Shimmy

[Ccitis]

1980 11G. What would cause a front wheel shimmy at 80mph. Past that it smooths, before that it is smooth. It is a front to back motion, the whole fork shakes and flexes front to back... I can see it shaking. It looked like the tire was out of balance, so I balanced it again... it is perfect. Wheel bearings feel good. Everything is tight on the fork...34 PSI in the shinko tire. Could be the tire itself, it is fairly new... maybe 3000 kms on it. What do you think? It is annoying, I like to cruise at 80.

[DiverRay]

Tire may have internal problems, causing the shimmy. Start with the "easy" things. put bike on center stand and use a jack to get the front tire just off the ground. Pull VERY lightly on one handlebar, for just a second, and see if the falls that way as it should. Then center and go the other way.
Now go to the front tire and try to lift just a little. If there is play in the steering stem bearing that you can feel, you have a problem. I've found that the bearings will develop a "flat spot" after a lot of years, and this can cause the shimmy.

[Radioguylogs]

I've had loose/notchy steering bearings cause that type of behavior.

[Ccitis]

I've had loose/notchy steering bearings cause that type of behavior.

I have felt that before, but usually in the bars. This is different... where the fork is flexing backwards and forwards.

[DEEBS11]

The tire was the last part that was altered. Other than that, steering head bearings. Also, don't discount the rear tire having effect on the front. Check the balance of that unit as well.

[Socer4m]

also,,,put a jackstand, lift under the frame just enough to lift the front tire off the ground,,,give it a spin and check to see if there is no out of shape tire, it should be smooth with no tread bump,,,then pop the rear stand up and also check the spin on the rear for tread twist. Usually the balance if off would show up at a lower speed, also check the pressure in the forks that its even on both sides if you have an xs with air front forks,,,,keep us informed,,,Mike in S.Diego and Pa

[LAB3]

There's a difference between static balance and dynamic balance. Static balance would be putting the tire and rim on a truing stand then using weights to balance it. Dynamic balance uses one of those newfangled machines that spins the tire up to speed and gives the operator the info they need to properly place the weights.

With all that said, I don't bother with either method and use this stuff instead, it doesn't work for squat when it comes to punctures but does a great job at dynamically balancing as you ride. A LOT of shops are using it these days instead of other balance methods and for about $20 per tire a DIY guy like me can easily not give it second thought.

https://ride-on.com/

[cajun31]

1980 11G. What would cause a front wheel shimmy at 80mph. Past that it smooths, before that it is smooth. It is a front to back motion, the whole fork shakes and flexes front to back... I can see it shaking. It looked like the tire was out of balance, so I balanced it again... it is perfect. Wheel bearings feel good. Everything is tight on the fork...34 PSI in the shinko tire. Could be the tire itself, it is fairly new... maybe 3000 kms on it. What do you think? It is annoying, I like to cruise at 80.

Driving those speeds why are you only running 34 psi? I would bump that up to about 40 then see if the shimmy goes away. I run biased Bridgestone H rated tires and I weigh give or take 200 most of the time and I always run 40 psi in both front and rear. The owner's manual states to do that when running at higher speeds.

[bikerphil]

^^^
What Jim said +1

[gtem]

The tire was the last part that was altered. Other than that, steering head bearings. Also, don't discount the rear tire having effect on the front. Check the balance of that unit as well.

My money is on the tire as well. Now, this was at lower speeds for me not higher, but you could always check that the new tire is correctly seated on the rim. I had a case where I was getting a low speed (30mph) "bobble" up and down and it was a tire that hadn't fully/evenly seated (had a low spot).

[Ccitis]

I will test at higher PSI, good idea (DUH).... The motion led me to believe out of balance tire... certainly could be pressure. It is a Shinko as well... I had to scrap a NEW one off my GS1100E... Could not balance it.

[gtem]

I've been lucky perhaps, have not had any manufacturing defects with my shinkos (712s and 230 tourmasters) and I've bought about 6sets in the last 5 years for various revivals/restorations, and they've all needed impressively little weight to balance (sometimes non at all). But I've heard of plenty of other people having defects with Shinkos on and off over the years.

[DEEBS11]

Shinko tires ruined one of my cross country trips in 2017. I was in Mexico NY next to Lake Ontario when my Shinko rear radial tire developed a bubble that was a result of the belts failing. F*ck Shinko tires.

[DEEBS11]

I sent Shinko these pictures and they apologized for any inconvenience and refunded the purchase price. $130.00 did not pay the cost of a ruined trip. The tow alone costed $250.00. This was the main reason I started using car tires on some of my bikes.

[LAB3]

I've had good luck running Shinkos on several different bikes although I'm quite suspicious of the 733 front that I recently replaced since I've seen Dunlop 404's do something similar. That being it just didn't LOOK centered on the rim to me. Since I use Ride-On instead of balancing I can't comment on not being able to balance them right.

What I CAN say is the the Shinko Tourmaster 230 up front right now feels rock solid, perhaps pumping it beyond the 36lbs that Yamaha suggests up to 40 is the reason although I'm skeptical of that. Since I did replace my fork oil at the same time I spooned on the new 230 that may well being making a difference as well. Then again the stuff I drained out looked like it did the day I put it in there about two years ago.

Anyhow, Shinkos have treated me well and at a similar price I'll take them over a Dunlop 404 or ANY Kenda. The absolute best ride I've ever had was with Bridgestone bt46 BattleAxe, unfortunately with as many tires as I go through a year I can't justify the cost.