Topic: Bouncing front end after new tire CB750 K3

[Sigop]

Replaced old tires on front and back of bike with stock size Avon Road Riders AM26. Prior riding it had ridden smooth and straight. After putting new tire on now between about 15 and 40 MPH front end hops up and down accelerating and decelerating.

No other change to bike after replacing front tire.  New tire was changed and balanced by a shop.

Ideas? Can a new tire be out of round?

[BomberMann650]

Probably didn't seat on the rim correctly.  Balancing machine would not have noticed that.  Take it back to the shop for re-seating.

[flatlander]

let out the air, roll it around a bit, pump up again. that should smooth it out. most guys in the shops these days don't know any more how to deal with tyres that use inner tubes.
pump it up to the tyre manufacturers spec. the old honda pressure spec is too low for modern tyres.

[turboed13b]

I bet the rim isnt true. Wrestling the tire off will knock the rim out of round if it hasn't been trued in a while.

[Sigop]

Thanks guys.  Will try all 3 with simplest first. One of the posters on here talked about the front disk grabbing some; would that cause the same symptom?

[PeWe]

That''s almost standard for me when getting new tire on my bike. Deflate and pump again with much higher pressure until it will seat correctly on rim. +50% pressure no problem.
I had one tire once that had to be ridden on bike on a clean road with almost no air 100-200m, then pump again.
Lubricate the tire where it seat to rim when completely deflated will help, floating soap or similar.

[Desert-SOHC]

Mine did the same thing and the tire wasn't seated on the rim correctly

[Sigop]

So I bled it low and refilled up to 40 psi.  Still the same bounce--like a pogo stick between 20 and 40, as someone has said before (for some who know what I refer to).

I'm going to go out on a limb and guess that it is not seated properly.  See pics.  Note the difference in distance from the beading. Think that is the issue?  (Just a hassle to take it back to the shop that didn't pay attention.)

[evinrude7]

Lubricate the tire where it seat to rim when completely deflated will help, floating soap or similar.

+1

[andy750]

As others  have said deflate then reinflate to 80-100psi to get seated correctly. I have done this successfully!

[Sigop]

Andy750,
Will try that.  Did not know tire/tube could take that much inflation.  No experience in tire work.
Thanks.

[lrutt]

Make sure when you put the wheel and axle back together you leave things loose, get it back on  the tires then pump the front end to make sure forks aren't binding then tighten up. You can easily get things off just a little which will bind forks and you can get a bouncy front end as a result.

[Sigop]

lrutt.  I'm sorry, I'm not following. Don't mean to be thick.  Are you saying the tires would expand so much they would contact the forks, and also that I should first have the axle nut loose before inflating?

Thanks.

[Sigop]

Update, regrettably. Have had the tire reseated which looks right now. Rebalanced with about 1 ounce less so there was something going on. Replaced all front bearings. Changed and replaced fork oil and changed brake fluid. Not much left but still get a #$%*in' bounce between 30 and 40 mph. Touching the brake smoothes it out. Spikes all ping pretty well when I tap them with screwdriver. What's left?  Check tire round with a box or board or something in front while jacked up. If tire good then thinking only thing left is bad rim, which first shop might have dinged when ironing off the first tire.
Happy for additional thoughts but will update as/when I solve this. Hard to enjoy a curve at 40 with a bounce in it. Uh, yeh.

[Stev-o]

If you are certain there is not an issue with the install of the new tube and tire, this now points to a defective tire.

Although I doubt this as Avon manufactures excellent tires, it is possible.

[Sigop]

Yes. Will have another shop recheck tube and tire. I agree. A little hard to believe the Avon would be defective.

[evinrude7]

sigop, maybe someone has mentioned this but could you have brake drag at the front brake?  mine does and it sort of hops a bit around a curve around 40-45 mph. 

[Sigop]

Evinrude7
Didn't you have a similar issue? I have seen that on here but it spins pretty clean and quiet when up on the jack. Not sure how else to test that.

[evinrude7]

yeah man mine drags and i feel it around a curve.  i think if your's spins free then that's not the issue.  just popped into my head as a possibility.  i worked in my dad's goodyear tire shop growing up and the only things i can think of tire related is the wheel is not round or the tire is defective.  other than that maybe it's a front suspension thing.  it didn't happen before you changed the tire but you had the tire off the bike to do that.  perhaps something came loose or readjusted during removal/mounting of the wheel.  keep us posted.

[Bodi]

Tires can be defective. Lift the front end and rotate, see if the tread moves in and out as it turns. It should run VERY close to true, a couple of mm might be OK but not much.
If the wheel rim runs true, the tire's bead line is equally spaced from the rim all the way around, and the outside of the tire goes up and down: demand a replacement tire.
If some runout exists check that the bead line to rim distance isn't following the tire runout: if it is, the thing is still not seated properly. It can be a mental hella hard job to fully seat a tubeless tire on our tube-type rims.
If the wheel has been balanced and the weights are strangely large, suspect either incomplete seating, a bad tube (cheap tubes can be way out of balance because the rubber thickness varies too much) or a bad tire. You can't see the bad tube, and it won't cause problems once balanced... but poor seating or a bad tire can give you the radial runout that will cause bouncing.

[Stev-o]

Good point about the tube, was that new too?

[evinrude7]

Good point about the tube, was that new too?

sigop do you know if they put the correct size tube in there? 

[754]

If your rim is bent, you will see it if you spin it. 30thou is acceptable.

[Sigop]

New tube but not sure of size. If I place a straight line across front of tire when jacked up, I get a variance between highest and lowest spots at middle of tread as it spins of at most 1/8 inch. Is that a significant amount?

[Bodi]

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

[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.