High Speed Thumping

Kirrilian · Oct 22, 2008

I've searched the forums several times with as many keywords as I could think of and haven't found anything similar but perhaps I missed it. Ever since I bought my bike I feel a thumping through the bike at high speeds (100 MPH+), as soon as I slow down it goes away. It has happened on many different road surfaces and after I swapped tires so I'm fairly certain it isn't either of those. I have to admit, I'm stumped as to what may be causing this, any idea what it could be? It concerns me that something may fail and I'd much rather find out what it is now than at those speeds.

Glen

Slappy · Oct 22, 2008

Please define thumping? Is it a noise or a feeling? If a noise where do you believe you hear it? If a feeling describe it and where you feel it.

Bungie · Oct 22, 2008

Kirrilian said:
Ever since I bought my bike I feel a thumping through the bike at high speeds (100 MPH+), as soon as I slow down it goes away.

I experienced the same thing at high speeds. Then my cardiologist told me to slow the fa' down!

Seroiusly though, just because you have new tires don't discount unsprung weight issues. A tire, or a wheel out of round/balance, or a loose wheel bearing can be winding up the suspension and cause the thumping your hearing.

Jagermeister · Oct 22, 2008

Am I the only one expecting NWS material here? The "High Speed Thumping" title invoked other mental images. :huh:

Hopefully, you're feeling an out-of-balance, or seperated belt in a tire. If not, it could be more sinister.

Have you checked the axle and steering head bolts?

Also, you may check to be sure the right/left forks for even spring, compression dampning, and rebound settings. The garage monkeys at the local stealer screwed with my settings more than once.

Kirrilian · Oct 22, 2008

Slappy said:
Please define thumping? Is it a noise or a feeling? If a noise where do you believe you hear it? If a feeling describe it and where you feel it.

I feel it through the bike, handlebars, pegs etc, I am going 100MPH+, don't hear much at those speeds LOL

It has done this from day one, and here are the things I've done to it recently:

New tires (took wheels off and on myself )

8K Service (TBS, sparkplugs, replaced final drive oil, engine oil change, air filter, all done by me)

Tightened the stem nut, it was only hand tight!

It feels like those bumps on a concrete paved interstate but only when going high speeds. I will check the suspension settings since I haven't tweaked those yet, hopefully that will fix it.

Bogey907 · Oct 22, 2008

Is your wife on the back seat when this happens?

Kirrilian · Oct 22, 2008

Bungie said:
Kirrilian said:

Ever since I bought my bike I feel a thumping through the bike at high speeds (100 MPH+), as soon as I slow down it goes away.

Click to expand...

I experienced the same thing at high speeds. Then my cardiologist told me to slow the fa' down!

Seroiusly though, just because you have new tires don't discount unsprung weight issues. A tire, or a wheel out of round/balance, or a loose wheel bearing can be winding up the suspension and cause the thumping your hearing.

I know for a fact that the guy that put my tires on rebalanced them afterwards. I checked all the bearings when I put the wheels back on and didn't see anything glaringly obvious but that is a good point. I would think that it would do that at any speed though if a bearing was loose or bad.

radman · Oct 22, 2008

You may be getting a high speed misfire. Can't hear through that quiet exhaust and all the wind noise. Check plug wires for firm connections, or slap that puppy on a dyno.

Kirrilian · Oct 22, 2008

Bogey907 said:
Is your wife on the back seat when this happens?

I don't go that fast with someone on the back, so I'm not sure if it would still do it or not.

Kirrilian · Oct 22, 2008

radman said:
You may be getting a high speed misfire. Can't hear through that quiet exhaust and all the wind noise. Check plug wires for firm connections, or slap that puppy on a dyno.

That's a good suggestion, I wouldn't have thought of that. I can hear my exhaust pretty good because I have Staintune mufflers but it is hard to hear anything going that fast. I know the plug wires are good, I just replaced the plugs last weekend. Wouldn't it do it if I was wrapping it out going through the gears too though? I have the sinking feeling it has something to do with the driveline, gears, tires or something like that.

ionbeam · Oct 22, 2008

Does it still have the vibrations if you pull in the clutch?

Mechanical problems like U joints tend to have a resonant point where the vibration is at its worst but falls off below and above that point. Ring gears will have noise to go with the vibs.

It sounds like the vibrations start at a certain mph and remain the same or get worse as speed goes up, if this is ture then the problem is more likely to be wheel balance or wheel run-out. You will need to have someone check your wheels for balance (different from the person that mounted your most recent tires). If that doesn't find a problem then you need to have someone with a dial indicator check the rims for roundness, check both the right side and left side of the rim and check for run-out on both sides.

If you have light hands on the bars do you see or feel any movement in the bars?

Edited to add: A lot took place while I was grinding out my reply. My clutch suggestion would be to check for misfire or other power train problems.

Kirrilian · Oct 22, 2008

ionbeam said:
Does it still have the vibrations if you pull in the clutch?

