92KK 84WW Olaf wrote:What do you mean by old tyres?

Anything 2012 or older should be binned.

ERasberg wrote:. . .
a) I was cruising at around 110km/h when I let the bike gently brake on the engine from about 120km/h to 90km/h. 
b) At the same time i lifted the left hand from the handlebar, steering with just the right hand.
c) The bike suddenly started to progressively wobble on the tail until I, rather stunned, had to grab with two hands and engage the clutch to stop it. . . .

. . . I worry about driving her now, should I park her until further notice ? . . .

• Integrity / Age :
  a. Although the tyres might appear fine on surface (despite age), there could be internal cracks impacting stability
  b. I researched tyres all yesterday evening and will most likely order either Avon Roadrider am26 or Bridgestone Battlax Bt-45 tyres. Opinions welcome of course.
  c. Balancing is key. I will definitely have to check that. They have been balanced and do have weights on them, however if there are internal cracks this could change all that.
  

• Inflation
  d. The recommended inflation pressure dating back to the 80s might not be a good guide. Most people seem to inflate to higher pressures than the recommended 2.25/2.5 bars. I will increase pressure in the current tyres and see what happens.
  

• Rear shock adjustment
  The theory here is that too soft/too stiff will create a wobble
  I have left it as per the previous owner which appears fine, but I will do a few adjustments and see the difference.
  
• Forkes
  Fork oil was changed 5 years ago.
  I will replace it when possible, although I don't expect it to be the source of the vibration.
  

1. Steering with one hand
   In my opinion, and looking at motorcycle built physics, a bike should be able to run in a straight line pretty much by itself. Steering with one hand should be highly doable from a driving technical standpoint. The safety aspect is something completly different of course.
   
2. How much is the bike driven
   I drive it regularly and have covered about 7000km/4000miles since buying it last year. She was not driven much in the 10 years prior to the purchase and the bike still has the tyres from the previous owner on. The were hardly worn at purchase, but a bit flat probably due to underinflation.
   
3. Where did I find Two-Wheels-Better's explanation?
   Nothing escapes my microscope when I research bike-issues.
   

ERasberg wrote:Thank you to everyone (@Olaf, @Point-Seven-Five, @Laitch, @Two-Wheels-Better, @nobbylon, @Ringfad, @Dai, @yamaguzzi) for the great input ! Much much appreciated.


To recap, there are two main contributors to investigate : Tyres & Suspension.

Tyres

• Integrity / Age :
  a. Although the tyres might appear fine on surface (despite age), there could be internal cracks impacting stability
  b. I researched tyres all yesterday evening and will most likely order either Avon Roadrider am26 or Bridgestone Battlax Bt-45 tyres. Opinions welcome of course.
  c. Balancing is key. I will definitely have to check that. They have been balanced and do have weights on them, however if there are internal cracks this could change all that.
  

• Inflation
  d. The recommended inflation pressure dating back to the 80s might not be a good guide. Most people seem to inflate to higher pressures than the recommended 2.25/2.5 bars. I will increase pressure in the current tyres and see what happens.
  

Suspension

• Rear shock adjustment
  The theory here is that too soft/too stiff will create a wobble
  I have left it as per the previous owner which appears fine, but I will do a few adjustments and see the difference.
  
• Forkes
  Fork oil was changed 5 years ago.
  I will replace it when possible, although I don't expect it to be the source of the vibration.
  

Other subjects mentioned

1. Steering with one hand
   In my opinion, and looking at motorcycle built physics, a bike should be able to run in a straight line pretty much by itself. Steering with one hand should be highly doable from a driving technical standpoint. The safety aspect is something completly different of course.
   
2. How much is the bike driven
   I drive it regularly and have covered about 7000km/4000miles since buying it last year. She was not driven much in the 10 years prior to the purchase and the bike still has the tyres from the previous owner on. The were hardly worn at purchase, but a bit flat probably due to underinflation.
   
