Topic: Bouncing front end after new tire CB750 K3

[Stev-o]

1/8" = 125 thou... over four times what 754 considers acceptable.

+1....there is your "bounce"

[754]

So is it tire or rim that you should see by eye...use a pencil held against the fork if need be.
 If the rim appears true, ie no flat spots... You can probably do it on the bike, worst case you lose the tube....remove all air.

[Sigop]

Might as well finish front end while I have wheel off. Reworking caliper and replacing pads now and cleaning entire assembly. Side of rim looked true with pencil test, but tire had some high spots.  I am taking tire to another shop tomorrow and tell them to get it right.
Later all.  Thanks for all thoughts.  It's always a process of elimination isn't it?

[754]

So you are saying you went to the effort of checking sideplay, but NOT up and down ?
 So know you still dont know whats wrong...?  ?
How did you determine tire was going up and down, and not check rim.. You should be able to spin it and see it... Can you do that ?  ?

[Sigop]

First measure was putting a solid straight edge at front of tire, flashlight to light it up and then spun it.  Variation from high spot to low spot of middle of tire tread as it spun was max of about 1/8 inch.  Think you said should be no more than 0.030, unless you were talking about side of rim variation.  Pencil to side of rim looked good on both sides when I tested that.

[Nic]

What Frank is saying is, did you check the out of round on the rim, not the sideways but the up n down on the rim, not the tyre.

[754]

Again, rim 30 thou or under BOTH ways. Now if you determine rim is ok, then its the tire.
 
If you can see tire out an 1/8, anyone should be able to see that much on a rim..
 And if you got loose spokes wheel needs work. I am done here.
 Btw , I dont care if you use a steel Rule, stick, pencil, knitting needle, or carrot or straw, but one will scratch your rim.

[Stev-o]

Keep in mind he did not have the issue until the tire was changed out.

[754]

 I know that , that points to the rim..... He just had to spin it, and look at it..

[Sigop]

Update and eureka!  So I applied the classic shotgun solution and have no idea what made the difference, but she rides smooth as glass now, finally.

1. After much opinion offered from multiple bike shops the tire was reported as fine and the wheel needed truing.  Was done, though reported not off by much.
2. I replaced the wheel bearings in the front wheel while I was at it.
3. Removed and reconditioned the front forks.  Stripped, cleaned, new seals, fork oil, the works.
4. Removed and rebuilt the front caliper, new brake lines, all but a MC rebuild. (It pumps fine)
5. Could not bring myself to replacing the steering bearings.  I want to ride it.

BTW, what is the best inflation for an Avon Roadrider front tire on a CB750K?  Anywhere from 28 to 40?  Any opinions?  Looks like some posters on here recommend inflate to tire specs, others say inflate to the bike specs.  Don't want to start an oil debate, but what would be the safest and best riding inflation spec for weekend country road riding?

Thanks all.

[Bodi]

The sidewall rating is for max pressure at max weight. I don't have your tire or know the weight on it... but probably (hopefully?) this is less than what the max load is. Of course the front tire load goes waaay up on braking...
Honda spec'd pressure for the tire they sent with the bike many years ago... and that was pretty much with Japanese (=small and light, excepting Sumo wrestlers) riders in mind.
It's not as simple as with flat tread car tires where you can look at the tread and see if it's been over or under inflated: your riding affects the tread wear. Highway cruising will flatten the crown. Carving twisties will wear down the sides of the crown.
I adjust tire pressure for handling. Too low and the bike falls into turns, too much and it tends to stand up in them. Spring sag, shock length, and fork position in the triples affects this as well... so how can you know what's really going on? No definitive answer from me, sorry. I have adjusted shock preload and put the forks up in the triples a bit so the bike has neutral handling at close to Honda spec pressure.
Rossi gets (many?) specialists in chassis and tire setup in his pit... I fumble in the dark.

[Sigop]

Thanks Bodi.  Ultimately it looks like it comes down to personal weight, cargo, and FEEL.  Suspected that and will just experiment.
Thanks.