Can I safely overinflate my tires?

[Bob Ladbury]

I use Continental CityRide tires on my hybrid city bike, which carry inflation limits of
56psi-70psi. I ride solely on pavement. I read that its better to inflate the rear tire more than
the front (people usually overinflate by 10psi). But is it safe to inflate the CityRide's to 80psi,
or do I risk a blowout, particularly in the summer? A lot of people seem to be saying the
manufacturer's limits usually don't mean much. And a maximum rating of 70psi seems to be pretty darn
low for a bike tire (700C). But maybe there's a good reason for this low rating and they shouldn't
ever go past 70??

 

[Art Harris]

Bob Ladbury wrote:
> I use Continental CityRide tires on my hybrid city bike, which carry inflation limits of
> 56psi-70psi. I ride solely on pavement. I read that its better to inflate the rear tire more than
> the front (people usually overinflate by 10psi). But is it safe to inflate the CityRide's to
> 80psi, or do I risk a blowout, particularly in the summer? A lot of people seem to be saying the
> manufacturer's limits usually don't mean much. And a maximum rating of 70psi seems to be pretty
> darn low for a bike tire (700C). But maybe there's a good reason for this low rating and they
> shouldn't ever go past 70??

Depends. Sounds like you've got the 700 x 37 version of CityRide. That's pretty wide, and 70 psi is
probably reasonable unless you're very heavy. Wider tires are generally run at lower pressure. I
doubt that you'd get a blowout at 80 psi, and I wouldn't worry about summer temperatures.

Art Harris

 

[Pete Geurds]

Your weight and tire size would be a help. I weigh near 230 so I pay attention to tire size and
inflation pressure. Bigger tires don't need to be pumped up as hard as a skinny little 700x20. The
10 psi extra in back (or 10psi less in front) works well. Makes ride a little better. Hook bead rims
tolerate high presures better than straight bead rims.

From: [email protected]
>I use Continental CityRide tires on my hybrid city bike, which carry inflation limits of
>56psi-70psi. I ride solely on pavement. I read that its better to inflate the rear tire more than
>the front (people usually overinflate by 10psi). But is it safe to inflate the CityRide's to 80psi,
>or do I risk a blowout, particularly in the summer? A lot of people seem to be saying the
>manufacturer's limits usually don't mean much. And a maximum rating of 70psi seems to be pretty
>darn low for a bike tire (700C). But maybe there's a good reason for this low rating and they
>shouldn't ever go past 70??

Pete Geurds Douglassville, PA

 

[Sheldon Brown]

Bob Ladbury wrote:

> I use Continental CityRide tires on my hybrid city bike, which carry inflation limits of
> 56psi-70psi. I ride solely on pavement. I read that its better to inflate the rear tire more than
> the front (people usually overinflate by 10psi). But is it safe to inflate the CityRide's to
> 80psi, or do I risk a blowout, particularly in the summer?

Shouldn't be a problem on a decent rim. Continentals are known to be tight fitting in general.

> A lot of people seem to be saying the manufacturer's limits usually don't mean much.

That's absolutely correct. In my opinion, manufacturers' pressure ratings are generally completely
worthless. I explain the reason for this, and give some guidelines for determining the proper
pressure for _you_ and _your_ conditions at:

http://sheldonbrown.com/tires.html#pressure

> And a maximum rating of 70psi seems to be pretty darn low for a bike tire (700C).

The correct pressure is a function of the _width_ of the tire, among several other factors, but has
_nothing_ to do with its diameter.

> But maybe there's a good reason for this low rating and they shouldn't ever go past 70??

Nope, but a 37 mm wide tire is liable to give a harsh ride and less than ideal road holding if you
go much over that, unless you're using it on a tandem of otherwise heavily loaded application, or
are riding on unusually smooth pavement.

Sheldon "Experimentation Is Best" Brown +---------------------------------------------+
| Life is made up of sobs, sniffles, and | smiles, with sniffles predominating. | --O. Henry |
+---------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Doug Milliken]

When I wanted to know this information for a particular tire-rim combination I took a good used tire
(not cut, just worn down), and performed a blow-off test.

I'd present my data here but that tire is no longer available so it's kind of a moot point...in my
case I needed a track pump because the pressure at failure was about 220 psi on the pump gage. I
inflated the tire in stages of about 10 or 20 psi and then let it sit at each higher pressure to see
if the tire was "creeping" on the rim.

Of course with a sample size of _one_, the data is NOT conclusive, so I never pumed that type of
tire anywhere near 220 psi on the bike, but I did run it at 120 which was somewhat over the sidewall
rating. The test gave me some idea of my margin of safety.

