It’s a common question so we wanted to really explore the issue – look at the facts, talk to carseat engineers who know more than we do and set the record straight once and for all.
First, a little background info – when carseats are crash tested in a lab the tension on the belt webbing has to measure between 53.5 N (newtons) and 67 N. That tension is measured by a load cell device placed on the webbing. This is done to maintain repeatability between tests. The tension range was chosen because it represents the average tightness achieved by parents in the field.
In the real world no one expects parents and caregivers to measure the tension on the seatbelt or lower LATCH belt webbing that is securing their carseat. CPS Technicians are taught that a carseat is properly installed if it moves less than 1” from side-to-side and front-to-back when you check for tightness at the beltpath.
But is it possible to install your carseat too tightly? To the point of it being a detriment instead of a benefit?
Survey says…. No! (with a few exceptions)
In most cases, there is no such thing as too tight – only too loose. If you’re just using typical human strength and maybe a few installation tricks like getting behind a rear-facing carseat or using the reclining seatback trick, you do not have to worry about getting the seatbelt or LATCH strap too tight. Carseats and seatbelts are not delicate objects that are going to be compromised by a really tight installation.
We know that the tighter you can couple the carseat to the vehicle, the better. This is why rigid LATCH/ISOFIX attachments are so beneficial. On the flip side – the difference between a carseat installed rock-solid (with seatbelt or flexible LATCH attachments) and a carseat installed acceptably with just a little bit of movement at the beltpath, in a crash, is negligible. Don’t convince yourself that a rock-solid install is going to keep that seat tight during a moderate to severe crash – but it’s certainly better than starting out in a crash with a loose installation!
However, there could be cases where too tight is possible. If you’re using a mechanical tightening system that is part of the carseat (or something like a Mighty Tite device) and going overboard with it or applying brute strength to a force-multiplying system like Chicco’s SuperCinch system on the NextFit, you could actually damage the seatbelt, the retractor or the carseat. In cases where you do have a mechanical device or a force-multiplying system you really need to take it easy and carefully follow the directions in the manual.
With typical carseats, if you can use a few tricks or installation techniques and achieve a really solid installation, that’s great. But if you’re fighting with the install and the best you can achieve is just a little bit of side-to-side or front-to-back movement and it’s not more than 1″ of movement, that’s perfectly okay too. It’s not always possible to get a rock-solid install but if you can – there is certainly nothing wrong or bad about that. For the record, in my vehicle with stiff leather seats, I almost always need to put a knee in a forward-facing carseat to get an acceptable install. Occasionally I need to put a knee in the seat AND use the reclining seatback trick. These are easy things for me to do quickly and it sure beats wrestling with an install for 20 minutes.
To clarify, I don’t always need to put my knee in a forward-facing carseat – but when I do, I certainly don’t feel like I’m doing something wrong.
Ultimately, you always want to read and follow the carseat manufacturer’s recommendations. There are situations where getting the seatbelt too tight will prevent you from closing a lockoff (or a Britax ClickTight compartment) or perhaps a lockoff will pop open because there is too much tension on the belt. There are also situations where a LATCH belt with hook connectors is so tight that you can’t get enough slack in the belt to loosen it when you have to take it out. (Tip: if this happens on a vehicle seat that reclines – recline the seat back and that should introduce enough slack to allow you to loosen the LATCH belt). Obviously, in these cases you have a compelling circumstance and you may need to lighten up a little on your regular installation technique.
Bottom line: Unless there is some compelling reason not to, get the carseat as tight as you can with *reasonable* effort but don’t feel guilty if you can’t get it rock-solid. On the flip side, it’s not bad or wrong if you can get that sucker installed like it’s part of the car with reasonable effort.