoSilver]

spineman,

Perhaps you should get an '03 design, 'cause mine does not shake or wobble at all in the triples even with bags...

if it is not the tires, you may need to firm up your suspension settings. Mine did wobble with bags on a 32k suspension and tightening up the suspension cured the problems.

The other time it did wobble is when the Tires were out of Balance at speeds above 80+ ...the Dealer remounted and balanced and this cure the problem. (Prior to my usage of the DynaBeads)

You may want to try this in your tires: https://www.tntperformancedyno.com/DynaBead...ml#Dyna%20Beads

It takes about 1 oz in the Front tire and about 2 oz in the Rear.

The Design is the most aerodymanic design I have ever had.... good luck with you solution.

 

[Rolavine]

Ok it's later. This is my theory on head shake.
The following excerpt is from Lee Parks' book Total Control, and I quote

"As a motorcycle travels down the road it actually moves in a nearly undetectable low amplitude weave. Even when the rider thinks it is going straight. This is due to a multitude of factors, like uneven pavement, tire profiles, the elastic properties of tire rubber and the constantly changing weight distribution from rider and suspension movements.

When this happens the bike begins to fall to one side and the phenomenon known as gyroscopic procession causes the wheel to turn in the direction of the fall. At this point our old friend centrifugal force pushes the motorcycle in the opposite direction, and the process of repeated over and over creating the low amplitude weave."

end quote.

That being said, some if not all of you are familiar with the properties of frequency resonance. https://www.google.com/gwt/x?source=m&u...3c31354b4cdefb3.

Resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's natural frequencies. At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy.

So my theory is this: when we are riding down the road we are already experiencing a vibration resonance through the engine vibration and the frequency of the low-amplitude weave that Lee is referring to. Every tire therefore must also have its own naturally occurring frequency, which I hypothesize changes with the rubber compound and tread pattern. Normally it doesn't produce any result or visible indication. Like the wine glass that is just sitting on a table. When the tire is traveling at just the right (or wrong for us) speed, that creates a vibration which matches its naturally occurring frequency resonance it will shake violently like the wine glass having a sound matching its own frequency directed back at it at sufficient intensity can cause the glass to spontaneously shake and ultimately shatter. I'm not saying of course we are going to shatter tires but what I am saying is that the head shake is a direct result of frequency resonance occurring in a manner that speed, rubber compound, tread design, low-amplitude weave, and vibrations all come together to manifest themselves in such a way that causes the head shake.

I would be willing to bet a beer that if there were a scientific way to measure the head shake, the frequency of the head shake would be an exact match to the frequency of the low amplitude weave that we all experience without knowing it. The only difference is that the amplitude(the peaks and valleys) are much greater.

There is a way to measure using accelerometers. I'm sure that Yamaha used this technique to test various points of the bike when they designed it.

Based on the orginal post about the azaros lefty righty center thread this would give us about 14.6 hz at 50 mph, linear to speed changes.

According to the spreadsheet at the Yamaha FJR1300 Supersport-Touring website, the engine would be turning about 2700 rpm or about .75 hz.

Of course, the engine will put out a lot of harmonics both even and odd, but it's the odd ones tend to propagate (If I remember correctly?). These frequencies are easily captured by even inexpensive accelerometers these days. I have several but no way to run a laptop while riding (yeah, I'm an injunear too), I don't think I'm going to be doing any testing, but it might be very interesting. My guess is that the engine is just a source of lots of low frequency noise with related higher harmonics, and is is coupled to that large aluminum tuning fork - bridge truss - of a frame, then to the head where the tire oscillation is coupled in, with other interferrence from the moving air, back tire patterns, read shock coupling, front fork coupling, any slight contact from the brakes, conditions of the road surface, and almost everything changing with temperature, yeah total chaos.

 

[Rolavine]

Ok it's later. This is my theory on head shake.
The following excerpt is from Lee Parks' book Total Control, and I quote

"As a motorcycle travels down the road it actually moves in a nearly undetectable low amplitude weave. Even when the rider thinks it is going straight. This is due to a multitude of factors, like uneven pavement, tire profiles, the elastic properties of tire rubber and the constantly changing weight distribution from rider and suspension movements.

When this happens the bike begins to fall to one side and the phenomenon known as gyroscopic procession causes the wheel to turn in the direction of the fall. At this point our old friend centrifugal force pushes the motorcycle in the opposite direction, and the process of repeated over and over creating the low amplitude weave."

end quote.

That being said, some if not all of you are familiar with the properties of frequency resonance. https://www.google.com/gwt/x?source=m&u...3c31354b4cdefb3.

Resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's natural frequencies. At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy.

