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Author Topic: Tire Pressure recommendations  (Read 14451 times)
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Ron Gibson
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« Reply #30 on: June 09, 2015, 10:16:35 AM »

While you have the front end apart for springs, I would (if you haven't already) check bump steer and scrub radius. Both of those can cause handling problems.


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« Reply #31 on: June 09, 2015, 10:49:14 AM »

I'm with Ron on this. Check your bump steer-- toe-in should not change much as the nose of the car dips down from braking or aero forces.

Regards, Neil  Tucson, AZ

Regards, Neil  Tucson, AZ
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« Reply #32 on: June 10, 2015, 08:47:01 AM »

I'm with Ron on this. Check your bump steer-- toe-in should not change much as the nose of the car dips down from braking or aero forces.

Regards, Neil  Tucson, AZ

If the front suspension "toes out" in bump travel, it will make the car "twichy" (at least) under braking.    Large amounts of "toe out" change can make the car "wander" or "hunt" unpredictably/uncontrollably.

Try to limit the toe change to less than .03" per wheel through the dynamic ride height range you are using.     If you have "large" changes in toe dimensions, revise the suspension geometry to minimize the changes.    Carroll Smith's book "Tune to Win" (although road racing centric) has a great practical chapter on toe/geometry and how to measure and alter toe characteristics.   The book is available on Amazon, etc.

I used to be a people person.  But people changed that relationship.

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"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."     Albert Einstein
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« Reply #33 on: July 17, 2015, 12:29:04 PM »

Here is more information that may be useful when choosing tire pressure and tire type to achieve a balance among speed, safety, and cost.

One reason to increase tire pressure is to reduce rolling resistance, which along with aero drag and peak engine power pretty much determine maximum top speed.  Rolling resistance can be as important as aero drag (details are on the Design Topics page on my website).  Higher tire inflation pressure reduces rolling resistance by reducing tire flexure (which dissipates power) where the rubber meets the road.  A caveat is that increased tire pressure reduces the contact (footprint) area, which reduces available traction for steering, acceleration, and braking.

Actually achieving the maximum possible top speed also depends on several other factors.

Re Goodyear Frontrunner tires, see the 2015 list at URL 
Goodyear makes “Eagle Land Speed” tires rated for 300 mph (with load and inflation pressure specifications) and “Frontrunner” tires that are used on dragsters and list no speed rating.  Goodyear and SCTA have authorized the new D2904 Frontrunner for LSR use up to 300 mph at 90 psi and less than 1200 lbs radial load.  It is my understanding that the other Frontrunner tires (at least the 17”) are restricted by SCTA to use only at considerably lower speeds and lighter loading because the tire construction may not reliably stand up under sustained high LSR speeds.
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