Page load times will always be a hot topic of debate and its one of the many clashes between IT professionals and Digital people around how tag manager (TMS) slows down the website. Many studies have shown there is a positive correlation between page load times and it’s impact on key metrics such as conversion rate leading into revenue and the bottom line.
In summer 2020 I completed a test to understand the impact of Google Tag Manager and load times for an SME in E-commerce.
Testing Requirements
To establish a balanced testing approach:
- https://webpagetest.org was used to complete the testing
- Testing was done on Mobile v Desktop
- Testing was done on 3G fast v 3G slow
- Testing was done on Doc complete v fully loaded
- Completed 6 different tests over 6 weeks
- Test was done everyday at 12pm
The 6 different tests would be:
- No tracking codes
- Hardcoded deployed tags in the <head>
- Empty Google Tag Manager (GTM)
- Tags via GTM (on gtm.js)
- Tags via GTM (on gtm.dom)
- Tags via GTM (on gtm.load)
Tags deployed for testing:
- Google Analytics pageview
- Google Analytics e-commerce
- Facebook pageview
- Facebook e-commerce
*There so are many variables and factors that impact page load times, these results need to be taken lightly but could be used as a guideline.
Testing Results
No Tracking Code
7 second difference between 3G fast v 3G slow.
Hardcoded deployed tags in the <head>
12 to 15 seconds difference between the 3G fast v 3G slow
Empty Google Tag Manager (GTM)
7 second difference between 3G fast v 3G slow.
Tags via GTM (on gtm.js)
12 to 15 seconds difference between the 3G fast v 3G slow
Tags via GTM (on gtm.dom)
12 to 15 seconds difference between the 3G fast v 3G slow
Tags via GTM (on gtm.load)
12 to 15 seconds difference between the 3G fast v 3G slow
Results
The key insights from the test:
- Significant impact on load times with no tracking tag deployed
- The impact of an empty GTM v no tracking tags is very similar
- The load times of hard-coded tags v GTM is very similar
- Significant difference in load times between 3G Fast v 3G Slow across mobile and desktop
- Mobile load times lagging behind Desktop (test was done in summer 2020)
The Solution
Tag Manager is a core component of the martech ecosystem but there could be an argument for not implementing any tags at all and going taggles. Server side tag manager could be the answer as the tags will be loading directly into the server not directly into the users browser and help improve load times.
