front wheel bounce

[drlapo]

it feels like the front wheel on my 05 Thruxton is bouncing
there is an evenly spaced "oscillation" of the front wheel at cruising speed that fees like evenly spaced bumps in the road
I have installed a new front tire, the wheel is true and balanced, progressive fork springs and I have installed RaceTech emulators with 15w oil
seal stiction????

 

[Motley]

Is the OD of the tire true?

 

[whyme]

interior tire damage or manufacturing mishap?? I had a bicycle that had interior tire damage and it did the same thing...it was very odd

 

[B06Tang]

what kind of tire did you put on your bike?

 

[JRMSR]

it feels like the front wheel on my 05 Thruxton is bouncing
there is an evenly spaced "oscillation" of the front wheel at cruising speed that fees like evenly spaced bumps in the road
I have installed a new front tire, the wheel is true and balanced, progressive fork springs and I have installed RaceTech emulators with 15w oil
seal stiction????

Have you checked the amount of for oil you added? Is the fork sag set correctly? Do you have the proper spacer at the top of the fork. Do you have the tire rotation going in the right direction? Allot will depend if you've done all this correctly. Not enough oil, not enough rebound dampening, it will bounce and cause the front end to sag to much. Too much fork oil it will be to hard and can cause it to bounce on the tire. If you haven't set the fork sag correctly, it may also cause it to bounce.

 

[drlapo]

new Avon Roadrunner, stock size, runs true on the stand ; no run out
balanced, mounted in the right direction
same symptoms with the stock tire
15w fork oil at 140mm from top, no springs and fork collapsed, according to the RaceTech specs
it bounced with the stcok springs and it bounces with progressive springs

 

[jphickory]

I'd check to make sure the tire is seated properly on the rim. If any doubt, maybe break the bead and reseat the tire.

Possibly a slight flat spot or bend in the rim? I've heard slight ones can be hard to detect.

 

[JRMSR]

new Avon Roadrunner, stock size, runs true on the stand ; no run out
balanced, mounted in the right direction
same symptoms with the stock tire
15w fork oil at 140mm from top, no springs and fork collapsed, according to the RaceTech specs
it bounced with the stcok springs and it bounces with progressive springs

If it bounced with stock springs before you changed them I'd bet it's the rim. I would suggest you check the outside diameter of the rim and make sure it hasn't been bent. You can do it with a tape measure on the bike. It's tedious but you measure from the center point of the hub to the rim edge about every 2". It will indicate where the rim has been bent.

The only other thing I can think of would be, the actual fork alignment. Did you remember to unbind the forks after you reinstalled? It's simple, just loosen the upper and lower pinch bolts enough to release any bind tighten them slightly so they won't push up through the triple tree and then press on the forks several times.

Last but not least, have you checked the steering stem for proper adjustment? They loosen and can amplify any movement of the forks in/out. It would feel like the front end is bouncing. Lift the front end of the bike off the ground. Grasp both fork legs and see if they will move forward and aft. If it does then it's time for them to be tightened. Remember the Triumph stem bearings are ball bearing type not tapered caged rollers. So they're more prone to frequent adjustment. With the ball bearings, I've seen steering stem races wear out with as little as 12000 miles, if they weren't adjust correctly.

 

[B06Tang]

new Avon Roadrunner, stock size, runs true on the stand ; no run out
balanced, mounted in the right direction
same symptoms with the stock tire
15w fork oil at 140mm from top, no springs and fork collapsed, according to the RaceTech specs
it bounced with the stcok springs and it bounces with progressive springs

The bike gets light and squirrely feeling at higher speeds...say above 70 mph? I ran into the same exact problem and have known two other people with the same exact situation. The Avons do that...at lower speeds they stick like glue on the road but then get real light and unpredictable at higher speeds

A good friend of mine is on a carb'd Thruxton as well and went through the same exact problem and this is what he surmized after extensive studying/scratching his head:

Just spent the afternoon sorting out a ton of old bike mags, and came accross something interesting.

Remember the debate about how Avon RR tyres affect the handling of Thruxtons in particular over on Trat?

The problem I experienced was a feeling of instability and a wobble at 90mph plus speeds. Something I still notice with the Bridgestones I have fitted now, though its no where near as bad.
Opinion was divided. Some owners saying the Avon RRs were great others saying they were getting similar problems to mine. Well I think I may have discovered why my bike is so sensitive to tyre choice. I ride a 2007 model. I was reading one of the old mags and came accross an article about the 2008 Thruxton. (the year EFI was introduced) The 2008 model and subsequent models have a longer swinging arm. The 2007 model's wheelbase is 1490mm, whilst the 2008 is 1510mm. Rake and trail remain the same on both so the later ones must have a longer swinging arm! That would explain why some owners say theirs is rock steady at speed whilst others have a twitchy bike. I have to say the shorter wheelbase makes the bike super nimble round the twistys but clearly theres a pay off in stright line high speed stability which any other tyre than the standard fitment Metzlers seem to exagerate.Iit would be interesting to go back and see if the wobblers were pre 2008 models?

So maybe a steering damper is on the carsds or a swap to a longer swing arm. I suspect the steering damper might be the cheaper option.

I think the mystery is solved.

 

[drlapo]

I like the lightness the AVON tires add to the handling and find no instability at speed
I'll pull the wheel again and check the runout on the truing stand
both the wheel and the tire had minimal runout when I last checked

 

[Texas94fs]

I don't buy that about the avons. I ran em on my thrux for several track days and they performed just fine at high speed.

 

[B06Tang]

I've gone through 4 sets of tires on my bike and Avons by far gave me the most problems on exactly what the OP described. Wobble and instability while cruising at speed. I don't think you are going in a straight line at speed for any kind of distance on a track. Cornering and twisties/track, then the Avons are a dream. A real Jeckyll and Hyde syndrome. This has been my experience with them as well as a handful of friends that I personally know that ride the same bike.

 

[ratlab]

try sport demons-cured my instability and wobble problems-i have hagon rear shocks,racetech forks,steering damper and fork brace -nothing would help until i used these tires-also thruxtons really don't like to have any weight on the front-forks need to be flush with top clamp to get straight line stability

 

[Flaco]

So maybe a steering damper is on the carsds or a swap to a longer swing arm. I suspect the steering damper might be the cheaper option.
I think the mystery is solved.[/I]

Tapered bearings are less expensive that steering dampers...
I'd try that first as I have read that others have had great success with tapered bearings...
Mine are going in soon and I'll report back when completed...

good luck...

btw, my '05 has the shortest whealbase @ 1484 mm...
and I run Avon RR...
I do not believe it's the tire...

 

[B06Tang]

It certainly is a weird dilemma; I have gone through 4 sets of tires now and the Avons give me the most trouble as far as getting light and squirrely at speed. I think I am just going to go back to the Metzelers and be done with it. Granted that they are not as nice as the Avons in the twisties but overall picture they are a better tire for me.

 

[strokerlmt]

Tapered bearings, fork brace, steering damper......
Do the first two and see if problem solved.
LMT

 

[roadie]

Fork brace did nothing for me, took it off. The steering damper though is awesome! So much more stable and confidence inspiring when the going gets fast and rough.