TEST: Tire Temps and Pressures for the Street
05-26-2009, 12:23 PM
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TEST: Tire Temps and Pressures for the Street
To determine correct tire pressures to even out tire wear across the tread, I made some freeway runs and measured tire temperatures. I also hoped to justify increasing front tire pressure to reduce understeer. (I believe manufacturer's recommended pressures are largely determined by legal staff who are more concerned with inducing "safer" understeer than with tire wear or crisp handling.)
The data from three 80mph runs is below. Just as on my SLK, the high inside temps indicate a lot of negative caster. Based on these tests, I will be running 36psi on the front and 34 psi on the rear. (Also see me separate post: "CLS On Track, Round 1" for initial track testing and impressions.)
RUN 1 (pressures set to Mfr Max Load values. No way I'd run 27 on all 4.)
Freeway Speed 80mph
Air Temp: 84 F, Cold Pressures: Front 29psi, Rear 30psi
Left Front - 29psi - Right Front
Outside Center Inside | Inside Center Outside
116 --- 111 --- 119 --|-- 118 --- 112 --- 114
----------------------------------------------------------------------
Left Rear - 30psi - Right Rear
Outside Center Inside | Inside Center Outside
111 --- 109 --- 119 --|-- 119 -- 108 -- 106
Highest temp on inside, low in center: raise pressures
=================================================
RUN 2
Increase Front by 3psi, Rear by 2psi
Left Front - 32psi - Right Front
Outside Center Inside | Inside Center Outside
116 --- 115 --- 122 --|-- 128 --- 120 --- 116
----------------------------------------------------------------------
Left Rear - 32psi - Right Rear
Outside Center Inside | Inside Center Outside
112 --- 112 --- 120 --|-- 123 --- 110 --- 114
Better, but stil high on inside: try raising pressures more
=================================================
RUN 3
Increase Front by 4psi, Rear by 2psi
Left Front - 36psi - Right Front
Outside Center Inside | Inside Center Outside
117 --- 117 --- 120 --|-- 123 --- 122 --- 119
----------------------------------------------------------------------
Left Rear - 34psi - Right Rear
Outside Center Inside | Inside Center Outside
115 --- 115 --- 120 --|-- 123 --- 116 --- 113
Looks good -- pretty even temps across the tread. I'll go with that for a while and take some more wear and temperature measurements. If I'm carrying a heavy load, I'll increase the rear pressures by 1-2 psi.
The data from three 80mph runs is below. Just as on my SLK, the high inside temps indicate a lot of negative caster. Based on these tests, I will be running 36psi on the front and 34 psi on the rear. (Also see me separate post: "CLS On Track, Round 1" for initial track testing and impressions.)
RUN 1 (pressures set to Mfr Max Load values. No way I'd run 27 on all 4.)
Freeway Speed 80mph
Air Temp: 84 F, Cold Pressures: Front 29psi, Rear 30psi
Left Front - 29psi - Right Front
Outside Center Inside | Inside Center Outside
116 --- 111 --- 119 --|-- 118 --- 112 --- 114
----------------------------------------------------------------------
Left Rear - 30psi - Right Rear
Outside Center Inside | Inside Center Outside
111 --- 109 --- 119 --|-- 119 -- 108 -- 106
Highest temp on inside, low in center: raise pressures
=================================================
RUN 2
Increase Front by 3psi, Rear by 2psi
Left Front - 32psi - Right Front
Outside Center Inside | Inside Center Outside
116 --- 115 --- 122 --|-- 128 --- 120 --- 116
----------------------------------------------------------------------
Left Rear - 32psi - Right Rear
Outside Center Inside | Inside Center Outside
112 --- 112 --- 120 --|-- 123 --- 110 --- 114
Better, but stil high on inside: try raising pressures more
=================================================
RUN 3
Increase Front by 4psi, Rear by 2psi
Left Front - 36psi - Right Front
Outside Center Inside | Inside Center Outside
117 --- 117 --- 120 --|-- 123 --- 122 --- 119
----------------------------------------------------------------------
Left Rear - 34psi - Right Rear
Outside Center Inside | Inside Center Outside
115 --- 115 --- 120 --|-- 123 --- 116 --- 113
Looks good -- pretty even temps across the tread. I'll go with that for a while and take some more wear and temperature measurements. If I'm carrying a heavy load, I'll increase the rear pressures by 1-2 psi.
