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Guidare sotto pressione
Una lettera dell'istruttore della polizia americana
#1
Driving Under Pressure

Proper Tire Pressure Could Save Your Life

Posted: Wednesday, December 21, 2005

SGT. DAVE STORTON
EVOC Contributor

Officer.com

How many officers check the tire pressure on their patrol car on a regular basis? We all seem to be great at checking that the lights and siren work, because the time to find out they don't work is not when you get a Code 3 call. Likewise, the time to find out your tire pressure is too low is not when you are in a pursuit and trying to take a corner at high speed.

What is proper pressure?

The proper tire pressure for the Police Crown Victoria is 44 psi. If you look on the sidewall of the tire, you will see that it lists 44 psi max pressure. Regardless of what vehicle you have, use the maximum pressure listed on the sidewall. Higher pressure results in better performance, decreased tire wear, and it lessens your chance of hydroplaning at a given speed. This number on the sidewall lists the maximum amount of pressure you should ever put in the tire under normal driving conditions. Pursuits and Code 3 responses are not normal driving conditions. Many agencies maintain tire pressure at 35 psi since this is what is listed in the owner's manual and on the door placard. The reason the owner's manual lists 35 psi is because we get the same manual as the civilian version of the Crown Victoria. The police version, however, is fully loaded with communications equipment, a cage, and your gear. You are not looking for a soft and cushy ride, you want performance.

Myths about pressure

Let's put to rest some common misconceptions. The tires will not balloon out creating a peak in the center portion of the tread when tire pressure is above 35 psi. There is a steel belt that prevents this from happening. Also, you are not overstressing the tire with higher pressure, and the tire will not be forced off the rim with higher pressure. The picture above is Bobby Ore of Bobby Ore Motorsports driving a Ford Ranger on two wheels. The tires on the left side have 100 psi in them, and they happen to be tires and rims from a 1999 Crown Victoria! This is a dramatic example of how pressure holds the tire in shape, and how much stress a tire can handle.

Performance

If you were able to watch a tire as it travels across the ground at high speed, you would see that it deflects to one side during cornering. The faster you are going through a corner, the more tire deflection you get. As the tire deflects over onto the sidewall, you get less traction and more of a tendency to understeer or oversteer. This could spell disaster when negotiating a corner at high speed during a pursuit or a Code 3 run. Higher pressure keeps the tire from deflecting onto the sidewall as much, which keeps more of the treaded portion on the road.

A good demonstration for EVOC instructors is to have students drive a high-speed course in a vehicle with 32 to 35 psi. Then have them run the same course with 44 to 50 psi in the tires. The student will experience a marked difference in performance. Having officers experience this difference in vehicle performance is much more effective than just telling them to check their tire pressure.

Hydroplaning

When a tire rolls across a road covered with water, the tire tread channels water away so the rubber remains in contact with the road. The factors that affect hydroplaning are speed, and water depth. Conventional wisdom says that vehicles will hydroplane in as little as 1/16th of an inch of water. Not so coincidentally, legal tread depth is 1/16th of an inch.

Tire manufactures and the Association of Law Enforcement Emergency Response Trainers International (ALERT) have shown that tires have more of a tendency to hydroplane when pressure is low. This happens because the tire footprint (the portion of the tire actually in contact with the road) is larger. For those of you who water ski, think of which is easier to get up on: a fat ski or a skinny ski. More tire surface in contact with the water makes it easier to hydroplane, just as it is easier to water ski on a fat ski. Also, a soft tire can be pushed in more by the pressure of the water on the center portion of the tread. This results in less rubber in contact with the road.

Tire wear

Much better tire wear results from maintaining proper pressure. Tires with lower pressure will wear off the outside of the tread faster from the deflection of the tire during cornering, and the tires will heat up more from increased road friction. This is one of the factors that caused the failure of a certain brand of tires on Ford Explorers some years ago. In 1999 the San Jose Police Department realized a significant cost savings by increasing the pressure in the training fleet to 50 psi. They soon followed up by increasing the pressure in the patrol fleet to 44 psi. For liability reasons, most agencies are reluctant to exceed the maximum pressure listed on the tire for actual patrol vehicles, but they reap the cost saving when going to 50 psi on training vehicles.

