Can one buy the spacers that go under the Britax chest clip, with the chest clip (and will it fit onto the Radian straps). My husband is FOREVER clipping it too low, and i think the spacer would be a wonderful reminder to get the chest clip up, well into the chest area.
No, you could not use those on a Radian carseat. To do so would compromise it's crash worthiness.
The reason for this, is that those rubber pads are HUGS and are proprietary to Britax. HUGS stands for "Harness Ultra Guard System" and it's designed to spread the forces more evenly along the child's shoulders and chest in a collision. HUGS changes how the harness sits on a child. In a high impact speed it may increase head excursion slightly. On a Britax seat, it's no problem - Britax tests the seats with both HUGS and the energy absorbing tether.
The Radian, OTOH, uses a system called the Safestop to reduce the loads on a child's neck when he/she is ff'ing. (The safestop is not used when a child is rear facing, and it has to be removed once a child is over 40lbs.)
You do not want to use part of another manufacturer's seat on the Radian. There's just no way to know how it would affect crash test performance. The HUGS aren't a chest clip positioner, they're part of the energy management of the carseat.
A Britax chest clip is different because Sunshine Kids originally tested the Radian with a Britax style clip, and Sunshine Kids has ok'ed the use of that style chest clip on the Radian. A chest clip is a pre-crash positioner. It's positioning the harness properly, and that's it's only job. It's much different than changing the harness geometry itself which is what adding HUGS would do to the Radian. (Though you still wouldn't want to switch a chest clip with a different brand without manufacturer approval. :thumbsup: )