Tires Pressure at Holy Cow Speeds

Thanks to Sheriff Buford T. Justice:

Dear SHO Folks,

The other thing I learned at the tire dealership was you are supposed to over inflate speed rated tires for high speed use.

The tire store had this data in a foot note for BFG EMS tires and it meets some European standard

MPH	Add PSI	% Load Cap
118	0	100%
124	1.5	100%
130	3	100%
136	4.5	100%
143	6	100%
149	7.5	100%
155	7.5	95%
161	7.5	90%
168	7.5	85%

I don't like surprises and so because I never saw the table before I called Yokohama motorsports.

The slight over inflation decreases footprint, decreases heat build up add helps keep the tire together. Doesn't that decrease tire grip to over inflate to decrease grip?

Yap.

Sample inflation calc with Plus 1 size tires/

Recommended OE inflation. 225/55 R16 ~ 1268 # at 30 psi (each) from tire load range table

~ Plus 1 size - not 245/45-17 due to narrow rim (only 7.5" wide)

use 235/45-17 look up 1268#

PSI	Load
32	1235
33	1249
34	1264
35	1278

If 1264 ~ 1268 then use 34 psi base pressure.

Then adjusting for max anticipated speed

MPH	Add PSI	% Load Cap	speed PSI	Load Cap at speed
118	0	100%	34	1264
124	1.5	100%	35.5	1264
130	3	100%	37	1264
136	4.5	100%	38.5	1264
143	6	100%	40	1264
149	7.5	100%	41.5	1264
155	7.5	95%	41.5	1201
161	7.5	90%	41.5	1137
168	7.5	85%	41.5	1074

So to drive 143 mph I should have had all 4 tires at 40 psi cold.

And one may choose not drive every day with their 45 series rim protectors overinflated to 40 psi. I typically ran them at 35-36 psi which would be safe for 124 mph for a half hour,

I also learned the speed ratings have a 10% safety margin so a 149 mph tire was tested for a half hour at 166 mph.

If I do see myself doing 1/2 hour at 130 mph again, I would stay with 35-37 psi depending how the center wears.

Disclaimer:

As always, YMMV and you and your "Higher Power" may be not on speaking terms with you so don't try this at home kidz. Cuz I assume no liability, zilch, nada, kaput.

If You die I'll feel real bad for a long time but will not enrichen your family financial prestige one brass tubbence.

Timothy Wright
`97 SHO

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