The verdict in three sentences
A 4.8 s mobile LCP puts a manufacturer's site almost twice above Google's 'good' threshold of 2.5 s, and each lost second costs on average 5 to 15% of conversions according to industry studies. In 2026, a performance audit costs roughly EUR 1,500 to 4,000 and fixes EUR 4,000 to 15,000 depending on technical debt. On a technical catalogue with PDF datasheets, the fastest wins come from images, fonts and deferred PDF loading, long before a full rebuild.
Core Web Vitals thresholds and what degrades them on an industrial site
Google assesses three metrics on real visitor data (CrUX report, 75th percentile). A technical parts site usually stacks the same issues: uncompressed product images, heavy JavaScript configurators, 5 to 20 MB PDF datasheets linked at the top of the page and multiple tracking tools.
| Metric | 'Good' threshold | 'Poor' threshold | Common cause on a manufacturer site |
|---|---|---|---|
| LCP (largest element rendered) | Under 2.5 s | Over 4 s | 1 to 3 MB product photo, slow server, blocking font |
| INP (interaction responsiveness) | Under 200 ms | Over 500 ms | JavaScript catalogue filters, configurator, chat |
| CLS (visual stability) | Under 0.1 | Over 0.25 | Cookie banner, images without dimensions |
| TTFB (server time, indicative) | Under 0.8 s | Over 1.8 s | Shared hosting, no caching |
| Mobile page weight | Under 1.5 MB | Over 4 MB | Carousels, autoplay videos |
| Third-party scripts | Fewer than 5 | More than 12 | Marketing tags, maps, widgets |
What optimisation costs, line by line
The audit lists the fixes and their expected gain. The fix budget depends mostly on the CMS and on whether the theme can be changed without breaking everything.
| Item | Typical LCP gain | Indicative 2026 cost | Timeline |
|---|---|---|---|
| Performance audit (CrUX, Lighthouse, traces) | Diagnosis | EUR 1,500 to 4,000 | 1 to 2 weeks |
| AVIF/WebP images, responsive sizes | 0.8 to 1.8 s | EUR 1,000 to 3,000 | 1 week |
| Self-hosted fonts, preloading | 0.2 to 0.6 s | EUR 400 to 1,000 | 2 to 3 days |
| CDN and server cache | 0.3 to 1.0 s | EUR 800 to 2,500 + EUR 20 to 200/month | 1 week |
| PDFs: thumbnail + on-demand loading | 0.3 to 0.9 s | EUR 800 to 2,000 | 1 week |
| JavaScript reduction (INP) | INP from 450 to 180 ms | EUR 2,000 to 6,000 | 2 to 4 weeks |
| Third-party script clean-up | 0.2 to 0.7 s | EUR 500 to 1,500 | 3 to 5 days |
A complete project therefore lands between EUR 4,000 and 15,000 in fixes, plus the audit. Beyond EUR 15,000, compare with a rebuild on a modern architecture where performance is built in.
Handling PDF datasheets without sacrificing them
Industrial buyers download datasheets, so removing them is not an option. Three measures are enough in most cases. First, show the key specifications in HTML on the product page (dimensions, materials, standards), which also helps SEO. Second, compress the PDFs: a 12 MB sheet often drops to 1.5 to 3 MB with no visible loss. Third, never load an embedded PDF preview above the fold, only a link or a thumbnail.
Mini case study
Illustrative scenario: Claire, marketing manager at a machined parts manufacturer near Lyon, measures a 4.8 s mobile LCP and a 420 ms INP. The site gets 9,000 visits a month and generates 45 quote requests, a 0.5% rate. Budget committed: EUR 2,500 audit and EUR 7,500 of fixes, delivered in 6 weeks.
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After the fixes, LCP drops to 2.1 s, a 2.7 s gain. Using the cautious assumption of 5% more conversions per second, the rate rises to about 0.57%, or 51 requests a month, 6 more. With a 15% close rate and an average margin of EUR 3,000 per order, the gain reaches EUR 2,700 a month. The EUR 10,000 invested pays back in under 4 months.
FAQ
Do Core Web Vitals really affect rankings?
They are part of Google's page experience signals, with modest weight compared with content relevance. Their clearest effect is on conversion: 5 to 15% gain per second according to industry studies.
Why is my Lighthouse score good while Search Console flags a problem?
Lighthouse measures a simulation, Search Console real visitors over 28 days. A lab score of 90 can hide a real-world LCP of 3.5 s on your customers' phones.
How long before Search Console shows the improvement?
Field data is aggregated over a rolling 28 days. Allow 4 to 6 weeks after the fixes go live for URLs to move to 'good'.
Do we need a rebuild to get under 2.5 s?
Rarely: 70 to 80% of cases are solved with images, caching, fonts and third-party scripts. A rebuild is justified if fixes exceed EUR 15,000 or the CMS blocks optimisation.
What should we monitor after the fixes?
Monthly tracking of the three metrics and page weight, with an alert if LCP goes back above 2.5 s. Each new marketing tag can cost 100 to 300 ms.
Let's scope your project. Send us your site URL and priority product pages, and we will price the audit, the fixes and the expected gain, with an indicative budget and delivery date. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
