From this article Seattle spends:

• Bonds: $14,748,947 (50.20 percent)
• Bridging the Gap Property Tax: $9,693,410 (33 percent)
• Bridging the Gap Commercial Parking Tax: $4,801,062 (16.34 percent)
• Gas Tax: $129,981 (.44 percent)
• Grants: $4,325 (.01 percent)
• All of SDOT's non-arterial paving work was 100 percent funded by the gas tax, but non-arterial work only accounts for .9 percent of total paving expenditures for 2009.

Gas tax and Commercial Parking Tax are 100% car based.

So based only on that, sure, cars only pay 16.47%...

...except that it's only for arterial roads and doesn't take into consideration the vehicle taxes NOT used for road work.

Per the same article, Gas Tax and Commercial Parking Tax total $18,201,062. The total for Seattle roads is $29,638,725. So drivers pay for 61.4% - far more than the 25%-33% you claim.

Second, people don't take into consideration the costs of making a perfectly good vehicle road bike friendly (e.g. Evergreen Parkway....), clearing the lanes of debris so that bicyclists don't ride in traffic, and the fact that a majority of bicyclists rent, so don't actually pay the property tax bringing up the remainder.

Every single Google result (the first two pages are nothing but pro-bike sites) I saw plays fast and loose with the numbers to make it look like taking bikes into consideration is free.

There is a cost. And it's time bicyclist start paying it.

In the mean time, fucking stop at stop signs/stop lights and realize that you're not considered a pedestrian when you are on your bike in a crosswalk.