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Discussion Starter · #1 ·
I had a new front tire fitted . Pressure is at 32psi. Rear is at 34psi. Got a wobble. Got a bad wobble at 90mph.I dont see any fork leaks or any sign of oil. I checked the neck bearings and they seem tight enough for the front end not to rock back and forth with tire off the ground when rocked.I know the bike was dropped at some point before I purchased it, and am now hoping the frame is not bent. It is on my Legend, directional tires going the right way per the arrows.
The roads here in San Diego are concrete and grooved.
Any ideas?
 

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The spec on my TBS tires is 36/42 F/R. I think your Legend should be the same. I noticed a distinct improvement in handling when I got it right on. PS: I know those San Diego grooves. What a pain!
 

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IME the front needs 36psi pressure, a couple less than the 42psi spec for the rear is ok for lighter/solo load.
 

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I run 32 psi up front and 36 in the rear. For whatever that's worth.
When I first picked up my TBS in Tucson, it wanted to go into a wobble in the worst way. It didn't take much to get it started. I had about 35 pounds packed on the back of the seat. I think that along with the front and rear having just about no preload made it susceptible to the wobble. I put more preload in it in front and rear.
Now, I have clubman bars, the forks are an inch above the top clamp, I have my preload adjusted to the correct sag for my weight, and I can't even begin to get the bike in a wobble, at any speed. It just won't do it.
I would take a look at your preloads, front and rear, and try firming up the ride.
 
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I'd get the front end off the ground pronto and go through the whole thing with a fine tooth comb!

Check all the bolts holding the front wheel in, maybe they forgot to tighten something. Also check for correct installation by making sure the disk rotor is sitting in the middle of the pads. Maybe the tyre isn't sitting properly at one point on the rim, or they removed the old balancing weights and didn't re-balance the wheel :dunno
 

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Like Arfer said, my first thought was an improperly seated tire. Just go around the rim on both sides and make sure its even.

Also, I'd try pumping up the pressure. Could be your gauge is wrong. I had a vibration issue on my car and it turned out my gauge was 5psi off.

Scott
 

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I would just point out (the obvious?) that Charles' bike is a TBS with very different suspension and forks, hence tyre pressures will likely have different effects. My findings were on every tyre type I used with the stock(ish) Legend forks :)

The preload, or sag, esp at the rear, will be a factor at speed. Esp at the rear where too much sag will tend to add to front end lift at speed thru' increased squat under chain pull.

Fork oil changes are often neglected too which won't help front end damping.
 

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A while ago I watched an old - 80's ? - video by Murray Walker about weave and wobble. One of the golden rules to avoid weave was you do not get a new front tyre and leave an old rear tyre, with a possible flat central strip, on the bike.

Wobble he defined as a low speed phenomenon.

The three other factors that contribute to weave were a light rider, high speed and a heavy top box.

The thing to do when you get weave, and I assume this is for severe tank slappers too, is lie low over your tank. He was not clear about whether you should let go of the bars.

Now I realise this is all about bikes with narrower tyres than we have nowadays, but I post it for what it's worth. I will certainly be replacing both tyres when the time comes.

Maybe I had a fright with a tank slapper when I was young, but I also rode 60's Triumphs with screw down friction steering dampers. The result is that I approach high speed on my modern bikes with trepidation.

I would like to find a more modern analysis of the problem.
 

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My book on T-3's says 36psi front/ 42psi. rear. I have experienced this with all my bikes. A low front tire will do this. A low rear will make the rear handle a little loose....J.D.
 

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Discussion Starter · #12 ·
the op posts when she has time. I corrected tire pressures to 36/42. Just need to see if that makes a difference. I did notice now that the back tire has the correct pressure in it there seems to be about 50% tread left. I have in my 37 years of riding replaced tires usually on the 2 to 1 ratio.
Thank you all for your insight and suggestions. :doublethumb Namaste
 

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Discussion Starter · #13 ·
quick blat down the freeway.....got it to about 88 or so and thought I was gonna die. All I could see was the videao of the guy at the IOM on an ols bike tank slapper big time and he hit the curb and crashed hard, . I gripped the bars decelled a bit and rode it out. Clean panties please. Got home , checked the spokes on the rims all nice and tight. Pulled on back wheel to see if swing arm lose. Nothing. So whats left? Bent or out of round rim? Incorrect alignment? Suspension not dialled in? I like riding fast but this is rickydudalus. My old TR65 could run rings around my legend handling wise. Any suggestions other than slow down would be appreciated. Tire pressures are 36/42.
 

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The fact that this trouble developed with a new tire is very suspicious. I bought a new tire for my Honda 919 and ended up with a front end wobble which was not severe but annoying. I accused the bike shop of messing up the balance job. They re-balanced it and the trouble was still there. I tried doing a "cut and try" balance with stick-on weights but could only make it worse, not better. I took it back to the shop and asked them to try again. They did and I was interested that the balance weights were in a different place with a different total weight. The wobble continued. I finally took the tire off and looked inside and found that there was a construction flaw visible from the inside. Somehow there was a fabric overlap that was causing a radial force variation in the tire which could not be corrected by balance. A different tire fixed the problem.

I'd suggest you either go back to your original tire or try a different one and see if the problem goes away.
 

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Here are some things to check:

worn tires or low profile tires
loose / worn wheel bearings
worn / loose suspension, check all the pivots
worn / loose steering head bearings
frame geometry, hard to check, but could have a bent frame if you hit something hard or dropped bike

All else fails add a steering damper :)



J
 

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If it started when you put the new tire on then it has to be connected to the tire or something that was disturbed in its installation. Get the front wheel up and spin it. Does it run true in all dimensions? Does it stop in the same position every time?
 

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Have to agree with the other opinions here. Hoofprints are usually horses, not zebras. Since the last change was the tire - focus there. Its unlikely anything related to the rear end.

I would guess the tire itself (like dober mentioned), something in the mounting (like it not seated correctly) or something in the physical attachment to the forks.

If none of those plays out (all the way to switching the front tire), then possibly something related to the forks/seals/oil as they would have likely gone to full droop (abnormal) when the tire was changed and something internally might have happened.

Scott
 

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We still haven't heard definitively that it started after the tire change. Alternatively, did you ever go that fast on the old tires? If not, we just don't know...
 

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I live in San Diego and do not have problems with wobble on groovy roads even on my '82 Honda at any speed.
Do yourself a favor and take it back to the shop to inspect it and re balance the tire even though i think that wobble would be noticeable much sooner than 90mph.
Wobble more often than not points to the suspension and it could be front or back or combination of both. Faster you go, front gets higher and therefore it becomes lighter which in turn could cause wobble. If you lean over the bike when it starts to wobble does it stop?

1. There could definitely be issue with steering stem bearings, how many miles on the bike and did you ever had head bearings changed? if it has over 20k miles, there is a good chance that they need changing.
2. Maybe its a matter of adjusting the bearings
3. When was the last time you had your rear shock linkage lubed? There are 4 nipples for lubing.
4. Do both forks have same amount of oil?
5. Have the rear shock properly adjusted

Do this test,
1. Take it to some quiet street and speed up to 25 mph and briefly take your hands off handlebars just a bit, does the front shake?
2. If no, speed up to 35 or 40 mph and do the same, if it doesn't shake, try 50mph and than 60mph.

If you need shop recommendation in san diego PM me

Sasha
 
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