There are Flat Tires, and Flatter Profile Tires. But then, there are Tire Flats.

[rdfrantz]

I had a challenging and fulfilling trip this summer between Los Angeles and southern New Jersey. I continue to write about the events and will post them across time. But, one oddity showed up that just smashes into my Wonder Bone, and I can't wait longer for some relief.

 

So, there's a Revaluation toward the end of this post, and some Question... about which Answers, or just Greater Understanding, is probably a complexity, rather than a simplicity. At least I expect, and somewhat hope so.

 

Consequently, in service of that view, here's some background information.

 

 

A few years ago, to perk up the steering, and the cornering feel of my K1200RS, I fitted a set of Avon Azaro tires. Not only were they successful at that, their soft, supple, gripping feel in cornering, and even on straight roads as well, pleased me to levels I'd characterize as thrilling. And, on top of that, the hard center compound of the rear dual compound AV46 lasted 8,500 miles in the almost exclusively high speed use I put the K12RS to. That pushed it's no-tire-change-range into a truly useful region, and removed a major physical, and thus emotional restraint on travel. No longer would I need to "baby" the tires on a long trip, or plan and schedule a tire change, and then worry if I'd be able to make the appointment, or even have enough tire left to do so. Anyone who has gotten to Torrey on Dumlop D220s "with 2000 miles left on them", and then watched that tread disappear in less than 500 miles, is well acquainted with the resultant "Worry" I'm relieved from.

 

Along the Experiential Trail on the Avons, events had me encountering the low stability regime of the K12RS in quartering headwinds, specifically solo and with a top cased fitted - my beloved GiVi E50. That situation sets up a minuscule, two cycle oscillation of the front wheel. Along with that, the exposed shou8lderas and arms of the rider are subject to a rhythmic force (turbulence). If the rider "places any weight on the handle bars", actually, "has a stiff connection between his/her hands and shoulders", the two rhythms join and amplify, and a medium amplitude (~0.8 in.) wobble of the bars takes place. Remove the rider's body connection to the bars and it stops.

 

Anyway, it seemed to me the Azaros were more prone to this behavior, and that the behavior was stronger when they were fitted than the (not impertinently) stiffer constructed ME-Z4s had been. Consequently, I tried a set of Michelin Pilot Roads, because of generally good reports about them, notably "their handling", and because they apparently possessed some of the stiffer construction elements of the Metzler tires. I found the "wobbly" behavior diminished. So that's the primary reason they had been fitted, and their fittment filtered on down to being present during my cross-continental trip.

 

This should not pose as a condemnation of the Azaros, nor even a "finger pointing" - They remain my favorite tire for fittment to any bike I'd commonly own. Comparative circumstances were never presented: Never the same winds, load, road surfaces; Bike configuration might have varied as well with changes of handguards, windshields and such. It was just that I decided based upon some quantum of better Feel that I'd ride the Michelins -- and then later actually did encounter a similar magnitude of The Phenomenon, but also only once instead of often.

 

Now, looking further into the characteristics of the Pilot Roads. I was very pleased with several discoveries. First, they returned wear of 8,000 to 8,500 miles for me on the K12RS. Secondly, they impressed me, across several sets, as light and quick steering: Contrasting to Laney's impression they were "dog slow" and unpleasant in that regard on my bike, compared to Azaros on her own K12RS. The last set I've fitted still very much seem to me to "just whoosh on over", sometimes catching me out a slight bit, and requiring some control input to stop their rolling moment.

 

Another pleasing discovery was their traction performance, and feedback or feel when cornering. I found I could run "My" speed and lean angle across all my curvy road riding without encountering any slippage, hops, skips or jumps: They went around corners as stably as ME-Z4s. They have both a more supple, and more grippy feel, though only the tiniest but still meaningful suppleness. The feel actually comes from greater slippage than he Z4s -- all tires are always slipping during cornering, or else no cornering force would be generated. It's that during the slippage, the rate of slip at the same lean angle did not change because of heating changing the grip, and as well, the amount of slippage did not change, either "much", or to an unpredicted/unexpected degree as lean angle increased. In summary, these were "good, confidence inspiring tires".

 

Comparing the Azaros in the same way. the Azaros slip the tiniest margin more, but that is counter-effected by the feel they are "nibbling and grabbing, and 'just eating up the pavement having a happy time' while they 'glide across the pavement in supreme partnership with the Rider's lead to Dance'". OK, I know it's Flowery, but damn if y'all haven't felt Azaros used in anger, you're missing an incredible treat. They feel a lot like Sport (not Race) tires.

 

As best I can tell the difference between the two tire models (an the pertinence to this overall post), seems to stem from the fact the Azaros use a textile re-inforced belt and supple body plies, and the Pilot Roads use a steel reinforced belt and stiffer body plies. Then, each company applies a compound to co-operate with the belt and carcass construction. It seems, the Michelin uses a softer compound, one that grips nicely, but that can endure because the stiffer belt reduces squirm. The reduced squirm manifests itself in lower Feel values than the Avons, but also lower heat generation vs. dissipation and thus a similar durability.

