MOTOBRICK.COM
TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: HCorn on November 26, 2011, 06:39:11 PM
-
I just spent the last day and a half on "quality time" wrenching on the K75. I installed new springs and changed the oil in the forks (apparently it needed it pretty badly :-[). While I had the front wheel off, I noticed the left side of the tire was really worn and the right side still looked like new (Lasertecs). You can actually see the difference in the profile of the tire.
I never really noticed any odd handling, but after seeing this I'm thinking that maybe I did have to use more counter-steer while turning left. The bike seems to track straight. I'm thinking the wheel wasn't in straight or maybe a fork brace issue. ??? Visually, the wheel seems centered.
The wear is bad enough I think I might actually replace the tire. But I'd like to resolve the underlying issue.
-
It's pretty common for the right side of the front tire to show more wear. Theories run from road crowning to right hand, right hand turns are more plentiful to the wight of the swingarm and crank on the right. I have no idea why myself. If yours is worn on the left that would be unusual. The Metzlers are directional so hopefully they were not installed backwards. You can put the wheel on either way.
-
Tread arrow is definitely facing the right way. It's the left side as seen when sitting on the bike.
It's really pretty strange. If you're looking down the profile, the left side looks pretty much flat while the right side still has a round profile. And the demarcation is exactly the center - no chicken strips. In fact, the entire right side from the center over barely looks worn.
Maybe I'll post a pic.
Edit: Actually, I would think the crown of the road (U.S.) would actually lead to left side wear - just not this severe.
Edit2: Hmmm, a little more researching. Apparently the road crown has nothing to do with it. But in countries where you drive on the right side of the road, left-hand turns (i.e. outside lane) are twice as long as right-hand turns.
-
I am from Oz and we have the same problem on the right side of the tire and it is more pronounced if there are lots of roundabouts as the distance traveled on the side of the tire is near tripple.
-
Ooops, you're right. It is the left side that shows more wear. If it helps, "they all do that" then pick your favorite explanation. I must of had a brain fart moment saying they wear on the right. Sorry.
-
This page does a pretty good job of explaining.
http://www.rattlebars.com/tirewear/index.html (http://www.rattlebars.com/tirewear/index.html)
-
greetings hcorn...
how about posting up some photos so we can see whacha you be talking about...
j o
-
I don't think the pics quite catch the severity of it, but if you actually look at the comparative tread depth you can get an idea.
Thanks for the link CRASH. I actually saw that yesterday and it helped ease my mind a little. But even still, the right side looks new and that band about an inch over from the center on the left side looks about 80% worn.
On another site, somebody speculated that a bad left shock/spring could cause excessive left side wear. I rebuilt the forks yesterday and can tell you the fluid in both sides looked awful. But it looked equally bad on each side.
(https://lh6.googleusercontent.com/-L1uurfVBKGQ/TtJRuGrnUwI/AAAAAAAAA3c/XsQoZs3mddU/s446/profile.JPG)
(https://lh6.googleusercontent.com/-TPVPwIi4U-A/TtJRu9Foc8I/AAAAAAAAA3k/DcwQTyc4yM0/s754/tread2.JPG)
-
back in the late 70's we ran a new suzuki 550 in the 24 hrs of nelson ledges in ohio. after the race, we pulled the 750 carbs and the kerker pipe off, but left the tires as is. sold the bike to a guy as a "only used a short time" deal. since the race was basically clockwise, there was a pronounced wear on the right sides. we told him it'd be ok, just don't turn right a lot.
-
The factory manual has a spec for the amount of offset that the rear tire is allowed with respect to the front, seems like "acceptable" was from 5 to 8, or 8 to 13 mm toe displacement--some ocd mofo can look it up exactly. It has always seemed to be a violation of the laws of nature that you can't align the centerline of the front and rear tires exactly. They make a special tool for the measurement that most dealers don't have, but i've just used the string method to verify that this is the case and to try to correct the situation.
The further that the rear tire is offset to the left of the front, the worse will be your front left-side wear patch due to the need for constant pushing with your left-hand to make the bike run straight down the road. Try to ride with no hands and the bike starts turning to the right immediately.
This seems to be related to the design of the BMW single-sided swing-arm--all my chain bikes are perfectly aligned front and rear, even the SSSA of the honda hawk, vfr and ducati 916. They still have a bit of left-side wear patch due to the extra distance travelled in left hand turns, but it is not nearly as noticeable as on the K bikes.
Some years ago when i was actively trying to solve this problem i machined the front motor mounts on the engine and used shims to try to bring the rear into alignment with the front. Probably got it down to about 2 mm of offset, but couldn't get it all out. It did help reduce the wear patch but i got tired of messing with it. i prefer that a bike run straight when i let go of the grips. On a long flat clear slab on interstate it gives your wrist a break to be able to set the throttle lock and steer by shifting your weight with your knees against the tank...
2016 Edit Note: So the OCD mofo is me, and i downloaded the old 2V kbike manual and grabbed some screen shots. The 4V may be where i read about the greater offset values but i don't have that manual.
-
I never really thought about the alignment. I'll have to see if I can measure it accurately.
Any thoughts about the usefulness of that front tire? Wear it out or throw it out?
-
Any thoughts about the usefulness of that front tire? Wear it out or throw it out?
GS runs mixed bias % radial tires. FACTORY selection, I might add.
New rubber is semi cheap, fresh shoes are ALWAYS a winner.
-
Wear it out.
-
I'd probably run it the wear bars on the side that's wearing first if it's not causing any vibration or other odd handling behavior.
But, as DRX points out, new rubber is fairly inexpensive so if you're worried about it then replace it for peace of mind.