Tire pressure/recommended psi and rider's weight

I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in
rider + bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I
was riding 120psi 23mm until recently.

Thanks for a straight answer.

Joss

Joss Winn wrote:
I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in
rider + bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I
was riding 120psi 23mm until recently.

Thanks for a straight answer.

The rating on the sidewall is a guide determined by the lawyers and
marketing department. It's unlikely that the tyre will blow off the rim
at even 50% above that. However, 110psi sounds about right if they are
genuinely 25mm wide. I'm 20lb lighter than you and I use 120psi rear,
100psi front in 20mm tyres.

"Recommended" pressures are pretty flexible. They're subject to a lot
of factors, not the least of which is how you feel riding on them.
Weight definitely enters into it, too.

Sheldon Brown discusses it better than I could ever hope to:

http://sheldonbrown.com/tires.html

Look about 2/3 of the way down the page for the pressure discussion.

Joss Winn wrote:
I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in
rider + bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I
was riding 120psi 23mm until recently.

Thanks for a straight answer.

Jos

Don't worry-go ahead and use the inflation pressure that gives you the
best comfort and performance (within reason, of course). My 700x24mm
Veloflex tubulars are rated at 6-7 bar. That is only 90-103 psi,
however, I generally run the rear tire at 120 psi with no problems.

"Joss Winn" wrote:
I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in rider
+ bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I was
riding 120psi 23mm until recently.

If these are the newer (black sidewall) Avocets that measure a true 25mm,
then at your weight (I weigh the same) I'd run 100-110 psi. No way 120 psi.

See:
http://www.precisiontandems.com/phot.../tirechart.jpg

Art Harris

Joss Winn wrote:
I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in
rider + bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I
was riding 120psi 23mm until recently.

Thanks for a straight answer.

Joss

Run about 105 psi as during heating, they will rise in psi. This psi is
to prevent them blowing off the rim. Do not exceed. If they feel soft,
get a higher psi rated tire, like a conti tire.

wrote:
Jos

Don't worry-go ahead and use the inflation pressure that gives you the
best comfort and performance (within reason, of course). My 700x24mm
Veloflex tubulars are rated at 6-7 bar. That is only 90-103 psi,
however, I generally run the rear tire at 120 psi with no problems.

On a tubular, no surprise there as it won't blow off. Recommending
higher than rated PSI particularly the gent that said even 50% higher
is no big deal(150psi on a 110 rated tire) is DUMMMM.

Get a higher rated psi, synthetic tire that's rated to 140 psi, then
run about 120, if the Avocats feel 'soft'. Arbitrarily adding lots of
air above the rated is not smart. Blow a tire off a front, during a
fast descent, while cornering, and you'll see why.

Thanks for everyone's advice. I'm running them at 110psi and will try
to get used to the softer feel. They are generally more comfortable
than my old 120psi 23mm tyres but I kind of miss the sound of rock hard
tyres rolling on the road and the feel of smooth tarmac underneath the
tyre. These new tyres dampen this experience.

It's the first time I've ridden 25mm and the first time with Avocet
tyres. I had to import them to the UK as they don't distribute them
here. I'm very impressed with the wire bead, non-kevlar type I bought.
They look like no nonsense tyres having made no concession to
marketing. (i.e black, smooth, bold, informative graphics and a really
'rubbery' feel).

Joss



Arthur Harris wrote:
"Joss Winn" wrote:

I've searched the archives but can't find a straight answer...

I ride Avocet 25mm road tyres. Recommended 110psi.

I weigh 195lbs. I ride a fixed gear road bike that weights less than
20lbs. I commute with a carradice saddle bag.

Does the 'recommended' tyre pressure change with the differences in rider
+ bike weight?

I find that with 110psi, the tires feel too soft sometimes, but then I was
riding 120psi 23mm until recently.


If these are the newer (black sidewall) Avocets that measure a true 25mm,
then at your weight (I weigh the same) I'd run 100-110 psi. No way 120 psi.

See:
http://www.precisiontandems.com/phot.../tirechart.jpg

Art Harris

Joss Winn wrote:
Thanks for everyone's advice. I'm running them at 110psi and will try
to get used to the softer feel. They are generally more comfortable
than my old 120psi 23mm tyres but I kind of miss the sound of rock hard
tyres rolling on the road and the feel of smooth tarmac underneath the
tyre. These new tyres dampen this experience.

For fun & revelation, why not time yourself, over several attempts,
over a fixed course at say 100, 110, and 120psi. I would say a minimum
of three times at each psi, unless the differences are dramatic. If you
do it all on the same day (i.e. short course) then you have to pay
attention to getting an alternating ordering to check fatigue effects:
e.g. first try 100 110 120, second 120 100 110 third 110 120 100, with
adequate rest intervals between each rep. This does not cover all
possible permutations but it is good enough. (Some would randomize the
order but that is unsuitable.) You might be very surprised at which
produces the fastest ride average. Of course, the results might very
well permute according to the road surfaces, so you might try more than
one course. Do report back with any results, if you try it..

41 wrote:
Joss Winn wrote:
Thanks for everyone's advice. I'm running them at 110psi and will try
to get used to the softer feel. They are generally more comfortable
than my old 120psi 23mm tyres but I kind of miss the sound of rock hard
tyres rolling on the road and the feel of smooth tarmac underneath the
tyre. These new tyres dampen this experience.

For fun & revelation, why not time yourself, over several attempts,
over a fixed course at say 100, 110, and 120psi. I would say a minimum
of three times at each psi, unless the differences are dramatic. If you
do it all on the same day (i.e. short course) then you have to pay
attention to getting an alternating ordering to check fatigue effects:
e.g. first try 100 110 120, second 120 100 110 third 110 120 100, with
adequate rest intervals between each rep. This does not cover all
possible permutations but it is good enough. (Some would randomize the
order but that is unsuitable.) You might be very surprised at which
produces the fastest ride average. Of course, the results might very
well permute according to the road surfaces, so you might try more than
one course. Do report back with any results, if you try it..

Dear 41,

Unfortunately, it's unlikely that a series of real-world test-runs will
show any speed difference between 100, 110, and 120 psi inflation on
high quality tires.

This calculator uses Jobst's rolling resistance data to predict exactly
that kind of effect:

http://www.analyticcycling.com/ForcesTires_Page.html

Below are the predicted changes for a 40.0 km ride, using two speeds
with the default values and a premium clincher.

5000 3600
seconds @ seconds @
tire 8.00 m/s 11.11 m/s
inflation 28.8 k/h 40.00 k/h
in psi 17.90 mph 24.85 mph

change change
in seconds in seconds
140 -14 -7.0
130 -8 4.0
120 0 0.0 \
110 +11 +5.5 12.5 seconds/3600, 0.35%
100 +26 +12.5 /

The range of difference in a 1-hour 40 km ride at about 25 mph is less
than thirteen seconds for inflations from 120 to 100 psi.

A headwind of 0.2 to 0.3 km/h will slow the 40 km/h rider 9 to 18
seconds over the same 40 km ride.

This shows how easily we end up wondering about physical effects too
small to demonstrate by just timing a few test runs. Very few riders
would expect to finish within a few seconds of the same time on two
25-mile rides on the same bike, but we still keep hoping to distinguish
such small equipment differences with a test run or two.

This kind of tiny change is why drum spin-down tests are necessary to
provide rolling-resistance data and why our impromptu roll-outs are so
unreliable.

Carl Fogel