Trailer engineering FAQ
What does a trailer engineer do?
A trailer engineer works out how loads travel through a trailer and onto the road: where the axles should go, what each axle group carries, whether the frame and connections are strong enough, and whether the finished rig meets axle-weight laws. The result is usually a layout, a calculation package, a letter or a drawing.
What is the federal bridge formula?
It is the federal rule that limits the weight on any group of two or more consecutive axles: W = 500 × (LN/(N−1) + 12N + 36), where L is the distance in feet between the outer axles of the group and N is the number of axles. Interstate limits are also 20,000 lb per single axle, 34,000 lb per tandem and 80,000 lb gross. States can add their own rules.
Is the Bridge Law Calculator an engineering review?
No. The Bridge Law Calculator gives estimates for planning. It is not an engineering review, the quick check does not check state rules, and it does not replace an engineered layout or a scale ticket.
What information do you need for a quote?
Trailer and truck drawings or spec sheets, axle spacings and ratings, empty weights (scale tickets are best), payload weight and position, the states you run in, and what the engineering is for. Photos help for modifications.
Can you review drawings someone else made?
Yes. Existing drawings can be reviewed and checked, with mark-ups and written findings. The scope is agreed up front.
Do you work with trailer manufacturers?
Yes. Manufacturers, upfitters, fleets and owner-operators all use weight distribution layouts and design reviews. Send the model details and what you need documented.
What is the Bridge Law Calculator?
The Bridge Law Calculator is axle weight layout software for trailer companies. It works as a federal bridge formula calculator and adds state bridge law checks, doubles, lift axles, a truck and trailer library and printable weight sheets. The free calculator covers straight trucks up to 3 axles and tractor-trailers up to 5 axles on the federal bridge formula; state rules, doubles, triples and truck + pup are in the full version. The quick check on this site is a trimmed, federal-only version. Company accounts with private and shared design libraries are coming soon.
What do I get?
Deliverables are engineering calculations, layouts, drawings and written findings prepared by Dustin Randle.
Need an engineered layout? Request a quote.
Send your trailer details, drawings or scale tickets. You will get a scope and a quote before any work starts.
Request a quote