if you read your civic hybrid's manual in the section about tire pressure, it recommends that you increase cold pressure to 35 psi when driving over 100 miles per hour. in other words, 35 psi in the tires is acceptable by the manufacturer.

i've pumped my civic hybrid's tires up to 40 psi before but found the ride to be too harsh and bumpy. where i live in california, the weather can also be quite unpredictable, sunny and hot one day and cold and rainy the next. for simplicity's sake, i run my tires at 35 psi. it's a good tradeoff between slightly increased mileage and tire wear, handling, and braking.