The Beginning of a Potential Problem

[jimz49]

I'm hoping you guys can give me some ideas on where to look for what appears to be the start of a developing problem. First, I'm riding a 99 R1100s with a little less than 17k miles. About two weeks ago a buddy and I took a ride that was about 400 miles long. Approximately 250 - 300 miles into the ride, I noticed (felt) the beginning of a thumping, similar to slight flat spot (or cupping) on the rear tire. The odd thing is I only noticed it in 5th gear. I checked the tire and didn't see/feel anything that would raise a red flag. My initial thought was maybe its in the transmission. Thinking that 5th gear might be a 1:1 straight through ratio. I checked the specs and determined that was not the case. If it were the driveshaft, tires or any other moving part common to all the gears, wouldn't I feel it more in 6th gear?

I don't want to blindly start tearing things apart without some logical approach. Any suggestions on what this might be, will be greatly appreciated.

[Peterr]

I have felt a similar sensation at 45-50 mph in 4th.

[ckcarr]

More info on the tires, which I'd suspect.

How old, mileage, type.

[roger albert]

ditto

[Peterr]

Pirelli Diablo with less then 500 miles.

[Peterr]

Also, if I pull in the clutch at speed the vibration stops.

[jimz49]

The front tire is a metzler sportec M-1 and the rear is a dunlop sportmax D220 ST. I don't know how many miles are on the tires, they were on the bike when I bought it 6 months ago. They look to be about half or more worn.

[jimz49]

Another question about the tires....wouldn't the sensation be more obvious in 6th gear if it were the tires?

[SergioK]

Does the thumping increase with engine rpm? (pull clutch lever in - thumping still there or gone?)

Or does it increase/decrease with speed (wheels)?

I guess the thing to determine is if it's coming from the tires or the engine or the trans or a combination of all three. I've noticed some high speed droning (coming from the exhuast) which is barely perceptible. I think my bike is turning into a tuning fork of some sort.

[jimz49]

I'll take a ride later on today and see if pulling the clutch makes a difference. I seem to remember that it made no difference during the previous ride.

[ckcarr]

It is worth replacing the tires regardless.

1. Mismatched.
2. > 1/2 life gone. Visually, the truth is that the best performance is in the first 25% of a tires life, then they deteriorate rapidly.

[Flatbutt1]

any cupping on the tires?

[AntonLargiader]

Originally posted by jimz49
[B]...Approximately 250 - 300 miles into the ride, I noticed (felt) the beginning of a thumping, similar to slight flat spot (or cupping) on the rear tire. The odd thing is I only noticed it in 5th gear.

It's possible that there's a tranny issue, but it's pretty unlikely. The 6-speeds are very reliable. The first step in any suspected drivetrain problem like that is to drain the gear oil from the tranny and the final drive. If the oil is clean, it's highly unlikely that there is a problem with those components.

If you want to check out the driveshaft, put the bike on the centerstand in first gear and bump the wheel back and forth to take up the slop in the drivetrain. The character of the 'bump' at each end is what you're feeling for. If it's a clank, you have a problem. If it's a clunk, it's probably OK. Make sense? Well, at least compare it to another bike if you can.

It might just be some harmonic between the tires and the engine at that speed.

BTW I don't know that any BMW bike has ever had a straight-through gear; they certainly haven't for the last 55 years or so.

[Rapid Dog]

...do a search for "thrum" ...

[jimz49]

Thanks rapid...did the search and discovered the thrum can be caused by anything from tbs needing balanced to having a bad hair day. It did remind me that shortly after I bought the bike I wanted to do a maintenance update....you know, change fluids, adjust valves, balance tbs, and do the infamous spline lube. I didn't remove the trans because I read several discussions on the clutch/input splines not needing greased until 25-30K. However, I did do the driveshaft splines. Now this brings into play pivot bearings and the ( I still don't understand how this is done) driveshaft alignment. I'll plead ignorance on the driveshaft alignment because I didn't know about it until well after my maintenance was done. But the problem just started to occur at 17K and I did my maintenance around 15K.