Browsing clearnet at the same time won't hide your Tor use, because the ISP can easily read the packet headers and discover which streams are going to entry guards. You would need to use bridges (that the ISP doesn't know belong to the Tor network) to hide your Tor use. You can use obfsproxy bridges, which make the connections look like something other than Tor. The obfs3 protocol makes it look like random data. On a related note, the Chaos Computer Club published an attack a few years ago where they could fingerprint encrypted Tor connections to specific web sites with something like 55% accuracy by watching the user's end of the connection, but it was trivially defeated by browsing with two tabs open. The Tor Project is against padding because they believe it will slow down the network even more, and that's a major complaint about Tor. They accept many usability over security trade offs, because a large, diverse userbase increases your anonymity.