 

 

So, there we have the stage set. Pilot Roads were fitted to the RS, fully expected to last the trip -- and then a session at Torrey Gathering Number Ten. The bike is loaded to the gills, every crevase filled with Trip Stuff, and the added mass of Super Laptop and The Camera Gear.

 

And then we've got Dickiebird attached to the top of the K12RS (back straight, feet and legs supporting a goodly portion of the rider weight), flyin' on across 3000 miles of the US in four and a half days. That's followed by a week of fun, and then... 3000 miles right on back. Then we Played Torrey. Zoom.

 

There'd been "a buzz", a noise. It seemed like it came from the front tire. It wasn't The Howl we often hear from the Pilot Roads, but rather a very different hum. It had appeared, or been noticed, about Day Three Outbound. It didn't get louder, and was forgotten about.

 

About Day Two Return I noticed more of a vibration. It seemed to be constant, and consistent, but of a low amplitude. I can't really give it a distinct description, one truly fitting its nature. I think I was diverted into "adding" its character to the earlier heard hum that seemed to come to the front tire. The result was a sense "'It' had gotten stronger"; "louder", in that unlike the earlier phenomenon, I did not need to open my chin bar, go slower, and listen carefully for it. It was more felt, or also felt, or not really Heard now.

 

Rolling down UT-24 from I-70 toward Torrey, there came forth a "cyclic vibration", a very distinct one. It seemed like a front wheel bearing was in the process of destruction. It would grow in magnitude across the coming days.

 

I mention this vibration because it's what led me to examine the front end of the bike, once again, and to look at the front tire more closely. Otherwise, it in fact has nothing to do with this discussion, and so an entirely separate "problem" that I'll cover or not at some other time.

 

Anyway, as I examined the front tire, a completely circumferential, very, very smooth, very flat ring at tire centerline was revealed. It ranged from just under to just over a quarter of an inch wide. Smooth, sharp, shiny, it stood out like a sore thumb.

 

Tire pressure had dropped somewhat less than two pounds during the trip to that point from 40.5F/41.5R.

 

"Handling" was virtually unchanged from trip start. The K12RS still dove like a dolphin into corners with the usual amount of pressure. If anything, it sought "Dick's lean angle" more stridently than when new.

 

The tires were replaced upon returning to Los Angeles (unfortunately without taking photos), and appeared to have about 1,000 miles of tread left. No anomalies were found inside or outside the tires other than this Tire Flat that appeared like it had been machined in.

 

 

So... I haven't seen anything like this in over a million miles of motorcycle riding. Have you ever seen anything like this?

 

On a FRONT tire?

 

If you did, what were the tire brands and models?

 

On what model of motorcycle?

 

What was the nature of those tires' construction?

 

How had they been used?

 

 

Best wishes with a Halloween Mystery.

[Ken H.]

Is this a trick question?

 

The answer will be reveled on October 31st at mid-night right?

 

Actually anything that stumps Dick Frantz is way beyond me. My only thought, ruled out by you long ago no doubt, is something in the wheel well that was rubbing exactly on the tyre's center line. But that's so far-fetched I'm not even sure why I typed it!

[russell_bynum]

Dick,

Now that you mention it, I have a vauge memory that I may have seen the same thing on my RT, also running Pilot Roads. I think I still have that set of tires somewhere hiding in the garage, so I'll check 'em out tonight. If my memory is correct, I'll snap a picture and post it so we can see if we're talking about the same thing.

[Corkus]

Dick, I very much enjoy your writing, so I am happily reading along finding out about the zen of this tire siuation when, the author springs a great surprise and ASKS ME if I know the ending to the story?!

 

This is shocking. Of course I don't know, that's why I bought the book. Now I'm hanging. What's the ending?

[ghaverkamp]

Yes. I'd seen precisely this before, on my first set of Pilot Roads, when I kept the front up around 40 lbs. I dropped it to 36 after that. Can't say for sure that that fixed it, because I shifted to a Sport front/Road rear for the next two sets. However, I kept the front at 36 for each of those, and the fronts easily outlasted the rear Roads.

[ShovelStrokeEd]

Oddly enough, my recently departed Pilot Road rear did the same thing, without, however the consequences to the steering you encountered. I got superb milage out of that tire as it was very lightly loaded being on my 1100S and in the 180-55 size. My stripe was just a bit off center, possibly reflecting my unconcious compensation for pulls to the right or some such. Funny thing is the stripe showed up quite early and never went away. It was not raised over the tread surface that I could tell nor did it in any way interfere with traction.

 

I just replaced the tires with ME-Z6's. Actually the front about 5K miles ago and the rear last week. I have about 2K on the rear now, almost all of it freeway and above 80. No such sign with the Metzlers. I have to admit that this will be my last set of these tires. I had them on for Cody last year and wan't impressed and I am again unimpressed. I don't like their feel when heeled over nor the way the react in the rain.

 

I'm coming up to crunch time on the S and I have to decide in December if I want to keep it or return it to BMW under the "Special" financing agreement. I won't put another set of tires on it till then. In fact I doubt I'll keep it. At 50K plus miles the shocks are shagged and the buy out is over 7K for the bike. I can send this back and at the same money, get another bike on the used market that will already have Ohlins on it. I may not replace it at all as for about 2K, I can fix my VFR and have a similar motorcycle.