From: Patrick Jankowiak (recycler@swbell.net)
Date: Sun May 02 2004 - 11:02:03 PDT
report: 900x20 vs 1100x20 on M35
900x20 and 1100x20 tires were put on the duals and clearances
were measured on an M35A2.
The 9.00x20 tires have about 1.75" clearance between the closest
surfaces at 50PSI.
The 1100x20 tires have about 1.25" clearance between the closest
surfaces at 55PSI.
From this it seems acceptable that the 1100x20 tires are a good
alternative choice for those wishing to slightly reduce the RPM
for the same highway speed.
Additionally, in my case (not sure about how other trucks run),
the engine has always pulled strong up to about 2100 RPM, then
gotten a bit flat, till 2650 RPM (max. allowed under load). At
2500-2650 RPM, the turbo seems to be doing its job best and the
truck seems to get a 'second wind' which can easily go beyond
2650RPM / 56MPH, but this was not explored.
With the 1100x20 tires, at 2500-2650RPM, I could feel this
'second wind' being put to use, loading the engine a bit more,
and giving me a few more MPH..
The 900x20 tires were about 40" tall.
The 1100x20 tires were about 43" tall.
This translates to the following data:
2650 RPM = 56MPH(900x20) -> 60MPH(1100x20)
56MPH = 2650RPM(900x20) -> 2465 RPM(1100x20)
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