Front Tire Bounce

[bikerphil]

Ok, I was helping another member change his front tire on his 79F. We put a Shinko 712 on without a tube. His previous tire had a tube in it. This is a older rim before they were stamped "suitable for tubeless". Tire went on fine, no leaks. Balanced the tire with no problems. Took a ride down the road and the tire starts bouncing at about 30 MPH, much rougher than before. We re-aligned the forks and they are parallel to each other, checked with a plate glass. Caliper is centered. It has a fork brace which doesn't seem to be binding. I've never ran into a problem like this before. We even tried a set of different forks because his were pitted, but no change. Anyone have any ideas?

[prometheus578]

Well, the first problem is with mounting a tire on a "tube" rim without a tube. Rims that require tubes have a differently shaped bead area compared to rims that are tubeless. The tube, to some degree, actually helps hold the tire on the rim. I suggest that you take the tire off, install a tube and then try again.

Also, ensure that the 'alignment' line, for lack of a better word... is clearly visible on the tire all the way around the rim. This line, actually a thin raised bead usually is positioned about 1/8 to a 1/4 inch away from the rim when the tire is mounted. If you see the line next to the rim bead... and then it suddenly disappears under the rim, the tire is not fully seated against the bead area. That would make it slightly out of shape... hence, the bounce.

I believe there was just a recent thread here with Pics of this bead line.
Do a search... and then go out and buy a tube.



Ahhh.. found the thread with the bead photo:

http://www.xs11.com/forum/showthread.php?t=11700

[cppd1]

I understand the differences between tube and tubeless rims but I have been running tubeless on my rim without trouble and it is not marked as tubeless.

[prometheus578]

Ok, I was helping another member change his front tire on his 79F. This is a older rim before they were stamped "suitable for tubeless".

I can only go by the info given.
Rims for the '79F require tubes.
I've seen people plug the holes and run the rear tires without rim locks, too. Sure, it'll work... but you run the risk of spinnin' the tire offa the rim.

There's a reason why bike shops won't mount a tire without a tube when the rim clearly states that it needs one. (Same as they won't mount a tire that states "For Rear Use Only" on the front end of a bike, etc)
Uhm... something about liability and legal fees, I believe.

[bikerphil]

Yep Prom, the bead line is fully visable all around, carefully checked that when I inflated it. When you spin the tire, it looks perfectly round. I even rode the bike at about 45MPH, looking over the front fender and it looks perfectly true. I've read plenty about the front tube and tubeless rims being the same sitting side by side. First, I might try the tire and rim off one of my bikes, just to see if the tire/rim is the actual problem. This bike had sticking forks prior to the tire swap and didn't ride very smooth in the first place, but now it's much worse.

[petejw]

hi phil,
i had a similar problem with my bike
for years but mine was at speed anything
over 120km/h, you could see the calipers bouncing up and down,
i went thru 2 different brand
of tyres, shinko and bridgestone battleaxe,
numours amounts of balancing and swapped forks, and swapped front rims,
nothing seemed to have fixed it til i bought a meztler,
i also had adjusted the swing arm around the same time
so not sure if that had anything to do with it,
i know its the front end but id also check the uni joint
and drive line.

[prometheus578]

Ok... we can figger that the bead is nicely seated.

Tires can warp just by sitting... and that goes for new tires sitting on a rack at a dealership or in a warehouse somewhere. Yeah, these are extreme cases, but I've seen them. That's why, if'in ya plan to store a bike for a while you put it on the center stand and jack up the front end so that the tire doesn't flatten out on the bottom and bounce you down the road. Usually, though... most flat spots like that, after a hundred miles or so of heating up and cooling down work themselves out.
New Triumphs would sit in shipping crate for.. I don't know, a year maybe? I'd tell the new owners to expect a little bounciness for a while but if it didn't smooth out in a hundred miles to bring it back in. (No one ever brought one back because of out of round tires.)

Now, the tire may have a manufacturing defect. Sure, you've balanced it, meaning... you added weights to compensate for possible uneven distribution of lumps of rubber somewhere, but is the tire truly round?

Brace the bike and put the front end in the air. Turn the handle bars all the way to one side so that the tire can't swing and give it a spin. Watch the lines of tread whiz by. (It's nice if the tire has a tread groove right down the middle) Does it look like the tire is warping from side to side?

