Rain-groove causes crazy wobbling? Or is it me?

Hello all- so, my '68 Cdo with Avon Roadriders, stock wheels and suspension, at about any speed over 30mph on a rain-grooved California concrete freeway surface. The bike is so wobbly and oscillating that it feels as if I am hydroplaning on dry road, as if the tires aren't really making contact with the road surface. It's completely unnerving, really gets to feeling like the bike could go in any direction at any moment. Same speed, same road, the surface changes to asphalt, the bike is smooth as silk at any speed. On the grooves, leaning into a turn feels like a life-threatening experience; again, on asphalt, no sweat. I'm just wondering if others have had this experience? Or is there something wrong with my setup? It sure feels great on the blacktop, but man oh man it's crazy on the grooves. Thanks for your thoughts as always- eric

Sounds pretty normal but you might want to get your tire pressure up. Roadriders like about 32 front and rear or 34 in the rear if you carry weight back there. Jim

Thanks Jim- I will check the pressure. The only weight I carry back there is my arse, which means I should probably go with 34

Some tyres are more susceptible to the grooves and make it feel as if the front contact patch is on ball bearings. I prefer a tyre without a central groove.

I suffered quite badly from this and it only disappeared after fitting a Taylor headsteady. I can only assume that the frequency of the front wheel vibrations was being amplified at the isolastics and that more precise control at the top mounting prevents it getting out of hand.

It's not a nice feeling at all.

I'd check tyre pressures as advised, steering headbrgs and get someone else to ride it. The standard Norton forks can have lots of stiction that would make it feel worse in the wet, are they moving freely?

This rain groove wobble is what made Bryan Tryee create the first rod front linkage in late 70's and solved it for him. I ride an almost freeway wide Gravel groomed path to the hiway and if my front tire, no matter the brand or size or wear of the front tire on Cdo's or SV650, if my front tire is not 2-3 lb lower air than rear, the front tends to control the aim INSTEAD OF THE REAR RULING THE ROOST and causes groin spikes of fright as bike tends to do opposite my intentions. Lowering tire pressure while maintaining the 2-3 lb lower front also helps tame the out of control sense, which can evolve into hingled handling if trying to just speed through this wobbling. It only seems like front steers a bike, but it really only acts as a rubber to aim the rear tire-whole bike to turn. If front has more traction than the rear things - when not spinning out rear on purpose things get scary. Anything from stem to stern that has more slack than it should can allow small oscillations of front to follow road build up so magnify tire pressure and profile wear upsets. A fully tri-linked Cdo is immune to this even with a flat tire on THE Gravel either end.
If ya go too low over all tire pressure it can make wobbles onset on smooth pavement sweepers.

The fork striction mention can also contribute as sticks/releases just enough tend to reverse expected front steering action. By far most striction is due to springs rusted rough inside stanchion so may have to clean that up too. Stem bearings worn stiff can feel similar but very rare in Cdo's or any bike but happens now and then to any bike.

All can be aggravated by too loose a front iso gap as rear patch tends to slap the front gap side/side and causing forks to wiggle in response, which feeds back through chassis to add and substract from rear patch slapping the front side/side. It take a like 1/4" slop in front to actually see this happening but much less to feel its effects on rain grooves or rough loose Gravel lanes.

Rain grooves are just something to get used to. I like the sensation but they make my wife ill. Appreciate them for what they are and enjoy the thrill. Let them heighten your senses and drive with increased spacial awareness. And, don't let that asphault put you to sleep. When hot it's like driving behind Dale Jr. with a blown motor.

Thanks Hobot and Pviss et al- looks like I have my weekend plans. Inflation, check bearings, iso's, etc. Forks slide freely, that much I know, fork oil is fresh too. And once all that is done, I will get my Zen on and just "enjoy the ride"..... Thanks guys! ejd

askdoctorday said:

Thanks Hobot and Pviss et al- looks like I have my weekend plans. Inflation, check bearings, iso's, etc. Forks slide freely, that much I know, fork oil is fresh too. And once all that is done, I will get my Zen on and just "enjoy the ride"..... Thanks guys! ejd

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Having driven in LA in car and was fearful of the grooves I can't imagine what it would be like on a bike.

I can take rain grooves by staying on power and kinda shifting butt back to let front do its thing by itself w/o as much notice by the rear which get the whole buggy oscillating. But one major reason gave up riding in Houston TX was the curved - diagonal 3-4" wide and deep gaps where on ramps and major intersection cement jointed - and would serious try to snatch me down, with traffic on all sides baring down 70-80 mph. This was on the P!! dragster so leaning type turning rather limited to dodge much either.

About only real danger is if grooves on long but fairly sharp sweeper or in clover leafs you'd hold a set lean for many seconds, oh LA LA can the hingle hit then.

Go faster! It'll go away after about 70 MPH. At least that's my experience. The avons are Waaay better than the dunlops. Also, check rear wheel alignment. If its off a bit it'll add to the wobble.

Yes gets better the more ya wick it up but conditions and traffic don't always allow it and its mostly if entirely solvable at its base.

Every bike I have ever owned has behaved badly in the grooves. Tire pressure helps but just be careful.

Yes doctorday it is definately your fault. You did not pay enough road taxes and gasoline taxes and permit taxes therefore you end up with roads with indefinate road resurfacing time schudules. My wife likes to scream in terror when we hit the snakey road groovy things so it is worth all the money. The absolute lack of notification of upcoming situation is a cost saving measure to be sure. Drive on , enjoy.

