Optimal Tire Pressure
in [Toyota Prius]
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From: News on 24 Dec 2007 15:18 Elmo P. Shagnasty wrote: > In article <1i9mhp6.vsbn1vhsswrzN%bwilson4use(a)hotmail.com>, > bwilson4use(a)hotmail.com (Bob & Holly Wilson) wrote: > > >>The studies I've followed, "Transportation Research Board Special Report >>286, Tires and Passenger Vehicle Fuel Economy" indicates the more a tire >>is inflated, the lower the hysterisys losses and deformation during >>driving. This leads to crisper steering and handling. > > > No, it doesn't. > > That's ridiculous. > > So if I inflate my tires to 100psi, by your take I should have the > handling and steering of an F1 car? > It certainly would. After inflating to 100psi, you'd have the handling and steering of any car with exploded tires.
From: Marc Gerges on 24 Dec 2007 15:55 Bob & Holly Wilson <bwilson4use(a)hotmail.com> wrote: >> >> Mine came from the dealer with huge overpressure, and I let it off >> gradually till it became driveable in my eyes. I think I even save gas >> driving it that way, because cornering speeds are higher, so I don't >> have to brake as much ;-) > > The studies I've followed, "Transportation Research Board Special Report > 286, Tires and Passenger Vehicle Fuel Economy" indicates the more a tire > is inflated, the lower the hysterisys losses and deformation during > driving. This leads to crisper steering and handling. Within limits that's correct. More pressure results in stiffer sidewalls, giving crisper handling. I've found the 'sweet spot' on mine (standard Michelin tires) at around 2.6-2.8 bar. OTOH, my real world driving has many less than perfect road surfaces, and especially smaller ripples are no fun with this tire pressure. Light braking may even activate the anti lock system, and cornering makes the car wander to the outside. By lowering pressure to around 2.4 that tendency is completely gone, the car feels considerably safer at comparable speeds. I have around 2.2 at the rear tires, because it make the car somewhat less front heavy. This is with light load, usually only driver or driver plus one passenger. If your driving is mostly smooth roads and highways, higher pressure may work. cu .\\arc
From: Mr. G on 24 Dec 2007 16:52 I've found that running at 42/40 psi (front/rear) gives me the best trade-off between ride, handling and MPG. Using the factory pressure of 35/33 causes a significant drop in fuel economy, without (IMHO) an offsetting increase in drivability. Whatever pressure you decide to use, you should have the front pressure slightly higher than the rear due to the weight distribution. In article <lvi545-pas.ln1(a)pascal.gerges.lu>, marc.gerges(a)gmail.com says... > > Within limits that's correct. More pressure results in stiffer > sidewalls, giving crisper handling. I've found the 'sweet spot' on mine > (standard Michelin tires) at around 2.6-2.8 bar. > > OTOH, my real world driving has many less than perfect road surfaces, > and especially smaller ripples are no fun with this tire pressure. Light > braking may even activate the anti lock system, and cornering makes the > car wander to the outside. By lowering pressure to around 2.4 that > tendency is completely gone, the car feels considerably safer at > comparable speeds. I have around 2.2 at the rear tires, because it make > the car somewhat less front heavy. This is with light load, usually only > driver or driver plus one passenger. Isn't 2.4/2.2 just at (or a little below) the factory recommendation?
From: Bob & Holly Wilson on 24 Dec 2007 20:43 Marc Gerges <marc.gerges(a)gmail.com> wrote: > Bob & Holly Wilson <bwilson4use(a)hotmail.com> wrote: > >> > >> Mine came from the dealer with huge overpressure, and I let it off > >> gradually till it became driveable in my eyes. I think I even save gas > >> driving it that way, because cornering speeds are higher, so I don't > >> have to brake as much ;-) > > > > The studies I've followed, "Transportation Research Board Special Report > > 286, Tires and Passenger Vehicle Fuel Economy" indicates the more a tire > > is inflated, the lower the hysterisys losses and deformation during > > driving. This leads to crisper steering and handling. > > Within limits that's correct. More pressure results in stiffer > sidewalls, giving crisper handling. I've found the 'sweet spot' on mine > (standard Michelin tires) at around 2.6-2.8 bar. > > OTOH, my real world driving has many less than perfect road surfaces, > and especially smaller ripples are no fun with this tire pressure. Light > braking may even activate the anti lock system, and cornering makes the > car wander to the outside. By lowering pressure to around 2.4 that > tendency is completely gone, the car feels considerably safer at > comparable speeds. I have around 2.2 at the rear tires, because it make > the car somewhat less front heavy. This is with light load, usually only > driver or driver plus one passenger. > > If your driving is mostly smooth roads and highways, higher pressure may > work. Thanks to Google books, I picked up the following graphs from: Gyenes, L. and Mitchell, C.G.B., "The Effect of Vehicle-Road Interaction on Fuel Consumption," Vehicle-Road Interaction, ASTM STP 1225, B.T. Kulakawski, Ed., American Society for Testing and Materials, Philadelphia, 1994, pp. 225-239. http://hiwaay.net/~bzwilson/prius/pri_tire_010.jpg Tire inflation lookup table: kN/m**2 - psi 200 - 29 225 - 33 250 - 36 275 - 40 300 - 44 325 - 47 350 - 51 375 - 53 http://hiwaay.net/~bzwilson/prius/pri_tire_020.jpg Speed lookup table: km/h - miles per hour 80 - 50 90 - 56 100 - 62 110 - 68 120 - 75 Tire rolling resistance is not a linear function with speed and inflation pressure and these charts give a clue about tire drag. For those who prefer a softer ride, go for it. For me, local speeds and roads are such that maximum sidewall pressure up front and -2 psi in the rear works quite nicely. Bob Wilson
From: Bob & Holly Wilson on 25 Dec 2007 02:10
Elmo P. Shagnasty <elmop(a)nastydesigns.com> wrote: > You know, Mythbusters showed that . . . Exploding truck tires, can be a hazard; breathing air from a tire underwater doesn't work; and driving in reverse on ice is ineffective tire traction improver. However, Gyenes and Mitchell have shown: > http://hiwaay.net/~bzwilson/prius/pri_tire_010.jpg > Tire inflation lookup table: > kN/m**2 - psi > 200 - 29 > 225 - 33 > 250 - 36 > 275 - 40 > 300 - 44 > 325 - 47 > 350 - 51 > 375 - 53 > > http://hiwaay.net/~bzwilson/prius/pri_tire_020.jpg > Speed lookup table: > km/h - miles per hour > 80 - 50 > 90 - 56 > 100 - 62 > 110 - 68 > 120 - 75 Bob Wilson |