SIKO Case Study: 2.5x Faster Load Times and 7x Better Layout Stability

SIKO is one of the largest bathroom and kitchen retailers in Central Europe, with a vast e-shop in the Czech Republic, Slovakia, and Hungary.

Website speed is crucial for SIKO, but the new JavaScript-based frontend showed significant issues with Core Web Vitals user experience metrics.

After launching the new website in February 2024, loading speed (LCP) and layout stability (CLS) on mobile devices worsened.

After the website redesign, we collaborated with SIKO's e-commerce team to optimize the new site's performance.

How did we accelerate SIKO's website?

During the optimization process, we followed these steps:

  • The SIKO team involved all key partners, including us, in a regular performance tuning process.
  • We identified optimization opportunities, assigned them to developers, and maintained communication with them.
  • We implemented speed monitoring enhanced by SpeedCurve RUM.
  • We reported the status to the client and shared our expertise.

Selected adjustments successfully implemented through cross-team collaboration include:

  • Partial transition from client-side rendering (CSR) to server-side rendering (SSR).
  • Improved infrastructure setup (caching static resources, using WebP images, implementing Cloudflare, and more).
  • Elimination of duplicate rendering of the main image on the product detail page.
  • Layout optimizations for the header, filtering, and gallery on the product detail page.
  • Ongoing optimization of unwanted layout shifts (CLS).
  • Optimization of the main website navigation rendering.
  • Change in lazy loading implementation.
  • Adjustments to image settings in the CMS.
  • Modifications to loaders and skeletons.

The graph shows the difference in loading speed between the server-rendered page (SSR) and the original client-side version (CSR):

With SSR, the page can render significantly faster—without waiting for JavaScript processing in the browser.

As a bonus, at the start of our collaboration, we fixed the Google Analytics measurement, which ironically failed due to excessive speed optimization.

Impact of Collaboration

Over the year of collaboration, we significantly improved key loading speed (LCP) and layout stability (CLS) thanks to the involvement of all parties.

This would not have been possible without the excellent collaboration with the SIKO team, who were clear about their priorities and business goals.

Martin Lipový says about our collaboration:

Rather than seeing PageSpeed.cz as external consultants, we view them as experienced colleagues in performance working within the same team focused on creating a functional and fast eCommerce website.

Martin Lipový, Head of Online and Product Development

We improved loading speed (LCP) by 62% year-over-year and layout stability (CLS) by 86%.

However, it’s not just about metrics; our collaboration also enhanced the overall user experience:

  • More than 2.5 times faster loading on mobile devices (LCP).
  • 7 times better layout stability (CLS).
  • 2-5% lower bounce rate across various language versions.
  • +17% increase in search visibility year-over-year (Source: Google Search Console Q1/2024 vs. Q1/2025)

Speed optimization is an ongoing process

After several months of intensive collaboration, we continue with further minor adjustments. We maintain regular contact, oversee speed for the client, and train the internal testing team as part of building a “speed culture.”

Through this collaboration with the SIKO team, we demonstrated that even architectures heavily reliant on client-side JavaScript can achieve significant speed improvements.

By speeding up the website and improving Core Web Vitals, SIKO also gained a more stable foundation for marketing campaigns and expansion into new markets. Further optimizations await us as a standard part of development.

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