Harbor Freight (Fright) has a cheap dial indicator and a magnetic base for it that's real handy to check if'in the rim is warped which also could be a cause of your bounce.

Ain't got one of those... improvise.

Get a spray can.. like of carb cleaner. Stand it on the floor next to the tire and place the spray nozzle straw close to the tire tread. Spin the tire. Now, a little play, a little in and out motion can be expected, but if you have a section of tire that really varies the gap between the "spray straw" and the tread, you might want to take the tire back to the shop where you purchased it.

"Oh, but we bought the tire offa the internet."

Have fun!

Now, I've no experience with Shinko tires. Are they anything like tires made by Chen Shin? (Chicken Skins) Sometimes buying the least expensive tire is not a good thing.

As for tires, it's my opinion that...

Oh...Oh.. what's going on? The room is spinning...! My mind... I can't...
I must be having another flash back to the late '70s...

I see... I see... a young stud buying K-Mart tires for his Chevelle... and buying them, and buying them, and buying them...
Sure, money was tight then, as now... but ya know... Had that young man just paid an extra $10 per tire he could have bought different tires that would have lasted three times as long.

OK, 2:00am and I'm a little "TIRE"d and starting to ramble.

"Bedways is rightways now, so best we go homeways and get a bit of spatchka. Right-right?"
(No, Ken... you can't play. You know all my movie trivia)

[prometheus578]

Sitting here now in my Sponge Bob jammies and bunny slippers...

Jusr reread what you wrote, Phil... Hmmm....

Bounces, huh?

Constants and variables:
Forks have been changed... still has problem.
Bike bounces... but had bounced before.
What has been changed is the tire and the forks... not much difference.
What HASN"T been changed is the rim... and the rear tire.

Check the rear tire using the carb cleaner can method and see what that shows.
Put YOUR wheel on the bike and see what that does. Yeah, just throwing parts at a problem isn't the professional way to do things... but sometimes it's the quickest and most effective.

PeteJW is correct in that sometimes the drive-line can cause weirdness, too.

(Hard to diagnose things without actually standing there, staring at it with a cup of coffee in your hand)

[CatatonicBug]

I had EXACTLY the same issue, with EXACTLY the same tire on mine. I rode 700 miles to MOTM this last Spring, watching the radio on my fairing wave at me like crazy over 70mph. It turned out to be that the tire itself was out of round. If you lift the front end off the ground (centerstand should do it), and look over the surface of the tire while spinning it, look for any changes in height on the surface of the tire. Mine had a "bump" in one section that went up about 3/16". I took the tire back to the store I bought it from, and they replaced it (including mounting and balancing) for free.

[TADracer]

Just a thought. Maybe during manufacture the belts or cords shifted. I had a tire like that when I bought my first front tire replacement back in 1981 or so. It was balanced, ran true and everything except when it was on the ground. It bounced from 25 up. Finally the dealer took it back and exchanged it for another of the exact make and size (it was a Dunlop by the way). Voila! Problem solved. Could be you just have the bad apple out of the barrel.

[bikerphil]

Thanks for the input everybody. The back tire was changed at the same time and required a lot of weight to get her in balance. This rear rim is a tube type with the extra holes blocked off with no tube. I'll have to check it for roundness too, as it may be throwing the problem towards the front. As for the Shinko 712 front, I have them on both of my bikes and have no problems with them. They handled fine since the first moment. This weekend, I'll put this supposedly funky handling tire on my bike and see if it is the real problem. I've spun the rim and tire several times and stared at it and they both look fine with no bumps or warp.

[Wet Rock]

Maybe TT bearings

[Giggity]

prometheus578,

Clockwork Orange?

[prometheus578]

Hahahha...
You win, Giggity!

Head on over to the Korova Milk Bar and have a tall, cold glass of Moloko Vellocet. Tell 'em to put it on my tab.

[bikerphil]

Ok, got a little update here:

The fella lifted the front wheel off the ground and placed a 2X4 under the tire. After getting the bike at the right height, he noticed a 3/16" out of roundness of the tire when spinning it. I know it was mentioned that slightly out of round is normal, but is this too much? Seems like this might cause the 30 mph bounce. I'm gonna go check one of mine that way and see if it's like that. He hasn't checked the new back tire yet. Probably going to have to contact Motorcycle-Stupidstore and see how they're going to deal with this.