Author Topic: Fork vibration at highway speeds  (Read 1715 times)

0 Members and 1 Guest are viewing this topic.



cjbear11

  • Guest
Fork vibration at highway speeds
« on: April 13, 2008, 04:26:42 PM »
I have a problem.  Or at least it might be a problem.  I went on my first long distance bike ride this weekend.  The Moonshine lunch run.  I had no problems until i hit about 80mph, when i noticed that i had a large amount of vibrations coming from the front end.  I looked down and noticed that my forks where moving up and down rapidly as if there was a bump or something on the tire.  The thing is it would only happen at about 80 or 85.  Nothing slower.  So i don't quite know what to make of this.  The tires are brand new, and they were balanced when they were installed.  I don't know what else this would possibly be.  It didn't hinder the performance at all, it was just annoying and i'm pretty sure it's not supposed to happen.  Help?



Offline Spikeybike

  • when planting C4 at your enemy's base make sure you don't use a
  • Really Old Timer ...
  • ******
  • Posts: 7,230
  • member #1150
Re: Fork vibration at highway speeds
« Reply #1 on: April 13, 2008, 04:29:44 PM »
did you have the wheel trued as well



cjbear11

  • Guest
Re: Fork vibration at highway speeds
« Reply #2 on: April 13, 2008, 08:28:01 PM »
Actually no.  What exactly does that mean?  Is that something i could do myself?



76 cb550

  • Guest
Re: Fork vibration at highway speeds
« Reply #3 on: April 13, 2008, 10:57:09 PM »
I am NO expert but here is what I think I know.

As far as I know you need a special tool called a truer.  It runs a stylus along your rim while the tire spins and detects...umm...trueness... It determines whether your tire is moving from side to side as it turns...

I've seen someone do a very dirty trueness test with a pencil.
They clamped the pencil to a table and positioned a camera with the point of the pencil at the center of the tire.  The pencil was a point of reference.  You could tell that his tire was very untrue from this simple test which told him that he needed to true it. 

Not sure exactly how you true a tire.  I think it has to do with tightening the spokes in balance to make the wheel perfectly round. 
« Last Edit: April 13, 2008, 10:58:48 PM by 76 cb550 »



Offline Spikeybike

  • when planting C4 at your enemy's base make sure you don't use a
  • Really Old Timer ...
  • ******
  • Posts: 7,230
  • member #1150
Re: Fork vibration at highway speeds
« Reply #4 on: April 13, 2008, 11:20:05 PM »

Not sure exactly how you true a tire.  I think it has to do with tightening the spokes in balance to make the wheel perfectly round. 

exactly , have a shop do it , its in the 30-50 dollar range (if you bring them the wheel not on the bike of coarse)



76 cb550

  • Guest
Re: Fork vibration at highway speeds
« Reply #5 on: April 14, 2008, 12:02:09 AM »
thanks for the +1 there Spikey.  Wasn't 100% about that.



Offline mystic_1

  • Really Old Timer ...
  • ******
  • Posts: 5,059
  • 1970 CB750K
Re: Fork vibration at highway speeds
« Reply #6 on: April 14, 2008, 12:13:17 AM »
Here's a fairly nice step-by-step on truing wheels:

http://www.thumpertalk.com/forum/showthread.php?t=485208


mystic_1
"When you are wrestling for possession of a sword, the man with the handle always wins. "  - Neal Stephenson, Snow Crash

My build thread:  http://forums.sohc4.net/index.php?topic=68952.0




Offline TwoTired

  • Really Old Timer ...
  • ******
  • Posts: 18,142
Re: Fork vibration at highway speeds
« Reply #7 on: April 14, 2008, 01:10:15 AM »
Probably could help if you told us details about the bike in question.

If you have tubeless tires mounted on tube type rims, seating the tire properly on the rim can take extra care that modern tire jockeys don't always perform.

Lift the front end so that the wheel will spin freely.  Watch as the tire spins and see if there are high points on the tread as it spins.  If the tire is out of round, or if the tire is not seated on the rim correctly, the tire may roll out of round and cause vibration.

Also, as the tire spins, look on the tire near the rim and fins a raised line on the tire.  This line should be the same distance from the rim all the way around the tire.  Check both sides.  If there is any variation, you can expect some kind of issue with vibration at speed, regardless of how well balanced the tire is.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC

Popeye: "Wrong is wrong, even when it helps ya."



cjbear11

  • Guest
Re: Fork vibration at highway speeds
« Reply #8 on: April 14, 2008, 01:17:50 PM »
Thanks guys.  I don't have vintage spoked wheels though.  They're aluminum five spoke type wheels.  So is trueing out of the question?  It sounds like i'll have to take it back to the shop.  Would rebalancing the wheel do any good?



Offline andy750

  • Really Old Timer ...
  • ******
  • Posts: 6,795
Re: Fork vibration at highway speeds
« Reply #9 on: April 14, 2008, 01:31:10 PM »
You might also want to check your tire pressure....same thing happened to me last year but the headshake came on at 40mp and went away either side of this. It turned out to be incorrect tire pressure. I had new BT 45s and was using 30psi in the front. The tire actually needs more than this - like 34+psi. I think Greg (Ofreen) pointed this out to me (as did others). Since you have new tires I would look at this as well as balancing.

good luck and let us know how it goes.

cheers
Andy
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico (CB750K4), 2003 - European Tour (CB750K4), 2004 - SOHC Easy Rider Trip (CB750K4), 2008 - Adirondack Tour 2-up (CB750K4) , 2013 - Tail of the Dragon Tour
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. VStrom DL1000 2003

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

The SOHC 2014 Calendar NOW ON SALE!  - http://forums.sohc4.net/index.php?topic=125085.new#new



Offline Bob Wessner

  • "Carbs Suck!"
  • Global Moderator
  • Really Old Timer ...
  • *****
  • Posts: 9,903
Re: Fork vibration at highway speeds
« Reply #10 on: April 14, 2008, 02:11:54 PM »
Would rebalancing the wheel do any good?

It certainly would if it wasn't done properly the first time. Not saying it wasn't but worth a check after you explain to them the problem you are having.
We'll all be someone else's PO some day.

 

Honda