Front end front to back movement

[sweet78xs]

ok, 78 XS11 STD 49k miles

Newer slotted rotors all way round

Bridgestone Spitfire S11 tires installed beginning of last season, 3 k miles on them

My problem is that when I brake, the front end shudders, and also cruising at highway speed, I get a vibration that comes and goes (not using the breakes).

I can watch the bottom of forks move fore and aft quickly. It makes the whole front of the bike feel rough.

On new asphalt, the problem is non existant. older roads it is there. Sometimes really bad.

I tightened the preload on the forks and that made it handle better in corners, but did nothing for the "oscilation".

I ordered and will be getting a tkat brace soon.

A friend of mine who is into brit bikes tells me that the rotors are warped and bad. If I replace them, my shudder will go away as well as the fore/aft movement.

I know the rotors are warped giving my braking shudder, but would that really cause the intermittant oscilation of the lower forks?

I'd really like to clear this up.

Carey

.

[bikerphil]

I'd make sure the front tire is properly balanced first. Could be a bad tire too. The rotors would probably have to be severely warped to cause such a problem I would think. Also, make sure all your bolts are tight, forks and wheel, calipers, etc.

[BigDick]

might be worth it also to check the neck bearings, and repack with grease if need be.

[fredintoon]

Hi Sweet,
first, check the forks and steering head bearings for wear and adjustment.
Jack the bike up so the front wheel is off the ground. Make sure it can't fall over.
Sit on a low seat in front of the front wheel looking back at the bike.
Grab the front fork lowers at the axle level and shove them back and forward real hard.
There should be zero movement between the lowers and the fork tubes.
If there is, the slider bushings are worn.
There should be zero movement on the fork tubes.
If the fork tubes/triple trees can rock back and forth the head races are loose.

[sweet78xs]

There is no mechanical looseness. This is a vibration movement at speed. I checked the neck bearings and the triple clamp, and also the fork seals/ bushing wear. no noticable movement until you are at 50 or 60. then she makes a rythmic da da da .... da da da ... da da da..... baffling.

Carey

[cywelchjr]

There is no mechanical looseness. This is a vibration movement at speed. I checked the neck bearings and the triple clamp, and also the fork seals/ bushing wear. no noticable movement until you are at 50 or 60. then she makes a rythmic da da da .... da da da ... da da da..... baffling.

Carey

As I understand it, these not quite stiff enough forks will do a little of this, and a fork brace will help a bit. I know I checked for play in mine and can't detect any but if I look down on rough pavement I can see the wiggle in there. It's not much, but just enough for my calibrated mark one eyeball to see. If I pay attention (which I have done a few times) I can see the same thing only writ larger with hard front braking. These forks flex, but I think it's just a normal thing (unless you replace your front end with a hayabusa front end).

[sweet78xs]

Well, tonight I decided to remove the front wheel and take it to the shop tomorrow, to have it balanced. I looked and there is no weight. I may have thrown it in my travels last season.

2 things I noticed...

1... the wheel spins extremely free when calipers are removed... I may not have installed these components correctly when I had the tires changed last year. Need to follow proper procedure along with new pads.

2... With calipers off and wheel spinning free, I held my finger perpendicular to the fender leading edge lip and observed what I believe to be the root of my problem. With tire spinning and finger almost touching the tire, I see a gap, flat spot, smaller gap, no gap, small gap, large gap, flat spot... repeat. Almost like a slight "bubbling effect".

MY TIRE IS OUT OF ROUND!!!

Would taking it to the shop and having it balanced eliminate or reduce my problem??

Are tires typically not perfectly round??

Or do I have a bad tire and need to shell out big bucks for a new set of shoes?

I also see slight cupping starting. Could the cupping be a result of an out of balance tire?

Carey

.,

[TopCatGr58]

Hey Carey,

Take a look at this tech tip:
http://www.xs11.com/forum/showthread.php?t=11700
Then inspect the bead area on your tire. If it wasn't installed properly and the bead seated evenly, then you can end up with the out of round type mounting, which then causes uneven wear, etc. Front tires on Motorcycles do cup a bit as they get worn, but out of round or balance can accellerate wear, as well as incorrect inflation!

You may not need to replace both tires, just the front.
T.C.

[fredintoon]

.. With calipers off and wheel spinning free, I held my finger perpendicular to the fender leading edge lip and observed what I believe to be the root of my problem. With tire spinning and finger almost touching the tire, I see a gap, flat spot, smaller gap, no gap, small gap, large gap, flat spot... repeat. Almost like a slight "bubbling effect".
MY TIRE IS OUT OF ROUND!!!
Would taking it to the shop and having it balanced eliminate or reduce my problem??
Are tires typically not perfectly round??
Or do I have a bad tire and need to shell out big bucks for a new set of shoes?
I also see slight cupping starting. Could the cupping be a result of an out of balance tire?
Carey

Hi Carey,
out of roundness and cupping feed on themselves and while re-balancing may slow down the rate at which it gets worse it won't get better.
The only sure cure is a new tire.
BUT FIRST check the wheel for being truly round and straight.

[sweet78xs]

The wheel is true as a tree... the tire is the culprit. I'm pricing a new tire today. 110/90-19. Any suggestions on tires that don't follow pavement elevation changes( patching ) or on pavement markings?? I have spitfire s11s. Anything that could somewhat match the s11 rear?

[sweet78xs]

took wheel to shop and they balanced it up for me. They said is was out 0.75 oz

[randy]

You mentioned that the tire was only a year old. How many miles are on it?

[sweet78xs]

2-3 thousand

[geniusloerts]

I had a vibration at 85mph that was really bad, I put new tires on and had them balanced and still had the problem.....I checked the steering bearings and the shock tubes and all was fine there.......took the front wheel off and took it back to the shop and told them where the bounce occured....the wheel was out of balance 70grams.

Try paying attention to see if it just occurs at certain speeds. thats what mine did.

[Axel]

S11

when I had a spitfire ,as soon as it was worn a bit the tar snakes would charm it . The Avon Roadrunners dont have this problem like any good quality tire - Battlax ,Lasertek,Elite 3, GT501 ,etc . I've seen harleys go all over the road from tar snakes with the flat bottomed tires .