Rain-grooved pavement

[Dwmadsen]

I have a - new to me - R65 and had a near death experience. I was riding the same highway I have been riding for 25 years and when I got to pavement with rain grooves, the bike began to shake uncontrollably. I was going around 60 mph and immediately began slowing down to 50…40…30 mph with the shaking threatening to pitch me into three lanes of traffic. Before I could cross three lanes to get to the shoulder, the pavement switched to non-grooved pavement and the bike was immediately stable. I have ridden various bikes along this stretch of road without ever having issues.

I have new Metzler tires with “C-block” tread pattern. The tires are inflated to 26/28 (front/rear).
The bike has new head tube bearings - no play.

So, my question is has anyone running tires with “C-block” tread experienced violent head shake on rain-grooved tires?

[Bob_Roller]

What model tires do you have??
I would also suggest you increase tire pressures to 32 psi .
Tires with a center groove in the tread seem to have issues with rain grooves .

[Barry]

Agree, the old under seat tyre pressures are too low for modern tyre construction.

On the head bearings, they need to be adjusted a little beyond no play. A touch of pre-load such that the bars will still fall side to side but not so fast that they bang against the stop. This provides a degree of steering damping.

[georgesgiralt]

Hello,
This was my experience back in the days. Now; with recent design tires and gum, the problem is less present or absent.
I second the pressure advice (I'm a metric man so can't vouch for the PSI number) but you need to go past the old pressure advice BMW gave 40 years ago.
I run Michelin tires (Pilot activ and now the Pilot classic) and the groove problem is non existent. It was the same with Heidenau tires beforehand.
Hope this helps.
P.S. : I always fear these grooves and strongly reduce speed when seeing them in front of me. Once bitten.....

[Burt]

Not so much rain grooves but when they are relaying the bitumen and they cut similar grooves into the surface prior to laying the new surface.  Horrible things. 

I'd be looking at 32/36 psi as a starter.  The lower pressures will also affect the handling in other ways. 

[dogshome]

All of the above. Pressures lower than 30 are horrible on wet, white lines. Combined with worn head bearings (or loose or tight) ones makes the experience very uncomfortable. Not a tank slapper, but wakes you up and slows you down in a hurry!

I just replaced head bearings. Adjustment allows the head to fall to each side, not bind or be slow. No free play by grabbing the front axle. Sounds like its mostly tyre pressures in your case. I have an R65 which is technically a slightly quicker steering setup than 80/90/100.

[Barry]

Back in the 70's airheads were known to be fussy about choice of tyres and this used to be discussed in the more enlightened motorcycle press. For stability they needed stiff tyres. My under seat chart lists a choice of 3 different makes and model of tyres to fit as well as the pressures which at 27 psi Front and 26 psi rear seem insanely low by modern standards. For years BMW maintained an ongoing  updated list of which additional tyres had been tested and found acceptable. They were communicated to the dealers by service bulletins and they were not supposed to fit anything else. Even if old tread patterns are still available the tyre construction will be modern and require a minimum of 20% higher pressures and more than that on the rear to work well. 

The other thing I've learned about tyres is that what feels like front end instability on grooved surfaces or white lines can be caused not just by the front tyre but also by the rear.

[Dwmadsen]

I changed the rear tire to an Avon MKII and that helped considerably. I then changed out the front to a BT46 and I’m back to ‘no surprises’. Pretty expensive lesson.

[dogshome]

Thank fo feeding back 


Tyre pressures didn't help? Or didn't you want to risk it!

[Tony Smith]

I have 4 airheads that I am responsible for. 2*R100RS, the wife's R65 with R80 engine. All of these have stock(ish) suspension and Ikon shocks.

My R860 has a K100RS front end and custom made Betors. The wife's bike wears Pirelli City Demons, the 860 has Highway demons. One RS has Avon's and the other has Contis.

Now it tested each of them after fitting the tyres and strangely enough I arrived at the same solo tyre pressures for each of them.

Namely 34psi front and 36psi rear, these pressures go up a few psi if carrying a pillion or luggage.

The tyre pressures stated by BMW back in the day should be ignored with prejudice.


As regards stability the 860 tracks like it is on rails and I have herded it over some fairly indifferent surfaces.

The R65/80 is likewise stable, but perhaps notctocthe same extent as the 860.

The 81 RS has shown occasional signs of nervousness and has given the bars a bit of an incipient shake a couple of times but hasn't ever looked like developing into anything.

Back in 1983 or thereabouts the 78 RS scared the crap out of me several times. It would suddenly enter a violent tank slapper at about 70kph that would continue down to 50kph and self terminate.

Make no mistake, these were violent, full on tank slappers, on one occasion the violence was sufficient to break the retaining locks and spit both panniers off.

I used to transit through the onset speed, both up and down, as quickly as I could, but to be honest the bike scared me spotless.

After consulting widely I took off the Pirelli Phantoms and went back to motel traditional tyres - Metzlers if memory serves.

The change in tyres tamed but did not completely remove the tendency to shake its head.

Not until some years later did I discover that the centre hole in the triple clamp top plate was worn oval. I replaced the top plate with a Luftmeisterachined alloy top triple clamp and it has never shaken again.

My own postmortem thinking is that the Phantoms were for whatever reason unsuitable tyres for an airhead and the tank slappers damaged the top plate and replacing that completely cured it.

[Kelvin]

I had a problem with tank slappers back in the 1980s with my R65LS. The problem was put down to worn Pirelli tyres, particularly the front one was a metric size but the bike was built for imperial. The problem was fixed by installing Metzlers in the original 3.25 H 18 size.

In 2019 the R65LS I purchased was wandering and feeling unstable (but not tank slapping) on grooved pavement. It had three year old Metzlers, I got it to behave better by swapping these for the Michelins that I usually run.

Like Tony I run 34psi front, but only 34psi rear. I've always found these bikes to be unusually sensitive to tyre pressure, you can notice it in the handling if you lose a few psi. Dropping the pressure as far as the original 26/28 I would expect garbage handling whether you got up to tank slapping speed or not.

[Barry]

I've found that a bit of steering instability crossing white lines and grooves can also be caused by a worn rear tyre as well as a worn front.

By today's standards, the oddest thing about my BMW original under seat pressures was that for solo riding the rear pressure was lower than the front. Presumably that was because the wider section rear could support more weight. I believe the need for higher pressures using modern tyres is not just down to changes in tyre construction, BMW were also claiming superior ride ride comfort compared to other bikes. What I also very distinctly remember is the motorcycle press saying airheads had a reputation for being very fussy about tyre choice and they needed relatively stiff tyre construction to ride well. BMW's original low pressures wouldn't have helped and it's no surprise that modern tyre of lighter construction need higher pressures to stiffen them up.