Some months back when I got some parts I added some footrest rubbers to the order after a non forum well meaning friend commented on how the worn rubbers took from the K [he professes to dislike Ks but secretly he is gutted that the Ks are more reliable and more fun that his so called fancy ride].


Anyway I recently decided to put them on, having taken a few attempts to get the bolt on footrest ends off.


Now when I was using the 92K100LT it had the familiar vibration around 4,000rpm. Not too badly, but it was there. Interesting the day I took the 84K100RT out for a test ride I noticed it didn't have that same vibration and it felt very smooth.


But when I took it out for a run after changing the RT footrest rubbers I was gobsmacked. NO vibration at all, felt like deep pile carpet. A quick revisit to the old rubbers made it clear the old ones were like a hard plastic and the new ones like soft rubber, especially the soft ribs. A big change for very small money. It's had a new seat in January and looks like its going to get new handlebar grips too.


Of course when I thought about it, its the same principle as old tyres and new ones. New rubber is nice and soft and pliable.

Very interesting!  Old, hard peg rubbers' effect on rider comfort never occurred to me.  But now that you've paved the way, it makes perfect sense that new, pliable rubber would be an economical upgrade if your bike's vibes are irritating.  Thanks.

It was just one of those little jobs one does sometimes.

I just didn't expect it to make such a difference. But feeling he nice soft flexible ribs on the new ones it makes complete sense.

Changing handlebar grips probably has the same effect as new ones are very clearly much softer. I do a lot of long runs so it may be just more noticeable on longer rides.

Thanks Olaf!
Funny how such a small thing will cause me to make such big decision; let me explain. My brother and I are taking a trip next month and the first 1200 miles are going to be flat and boring so we are planning to do a "saddle sore 1000"(1000 mile in 24 hours) to get to the good part (the bad lands and black hills) of the trip. We both hate riding the interstate but figure that's the best way to do this for better average speed and safer at night. I was planning on taking my 88 LT but talking to my brother just the other day I told him I was going to take my 87 RT because "the LT has a vibration around 4500 RPM, not like it coming apart but it makes my legs and hands numb". I thought it was some kind of engine harmonic and just would have to live with it. I will try changing the pegs and see if it helps the vibration issue, it would be great if I get the same results as you did!
caveman

Thanks Olaf!
Funny how such a small thing will cause me to make such big decision; let me explain. My brother and I are taking a trip next month and the first 1200 miles are going to be flat and boring so we are planning to do a "saddle sore 1000"(1000 mile in 24 hours) to get to the good part (the bad lands and black hills) of the trip. We both hate riding the interstate but figure that's the best way to do this for better average speed and safer at night. I was planning on taking my 88 LT but talking to my brother just the other day I told him I was going to take my 87 RT because "the LT has a vibration around 4500 RPM, not like it coming apart but it makes my legs and hands numb". I thought it was some kind of engine harmonic and just would have to live with it. I will try changing the pegs and see if it helps the vibration issue, it would be great if I get the same results as you did!
caveman

Hi Caveman

I hope it works for you. But it's only the rubbers I changed, footrest [pegs?] stayed in place. I am sure the rubbers are cheap enough off the BMW dealer even, but what is important is that they are not old and hard. Softness stops the vibes going through to the body..... which is why the handlebar grips are also going to be swapped. Having both the old and new in my hand at the same time was very revealing. For what its worth don't go buying used ones. From now on I won't give these more than a 5 year lifespan.

Out of curiosity is it a case that you also are comparing an LT and RT and also finding a difference in vibration at 4-4500 rpm? As far as I was able to see they are mechanically identical, down to and including the fairing, gearing, final drive, engine mounts etc etc etc and could find no difference that might account for the fact that the LT has it and the RT is so much less. Ok, footrest hangers differ but I think mountings are same. Only difference I could see was comparing 84 RT with 36k miles and 92LT with over 100k miles.