So my theory is this: when we are riding down the road we are already experiencing a vibration resonance through the engine vibration and the frequency of the low-amplitude weave that Lee is referring to. Every tire therefore must also have its own naturally occurring frequency, which I hypothesize changes with the rubber compound and tread pattern. Normally it doesn't produce any result or visible indication. Like the wine glass that is just sitting on a table. When the tire is traveling at just the right (or wrong for us) speed, that creates a vibration which matches its naturally occurring frequency resonance it will shake violently like the wine glass having a sound matching its own frequency directed back at it at sufficient intensity can cause the glass to spontaneously shake and ultimately shatter. I'm not saying of course we are going to shatter tires but what I am saying is that the head shake is a direct result of frequency resonance occurring in a manner that speed, rubber compound, tread design, low-amplitude weave, and vibrations all come together to manifest themselves in such a way that causes the head shake.

I would be willing to bet a beer that if there were a scientific way to measure the head shake, the frequency of the head shake would be an exact match to the frequency of the low amplitude weave that we all experience without knowing it. The only difference is that the amplitude(the peaks and valleys) are much greater.

There is a way to measure using accelerometers. I'm sure that Yamaha used this technique to test various points of the bike when they designed it.

Based on the orginal post about the azaros lefty righty center thread this would give us about 14.6 hz at 50 mph, linear to speed changes.

According to the spreadsheet at the Yamaha FJR1300 Supersport-Touring website, the engine would be turning about 2700 rpm or about .75 hz.

Of course, the engine will put out a lot of harmonics both even and odd, but it's the odd ones tend to propagate (If I remember correctly?). These frequencies are easily captured by even inexpensive accelerometers these days. I have several but no way to run a laptop while riding (yeah, I'm an injunear too), I don't think I'm going to be doing any testing, but it might be very interesting. My guess is that the engine is just a source of lots of low frequency noise with related higher harmonics, and is is coupled to that large aluminum tuning fork - bridge truss - of a frame, then to the head where the tire oscillation is coupled in, with other interferrence from the moving air, back tire patterns, read shock coupling, front fork coupling, any slight contact from the brakes, conditions of the road surface, and almost everything changing with temperature, yeah total chaos.

Daily Commuter, you may be on to something because I made a mistake in my math. The azaro 14.6 hz is about right but the 2700 rpm motor is no .75 but 60 times that, or about 45 hz. 14.6 is close to a third so a harmonic reaction is quite likely. Also, since both the azaro resonance and the engine resonance are both linear with respect to speed we can expect this pattern at all speeds. Actually quite amazing , not a proof but curious.

 

[GalaxyBlue]

I only get the shakes when the Yami top box is on.

Go figger

 

[dcarver]

Dang, Rolavine, you're good!

I fixed the problem by simply running quality tires, PR2's :lol:

Next time I'm in Salem I'm buying you dinner, doode!

 

[spineman]

spineman,
Perhaps you should get an '03 design, 'cause mine does not shake or wobble at all in the triples even with bags...

if it is not the tires, you may need to firm up your suspension settings. Mine did wobble with bags on a 32k suspension and tightening up the suspension cured the problems.

The other time it did wobble is when the Tires were out of Balance at speeds above 80+ ...the Dealer remounted and balanced and this cure the problem. (Prior to my usage of the DynaBeads)

You may want to try this in your tires: https://www.tntperformancedyno.com/DynaBead...ml#Dyna%20Beads

It takes about 1 oz in the Front tire and about 2 oz in the Rear.

The Design is the most aerodymanic design I have ever had.... good luck with you solution.

Thanks I will try that!

 

[CHRIS_D]

I been lucky over 26K on the bike with various brands of tires and have never had a head shake. In fact I'm currently running on the front one of those bargain Azaros. I have over 4K on this tire and it still looks like brand new. No weird wear patterns or flat spots. I have one more new Azaro in garage and hopefully this one will be as good as one I'm currently running.

 

[blufjr]

I been lucky over 26K on the bike with various brands of tires and have never had a head shake. In fact I'm currently running on the front one of those bargain Azaros. I have over 4K on this tire and it still looks like brand new. No weird wear patterns or flat spots. I have one more new Azaro in garage and hopefully this one will be as good as one I'm currently running.

I really like the Azaro's in the corners. The front just feels like it is diggin in and really gives you the feelling of control. I hate the way the tire wears and looks, especially after 5,000 miles. The left side wears down to the no tread first, 6,000, the right second and you remove it before the center wears to the wear bars. The one below was taken off at 9752 miles. If I had had to run another 1000 miles on the freeway, I would have, but the sides did not inspire any confidence in the corners when it was wet.

I measured the tread depth at the center as 3mm when new. It looked worn out with 2mm of wear at 6,600 miles. That equals approx. 3,000 per mm on the front. Totally uneven wear as you can see in the pics.

The head shake was terrible and is the only reason I'm not looking forward to installing the other new Azaro front sitting in the garage. The head shake was there from when the tires were new to the end. I kind of made it better by loosening all the fork pinch bolts and then retightened them, but after removing the tire to check the balance at 6,600 just before a 2,400 mile ride to MT, it made it worse than ever. At 50 mph it was outrages.