Here's a post from the BMW 1 series forum I belong to. He had an interesting angle from Uhaul's towing limit for the 135i.
I freely admit I understand near nothing about towing. I don't endorse or reject this view, it's merely one that I thought it was one worth sharing with y'all.
"The issue with a tow rating for our BMW cars is that BMW doesn't give them a tow rating. It would be best to stay within both the rating of the car and the hitch. But no rating for our cars.
Another source of some guidance is to look at what U-Haul
will rent us. It seems to be based upon the hitch. With a 2000 lb hitch, they will rent you a trailer that will carry 2000-the weight
of the trailer. They care about liability so this is a data point.
When you are towing, you have to worry about starting and stopping. My 128i has more hp and torque than my primary tow vehicle. So it should be able to pull things better. But it has smaller tires
, it weighs less, and it's drivetrain is probably not as sturdy. It's brakes
are great for a car but will they stop a heavy trailer?
If you do not exceed the Gross vehicle rating I am sure you would be OK - trade the trailer for a full load of people and luggage. But that won't be much of a trailer. If you want to tow more than that, you might need to think about brakes
on the trailer. If you did that, you should be OK - but it's up to you.
It is clearly safer to get a vehicle rated to tow. Like a X3 or X5. If I had to, I would tow a little utility trailer with my 128i but I would keep the weight
low, more like 1,000 than 2,000. I wouldn't tow a camping trailer at highway speeds. I think I could get it up to speed but you also have to handle it in the wind and stop it. Maybe a pop-up."