3. Where did I find Two-Wheels-Better's explanation?
   Nothing escapes my microscope when I research bike-issues.
   

ERasberg wrote:I found what I think is the problem : tyres are cracking. I have attached 2 pictures of front/rear tyre.

Over the last couple of days I have monitored the tyres closely, "over-inflating" them progressively until I got to Front=2.6bars/38psi and Rear=2.75bars/40psi when things started to happened rather quickly.

2 distinct perpendicular cracks started to develop, 1 on the front tyre and 1 on the rear.
I think by inflating the tyres I pushed some internal cracks to the surface. I am seeing more tiny cracks developing, so the tyre is likely quite porous inside. These cracks developed from literally nothing over the course of 45 km.

It is not loosing air pressure however.

I hope putting new tyres on will sort out the symptoms and wobbling.
Thank you for your very useful input ! Without your comments I probably would not have been so vigilant.
@Crazy Frog @Dai : I did the bearings check. They are fortunately fine.

nobbylon wrote:So far I’m really impressed with Sport Demons, 38/42 psi. They seam predictable so far but I’ve only done 1000 miles on them. Will keep an eye out for cracks now I’ve seen this thread, thanks.

ERasberg wrote:

nobbylon wrote:So far I’m really impressed with Sport Demons, 38/42 psi. They seam predictable so far but I’ve only done 1000 miles on them. Will keep an eye out for cracks now I’ve seen this thread, thanks.

Glad to hear that. I'm sure it's a great tyre and I do not think this is anything to worry about in your case.
I bought the bike last year, it had been stored for many years, so the tyres was not worn at all but 7 years old. This is most likely the cause of the poor performance.
I was told the golden rule for motorcycle tyres is max 5 years old.

ERasberg wrote:The cracked ones are Sports Demons. I'm thoroughly under-impressed with them despite all the praise they receive. Mine clearly didn't age well.

Two Wheels Better wrote:

ERasberg wrote:The cracked ones are Sports Demons. I'm thoroughly under-impressed with them despite all the praise they receive. Mine clearly didn't age well.

At seven years of age, as you said, I'd say a few cracks is alright.

ERasberg wrote:I just ordered Avons so I hope i wont have the same cracking issue with them.
The cracked ones are Sports Demons. I'm thoroughly under-impressed with them despite all the praise they receive. Mine clearly didn't age well.

And @nobbylon I agree fully with you and obviously parked the bike once I identified these cracks.

My key message was that internal cracks can surface quickly, in my case over the course of one 45km ride, and go from what appeared to be an intact tyre (seen from the outside) to a full perpendicular crack. AND without a noticeable difference in handling hence my newfound awareness for this topic.

@MartinW : thanks for the input on tyre choice. I was torn between AM26 and Battlax, in the end ordering AM26. I was looking for Michelin Pilot Activ, but couldn't find a matching front tyre. Will check out Shinko.

@Charlie99 : Thanks for the input. I think this is why inflation pressure is key, to ensure the risk of this type of damage is reduced. When leaning over have definitely not felt comfortable on these tyres, probably linked to the effect of the internal cracks. I have not seen anything like this on my other bikes, I have probably taken tyres too much for granted up until now. It has certainly given me a bit of a scare. Rubber is so important.

92KK 84WW Olaf wrote:I find the Battlax BT45 front tyre will scallop and crack if you let the pressures be too low.

Crazy Frog wrote:

92KK 84WW Olaf wrote:I find the Battlax BT45 front tyre will scallop and crack if you let the pressures be too low.

They are dual compound rubber. The sides are a lot softer than the middle.
If the pressure is too low, the sides will touch the pavement when riding straight and will deteriorate very rapidly. I experienced this with my first Battlax and had to replace the tire after only 5k.

nobbylon wrote:This is especially pertinent to the RS for overtaking as the short bars require me to stretch my neck so much to look over my shoulder it’s easier to take a hand off to give a better look over my shoulder (on motorways).

nobbylon wrote:I drive on the right (mainland Europe) so most of my motorway looking is over my left shoulder.