For safety I strongly suggest that you put the tire in some container (cardboard box, etc) while you
are pumping, and wear both eye/face and hearing protection. I also wore heavy gloves when handling
the tire at high pressures (need to attach/detatch the pump, etc).

Please report back if you run a test, the actual test samples, etc.

-- Doug Milliken www.millikenresearch.com

On 5 Aug 2003, Bob Ladbury wrote:

> I use Continental CityRide tires on my hybrid city bike, which carry inflation limits of
> 56psi-70psi. I ride solely on pavement. I read that its better to inflate the rear tire more than
> the front (people usually overinflate by 10psi). But is it safe to inflate the CityRide's to
> 80psi, or do I risk a blowout, particularly in the summer? A lot of people seem to be saying the
> manufacturer's limits usually don't mean much. And a maximum rating of 70psi seems to be pretty
> darn low for a bike tire (700C). But maybe there's a good reason for this low rating and they
> shouldn't ever go past 70??

 

[David Kunz]

Pete Geurds wrote:

> Your weight and tire size would be a help. I weigh near 230 so I pay attention to tire size and
> inflation pressure. Bigger tires don't need to be pumped up as hard as a skinny little 700x20. The
> 10 psi extra in back (or 10psi less in front) works well. Makes ride a little better. Hook bead
> rims tolerate high presures better than straight bead rims.

I've had tires tear / balloon along the rim when run overinflated. This was on a moutain bike when I
was doing a lot of road riding.

David

 

[Chris Zacho "Th]

When I load up my Voyager for a tour, I always increase the pressure by ten pounds to prevent
snake-bite (pinch flats).

I believe tires are tested at the factory at nearly twice normal pressure to insure against blowoff.
Certainly a few extra pounds/bar won't hurt.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Squid-In-Traini]

"David Kunz" <[email protected]> wrote in message
news:[email protected]...
> Pete Geurds wrote:
>
> > Your weight and tire size would be a help. I weigh near 230 so I pay attention to tire size and
> > inflation pressure. Bigger tires don't need to be pumped up as hard as a skinny little
700x20.
> > The 10 psi extra in back (or 10psi less in front) works well. Makes ride a little better. Hook
> > bead rims tolerate high presures better than straight bead rims.
>
> I've had tires tear / balloon along the rim when run overinflated. This was on a moutain bike when
> I was doing a lot of road riding.

My Hutchinson Python Airlite tire exploded off the bead when I inflated it too high. However, it did
it when I wasn't even in the room. The sidewall says 80 psi, and Giant OEM told me not to inflate it
over 45 psi. I now bring (the replacement) up to 40 and that's it.

--
Phil, Squid-in-Training

 

[Joe Riel]

Doug Milliken <[email protected]> writes:

> When I wanted to know this information for a particular tire-rim combination I took a good used
> tire (not cut, just worn down), and performed a blow-off test.

What happened to the tire when it blew off? Was it destroyed?

Joe Riel

 

[Qui Si Parla Ca]

'safely'...'overinflate'...'safely'...'overinflate'....

repeat after me.....

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"

 

[Doug Milliken]

On Thu, 7 Aug 2003, Joe Riel wrote:

> Doug Milliken <[email protected]> writes:
>
> > When I wanted to know this information for a particular tire-rim combination I took a good used
> > tire (not cut, just worn down), and performed a blow-off test.
>
> What happened to the tire when it blew off? Was it destroyed?

Hi Joe,

It was 32-369, Wolber rib tread. One bead wire broke next to the butt weld, in the "heat affected
zone", after sitting at 220 psi for ~10 minutes.

If there was a "magic" way to re-weld the bead wire with the carcass cords wrapped around it, that
tire would still be usable. Haven't repeated the test with any newer tires yet (have to wear one
down first). No damage to the rim.

-- Doug

 

[Doug Milliken]

On Thu, 7 Aug 2003, Phil, Squid-in-Training wrote:

> My Hutchinson Python Airlite tire exploded off the bead when I inflated it too high. However, it
> did it when I wasn't even in the room. The sidewall says 80 psi, and Giant OEM told me not to
> inflate it over 45 psi. I now bring (the replacement) up to 40 and that's it.

So you did some blowoff testing too...you just didn't know that you were running a test at the
time<grin>.

It's important to note what rim was used, tire-rim fit is not well controlled by many bike and tire
companies. My ancient copy of Southerland's Manual actually has a table of good, marginal and poor
fits between certain tires and certain rims.

-- Doug Milliken www.millikenresearch.com