Back rest vibration test

I tried something, well it kind of just hit me. I decided to bleed the pressure out of my shocks, left first then right. When I bleed the right the bike actually dropped a little. Enough to actually see it. This goes back to putting pressure in with rear tire off ground.

So I put 25 lbs in both and took wife for ride. She said the vibration was there and very noticeable. I then came back and emptied them to zero and we went for ride, no vibration what so ever she said.

My thought is, putting equal air in them with tire on ground causes a uneven balance with bike having more pressure on left side shock. I dont know, but it worked.

[Top Cat]

If you don't want to go to the trouble of lifting the bike off the rear tire everytime you air the shocks just buy an air balancing kit from Jay. $25 to your door.

I think you missed what I am trying to say. Even with what we think is equal because of the left side being compressed more they really are not equal. Now if this is a issue when riding I dont know, I do know what we discovered.

[ringadingh]

You will get an uneven reading in the shocks if you fill then on the ground while leaning on the sidestand. The LH shock will be sightly more compressed with the bike leaning on it. This will change the reading when the bike is standing up straight.
If someone holds the bike up even for you while you fill the shocks you should be equal in both of them.

[trosco]

Your swingarm doesn't flex when you lean over on side stand just like it dosen't flex when you go into a turn. Your shocks are compressed the same amount no matter what lean angel the bike is at.

I'd suggest you do a good examining of your rear tire. It's probably cupped and that is where your vibration is coming from. Air up the shocks and back end is stiffer and the wife feels the washboard vibration from the tire. Let all the air out and the back end is soft and vibration not as noticeable is all. It may even be the there is some tread separation if you have run the tire underinflated. Really give that tire a good looking at. It could be a real safety issue!

T Ross

[ringadingh]

Originally Posted by trosco

Your swingarm doesn't flex when you lean over on side stand just like it dosen't flex when you go into a turn. Your shocks are compressed the same amount no matter what lean angel the bike is at.
T Ross

Thats what I thought as well until I tried it. I filled the shocks equally on the sidestand but got a different reading when checking them with the bike up straight.

[cnc]

You may have discovered a reason for the vibration, but I do not think it is from uneven shock pressure. If I read your post right you tried a ride with 25 psi and then no psi. At 25psi uneven wear in the tire could be an issue, but It could also just be a stiffer ride and more of the road irregularities are transmitted through the bike.

I would think either there would have to be a lot of flex in the swing arm, or a pretty sloppy swing arm pivot shaft to compress the left hand shock more than the right just sitting on the stand.
This would be fairly easy to test. Pump up both shocks while the bike is on the side stand to equal pressure. Have someone hold the bike up right or jack the bike and check the pressure again with the no loss pump. if you use the jack the pressure in both shocks will be less but none the less pretty much equal.

[trosco]

Ring
The swing arm is a solid rectangle. I am not doubting that you find differences in shock pressure side to side each time you measure them. I am just saying that it is not from the shocks varrying in length side to side when the bike is leaned versus upright when it's stationary. If our swing arm was that weak then when we take a 35 mph curve at 60 riding two up we'd twist the thing so far that the tire would hit the fender.
Conceptually if you put say 1000psi in one shock and 0 in the other then put a couple 300 lb riders on it you might induce some flex to the swingarm. But that would make the bike track crooked and wobble in turns. It wouldn't cause a vibration.
Personally, I put my front tire in a chock so the bike is upright, then prop a 2x4 under my luggage rack to the ground at a angle so that shocks are fairly well extended then set both shocks to 32 psi. Then I check them and they are off. I keep checking till I get close (say with in 1 lbs) to same reading on both sides. And I start over if I get down to 25psi in either shock. And after I take 2x4 away and go for a ride they usually read 3-4 psi higher (compressed) and vary by 1-2 pounds side to side.
Regarless if we agree on this, tjam may have a serious saftey issue with his vibration and he needs to be examining things like tire condition, wheel bearings and so on to find it, because shock pressure may effect how much you feel a vibration but it won't be the cause of a vibration.

[VulcanE]

Originally Posted by Top Cat (TC)

If you don't want to go to the trouble of lifting the bike off the rear tire everytime you air the shocks just buy an air balancing kit from Jay. $25 to your door.

I'm not going to get in on the discussion of vibration (although I pretty much agree with Ross on there is an underlying problem), but I will say I'm a stanch supporter of the shocks being balanced. The good thing with the balance kit is that no matter what pressure you have, the shocks are ALWAYS exactly the same pressure wise. Maw Kawi should have taken a page out of the HD book and had shock balance as a standard feature on a big heavy cruiser.

[markclark57]

Side track on the same subject. . .
Is there any thing negative to No air pressure in the shocks???

[cnc]

Originally Posted by markclark57

Side track on the same subject. . .
Is there any thing negative to No air pressure in the shocks???

If I'm not mistaken the factory setup for the rear shocks is position 2 on the damper and atmospheric pressure which is 0 psi with no weight on the shocks. So no not in terms of damage to the shock. But you may bottom out easier depending on the weight of you, your passenger and luggage.

[cocheese72]

Originally Posted by Ringadingh

You will get an uneven reading in the shocks if you fill then on the ground while leaning on the sidestand. The LH shock will be sightly more compressed with the bike leaning on it. This will change the reading when the bike is standing up straight.
If someone holds the bike up even for you while you fill the shocks you should be equal in both of them.

Good tip. Does anyone know part numbers of the parts needed to get the single setup. I know someone makes them, but would like to make it myself.

[Top Cat]

Originally Posted by cocheese72

Good tip. Does anyone know part numbers of the parts needed to get the single setup. I know someone makes them, but would like to make it myself.

Jay sells the compleat set up for $25 to your door. How much would you save by doing it yourself, I don't know but to me it would not be worth the hassel.
Your opinion may vary Most people do. :)

[cocheese72]

Originally Posted by Top Cat (TC)

Jay sells the compleat set up for $25 to your door. How much would you save by doing it yourself, I don't know but to me it would not be worth the hassel.
Your opinion may vary Most people do. :)

I have a DIY spirit, much like Jay does I am sure.

[markclark57]

Originally Posted by cnc

If I'm not mistaken the factory setup for the rear shocks is position 2 on the damper and atmospheric pressure which is 0 psi with no weight on the shocks. So no not in terms of damage to the shock. But you may bottom out easier depending on the weight of you, your passenger and luggage.

Curently riding Solo @ 190 lbs. Planning on a bit of luggage for Crescent City in August, otherwise I ride light. I rarely ride hard but keep my options open.
If I "bottom out" with a 205/60 16 CT will I fender the tire or bottom the shock??? (Don't really want to find out on my own.)