Toronto, you are a funny guy. Brilliant- I had not even considered my part in the whole mess. Henceforth I shall pay more taxes! Oh, wait, that's happening now....

My 1986 Yamaha FJ1200, also shod with Avons, is smooth as buttah on any road surface. The grooves have no effect on the bike- solid and on rails. Of course, the Yama weighs in at about 600 pounds wet, plus 190 for me, so that could have something to do with it. And since that bike has been my only freeway experience prior to the Norton I was pretty alarmed when the Cdo started doing the Cha-Cha. Thanks for all the wisdom guys, I'll let you know how it goes- take care- ejd

And so we get down to the crux of the matter - any two wheeled life is dam risky and no one's skill or caution can over come every time. Best wishes on not discovering when that might be.

Crowds of cycles out here, reports of causalities routine. I came upon a fresh one in a long sweeper with a drop off. 53 yr bleeding from nose and head cuts did endo's into a fence 15 ft below. Said no idea what happened just suddenly bike shot off the edge just cruising parade style with others. I test myself in this spot and waiting for a low sun condition to video highlighted undulations unseen other wise but felt through chassis wanting to head off this way and that on its own. His vitals ok I asked him if he knew his ff/rr tire pressure balance, what's that? he asked. Guess where I really got a good sense for that importance.

Every bike and tire combo and rider has sliding scale of compromise, I get my sense for it now by zig zags in lane and diddle PSI till control is least effort and scares me the least. Not the end all to stability but helps with what ya got. I learned the hard way how much a particular bike can wobble and just self recover ignore or sense it getting to crazy and back off till it ain't. Sometimes through power to relieve the front is only way to go. Track days and Gravel commutes are fastest ways to learn bike and tire limit behavior - one of em is fun. Everyone should know what hinged onset is like so not to ever do it and ignore the normal Cdo dance on textured surfaces.

I live in Calif. also and had that problem too until I changed the front tire recently....went from a K81 to a Dunlop D401 ( a Harley tire, tried it because I got it cheap for $50) and the wobble is almost completely gone, still have a K81 on the rear wheel. Am guessing the D401 is less prone to tracking rain grooves since the tires center groove zigzags. FWIW remember that K81's were VERY wobbly on rain grooves even on non-Norton bikes back in the day when they were commonly used.

edit- read bpattons post below, had not thought that maybe tire size might have a role too...but did also went down a size when I changed tires, from a 4.10 K81 to a 90/90 D401

The tires I have run a noncontinuous "wavy" center groove- in principle similar to what you pictured- so one would think they would be okay. I think it's the ace work of our CalTrans Groove Masters that induces the Cha Cha I am experiencing... Checked the pressure- slightly low but not bad at 31 lbs. Raised front to 34, rear to match. Forks are smooth, steering head nice and smooth no slop, iso's were adjusted at the shop recently so I have no idea. Will let y'all know if anything improves!

http://www.motorcycle-superstore.com/1/ ... -Tire.aspx

The tires on the Yamaha have no real center groove- more like sportbike/superbike tread- so yet another reason for the non-issue with that bike.

As a shrink, I occasionally assess people's mental status after accidents in emergency rooms etc. One question I never thought of is, "What kind of tire pressure are you running? Front? Rear?" So Hobot, I will add that one to my repetoire- thanks!

Get as many crashes as me last decade and they begin fall into categories of causes and combo's of splashed together reasons originating with bike or pilot and a lot that have nothing to do with bike and pilot, except getting on it. Anything less less would go unnoticed.

Might just be me but I'm Pensive-Sensitive to front being as hard or harder than the rear. Had it happen with slow leaks over rides. I've saved some upsets trying to upset bike before entering fun sections, oil leak on tire, flat tire to missing shock mount discovered in time that way. Tuning a Cdo is like tuning a old piano, left alone goes out of tune and touching one area means must compensate in others ya might not suspect got thrown off scale.

The thing I found out about too hard a front - is the about nothing resistance-fighting with rear in this condition can suddenly reverse expected control-recovery reflexes needed. I suspect in the headoverteakettle event his counter steering lean to keep rear doing its job suddenly actually did steer the way front was pointed > SPLAT!

I now believe that too much dependence on forks and front tire is the basic down fall of anything trying to catch back up to me on Peel on or off road.
Just takes one unsuccessful crossing THE Gravel to show this up but about a dozen to for reason to sink in, aftger trying it the way of rest of the world, so almost never happens anymore on or off road. Forks must weave to stay upright at any speed, just not noticed unless on loose stuff or groovy frwys.

askdoctorday said:

The tires I have run a noncontinuous "wavy" center groove- in principle similar to what you pictured- so one would think they would be okay. I think it's the ace work of our CalTrans Groove Masters that induces the Cha Cha I am experiencing... Checked the pressure- slightly low but not bad at 31 lbs. Raised front to 34, rear to match. Forks are smooth, steering head nice and smooth no slop, iso's were adjusted at the shop recently so I have no idea. Will let y'all know if anything improves!

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I was curious about all this myself so did some Googling, sounds like the Roadrunners may be especially susceptible to CA freeway grooves..(K81's definitely are)

http://www.triumphrat.net/twins-technical-talk/102370-the-rain-groove-boogey.html