Tire pressure Zipp 404's

[mshep]

I normally race on 700x20 tires with 150lbs of pressure, but recently
got a set of Zipp 404's. The Zipps say they have a max of 120lbs of
tire pressure.

Does anybody know what the problem is with higher pressure on the
404's? Is this is this a true limitation, or can I exceed that on the
Zipps?

1) Stick with my 700x20's, but only go to 120lbs.
2) Switch to 700x23's which are rated at 120lbs.
3) Stick with my 700x20's, and try between 130-140lbs in the tires.
4) 700x20's with 150lbs... no problem

 

[Tom]

Why do you need to run such high tire pressures?? Doesn't make any
sense anyway. 120 should be more than enough, and in some cases too
much.

Tom

 

[TZ]

Floyd looks like he just found out somebody ****** in his corn flakes.

 

[jeremy]

Actually, he looks to me like he just got dropped and taunted on
Brasstown Bald.

 

[Philip Holman]

"mshep" <[email protected]> wrote in message
news:[email protected]...
>I normally race on 700x20 tires with 150lbs of pressure, but recently
> got a set of Zipp 404's. The Zipps say they have a max of 120lbs of
> tire pressure.
>
> Does anybody know what the problem is with higher pressure on the
> 404's? Is this is this a true limitation, or can I exceed that on the
> Zipps?
>
> 1) Stick with my 700x20's, but only go to 120lbs.
> 2) Switch to 700x23's which are rated at 120lbs.
> 3) Stick with my 700x20's, and try between 130-140lbs in the tires.
> 4) 700x20's with 150lbs... no problem
>

The only two reasons I can think of for Zipp to limit tire pressure are:
1/ due to the constriction force which reduces spoke tension. 2/ The
harsh ride above 120 psi.
For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/ your
guess is as good as mine, but as long as your fillings don't fall out,
the wheel should also be fine. Contact Zipp for the official skinny.

Phil H

 

[Laz]

"Philip Holman" <[email protected]> wrote in message
news:[email protected]...
>
> "mshep" <[email protected]> wrote in message
> news:[email protected]...
> >I normally race on 700x20 tires with 150lbs of pressure, but recently
> > got a set of Zipp 404's. The Zipps say they have a max of 120lbs of
> > tire pressure.
> >
> > Does anybody know what the problem is with higher pressure on the
> > 404's? Is this is this a true limitation, or can I exceed that on the
> > Zipps?
> >
> > 1) Stick with my 700x20's, but only go to 120lbs.
> > 2) Switch to 700x23's which are rated at 120lbs.
> > 3) Stick with my 700x20's, and try between 130-140lbs in the tires.
> > 4) 700x20's with 150lbs... no problem
> >
>
> The only two reasons I can think of for Zipp to limit tire pressure are:
> 1/ due to the constriction force which reduces spoke tension. 2/ The
> harsh ride above 120 psi.
> For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/ your
> guess is as good as mine, but as long as your fillings don't fall out,
> the wheel should also be fine. Contact Zipp for the official skinny.
>
> Phil H
>
>
How about rim failure ? Ever experience that ? Keep on pushing the limit,
and those bloody expensive wheels will be worthless.
Use the 23 or 20s as you like ( I like 20s in the summer, 23s the rest of
the year ) but don't go beyond 120.

Laz

 

[StanSD]

I've been running 404's at 150-160lbs in time trials for several years now.
This has been out of ignorance more than anything else, but I've never had a
problem (though I've never done any really serious cornering on them).

Stan


"mshep" <[email protected]> wrote in message
news:[email protected]...
>I normally race on 700x20 tires with 150lbs of pressure, but recently
> got a set of Zipp 404's. The Zipps say they have a max of 120lbs of
> tire pressure.
>
> Does anybody know what the problem is with higher pressure on the
> 404's? Is this is this a true limitation, or can I exceed that on the
> Zipps?
>
> 1) Stick with my 700x20's, but only go to 120lbs.
> 2) Switch to 700x23's which are rated at 120lbs.
> 3) Stick with my 700x20's, and try between 130-140lbs in the tires.
> 4) 700x20's with 150lbs... no problem
>

 

[Bob Schwartz]

In rec.bicycles.racing Laz <[email protected]> wrote:
> How about rim failure ? Ever experience that ? Keep on pushing the limit,
> and those bloody expensive wheels will be worthless.
> Use the 23 or 20s as you like ( I like 20s in the summer, 23s the rest of
> the year ) but don't go beyond 120.

120 isn't that high. And certainly not for a time trialist or
triathlete, which is an intended market for those wheels. If
someone told me they couldn't reliably take pressures greater
than 120 I'd be strongly inclined to take them back. That
would be greatly substandard.

Bob Schwartz
[email protected]

 

[Philip Holman]

"Laz" <[email protected]> wrote in message
news:[email protected]...
>
> "Philip Holman" <[email protected]> wrote in message
> news:[email protected]...
>>
>> "mshep" <[email protected]> wrote in message
>> news:[email protected]...
>> >I normally race on 700x20 tires with 150lbs of pressure, but
>> >recently
>> > got a set of Zipp 404's. The Zipps say they have a max of 120lbs
>> > of
>> > tire pressure.
>> >
>> > Does anybody know what the problem is with higher pressure on the
>> > 404's? Is this is this a true limitation, or can I exceed that on
>> > the
>> > Zipps?
>> >
>> > 1) Stick with my 700x20's, but only go to 120lbs.
>> > 2) Switch to 700x23's which are rated at 120lbs.
>> > 3) Stick with my 700x20's, and try between 130-140lbs in the tires.
>> > 4) 700x20's with 150lbs... no problem
>> >
>>
>> The only two reasons I can think of for Zipp to limit tire pressure
>> are:
>> 1/ due to the constriction force which reduces spoke tension. 2/ The
>> harsh ride above 120 psi.
>> For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/
>> your
>> guess is as good as mine, but as long as your fillings don't fall
>> out,
>> the wheel should also be fine. Contact Zipp for the official skinny.
>>
> How about rim failure ? Ever experience that ? Keep on pushing the
> limit,
> and those bloody expensive wheels will be worthless.

