Very minor differences in 50mm towballs?

Or, simply manning up? ;)

I say this because you've got us all interested now, so really it's your duty to go out and investigate, regardless of the conditions.

Are you sure you haven’t forgotten the “pre-adjustment” that the carrier requires first time it’s applied to any towball? My carrier requires a bit of adjustment before it will clamp the ball tightly. Once adjusted, you generally don’t have to fiddle with the adjuster, just clamp it straight on.

Tim

I only have experience of 'simple' tow hitches*, which work fine with painted tow balls and 'like' a bit of grease on the tow ball.

However, I've read about more sophisticated hitches which require the tow balls to be stripped of paint and grease free. You use a bit of abrasive paper etc to remove the paint before use. These tend to be found on caravans to reduce 'sway'.

I wouldn't have thought the removal of the paint would reduce the diameter enough to make a difference to your problem - it is done to ensure the friction parts on the trailer/ caravan hitch have a clean surface to work on.

I suspect your problem my be poor quality / manufacturing tolerances.

• I tow a car on a trailer behind a motorhome.

I hate that sort of design and have always ensured that I get a flanged towbar, rather than a swan-neck, allowing me to sandwhich a thick, flat mounting plate for my bike carrier between the hitch and the towbar flange. I distrust anything that clamps onto the ball.

I will have a look, but wasn't aware of any pre-adjustment. Given that it already fits one tow ball I would hope it should fit all!

Cheers

Dave R

Given that the carrier may be fitted to a worn ball and that it relies almost entirely on clamping force to hold it in position I think you will find that there is a “fine adjustment” somewhere on your carrier.

Tim

There is adjustment at the top to change the spread of the arms. This should slightly alter the clamping position on the ball.

There seems to be quite a bit of adjustment between 4 pairs of holes, but that then gives me the issue of finding a setting which suits both car and motor home. Unless it is adjustable for the USA 2" tow ball I'm not really sure why there is so much possible change for a 50mm ball.

The last thing I need is too weak a clamping force on one vehicle.

Anyway, onwards and upwards! Oh, and I checked my callipers against a ruler and the 50mm looks reasonably accurate.

Cheers

Dave R

This is my Thule rack adjuster.

No help to you of course, unless you fancy upgrading. ;-)

Tim

A suggestion. Replace the existing nuts and bolts that provide pre-load adjustment with appropriately sized clevis pins like these.

Tim

Before there were 50mm tow balls, there were 2 inch versions, which were slightly smaller.

Modern 50mm come with a standard neck, or a slightly longer one, to accommodate the AL-KO type hitch, with built-in damper pads.

They also come in plated, or painted varieties. For use with an AL-KO hitch, they need to be of the painted variety, and the paint should be sanded off the ball, to avoid it damaging the AL-KO friction pads.

Finally got back to this. Rough measurements: Old ball 49.5 mm New ball 49.9 mm Internal sockets to clamp onto the ball around 48 mm but not consistent. Query to Thule below.

"I have had a two bike folding towbar bike carrier for many years, which has fitted the towbar on my car. I believe it to be a V-Buzz (formerly called Gazelle). I cannot locate the invoice at the moment.

The rack refuses to clamp to the new towball. I have measured as best I can with some electronic callipers and the older towball is approximately 49.5 mm in diameter and the new one is approximately 49.9 mm. The internal diameter of the clamp part on the rack seems to be between

I can see that the measurement has to be under 50 mm to be able to clamp firmly, buy even with the greatest adjustment on the 4 holes it still will not clamp.

Do you have any guidance on the maximum towball size this should fit?"

Hopefully they should be able to give me some tolerances, and perhaps advice as well (angle grinder?)

Cheers

Dave R

By “greatest” I presume you mean moving the brace to its highest position?

If it still won’t clamp you could drill some higher holes. Odd that it won’t accommodate a “standard” towball size though.

Tim

When you say "won't clamp" do you mean that the clamp won't close on the ball, or that it does close but doesn't hold the bike carrier tightly?

The clamp won't close fully to lock around the ball.

Thule have replied to my query and given the minimum clearance below the top of the ball before any obstruction is encountered.

As far as I can tell at the moment, the swan neck starts to bend and thicken too soon, so that the two sides of the "socket" cannot close fully because they are fouling the bend in the swan neck.

Something like 65mm before the start of the bend, where 73mm is the minimum clearance required.

I have seen pictures of a swan neck which is a little U shaped which could give more clearance. The one on the car is like this. Top of the ball on the MH is about 400mm off the ground, and 430 mm on the car, so there looks to be scope.

It is not urgent now, as my new eBike is lightweight and I can lift it single handedly onto the Fiamma bike rack already on the MH.

However, looking to the future this could be an issue if I change to a heavier bike or get weaker in the arms.

Every day a school day. I assumed the carrier would fit onto any 50mm towball, but apparently not.

Cheers

Dave R

Thule do say that their bike carrier - in the same way as an ALKO hitch

- requires a "High Rise" towball - which means having a significant length of straight cylindrical shaft immediately under the ball.

Is your MH swan neck towball integral with the towbar, or is it detachable. If the latter, is there any scope for changing to a different swan neck ball, or even a flanged ball?

I can see two big bolts holding the towball on (haven't investigated in detail) so if there is a compatible "High Rise" towball that could be an option.

Cheers

Dave R