Yes, that's why I don't think it is an engine problem

Mechanical problems like U joints tend to have a resonant point where the vibration is at its worst but falls off below and above that point. Ring gears will have noise to go with the vibs.
It sounds like the vibrations start at a certain mph and remain the same or get worse as speed goes up, if this is ture then the problem is more likely to be wheel balance or wheel run-out. You will need to have someone check your wheels for balance (different from the person that mounted your most recent tires). If that doesn't find a problem then you need to have someone with a dial indicator check the rims for roundness, check both the right side and left side of the rim and check for run-out on both sides.

If you have light hands on the bars do you see or feel any movement in the bars?

I will have my wheels rebalanced, I noticed there were quite a few weights on the rear when I got them back, perhaps there is an issue with my wheels. I don't feel any movement in the handlebars, just the thumping, if I did I wouldn't ever go that fast again! Talk about pucker factor!

ionbeam · Oct 22, 2008

Silly but I just have to ask the age old question -- what are your tire pressures? And, if ya don't mind, what brand of tires are you running?

motorcycle-ed · Oct 22, 2008

Put the bike up with wheels off the ground push side to side way out on the wheel to see if there is any side to side movement. Spin the tire/wheel and listen to the bearings at a quiet time with no other noise. You might even have to back off the brake pads. Set up something solid with a point that will just touch the rim and turn each wheel to verify the wheel is tru and does not have a bent place either radially or axially. Since it did this with these tires and the previousl tires, it is reasonble to rule out a bad tire or out of balance tire...I think...odds are really long tires are at the bottom of this. When doing the side to side thing on the rear, make sure you look to see that the swingarm is not allowing the entire wheel assy to move due to bad swingarm bearings. If all that checks out you need an exorcist. I am agreeing with you though...having this reveal its true self when doing the ton might not be a happy thing.

Ed

radman · Oct 22, 2008

The plug wire thing has nothing to do with the plugs themselves-the wires screw into the plug caps. More than one guy has discovered them inadvertently pulled apart enough to cause odd/rough running, especially after doing a plug change-an inadvertent pull will do it . And a misfire can occur under load in a high gear that wouldn't necessarily in a low gear at the same rpm-high load, high rpm, high power output is the most taxing on an ignition system. May not be the cause, but a thump feeling does not suggest to me tire balance, though tire imbalance will reveal itself in a, usually, very narrow speed range of about 5mph.

Kirrilian · Oct 22, 2008

ionbeam said:
Silly but I just have to ask the age old question -- what are your tire pressures? And, if ya don't mind, what brand of tires are you running?

38 front

40 rear

dunlop roadsmarts, standard sizes

They are probably a month old, already have about 3k miles on them because I took a trip right after I got them.

Kirrilian · Oct 22, 2008

radman said:
The plug wire thing has nothing to do with the plugs themselves-the wires screw into the plug caps. More than one guy has discovered them inadvertently pulled apart enough to cause odd/rough running, especially after doing a plug change-an inadvertent pull will do it . And a misfire can occur under load in a high gear that wouldn't necessarily in a low gear at the same rpm-high load, high rpm, high power output is the most taxing on an ignition system. May not be the cause, but a thump feeling does not suggest to me tire balance, though tire imbalance will reveal itself in a, usually, very narrow speed range of about 5mph.

So if I was running at these speeds and have this issue I should be able to hear the misfire in the exhaust or engine noises right? If I have my windshield all the way up and lean down I can hear a lot better than when I am sitting up, I normally don't do that when I am going that fast since you don't have much time to react to obstacles. I will find a nice quiet strip of road that I can try this on, assuming that I will be able to hear something weird going on. Also, why do I still feel it when I pull the clutch in? Thats the first thing I tried since that would give me somewhere to start, either engine or drive components.

Kirrilian · Oct 22, 2008

motorcycle-ed said:
Put the bike up with wheels off the ground push side to side way out on the wheel to see if there is any side to side movement. Spin the tire/wheel and listen to the bearings at a quiet time with no other noise. You might even have to back off the brake pads. Set up something solid with a point that will just touch the rim and turn each wheel to verify the wheel is tru and does not have a bent place either radially or axially. Since it did this with these tires and the previousl tires, it is reasonble to rule out a bad tire or out of balance tire...I think...odds are really long tires are at the bottom of this. When doing the side to side thing on the rear, make sure you look to see that the swingarm is not allowing the entire wheel assy to move due to bad swingarm bearings. If all that checks out you need an exorcist. I am agreeing with you though...having this reveal its true self when doing the ton might not be a happy thing.Ed

Great suggestions, I will check these when I check the suspension settings. I've been wanting to try HaulinAshe's settings: https://www.fjrforum.com/forum//index.php?s...p;mode=threaded

Wolfhound · Oct 22, 2008

My roaddumbs were already showing bad wear signs by 3k & with a bunch of weight on the back one I'd be leaning towards that as the problem. I know I'd never buy another set (gone at 5K) but others have had mcuh better luck with them I hear . . .

High Speed Thumping

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