451 Towbar Fitting

Many thanks to Alan from Smart-Tow.com for donating this towbar to the site, it is generous offers such as this that
keep this site up and running. Before you start, ensure you have the following to allow fitting of this tow bar.

Drill with a 5.5mm drill bit (5mm will work),
6x M8 bolts 1 inch long (ideally plated so they don’t rust),
8x M8 washers (again with rustproof plating),
13mm spanner and socket,
Torx 30 screwdriver.

If you look below you will see what is being removed and what is being added. On the top is the original crash bar and below that is the new Smart-Tow.com replacement tow bar.

Firstly you need to remove the rear panels, seen here and remove the old crash bar, seen here. With the old crash bar off, turn it upside down and remove the Torx30 screws from the valence holders. These need to be fitted to the new tow bar.

With the plastic valence holders off you need to cut the tab off each one (circled) This takes a few seconds with a hacksaw or a Dremmel type rotary tool.

Offer the valence holder up to the new tow bar, make sure the hole is dead centre and as far back from the mounting plate as possible. Mark the hole with a felt tip pen and remove the valence holder. Repeat with the other holder on the other end of the towbar.

Using a 5.5mm drill bit, drill the holes. A 5mm drill and a bit of wiggling works too.

Reusing the Torx30 screws you removed earlier, screw the valence holders to the tow bar. The screws start out stiff as they cut a new thread but then become easy.

Put the tow bar in place and fit 2 bolts each side to the 2 outer edge bolt holes.

The outer edge bolts can be seen circled to the right of this picture. The final hole (circled on the left of the picture) is open so use one of your M8 bolts, add a washer, push it through, apply another washer and fit the M8 nut on the rear.

The picture below shows the final bolt in place with the washer each side and nut tightened.

Ensure that all 6 bolts are tightened fully before removing the valance and refitting the rear panels.

Now you need to cut a hole into the valence for the tow bar to appear from. The middle 2 valence tabs are 10 inches apart so mark the 5 inch mark on the valence with a pencil. This gives you your centre point. Measure out from the centre point 66mm each way and mark the valance. Measure straight down from the top edge of the valence 52mm and 67mm to give the top and bottom points of the hole.

Join these points with a rectangle, this is the plastic you need to remove.

Dill a hole in each corner and use a junior hacksaw or use a Dremmel. Cut the hole and tidy it up with a knife or a file.

Slide the valence over the towbar tongue, slide all of the valence tabs into the rear panel and clip the valence back in place.

The main part of the towbar is now fitted. You now need to add the finishing hardware available from a trailer shop or eBay. You will need a 50mm tow ball, M16 nuts and bolts and a tow bar wiring kit with a 2M wiring loom. I bought these off of eBay for less than £20.

Bolt the wiring loom plate between the tow bar tongue and the tow ball and tighten both M16 nuts. This size nut and bolt will take a lot of stress so don’t worry about over tightening.

With the hardware fitted, all that is left is the wiring which can be found here.

Towing Specifications

Maximum weight on the towball – 45KG
Maximum net towing weight – 450KG

If weight exceeds 45KG on the towball you can just shift the load in the trailer to be more even.
Maximum towing weight includes the weight of the trailer.

Towing Legality

It must be mentioned that this particular tow bar is for “offroad use only”. The smart 450, 451 and 452 Roadster weren’t homologated to tow anything so can’t legally tow.

Check your owner’s document. Technical permissible maximum towable mass of the trailer will either show zero or the field will be left empty. Both of with indicate that it has no legal towing capacity.

You can still legally use the tow bar for tow bar mounted bicycle racks etc. You just can’t tow anything.