Testing my Internet speed.

I'm getting 300mbps from Time warner when I connect my PC directly to the modem/router.

When i connect my wireless router to the modem from the cable company, and then my PC to the router, using speedtest, (i'd appreciate a better alternative if available) it drops down to 35 mbps. Does that seem normal considering there are 5 phones, 3 tablets, and a PS4 connected to wifi?

Thanks in advance for your assistance.