Tire issue ? or Not ? Question

[easyrider]

Recently installed a Michelin City Grip on the front of my PCX. Grips nicely and is great on the curves and turns, but I notice that when I make an abrupt stop the front wavers a bit side to side or has a wobble effect. The wheel is straight, rotor is fine and the disc brakes are all excellent. Fork bearings are fine.Only happens when you make an abrupt stop and when turning at the same time . Fine on a slow stop. Just wondering if anyone has experienced this effect? Thx for comments.

[chicaboo]

...I notice that when I make an abrupt stop the front wavers a bit side to side or has a wobble effect.

Do you mean like a shudder or vibration, or the scoot weaves left and right slightly like it's starting to do a tank slapper?
If it's a shudder or vibration, on bicycles that typically means something is loose from the rotor up to the head somewhere.
Otherwise, I got no idea. Maybe a defect tyre, or out of round/balance? Does it have any obvious signs of cupping?

[easyrider]

"scoot weaves left and right slightly like it's starting to do a tank slapper".. Yep..That's it!

[Alibally]

I've got city grips and haven't noticed anything like that.

I'm presuming the direction of rotation is correct. The arrow on the side of the tyre should point in the direction of rotation.

Is the pressure ok? It might handle funny if the tyre is soft.

[chicaboo]

"scoot weaves left and right slightly like it's starting to do a tank slapper".. Yep..That's it!

That's pretty dangerous mang. I'd get that tyre checked over quick smart, and not by the same place that fitted it.

Just out of curiosity: Does the red dot on the sidewall line up with the valve?

[PCX150Rider]

"scoot weaves left and right slightly like it's starting to do a tank slapper".. Yep..That's it!

I dunno. . .I don't own a PCX yet. . .I'm on cue with the rest of the wannabe owners. . .but is your combined braking system working OK? Any air in the line?

Steering head bearing tight enough? You claim it is?

And you only put a City Grip on the front wheel right? Is the back wheel still an older tire that is a different brand/type?

Radial tires grip like. . .well they grip. . .until they let go.

Bias tires will grip. . .slide. . .and then let go.

Seems like you're chopping away at the problem but not getting any chips.

[easyrider]

No red dot on this one.. pressure Ok, Ill check air in the brakes, and direction is correct based on the arrow although the grooving appears opposite as to what the Dunlop shows. I would like to see a pic of another front city grip on a bike and check it.It is baffling. It feels like water sloshing in a tank back and forth when I stop abruptly. May go back to the original tire for test purposes.. I have another spare wheel.

[chicaboo]

Yep, front City Grips have a backwards tread pattern from what is conventional.
Be warned, they are not exactly the same as the rear tyre tread pattern reversed.

[Chapel77]

Yep, front City Grips have a backwards tread pattern from what is conventional.
Be warned, they are not exactly the same as the rear tyre tread pattern reversed.

That had me rather confused when I first picked up my PCX, to the extent I went back to the dealer. Luckily he had previous customers with the same query so I didn't feel a complete idiot!

[kramnala58]

...... I would like to see a pic of another front city grip on a bike and check it...........

Here a couple ...

2013-10-07 16.27.00_800x600.jpg (62.94 KiB) Viewed 1314 times

PCX 001 C_800x600.jpg (60.84 KiB) Viewed 1314 times

[easyrider]

Yep, thats the way mine look too..I changed out the rim, tire, and rotor.No changes.Still has a shimmy or slight wobble when I apply the right hand brake only . Only happens when I abruptly apply the front (right ) side . When they get warm the stopping is much smoother and minimal wobble. I believe something to do with the front caliper. Next time you go out check your right side hand brake and apply it to an abrupt stop(no skid) and see if anyone has the same shimmy. Interesting ??

[chicaboo]

I wonder if your forks are worn or tweaked and consequently have some play or are not straight?

[easyrider]

That's a good thought. However,The axle bolt lines up perfectly with the other side when installing( through) the wheel.

[chicaboo]

That's a good thought. However,The axle bolt lines up perfectly with the other side when installing( through) the wheel.

You've checked or replaced everything else, so that only leaves the caliper or forks causing the issue.
On a bicycle with disc brakes if anything is the slightest bit loose you get crazy headshake when braking and shimmy at high speed.
I just saw a video of a bike doing what you describe, and his problem was a warped rotor, but you changed that.
Heck, maybe the oil pressure in your forks is too low causing a vibration that induces the shimmy?
I can only think of other things that should have been isolated by replacing the whole wheel, rotor and tyre like you've done.

[easyrider]

Yep, the caliper is next. I increased my tire pressure to 32 in front to see if the dynamic changes at all.Keep chipping away. When I use the CBS left brake, it seems fine ..Its basically when I use the right front brake alone and in an abrupt stop .Its like the front wheel does not want to turn or lean in your direction during the abrupt stop. Its kind of weird and maybe I am just overly sensitive as most driving conditions do not encounter this maneuver.I did bleed the front caliper to no avail. ??

[chicaboo]

Maybe one of the two pistons operated by the right/front brake is siezed or sticking?

[kramnala58]

Maybe one of the two pistons operated by the right/front brake is siezed or sticking?

I was wondering about a master cylinder problem .... is that what the reservoirs are called on a motorbike?

[doletotodole]

Hello, Sir,

The bruise on my left palm is iron-clad proof that you are not alone.

"Only happens when you make an abrupt stop and when turning at the same time "
this is similar to what happened to me, except I don't apply abruptly, just gently. I think it is the "turning at the same time" part which did the damage.

[doletotodole]

I would recommend any one riding a PCX to watch out on uneven road surface, be very careful, keep straight up.

[doletotodole]

So, I have reason to believe it is not the tire, as my pcx is new with Dunlop.