Evan Schuman's StorefrontBacktalk

Ironically, what’s slowing down some of the big-chain sites may not be problems that retail IT shops can easily fix. Inadequate bandwidth and not-fast-enough servers might be part of the problem. But a clear reason some sites can’t finish loading quickly is that they are calling out to third parties—such as Web metrics and tracking services—that drag down site load times but are outside the control of retailers.

That’s not in Pingdom’s study, but a little digging with Pingdom’s own tools makes it apparent. For example, slowest big-retailer site NeimanMarcus.com is actually 10 percent smaller than top-ranked Forever21.com. But almost all the HTTP requests for Forever 21 actually go to the retailer’s site, while one-quarter of Neiman Marcus’s HTTP requests go to outside sites—including one that, in a test run we made using Pingdom’s tool, took more than a second and a half to deliver a few hundred bytes.

That’s what kills Neiman Marcus’ response time. Or rather, it’s what slows the site’s speed down so it loads in under four seconds instead of under three seconds. That’s still fast—probably fast enough that customers don’t care. The must-load-in-three-seconds-or-customers-will-leave rule is also highly overrated—it’s based on studies of mainframe users from decades ago—but three seconds remains the target for most E-Commerce sites.

And that three-second target is probably the biggest challenge any E-Commerce team faces in trying to improve site performance. It’s pretty clear that if a relatively fat site can load in less than a second, the idea that sites have to be slim to be quick is dead. The fattest site in Pingdom’s survey (that’s Ticketmaster’s site, at 2.5MB) loaded in 2.33 seconds—well under that three-second target. Clearly, all that effort to speed up sites really has paid off.

Of course, once a site loads in less than three seconds, performance is obviously fine—which serves as an invitation to designers to add more complicated graphics, to CRM specialists to add more tracking tools and to anyone else connected with the site to fill up the bandwidth. If there’s any time to spare, they’ll fill it.

That’s not a bad thing in itself—CRM data is useful, and if fancy graphics make products look more appealing on a high-definition display, so much the better. But customer tracking and other functions will always end up soaking up more performance than is actually available. That means the site has to keep getting faster, and any headroom will attract even more speed-devouring ideas.

From here on in, keeping your site fast is going to require a lot more fine tuning—and you’ll get a lot less help from rules of thumb. The simple ways of speeding up sites have pretty much been used up.