Tyre pressure measurement



N

N Cook

Guest
Without going to the extent of a pressure meter - is there some technique
that is a bit better than squashing sidewalls of tyres to tell whether soft
or firm.
 
In article <[email protected]>,
"N Cook" <[email protected]> writes:
|>
|> Without going to the extent of a pressure meter - is there some technique
|> that is a bit better than squashing sidewalls of tyres to tell whether soft
|> or firm.

If the tyres are on a car, kicking them is better. If on a bicycle,
no. I don't know about mopeds and motorcycles.


Regards,
Nick Maclaren.
 
"N Cook" <[email protected]> wrote in message
news:[email protected]...
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether
> soft
> or firm.

Pressure gauge on a track pump...
 
N Cook wrote:
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether soft
> or firm.
>
Your tyres are too soft. I can tell you that from here.

There is an extremely slim possibility that someone who's asking this
question doesn't actually have underinflated tyres, but it is indeed an
extremely slim possibility.

A
 
N Cook wrote:
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether soft
> or firm.

Stick in a pin of known cross sectional area and time the hiss.
 
On 10/05/2007 17:47, N Cook said,
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether soft
> or firm.

Assuming you're talking about a road tyre, then press your thumb into
the tread, not the side. If you can press it in, it's too soft. Far
better to get a track pump with a built-in gauge though. These are
cheap enough these days, and although the gauges may not be wonderfully
accurate they're good enough for our needs.

You might also be surprised at how hard a tyre at 80psi is compared to
what you think is hard by using your thumb!

--
Paul Boyd
http://www.paul-boyd.co.uk/
 
N Cook wrote:
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether soft
> or firm.

On a more serious note, I usually judge 700x25C tyre pressure in
qualitative terms by how the ride "feels"; and 20"/16" fatter tyres by
how much lateral bulge is visible when I sit on the bike.
 
On May 10, 5:47 pm, "N Cook" <[email protected]> wrote:
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether soft
> or firm.

Are you on a road bike? If so, I'd recommend a track-pump (most have
a gauge built in). Hand pumps are okay for road-side punctures and
situations where you find yourself without a track-pump. But it
really takes a track-pump to get a high enough pressure into a road
tyre with a reasonable amount of effort (110-120 psi, depending on the
width of the tyre and your weight, if you're very light you don't need
so high a pressure). A high pressure decreases the rolling resistance
from the tyres on the road so will make you go further for the same
amount of effort, at the expense of a harsher ride - so you may want
to adjust according to your own preferences.

Hand pumps tend to **** out at around 70-80 psi, some claim to go up
to 100, but I've never managed it.

Regards,

Duncan
 
Paul Boyd wrote:
> On 10/05/2007 17:47, N Cook said,
>> Without going to the extent of a pressure meter - is there some
>> technique that is a bit better than squashing sidewalls of tyres to
>> tell whether soft or firm.
>
> Assuming you're talking about a road tyre, then press your thumb into
> the tread, not the side. If you can press it in, it's too soft.

Trouble is with a high pressure road tyre (eg. 23mm @ 120 psi), it might
still be too soft even if you can't press thumb into tread. It's easier to
squeeze the sidewalls, therefore easier to get some idea of pressure. With
a narrow road tyre this should be possible but hard - painful, even.

I agree it's a good idea to have a track pump with a gauge - but still
you've got to decide what pressure to use. What the manufacturer says isn't
always best.

~PB
 
In article <[email protected]>,
"Pete Biggs" <[email protected]> writes:
|>
|> Trouble is with a high pressure road tyre (eg. 23mm @ 120 psi), it might
|> still be too soft even if you can't press thumb into tread. It's easier to
|> squeeze the sidewalls, therefore easier to get some idea of pressure. With
|> a narrow road tyre this should be possible but hard - painful, even.

It's not helpful even with a wide road tyre (e.g. 42 mm @ 65 psi).
I can't move the tread significantly at that pressure.

|> I agree it's a good idea to have a track pump with a gauge - but still
|> you've got to decide what pressure to use. What the manufacturer says isn't
|> always best.

Yes. For example, the pressures recommended for wide tyres are usually
far too low for most use.


Regards,
Nick Maclaren.
 
On 10/05/2007 19:14, Pete Biggs said,

> Trouble is with a high pressure road tyre (eg. 23mm @ 120 psi), it might
> still be too soft even if you can't press thumb into tread.

I was using the term "road tyre" in perhaps too loose a sense! I had in
mind something like the 700x37s on my commuter :)

--
Paul Boyd
http://www.paul-boyd.co.uk/
 
"Nick Maclaren" <[email protected]> wrote in message
news:[email protected]...
>
> In article <[email protected]>,
> "N Cook" <[email protected]> writes:
> |>
> |> Without going to the extent of a pressure meter - is there some
> technique
> |> that is a bit better than squashing sidewalls of tyres to tell whether
> soft
> |> or firm.
>
> If the tyres are on a car, kicking them is better. If on a bicycle,
> no. I don't know about mopeds and motorcycles.
>

Driving the thing (if you are used to it with correctly inflated tyres)
works even better, though this is one of the reasons I don't believe in
power steering.

