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Tire pressure/recommended psi and rider's weight

post #1 of 12
Thread Starter 
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
post #2 of 12

Re: Tire pressure/recommended psi and rider's weight

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.
post #3 of 12

Re: Tire pressure/recommended psi and rider's weight

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.
post #4 of 12

Re: Tire pressure/recommended psi and rider's weight

"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
post #5 of 12

Re: Tire pressure/recommended psi and rider's weight

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.
post #6 of 12

Re: Tire pressure/recommended psi and rider's weight

mkrueger40@aol.com 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.
post #7 of 12
Thread Starter 

Re: Tire pressure/recommended psi and rider's weight

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
>
>
post #8 of 12

Re: Tire pressure/recommended psi and rider's weight

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..
post #9 of 12

Re: Tire pressure/recommended psi and rider's weight

carlfogel@comcast.net wrote:

> Tom Compton's calculator predicts less than 13 seconds per
> hour if we reduce a premimum-quality clincher from 120 to
> 100 psi--0.36%.
>
> If his prediction is off by an order of magnitude, that
> would be about two minutes and ten seconds per hour--3.6%.


As I said the problem is an effect different from rolling resistance
that varies with tire pressure in the opposite sense. If you think
about it you will realize that this effect has a very large potential
for variation, much greater than that typical for rolling resistance.


> What do you predict? (You cut most of the figures from the
> calculator without providing any of your own.)


The problem is undefined and therefore there is no prediction to be
made. Predict what? I've never met him and I don't know where he rides.
Besides, why shouldn't he just find out for himself?


> Where would such an effect not be obscured by the effects of
> wind, rider, posture, temperature, barometric pressure, and
> traffic, which vary considerably between 25-mile rides in
> England?


That is the reason for multiple attempts, if he is sensible under
reasonably similar conditions, perhaps over a much shorter circuit. If
in fact the rider cannot discern any difference in this way for his
typical riding, then he has the information he needs and should feel
free to make the pressure whatever he finds most comfortable or
entertaining. e
post #10 of 12

Re: Tire pressure/recommended psi and rider's weight

On 9 Jul 2005 23:56:38 -0700, "41" <KingGeorgeXLI@yahoo.fr>
wrote:

>
>
>carlfogel@comcast.net wrote:
>
>> Tom Compton's calculator predicts less than 13 seconds per
>> hour if we reduce a premimum-quality clincher from 120 to
>> 100 psi--0.36%.
>>
>> If his prediction is off by an order of magnitude, that
>> would be about two minutes and ten seconds per hour--3.6%.

>
>As I said the problem is an effect different from rolling resistance
>that varies with tire pressure in the opposite sense. If you think
>about it you will realize that this effect has a very large potential
>for variation, much greater than that typical for rolling resistance.
>
>
>> What do you predict? (You cut most of the figures from the
>> calculator without providing any of your own.)

>
>The problem is undefined and therefore there is no prediction to be
>made. Predict what? I've never met him and I don't know where he rides.
>Besides, why shouldn't he just find out for himself?
>
>
>> Where would such an effect not be obscured by the effects of
>> wind, rider, posture, temperature, barometric pressure, and
>> traffic, which vary considerably between 25-mile rides in
>> England?

>
>That is the reason for multiple attempts, if he is sensible under
>reasonably similar conditions, perhaps over a much shorter circuit. If
>in fact the rider cannot discern any difference in this way for his
>typical riding, then he has the information he needs and should feel
>free to make the pressure whatever he finds most comfortable or
>entertaining. e


Dear 41,

I suppose that I should have predicted your answer.

Cheers,

Carl Fogel
post #11 of 12

Re: Tire pressure/recommended psi and rider's weight

"41" wrote:
> For fun & revelation, why not time yourself, over several attempts,
> over a fixed course at say 100, 110, and 120psi.

<snip>
> You might be very surprised at which produces the fastest ride average.


Another experiment might be to ride a century at each of those tire
pressures. The comfort factor might turn out to be more significant than any
slight differences in rolling resistance.

Art Harris
post #12 of 12

Re: Tire pressure/recommended psi and rider's weight

Joss

How did you manage to get some Avocets imported?! I haven't had a reply
(so far) from either Avocet or Harris Cycles about getting them sent to
the UK.

I would happily act as a distributor as I'm sure many others would!

cccrider
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