How round is "round enough"?

I bought a new front tire for my CB900 last week. Since then I've been
noticing a small but distinct bouncing oscillation in the front end. I
don't feel it on the freeway, it's only apparent at street speeds (25-50
mph). Today I put the bike up, pulled the calipers, gave the wheel a good
spin, and watched.

This tire is not entirely round.

It's not out of round by much, I'd say maybe 3mm. It's also not quite true,
wobbling back and forth by about 5mm. The wheel itself is fine, it's easy
to see that the wheel tracks straight while the tire doesn't.

Is that much deviation tolerable? My last tire sure didn't behave like
this, and it was a good deal cheaper at that (this new one is a Metzler
ME880). Is this bad enough that I should return it as defective?

-Scott

 

Dollars to doughnuts they blame it on broken cords and won't do a thing
for you...

 

It sounds to me like it's not seated on the bead properly. It happens.

There's often a line running round the circumference of the tyre, close
to the rim, for you to check. If the line isn't equidistant from the rim
all the way round, that's the problem.

Quite often you have to blow tyres up to 50-60psi and higher to get them
to seat properly.

 

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Jim sez:
I agree with TOG on this.
Except, If you find where the tire's bead isn't seated evenly on the
rim, I would deflate the tire, lube the bead and then air it back up
to get the bead seated properly.
Like TOG said, it may take 50+ psi to get it to come out evenly.
Then deflate it to the proper pressure.

 

Ditto. If you didn't rip the cords apart when you were mounting it
that Metzeler 880 isn't out of round by 3mm, the beads aren't seated
right. I always use Ru-Glyde tire lubricant when mounting and
dismounting tires (which I just did last night, two new tars on my
ZG1000). It's amazing how quick and easy it is to swap tires when
you use the right tools and the right stuff. I usually air my tires
up to about 50 lbs to make sure they pop on correctly, one tire
popped in three places, so don't assume if you hear it pop once
that it's all done. I always look for the concentric circle that
TOG mentions, too.

 

Ah. The shop mounted it, not I. I hope they didn't break anything...I've
no doubt they'd make it right, but it'd mean downtime. They have a habit of
not stocking front tires in my size.

I'll check that first thing tomorrow.

Thanks, guys!

-Scott

 

I had to go to 90 with my recent front tire for my Concours... Yikes!

MAN, what a POP when that bead seated!!!

--
"Outback" Jon - KC2BNE

AMD Opteron 146 (@2.8) and 6.1 GHz of other AMD power...
http://folding.stanford.edu - got folding? Team 48435

2006 ZG1000A Concours "Blueline" COG# 7385 CDA# 0157
1980 CB750F SuperSport "CoolerKing"

 

Years ago, I remember seeing photos of some rally in Germany where
Continental were demonstrating just how much pressure tyres can take, by
blowing them up to something unfeasible like 200psi. They did use a
water bath and safety cage, mind.

And further to that, when I was editing a commercial vehicle title some
years ago, we got a report forwarded by a coroner (always a good sign)
with a letter saying: "Can you publish this to make certain no idiot
ever does it again?"

It ws an eight-wheeler tipper truck. Four steering wheels forward and a
bogie with four driven wheels aft.

The company wanted to replace a set of brake shoes on one of the rear
wheels, and so jacked one wheel off the ground, and removed the shoes.
Before fitting the new ones, they decided they wanted to check the
tachograph was working properly, so started the engine, put the thing in
gear, and ran it up to an indicated 55mph.

Has anyone spotted the error yet?

Like all 'eight-leggers', it had a four way differential on the rear
driven wheels. Three wheels were still braked, so the diff fed *all* the
power to the unbraked wheel. Which revolved at four times normal speed,
so 220mph, and took just 11 seconds to get there.

The tyre had previously been repaired, properly, but it wasn't designed
for this sort of stress and the tyre exploded like a bomb, killing
outright a fitter who just happened to be walking past....

 

message

That can also be caused by not using enough lube during mounting.

Ted

 

True.

 

....And the correct answer is: Manufacturing Defect.

The shop folks poked and prodded, checked the bead, the tire, the wheel, and
finally announced that the tire was, in fact, not quite round. The tech
thought it had maybe been molded incorrectly, and showed me what he
described as a weird mold line in the rubber.

Upshot is that they replaced the tire free of charge, and even apologized
for the inconvenience. Very cool. That's the kind of service that keeps me
coming back to this shop year after year.

-Scott

 

Wow. That is very, very rare.

I had it happen on a car, once, about 20 years ago.

 

message

I sincerely hope you published it with the headline "Eight-legger blows tyre
and gets fitter"


--
Beav

VN 750
Zed 1000
OMF# 19

 

<VVBG>

Any time you want a sub-editor's job....