Thread: 3500kg ADR towbar

Rathgar

I'm not sure how a type certification would work (or if it's possible).

As for the GCM - there is no GCM currently existing and so you (and the authorities and insurers) have two choices -

1. Use the military recommendation for a 1200kg towed weight (would probably still need trailer brakes on civvy street) + 3200kg GVM = 4400kg as the "existing" GCM and then to engineer a mod for each vehicle (perhaps becoming easier with precedence).

or 2. Using data for a similar vehicle as per either the NVD or Operators manual - all of which allow a towed weight of 3500kg or greater (up to 4000kg for a 110 Isuzu "cab chassis").

I have chosen number 1 because it is rigorous and wasn't much extra effort as I was also changing the seating capacity and needed a mod plate anyway.

And for the hair-splitters - you need to consider the tow-ball down weight when you calculate the towing vehicle load capacity so GCM is actually less than 3200 + trailer weight.

If the receiver tube were higher then it would need to have more rear-wards overhang as (AFAIK) only the 21126 TBM gives 3500kg with a short shank that wont foul the spare. A longer overhang is detrimental in terms of towing dynamics. This design was the best compromise for my situation.

Originally Posted by rfurzer

Rathgar

I'm not sure how a type certification would work (or if it's possible).

As for the GCM - there is no GCM currently existing and so you (and the authorities and insurers) have two choices -

1. Use the military recommendation for a 1200kg towed weight (would probably still need trailer brakes on civvy street) + 3200kg GVM = 4400kg as the "existing" GCM and then to engineer a mod for each vehicle (perhaps becoming easier with precedence).

or 2. Using data for a similar vehicle as per either the NVD or Operators manual - all of which allow a towed weight of 3500kg or greater (up to 4000kg for a 110 Isuzu "cab chassis").

I have chosen number 1 because it is rigorous and wasn't much extra effort as I was also changing the seating capacity and needed a mod plate anyway.

And for the hair-splitters - you need to consider the tow-ball down weight when you calculate the towing vehicle load capacity so GCM is actually less than 3200 + trailer weight.

If the receiver tube were higher then it would need to have more rear-wards overhang as (AFAIK) only the 21126 TBM gives 3500kg with a short shank that wont foul the spare. A longer overhang is detrimental in terms of towing dynamics. This design was the best compromise for my situation.

Fair Enough good work but i don't think you've "cracked the towing nut" for the wider population. Even if you make and sell an ADR approved 3500kg towbar the vehicle may be the limiting factor in towed load depending on your interpretation of the rules. Personally I think there are more than the 2 options that you put forward.

And I'm not sure I agree with your comments about deducting ball weight from the GCM but then it comes down to whether your talking a GCM of 6700 or a maximum towed load of 3500kg.

The nut is hard to crack without a civvy NVD, which isn't going to happen.

Having an ADR towbar that is designed to suit the unique rear chassis is (IMHO) a big step in the right direction. There is no overseas sourced solution. A self-made setup or a modification of a bar from another vehicle would be illegal. The setups that only use the pintle mount without side elements might not be strong enough.

Without a mod plate stating a max towed weight, you might have uncertainty if pulled over by a transport inspector, but I'd actually suspect that they'd be satisfied with the compliance plate on the bar, a OneTen drivers handbook and the closest NVD on their system (ie a 3.9 diesel 110).

The time in which you might need the rigour of a mod plate (and therefore the indemnity of an engineer) is if you had a prang while towing. Perhaps ask your insurer what they require?

Originally Posted by rfurzer

The nut is hard to crack without a civvy NVD, which isn't going to happen.

Having an ADR towbar that is designed to suit the unique rear chassis is (IMHO) a big step in the right direction. There is no overseas sourced solution. A self-made setup or a modification of a bar from another vehicle would be illegal. The setups that only use the pintle mount without side elements might not be strong enough.

Without a mod plate stating a max towed weight, you might have uncertainty if pulled over by a transport inspector, but I'd actually suspect that they'd be satisfied with the compliance plate on the bar, a OneTen drivers handbook and the closest NVD on their system (ie a 3.9 diesel 110).

The time in which you might need the rigour of a mod plate (and therefore the indemnity of an engineer) is if you had a prang while towing. Perhaps ask your insurer what they require?

Well said

I do find it amusing that there is a need to engineer a towbar when I can design, make and register a trailer (which I have dome) without the use of an engineer.

But I guess maybe as the manufacturer I take responsibility for what I have done. But it's most certainly a "legal" trailer.

Rulz iz rulz but. No need to make sense. We live in a land where you can't put a plug on an appliance. (I was given a scalectrix for xmas 1979 when we were in England and the plug came separate. I was 8.)

The prototype 3500kg bar. Subsequent ones will have a slightly different stiffener arrangement to allow the pintle to go back on.

Aaron (the certifying engineer) plans to join Aulro and will be keen to hear of any interest. The price point will be higher than an off-the-shelf bar for a mass produced vehicle.

Originally Posted by rfurzer

The prototype 3500kg bar. Subsequent ones will have a slightly different stiffener arrangement to allow the pintle to go back on.

Aaron (the certifying engineer) plans to join Aulro and will be keen to hear of any interest. The price point will be higher than an off-the-shelf bar for a mass produced vehicle.

Thats great work! Where are you located in Tassie?

Jc