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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > 2012-2019 BMW 3 and 4-Series Forums > General F30 Sedan / F32 Coupe / F36 Gran Coupe Forum > Fitment of towbar to BMW F31 Touring with 20inch 405m alloys
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      04-15-2019, 09:40 AM   #1
platty78
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Fitment of towbar to BMW F31 Touring with 20inch 405m alloys

Has anybody managed to fit a towbar to a BMW F31 touring which is fitted with 405M 20inch alloys. I getting mixed messages as to whether its possible or not.
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      04-15-2019, 01:32 PM   #2
Michael340i
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I've just fitted a towbar to a F31 with 19" alloys, can't imagine why the size of the wheels would make any difference to anything.

When you go to 20s you'd choose a lower profile tyre, so the gearing of the car would stay the same, if you didn't then your speedo and odometer would read incorrectly.

No part of the towbar goes anywhere near the wheels, and the nose weight can be up to 90kg, which is only about the weight of a slightly overweight person, so you're not putting undue pressure on the wheels and tyres.

Plenty of SUVs run 20" wheels successfully, so that can't be the issue.

Really can't think why 20s would be a problem at all, what are the concerns you've heard about them?
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      04-15-2019, 03:41 PM   #3
EBS0712
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Quote:
Originally Posted by Michael340i View Post
I've just fitted a towbar to a F31 with 19" alloys, can't imagine why the size of the wheels would make any difference to anything.

When you go to 20s you'd choose a lower profile tyre, so the gearing of the car would stay the same, if you didn't then your speedo and odometer would read incorrectly.

No part of the towbar goes anywhere near the wheels, and the nose weight can be up to 90kg, which is only about the weight of a slightly overweight person, so you're not putting undue pressure on the wheels and tyres.

Plenty of SUVs run 20" wheels successfully, so that can't be the issue.

Really can't think why 20s would be a problem at all, what are the concerns you've heard about them?
Which brand tow bar did you install?
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      04-16-2019, 03:33 AM   #4
platty78
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So I took the car to BMW stealer as i fancied the electric folding factory bar fitting etc. I was told that they cant fit the towbar on a car that's got 20inch alloys on the car. Something to do with load on the suspension etc.

So its a case of wheels or towbar apparently.

I'm about to have the car put on Eibach springs also. So i think that just fried the Stealers mind even more.

This is the car
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      04-16-2019, 04:39 AM   #5
Michael340i
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Quote:
Originally Posted by EBS0712 View Post
Which brand tow bar did you install?
I installed a Westfalia, they make the towbars for BMW and Audi. If you buy a towbar from BMW, it will be a Westfalia. Fitting was brilliant, everything went into place perfectly. I went for a removable bar, and it plugs in behind the diffuser, no cutting needed. When you don't need it, the bar drops out, the electric plug folds up, so you'd never know there was a towbar mount there.

The only difficulty was the exhaust which on the F31 340i goes over the top of the muffler and connects to the diffuser, so I had to get the optional heatshield bracket and attach the shield to that. That would be a problem for any towbar fitting to that model, the heatshield blocks off the place where the towbar brackets go.

If you can get a Westfalia electrical kit too, that would be better than the one I got which was a mess of sticky pads and wire connectors.
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      04-16-2019, 05:02 AM   #6
Michael340i
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Quote:
Originally Posted by platty78 View Post
So I took the car to BMW stealer as i fancied the electric folding factory bar fitting etc. I was told that they cant fit the towbar on a car that's got 20inch alloys on the car. Something to do with load on the suspension etc.

So its a case of wheels or towbar apparently.
Beautiful looking car.

You can get an electric towbar retrofit kit, Part Number: 71606883983-71602289549, I saw one on ebay recently from Germany for 900 ($1200?).

I read the instructions for the kit, and was disappointed to see that the button to extend and retract the towbar is in the trunk, so you walk round to the back of the car, open the trunk, reach in and press the button, and hold it in until the bar is fully in place. Can understand that its a safety issue, but it really killed the cool factor for me. So for less than half the price I'll reach under the car and push the removable westfalia towbar into its slot and swivel down the electrics socket.

I don't think your BMW guy could have thought through the 20" wheels thing, there are two additional loads that hit the car when you have something on a towbar, there is the downward weight on the towbar itself, which can't exceed 90kg (200lbs). How much weight do you put in your trunk? how much weight do you put on the seats in your car? How much weight could you put on a roofbox? 90kg is nothing.

The other additional load from a towbar is pulling then stopping whatever you've attached to the towbar. The pulling load, at the maximum, is whatever power and torque your engine delivers. It won't become more powerful because you've hitched a trailer on the back. So your BMW guy thinks that the suspension can't handle the load from the engine? I think you need to check what wheels he put on there. Or is it the braking load? If you have an unbraked trailer, then your brakes will have to do all the stopping, again, they don't become more powerful because you've attached a trailer. So does your BMW guy think the brakes on your car are so powerful that they could break the wheels?

I think you need to check with the BMW guy to see what he knows about the car he sold you, sounds like he thinks he sold you a car that wasn't built right. More likely, he just doesn't think.
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      04-16-2019, 07:44 AM   #7
platty78
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Thanks

I'm considering just having it fitted anyway and ignoring the stealer. Ive done a fair bit of reading and what your saying seems to make sense to me.

No the question of do i try and retrofit the electric bar or go detachable.
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      04-16-2019, 09:23 AM   #8
Michael340i
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Quote:
Originally Posted by platty78 View Post
Thanks
No the question of do i try and retrofit the electric bar or go detachable.
I use the towbar to carry bikes on a 3-week Euro tour each year, then it doesn't get used until the following year, so automating that brief episode isn't too important to me, but if you're constantly wanting to fit things onto the towbar throughout the year, then electric would make more sense for you. The mechanical side of it seems very straightforward, its the wiring that will be the bigger challenge, but it its all original kit, then it will all just need plugging in to the right places
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      04-17-2019, 05:30 PM   #9
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UK owner here - F36 - the towbar isn't compatible with the "M Sport plus" options (because of the rear air diffuser thingy). I have a standard 440i wth M Sport options and the towbar is great.
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