[rambo]

I recently got a CB750 back on the road. After riding it around for a few weeks, I notice that the front tire is wearing to a point. Left and right of center is wearing to bald, and the edges have normal wear. This results in a pointed tire that is almost impossible to ride in corners. Before I put a new tire on, I want to know what might be causing this so I don't wear out the next tire.

this is what it looks like:

|***|
|***|
|***| <-- edges are normal
\***/
>\*/<-- This has been worn resulting in a pointed tire (both sides equally).

The centerline is worn kind of patchy, a patch left, patch right creating kind of a zigzag. It's as if the bike doesn't want to ride down the center.

Possible causes:
I rode around will low air pressure for a few weeks.
They are old tires, maybe even originals.
I've been riding on them for about 1 month.
There is a possibility that my forks are not perfectly aligned. I lowered the right fork a few centimeters to make the rotor run parallel to the break caliper. (I would assume that this would result in wear on only one side if it was a problem.)

Any experience with this would be helpful. I don't want to put a new tire on and have the same result in a few weeks.

 

[kenessex]

I suspect causes 1 and 2 mostly and new tires will make the most difference. I don't understand how lowering one fork tube would change the alignment of the caliper and the disk. Sounds like that might be an issue like a bent axle which would also affect tire wear. Finally, if the forks don't have good damping that will affect tire wear. I suggest you take this opportunity to go through the whole front ed if you haven't done so.
Ken

 

[craig641]

If you've been riding around on thirty something year old tires for a month you're a lucky man. Throw those things out and get some new rubber. Put the correct amount of pressure in them. Then, does the bike pull to one side as you're riding? Can you take your hands off the bars and does it track straight? Have you aligned the front and rear wheels with string or bars? Don't rely on the marks on the swingarm.
Craig

 

[rambo]

quote:I don't understand how lowering one fork tube would change the alignment of the caliper and the disk.

There is a screw with a spring you can use to align the caliper to the disk, but there is no way to adjust the (tilt of the) caliper if it is not perfectly parallel to the rotor. If it isn't parallel, the pad wears at an angle and doesn't retract properly resulting front break squeal. My solution was to drop the right fork a bit, which aligns the rotor parallel with the caliper (attached to the left fork,) thus putting both forks on a parallel plane. I don't know another way to adjust the tilt of the caliper, or rotor.

 

[rambo]

Thanks for the replies. The bike pulls to both sides and is a bitch to maneuver at slow speeds and in corners. It does this because the tire is worn to a point. It doesn't track left or right because of a front to back alignment issue.

I'm thinking of putting the new tire on, and then chalking it and watching the wear carefully. If the situation is resolved by proper tire pressure, then problem solved. If not, then I'll revisit the issue here.

 

[kenessex]

Rambo,
I would absolutely get a new front tire and a rear if it is as old as the front. If the rear tire is worn square then it can cause issues too. Consider the Bridgestone BT-45s.
I still am not getting how dropping a fork tube can have any relationship to caliper alignment. The relationship of the disc to the caliper is fixed by the axle in the fork lowers and the mounting of the caliper to the same fork lower. Those mounting points are fixed and can't move. On these single piston Honda calipers it is possible that the pivoting aluminum caliper mount got twisted (never seen or heard of it), but the best way to compensate for that would be to use a shim washer under the pivot bracket either under the 2 top bolts or under the single lower mount point. Check out my FAQ on these brakes. If the caliper is not aligned with th disc then there is an issue that needs to be fixed. I think you have some issues that need some attention. On a bike of this age I would give a real good look at wheel alignment, steering head bearings, swing arm bushings, front fork bushings, wheel bearings, front fork damping and rear shocks in addition to tires. All in all it shouldn't take more than a few minutes of inspection to get a real good look at what you have, especially if you are replacing tires anyway.
Good luck and let us know what you find.

Ken

 

[parks61]

i'm with the new tire crowd. put two new tires on and call us in the morning.
-parks
ps. like your punctuational illustration though.