High Speed Thumping

[radman]

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.

Yeah, if it's still happening with the clutch in, it ain't the motor. Still, you may or may not hear a high speed miss-one cyl dropping quick happens so fast at high r's (at 7000 rpm each cyl fires 3500 times a minute, or about 58 times a second) it's easy to miss it-but still feel it. Doesn't sound like your problem though-and without riding the bike myself, I'm hard pressed to offer much in the way of ideas, just too many possibilities IMHO.

 

[Kirrilian]

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.

Yeah, if it's still happening with the clutch in, it ain't the motor. Still, you may or may not hear a high speed miss-one cyl dropping quick happens so fast at high r's (at 7000 rpm each cyl fires 3500 times a minute, or about 58 times a second) it's easy to miss it-but still feel it. Doesn't sound like your problem though-and without riding the bike myself, I'm hard pressed to offer much in the way of ideas, just too many possibilities IMHO.

I know it is hard to diagnose this stuff over the internet, I had hoped that someone else has had this before and knew what it was but it doesn't look like. I guess I will just keep my speed down until I figure out what is causing it, I don't really need to be going that fast anyway but it is hard to resist sometimes... :yahoo:

 

[Big Sky]

Does the frequency of the "thumping" increase when speed increases? If so, I'd bet on an out-of-round wheel(s). Have you hit anything exceptionally hard? These wheels will bend, as I know personally.

 

[Kirrilian]

Does the frequency of the "thumping" increase when speed increases? If so, I'd bet on an out-of-round wheel(s). Have you hit anything exceptionally hard? These wheels will bend, as I know personally.

That makes a lot of sense as that is the only thing that hasn't changed since I have had the bike. I haven't hit anything that I can think of but I am the second owner and there is no telling what he did to it. Wouldn't that come out when they balanced the wheels after putting the new tires on? That may explain why there are so many weights on the back rim, I'll have to look again tomorrow but I remember thinking that when I picked them up from the tire place.

 

[Big Sky]

Bent wheels can be straightened with a high degree of success, but it is a pain and disassembly (tires, rotors and bearings must be stripped) and reassembly and shipping winds up costing more than the straightening itself, but significantly less than a new wheel. And you would wind up with a fresh powder coat finish which allows you a chance to customize a little.

 

[E1Allen]

Would it do anything you can observe with the center stand up and run it up to 100mph, you wouldn't have to be on the bike then, maybe observe something that way.

 

[S76]

Would it do anything you can observe with the center stand up and run it up to 100mph, you wouldn't have to be on the bike then, maybe observe something that way.

I was thinking that or you could just put a piece of wood (or something) very close to the tread of the tires and rotate them to look for out of round. Also do it against the sides or the tires. You can mount a pencil to a piece of wood and put it against the side of the rim to look for out of true condition. A simple test but anything that would cause a thumping would probably be seen by doing this. Of course a dial indicator on the rim would be best if you have one.

Are the tire beads seated completely?

 

[Slappy]

Kirrilian, what tires do you currently have on the bike and how many miles? I know when by Bridgstone tires were ready to be replace the front tire felt like it had a flat spot in it. Its was terrible. I thought it was out of balance or something was wrong with the rim. If you are on Old warn tires this may be your problem. It may be time for some new shoes. If your tires are generally new you could also have a bad tire. If this is a new development I seriously doubt there is anything mechanically wrong with your steed.

 

[ionbeam]

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, what tires do you currently have on the bike and how many miles? I know when by Bridgstone tires were ready to be replace the front tire felt like it had a flat spot in it. Its was terrible. I thought it was out of balance or something was wrong with the rim. If you are on Old warn tires this may be your problem. It may be time for some new shoes. If your tires are generally new you could also have a bad tire. If this is a new development I seriously doubt there is anything mechanically wrong with your steed.

Since you have had the exact same problem through two sets of tires it looks like you should check your rims. In my post I said to have someone with a dial indicator check them for run-out but as others have mentioned, you can do a field check yourself. Spin the wheel while holding a fixed object very close to the rim. Check both the front and rear rims, if you find a problem don't assume it is just one bad rim. Check both sides of the rim, check for out of round as well as lateral run-out.

 

[motorcycle-ed]

The answer to your question about "wouldn't they find an out of round condition when they balanced it?" Is a resounding NO. You can balance a square wheel with four corners! It wouldnt roll so good, but you could spin it and it would be smooth and balanced. Nothing other than a physical check by rotation relative to a fixed point will pinpoint wheel distortion.

Ed

 

[Fred W]

That may explain why there are so many weights on the back rim, I'll have to look again tomorrow but I remember thinking that when I picked them up from the tire place.

Where in relationship to the valve stem are all of these weights? And, are they equally distributed on both sides or centered on the wheel (side to side)?

My guess is that the weights are all very close to the valve stem, right?

Here's why I say that. The lightest spot of the tire is marked with a yellow dot. The conventional wisdon is to align the lightest spot of the tire with the wheels valve stem, as that is thought to be the heaviest spot on the unshod wheel. But it isn't. In fact on my rear wheel, and as reported by several other folks that bothered to check the balance of their unshod wheels, the valve stem is actually the lightest spot on the wheel. So after they align the light spot of the tire and the light spot of the wheel they have made the balance as bad as it possible can be.

You might be able to get out of this mis-balance problem by rotating the tire 180 degrees and rebalancing, thereby reducing the amount of lead that needs be added to balance it, and also making sure that any weight that is added is centered on the rim's centerline.