The handlebar mounts also seem to be with dampers and I guess these too are worth a look.

Quite a topic but it does make sense. With these long rides these are the little details that make a very big difference in how you feel when you arrive at your destination. It most likely is an engine harmonic but one we can't eliminate but instead prevent from getting through to the body at the contact points [feet, hands and seat].

I have in recent months changed the rear shock and the seat but I had the bike for a run after each so I know it was the footrest rubbers that made the big difference. Also changed the handlebars last year but stayed with RT/LT bars.

If not done get front wheel balanced as it too can transmit a high frequency vibration.

Hey Caveman. I found that a recent throttle balance on my machine smoothed those vibes noticably.
Also, do you have handlebar end weights?
Cheers

Kaptain Holister wrote:Hey Caveman. I found that a recent throttle balance on my machine smoothed those vibes noticably.
Also, do you have handlebar end weights?
Cheers

Both of these make a big difference, can vouch for that. But it didn't eliminate the difference I found between the LT and the RT.

Kaptain Holistor and Olaf, Thanks for your replies.
My bikes are very similar the four things I notice; 1) LT seat seems to have firmer seat foam and better fit.  2) LT rear shock is a BOGE unit that from what I've read is suited for heavier loads and of better quality. 3) LT has heated grips. 4) LT has factory radio that works (most of the time something is loose inside there somewhere). None of those things would explain the vibration but are the reason I bought the LT so I could have one bike in ready condition to take off on long distance adventure trips on short notice and all those thing are helpful for burning up miles. The vibration issue even though it is minor it's still putting that plan on hold.
As for miles, it's the other way around. The LT clock shows 18,000 miles and I see no indicators not to believe it (like splines show hardly any wear) but, without any records you just can't be 100% sure. The RT clock now reads 47,000 miles and I think I got a creampuff, when I it bought I thought there was something seriously wrong with it do to the low price. One thing that concerned me was the right fork slider was plain aluminum and the left black but could not see any evidence of damage to trees or frame. So after a test ride I went all in, came back with a trailer and took it home. The big mystery was solved when I reviewed the paper work in a folder the previous owner gave me at time of purchase. The first 32,000 were put on by the original owner with all service records in BMW book with dealers all over the United States including a "defective lower fork tube" in New Mexico @ 3800 miles. The next/previous owner had it for 8 years , put 4,000 on, and showed receipts for two oil changes, three mirrors, and two rear turn signals.
OK SORRY back to the issue. The LT has Dunlop tires that are new just before I got it. I do not care much for Dunlops but would be surprised if they were the cause of vibration. Both have handlebar end weights and same feel and flex to top tree bushings. Throttle body sync makes all kind of sense, I tried to make a jig for this but was not satisfied to make adjustments with my crude first attempt to make this instrument.

Don't adjust the throttle linkages unless they have already been disturbed, the dabs of blue paint on the screws are the telltale signs. They are set by the factory and rarely need adjustment before about 100k
The adjustment that is refered to is done by way of the 4 Big Brass Screws (BBS) that adjust the airflow at idle and hence the vacuum. Have a search around the forum for "idle adjustment", there is plenty of reading on the subject.

yeah, sorry, my post #7 was refering to a 'Throttle Body Balance' not throttle adjustment on each TB.

Also I've found that spark plugs can induce vibration when you get one or two starting to fail.

Again thanks for replies Rick G and KH
I forgot to mention in my last post that I did check the foot peg rubbers and both feel soft and pliable.
Now at this point I am starting to feel a bit uncomfortable. What is proper etiquette on a forum like this if you start going off topic? Should I start a new topic, after all throttle body adjustment are a bit different than foot peg rubbers?

Wha....etiKette? We try not to use big sounding words here.

But you're right. As with any forum, respect should be given to the OP's topic, but throttle bodies related to vibration so all's good. :king:

If you have a question for discussion that relates to your own particular issues or is on a different topic, then it should be posted in its own thread under an appropriate forum heading.