OK, what is the explanation for a rim failure at 150 psi? Like I said,
150psi with a 20 puts less stress on the rim than a 23 at 120psi. I'm OK
with following Zipp's recommendation but it would be nice to know their
reasoning.

Phil H

 

[Philip Holman]

"mshep" <[email protected]> wrote in message
news:[email protected]...
>I normally race on 700x20 tires with 150lbs of pressure, but recently
> got a set of Zipp 404's. The Zipps say they have a max of 120lbs of
> tire pressure.

Are these clinchers with aluminum braking surfaces?

Phil H

 

[Laz]

"Philip Holman" <[email protected]> wrote in message
news:[email protected]...
>> >> The only two reasons I can think of for Zipp to limit tire pressure
> >> are:
> >> 1/ due to the constriction force which reduces spoke tension. 2/ The
> >> harsh ride above 120 psi.
> >> For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/
> >> your
Like I said,
> 150psi with a 20 puts less stress on the rim than a 23 at 120psi.
> Phil H
>
>
Hey, I missed that.
Could you take a moment and explain how that is for me please ?
Always one for science.

Thanks in advance

Laz

 

[mshep]

Yes, clinchers with aluminum rims.

Mike

 

[Philip Holman]

"Laz" <[email protected]> wrote in message
news:[email protected]...
>
> "Philip Holman" <[email protected]> wrote in message
> news:[email protected]...
>>> >> The only two reasons I can think of for Zipp to limit tire
>>> >> pressure
>> >> are:
>> >> 1/ due to the constriction force which reduces spoke tension. 2/
>> >> The
>> >> harsh ride above 120 psi.
>> >> For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/
>> >> your
> Like I said,
>> 150psi with a 20 puts less stress on the rim than a 23 at 120psi.
>> Phil H
>>
>>
> Hey, I missed that.
> Could you take a moment and explain how that is for me please ?
> Always one for science.
>
> Thanks in advance

The constriction force of a tire with a 45 degree bias ply is pressure
times cross sectional area.
The actual constricting component is P*A*2*tan^2(a) and the expanding
component is P*A so the resultant force for a 45 degree tire is P*A.
The bias ply acts like a scissor jack where the hoop tension is double
the longitudinal tension so the tire actually shortens in circumference
when inflated.
A 20mm tire at 150 psi exerts a 73 lb constriction force and a 23mm tire
at 120 psi exerts an 80lb constriction force. These forces are so low
that it is obviously not a reason for concern.

I'm thinking that Zipp has limited tire pressure on clinchers with
aluminum braking surfaces because of the reduced heat dissipation on
long descents (mostly carbon rims) resulting in possible overheating and
tire blowoff.

Phil H

 

[Philip Holman]

"mshep" <[email protected]> wrote in message
news:[email protected]...
> Yes, clinchers with aluminum rims.
>
> Mike
>

How did I guess......The problem is overheating on long descents. The
aluminum braking surface does not dissipate heat well when embedded in
carbon. The overheated tire can blow off the rim if inflated to a very
high pressure to begin with. Overheating the rim heats up the air in the
tire and increases the pressure beyond the tire's max rating. If you do
nothing but flat TTs ........well, you can decide for yourself. I would
still check with Zipp to confirm what I have stated.

Phil H

 

[Laz]

Thank you again Phil

My experience with clinchers, going past 120 psi caused the rim to weaken
and eventually fail. I even had a rear wheel literally blow-up on me after a
short ride to work, I locked it up and started to walk away- then
Ka-BLAM!!!! pieces everywhere. I don't recall what size tires I was using
but it was probably a folding 23 clincher, mavic reflex rim, usually at 110

Laz

"Philip Holman" <[email protected]> wrote in message
news:[email protected]...
>
> "Laz" <[email protected]> wrote in message
> news:[email protected]...
> >
> > "Philip Holman" <[email protected]> wrote in message
> > news:[email protected]...
> >>> >> The only two reasons I can think of for Zipp to limit tire
> >>> >> pressure
> >> >> are:
> >> >> 1/ due to the constriction force which reduces spoke tension. 2/
> >> >> The
> >> >> harsh ride above 120 psi.
> >> >> For 1/ , a 20 at 150 psi is equivalent to a 23 at 113 psi. For 2/
> >> >> your
> > Like I said,
> >> 150psi with a 20 puts less stress on the rim than a 23 at 120psi.
> >> Phil H
> >>
> >>
> > Hey, I missed that.
> > Could you take a moment and explain how that is for me please ?
> > Always one for science.
> >
> > Thanks in advance
>
> The constriction force of a tire with a 45 degree bias ply is pressure
> times cross sectional area.
> The actual constricting component is P*A*2*tan^2(a) and the expanding
> component is P*A so the resultant force for a 45 degree tire is P*A.
> The bias ply acts like a scissor jack where the hoop tension is double
> the longitudinal tension so the tire actually shortens in circumference
> when inflated.
> A 20mm tire at 150 psi exerts a 73 lb constriction force and a 23mm tire
> at 120 psi exerts an 80lb constriction force. These forces are so low
> that it is obviously not a reason for concern.
>
> I'm thinking that Zipp has limited tire pressure on clinchers with
> aluminum braking surfaces because of the reduced heat dissipation on
> long descents (mostly carbon rims) resulting in possible overheating and
> tire blowoff.
>
> Phil H
>
>