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Location: Removing a snake out of the neighbor's washing machine
3,095 posts, read 2,040,022 times
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Quote:
Originally Posted by Quietude
Extra-high pressures are a PITA - hard ride, light to squirrelly steering, extra centerline wear on the tire's critical main rib.
Here's a technique I was taught by an experienced race and performance designer: proportional pressure.
Take the tire's maximum cold pressure and USTA load rating.
Measure the load on each tire of the vehicle (for road use, just a front and back figure is enough).
Figure the proportion of actual load to maximum load.
Adjust the pressure to the same proportion.
So, if a tire has a 44psi max and is rated at 1500 pounds max, and the actual loading is 1150, the pressure to start with is (1150 / 1500) * 44... or 33.7psi.
In most cases this pressure should be close to the manufacturer recommendation, but a few pounds change and differential pressure front to rear can produce amazing results.
Of course, use extreme caution if a large difference (more than 3-4 psi) or a wide variance from manufacturer recommendations results from the calculation. OTOH, I have a high-performance car that runs 22psi front and about 14 psi rear... because it's very light and has huge tires.
1. "hard ride, light to squirrelly steering, extra centerline wear..": Some folks here seem to not care about those things, or they don't bother them.
2. "Proportional Pressure": I drive a 2015 Hyundai. Do you think the sticker on its door pillar will will include total max load, let alon individual axle weights? I don't think so! But I like and agree with the concept.
I don't get excessive centreline wear at 45 PSI. I've gone through to sets of tires at that and, if anything, I'm still getting a little extra at the edges.
2. "Proportional Pressure": I drive a 2015 Hyundai. Do you think the sticker on its door pillar will will include total max load, let alon individual axle weights? I don't think so! But I like and agree with the concept.
Downside of the technique: you need a weight pad to determine wheel loading.
Location: Removing a snake out of the neighbor's washing machine
3,095 posts, read 2,040,022 times
Reputation: 2305
Quote:
Originally Posted by Quietude
Extra-high pressures are a PITA - hard ride, light to squirrelly steering, extra centerline wear on the tire's critical main rib.
Here's a technique I was taught by an experienced race and performance designer: proportional pressure.
Take the tire's maximum cold pressure and USTA load rating.
Measure the load on each tire of the vehicle (for road use, just a front and back figure is enough).
Figure the proportion of actual load to maximum load.
Adjust the pressure to the same proportion.
So, if a tire has a 44psi max and is rated at 1500 pounds max, and the actual loading is 1150, the pressure to start with is (1150 / 1500) * 44... or 33.7psi.
In most cases this pressure should be close to the manufacturer recommendation, but a few pounds change and differential pressure front to rear can produce amazing results.
Of course, use extreme caution if a large difference (more than 3-4 psi) or a wide variance from manufacturer recommendations results from the calculation. OTOH, I have a high-performance car that runs 22psi front and about 14 psi rear... because it's very light and has huge tires.
Thanks a lot for the above calculations Quietude! And I did locate the GAWR weight figures, on a separate sticker nearby.
For my 2015 Hyundai:
Door pillar sticker(psi): F33, R33. Calculated: F35, R32.5
For a 2004 Toyota:
Door pillar sticker(psi): F30, R30. Calculated: F32, R29
I always did suspect that front-wheel drive econos like above would have a forward weight bias. Interesting how what the vehicle mfgs of these cars recommended ended up in between the calculated front and rear cold tire pressures.
For BMWs and many Subarus, the B-pillar stickers indicate the opposite, IE: F29psi, R34, or something to that effect. The Subarus tend to bump up the front psi to 31-33 for constant heavier loads, as indicated on their door stickers.
Summary:
I will run the pressures I calculated for a week and see what we think. Our commute times to and from work are both under 30 minutes, mostly highway and some local roads, varying amounts of traffic.
Last edited by TheGrandK-Man; 05-06-2019 at 06:06 AM..
Location: Removing a snake out of the neighbor's washing machine
3,095 posts, read 2,040,022 times
Reputation: 2305
Quote:
Originally Posted by EckyX
I don't get excessive centreline wear at 45 PSI. I've gone through to sets of tires at that and, if anything, I'm still getting a little extra at the edges.
Do you carry a full/excess load in your vehicle at least half the time you're driving?
Location: Removing a snake out of the neighbor's washing machine
3,095 posts, read 2,040,022 times
Reputation: 2305
Quote:
Originally Posted by Steve Bagu
Decades ago drove Cads.
Door jam sticker called for 24lbs...nice ride but wore the tread down.
Changed to 32 lbs and tires lasted longer.
Those days always would replace in pairs, new up front. Could always feel road grip even with pwr steering.
24psi. Sounds typical for the bias-ply tire era!
Because of their construction, bias-plys, compared to radials, had stiffer sidewalls relative to their tread.
Why do you think cars, especially larger domestic models, were so softly sprung back then, along with such cushy seats that you'd sink right to the floor in? Combined with the less advanced suspensions of 50+ years ago, bias ply tires tended to give a rougher ride. Softer seats plus gentle suspension tuning, along with higher profile tires, even 80-85-series, helped smooth things out, at the price of less than nimble handling or emergency responsiveness. Hence the recommended cold pressures back then in the low to mid-20s psi.
Do you carry a full/excess load in your vehicle at least half the time you're driving?
I don't. The rear end only weighs maybe 5-600lbs and, though I do tow occasionally and sometimes put 500lbs of wood or gravel in the back, it's more often empty.
I would think though that with steel belted radials, over-pressure would cause the sidewalls to bulge and make the center of the tread bend inward.
UPDATE: Filled up my tires once since starting this thread. Filled up each tire until the car's computer detected the appropriate level beeped. PSI has varied between 31 to 36. Varies depending on weather (it was winter, now we're into approaching) and how much I drive (usually 20 minutes, but every now and then over 2 hours).
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