 

[Big Sky]

No shops here will check the balance of the wheel before mounting a tire, and in my experience there is only one of the three I've tried that can even get the balance close. The least common denominator in the shop gets this job and is poorly trained or doesn't care. Just about every time I get new tires mounted, I wind up consider getting my own mounting/balancing set-up and doing it myself. Ought to solicit other local hardcores who burn two or three sets a year like I do and form a little cooperative.

 

[Kirrilian]

The answer to your question about "wouldn't they find an out of round condition when they balanced it?" Is a resounding NO. You can balance a square wheel with four corners! It wouldnt roll so good, but you could spin it and it would be smooth and balanced. Nothing other than a physical check by rotation relative to a fixed point will pinpoint wheel distortion.Ed

Thats a good point, I will check to see if there is any wheel distortion using the methods outlined in this post.

 

[Kirrilian]

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, what tires do you currently have on the bike and how many miles? I know when by Bridgstone tires were ready to be replace the front tire felt like it had a flat spot in it. Its was terrible. I thought it was out of balance or something was wrong with the rim. If you are on Old warn tires this may be your problem. It may be time for some new shoes. If your tires are generally new you could also have a bad tire. If this is a new development I seriously doubt there is anything mechanically wrong with your steed.

Since you have had the exact same problem through two sets of tires it looks like you should check your rims. In my post I said to have someone with a dial indicator check them for run-out but as others have mentioned, you can do a field check yourself. Spin the wheel while holding a fixed object very close to the rim. Check both the front and rear rims, if you find a problem don't assume it is just one bad rim. Check both sides of the rim, check for out of round as well as lateral run-out.

I'm good with what you are saying but I don't know what you mean by lateral run-out. I was going to check roundness by putting something under the tire as close as I can get it without touching and rotating it to see if it catches and check side to side by putting something fixed by the rim and rotating it.

 

[Kirrilian]

I hope it isn't my wheels

If that is what it is, where would I go to find a replacement? If you say the dealer I'll jack slap your ***! They are too damn expensive!

Sleezebay? Not sure I would trust something off there for something as important as this...

 

[Fred W]

I hope it isn't my wheels
If that is what it is, where would I go to find a replacement? If you say the dealer I'll jack slap your ***! They are too damn expensive!

Sleezebay? Not sure I would trust something off there for something as important as this...

You could always wait for a crash victim on here and offer to buy wheel(s). Of course you'd need to be selective with the kind of crash. Low sides only, no post or cage banging...

 

[Kirrilian]

Holy Crap!

https://cgi.ebay.com/ebaymotors/YAMAHA-FJR1...3390#ht_500wt_0

I'll just drive slow(er) if I have to pay that much for a replacement rim.

I hope it isn't my wheels
If that is what it is, where would I go to find a replacement? If you say the dealer I'll jack slap your ***! They are too damn expensive!

Sleezebay? Not sure I would trust something off there for something as important as this...

You could always wait for a crash victim on here and offer to buy wheel(s). Of course you'd need to be selective with the kind of crash. Low sides only, no post or cage banging...

Yeah but then I'd feel like an ambulance chasing lawyer. Would probably be cheaper though...

 

[SPORT]

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

Glen,

I may have experienced something similar too as I road the tarmac home at over 100+ for over an hour. For me, it seems to be the windscreen area. Although not certain, the windscreen seems to pick up some oscilation that vibrates the front end and of course buffets the wind over me. It has only happened a couple of times (that I recall), but I distinctly remember playing around with different speeds to identify when the problem occurs and where it might be coming from. Thought it was the front tire out of balance, but it is not. I've got no other ideas as to what it could be.

 

[ionbeam]

Rims can be reliably repaired by a good shop. Expect to pay ~$150 per rim plus shipping. The actual cost will be determined by how much the wheel shop has to remove before the wheel goes in the oven. If you can remove the tire, bearings, stem and rotors there won't be any additional charge. Some shops include painting (if required), others charge for the service. Good rim shops have been discussed in this Forum, you should be able to find the info pretty quickly. I believe one was in the Atlanta area and the other one was in one of the Carolinas.

What you suggest "putting something under the tire as close as I can get it without touching and rotating it" will tell you if the tire is out of round but won't tell you if the rim is bent.

You need to do the same thing while putting something at the rim, placed right at the bead. First put the indicator such that you can see if the rim is round, like you are going to do with the tire. This check will be to see if the rim is going up and down. Now put the indicator to the side of the rim, right at the bead. Standing facing the bike, you will be looking for any side to side variation, this is the lateral run-out. Do both sides of the rim for both roundness and lateral run-out. If you can see *any* movement the rim is bent. So, how much is too much? Typical OEM rims have specifications that say a rim can be .040 to .060 out of true. A good rim shop can usually get your rims within .020 using only bending techniques. If you want a rim more true than that the rim is typically machined.

Edited to add: This is the recommended shop I was thinking of.

 

[rbentnail]

I experience the [apparently] same thump, thump, thump at higher speeds. It shows up at about 110 and disappears at 115. Nothing above that. As someone mentioned it feels like the thump, thump of the seams of a concrete highway. 3 different tires, balanced by 3 different people on 3 different machines- no diff. I figure it is just the resonant frequency ( https://en.wikipedia.org/wiki/Resonant_frequency ) we experienced regularly with equipment on Navy subs. I just use the feeling as a eyes forward/110 mph go-nogo gage.