Niall
 
On 2007-05-10, Pete Biggs <[email protected]> wrote:
> Paul Boyd wrote:
>> On 10/05/2007 17:47, N Cook said,
>>> Without going to the extent of a pressure meter - is there some
>>> technique that is a bit better than squashing sidewalls of tyres to
>>> tell whether soft or firm.
>>
>> Assuming you're talking about a road tyre, then press your thumb into
>> the tread, not the side. If you can press it in, it's too soft.
>
> Trouble is with a high pressure road tyre (eg. 23mm @ 120 psi), it might
> still be too soft even if you can't press thumb into tread. It's easier to
> squeeze the sidewalls, therefore easier to get some idea of pressure. With
> a narrow road tyre this should be possible but hard - painful, even.

It's not clear whether the resistance your thumb encounters is more
directly related to tyre pressure or casing tension.

There was a discussion about this on r.b.t. a while back, with lots of
varying views and even some experiments. My conclusion from that was
that the thumb test probably _is_ a measure more of casing tension
rather than of pressure.

This means that a fat tyre will feel harder at a lower pressure (the
casing tension is proportional both to the pressure and to the tyre
minor diameter). So on that basis, you can ignore the pressure rating
and the diameter, and just pump up any tyre until it feels hard and it
should be about right.
 
In article <[email protected]>,
Ben C <[email protected]> writes:
|>
|> There was a discussion about this on r.b.t. a while back, with lots of
|> varying views and even some experiments. My conclusion from that was
|> that the thumb test probably _is_ a measure more of casing tension
|> rather than of pressure.

I doubt it :)

The reason is that the resistance to sideways pressure is also a
function of the curvature, especially when the applied pressure has
a comparable curvature to the casing - as with a thumb and a narrow
tyre!

I would have to do the calculations properly to estimate more
precisely what is going on. They aren't hard, but need a bit of
care for someone as rusty as me.


Regards,
Nick Maclaren.
 
Ben C wrote:
> On 2007-05-10, Pete Biggs
> <[email protected]> wrote:
>> Paul Boyd wrote:
>>> On 10/05/2007 17:47, N Cook said,
>>>> Without going to the extent of a pressure meter - is there some
>>>> technique that is a bit better than squashing sidewalls of tyres to
>>>> tell whether soft or firm.
>>>
>>> Assuming you're talking about a road tyre, then press your thumb
>>> into the tread, not the side. If you can press it in, it's too
>>> soft.
>>
>> Trouble is with a high pressure road tyre (eg. 23mm @ 120 psi), it
>> might still be too soft even if you can't press thumb into tread.
>> It's easier to squeeze the sidewalls, therefore easier to get some
>> idea of pressure. With a narrow road tyre this should be possible
>> but hard - painful, even.
>
> It's not clear whether the resistance your thumb encounters is more
> directly related to tyre pressure or casing tension.
>
> There was a discussion about this on r.b.t. a while back, with lots of
> varying views and even some experiments. My conclusion from that was
> that the thumb test probably _is_ a measure more of casing tension
> rather than of pressure.
>
> This means that a fat tyre will feel harder at a lower pressure (the
> casing tension is proportional both to the pressure and to the tyre
> minor diameter).

I agree the "hardness" we're feeling is really the casing tension.
Certainly a narrower tyre will feel softer than a wider tyre with the same
air pressure in it. No discussion is needed for that, that's obvious to
anyone who's inflated different size tyres using a gauge then felt with
thumbs.

When talking about testing with thumbs, I call it simply "pressure" because
that's quicker to write and easier to understand.

> So on that basis, you can ignore the pressure rating
> and the diameter, and just pump up any tyre until it feels hard and it
> should be about right.

Yes, except that with high performance fast road tyres (which coincidentally
tend to be narrow), you want them harder than tyres you would/could normally
use on a utility bike for the sake of lower rolling resistance. I don't
just mean higher pressure, I mean higher pressure in proportion to the size
as well. That's why I make a point about it being harder to dig your thumbs
into them.

~PB
 
squeaker said the following on 11/05/2007 09:25:
> To quote Schwalbe (at
> http://www.schwalbe.de/gbl/en/tech_...ache=2&ID_Seite=136&tn_mainPoint=TechnikInfos)
> "Use a pressure gauge to monitor inflation pressure. The widespread
> thumb-test method is very inaccurate as all tires will feel
> identically hard from a pressure of 2 bar up."
> For on-road use, a Topeak Road Morph (with gauge) or Cyclaire will
> both do 110psi.

The OP did actually say "Without going to the extent of a pressure
meter". There is a clear difference between being able to press your
thumb in (tyre soft) and not being able to press it in (tyre hard). It
may not be hard enough, but if you can't press your thumb in at all then
it's harder than soft and will be fine for general riding about.

--
Paul Boyd
http://www.paul-boyd.co.uk/
 
"N Cook" <[email protected]> wrote in message
news:[email protected]...
> Without going to the extent of a pressure meter - is there some technique
> that is a bit better than squashing sidewalls of tyres to tell whether
> soft
> or firm.
>
>

On Schwalbe tyres with the blue puncture proof band in they specifically say
to use a pressure gauge as you cannot get a proper "feel" by pressing the
tread. They go on to say that you should not test pressures by pressing the
sidewalls as this does not give you a proper idea of pressure.

Based on that the only other way I can think of is to get on the bike with
and luggage you may be going to carry and check that the tyre does not look
too under inflated. On the road after a repair or replacement it is
generally unlikely that you will put too much pressure in by hand anyway.

Dave
 
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