Next time you inspect your vehicle, make sure you check your tire pressure since your ability to performance drive is significantly affected by it. You are not driving to the store to get a loaf of bread! You may be called upon to chase a dangerous criminal or respond to assist another officer in trouble. You don't wonder whether or not your gun is loaded before you hit the street; don't wonder whether your tire pressure is correct once the pursuit starts. Check your tires routinely, just as you do with all other critical equipment.
--
Sgt. Dave Storton is the Director of the San Jose Police Academy, and he holds a Master's Degree in Adult Education. He is the lead instructor for the Emergency Vehicle Operations Course (EVOC) at the San Jose Police Academy, and is a lead instructor for the local regional academy. He teaches EVOC instructor courses, advanced EVOC instructor courses, off road EVOC, counter-terrorist / dignitary protection driving, and motion picture stunt driving. Dave has trained over 3,500 drivers.
Yes AKA The Tramp, fiero d'aver creato il Hybrid Synergy Forum con Lily in Agosto 2007 Yes
ChinoisPer chi volesse partecipare ai costi con un contributo, questa è la pagina da seguire. Chinois
SmartassNon fornisco assistenza tramite Messaggi in Privato. Aprite una discussione e vi sarà risposto.Smartass
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#2
Che dite, c'è necessità di una traduzione?
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#3
In estrema sintesi l'articolo suggerisce agli agenti di polizia negli Usa, di mantenere una pressione piu' elevata di quella indicata nel libretto. Arrivando fino alla pressione max indicata sul lato del pneumatico.
Cio' garantisce maggiore tenuta di strada/durata pneumatico/sicurezza(riducendo anche aquaplaning per la minore impronta a terra)

Bisogna dare la "tara" all'articolo (hanno auto MOLTO diverse dalle nostre e la Polizia non guida solo "normalmente"), in ogni caso io ho , dall'inizio, 3 bar (pneumatici 225/45 17")

PS Sicuramente il confort (inteso come capacita' di assorbire buchi/colpi) si riduce leggermente, poichè alla pressione superiore a quella indicata dalla Casa, il pneumatico viene parzialmente meno alla sua funzione nel sistema ammortizzante complessivo
PPS Il 90% dei pneumatici sono SOTTO gonfiati NonoNonoNono
Questo è il vero problema !
1happydream, Auris Hybrid Active+ 2013 GAS/E85 , da 3 a 5 Euro/100Km, Olio Toyota 0W-20 100% synth, Disolfuro di Tungsteno WS2, DRL Bicolor, Trattamento Nanotech, Android Torque, Chrome Pack, Pneumatici Ricostruiti All Season
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#4
Ma in tutto questo, avete letto sul fianco dei Dunlop 225 che pressione max è riportata?
Ovviamente non parlo dei consigli del manuale Uso&Manutenzione che riporta solo i consigli Toyota...
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#5
L'ho sempre sostenuto anch'io che gli pneumatici andrebbero gonfiati molto di più dei valori riportati sui libretti......io li tengo sempre poco sotto i 3 bar, me ne frego se sulle indecenti strada piene di squarci e buche che abbiamo in Umbria sento di più le asperità, la maneggevolezza (sicurezza) ed i bassi consumi con pneumatici ben gonfi è impagabile!
Nulla si crea, nulla si distrugge, tutto si trasforma......
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#6
C-è da dire una cosa: il sovvragonfiaggio protegge il cerchio dalle buche (nonché pizzicamento della spalla quando si prende una buca, che crea il famoso bulbo sporgente e addio gomma.

Yes AKA The Tramp, fiero d'aver creato il Hybrid Synergy Forum con Lily in Agosto 2007 Yes
ChinoisPer chi volesse partecipare ai costi con un contributo, questa è la pagina da seguire. Chinois
SmartassNon fornisco assistenza tramite Messaggi in Privato. Aprite una discussione e vi sarà risposto.Smartass
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#7
anche io le tengo a 3 bar anche se adesso in attesa delle gomme invernali e con la diminuzione delle temperature le ho portate a 2.6

ciao
Auris Hybrid 2013 Lounge
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#8
Questa discussione della pressione dei pneumatici è interessante.
Io sono sempre stato convinto che fosse necessario utilizzare la pressione 'ufficiale' specificata dal costruttore del veicolo, soprattutto anche per un discorso di consumo battistrada e tenuta di strada.
Ma a quanto pare è meglio tenere una pressione maggiore, soprattutto visto che le ultime due 'forature' gravi si sono verificate proprio a causa di copertoni 'lacerati' sulla spalla dopo 'lievi' contatti con bordi di buche Sneaky2
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#9
concordo in pieno che il vero problema sono le gomme sgonfie,
in questo caso, dato che la spalla si flette molto di piu, si ha
-minor controllo del mezzo (portandola al limite si sbanda molto piu facilmente)
-surriscaldamento della gomma che in autostrada può portare alle scoppio
-possibilità di fuoriuscita dal cerchione
-prendendo spigoli tipo marciapiedi, maggior facilità ti pizzicare/squarciare il fianco (come riportato da Tramp)

ecco qui di seguito la traduzione della lettera fatta con google translator,
per non occupare troppo spazio la riporto come ot

LupoEtrusco, proud to be a member of Hybrid Synergy Forum since Oct 2012.
Spritmonitor.de
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#10
D'accordo anch'io sto sopra la pressione ufficiale ma così non stressiamo di più i cuscinetti ruota?
blackivory, ibrido dal 24 settembre 2012.
Raduno Ibrido Roma Centro Italia - http://www.hybrid-synergy.eu/showthread.php?tid=43989
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