Lexus 2008 IS250 Owner's Manual page 126

Maximum downshifting speed
n
Adhere to the downshifting speeds in the following table in order to prevent over-
revving the engine.
Shift position
1
2
3
4
2-1. Driving procedures
mph (km/h)
Maximum speed
33 (54)
56 (90)
83 (134)
108 (172)
2
127