Fork sizing problem

Richard.S

Hi everyone.
Just joined this forum, as I am new to cycling and have a few issues which hopefully you more experienced bikers can help me with.

I purchased some front suspension forks which are 1 1/8” (28.6mm outer diameter).
I tried to insert them into my bikes head tube, which was advertised also as 1 1/8” - BUT, the forks do not fit, due to the top and bottom headset cups inserting into the headset, reducing the internal diameter of the hard tube to less than 28.6mm.

I have therefore, removed the top and bottom headset cups, and measured the internal diameter of the head tube, and my vernier callipers read the internal dimension as 30.1mm.

So, my question is - I only seem to have 1.5mm available space to insert new headset cups.
Is this as expected, or should there be more space between the steerer tube and the cups?

Also, the outer diameter of my head tube is 35.5mm. Do I need a special type of headset / cups?

I appreciate any help on this matter, and please remember I’m a biking newbie, so layman’s terms answers would be most appreciated

Thank you all in advance.

billycool

Any chance you can tell us which forks and which bike?

Richard.S

Unfortunately I do not have those details to hand, but I included the diameters above, as I figured that was the important issue. Thanks.

larkim

Surely you know the name of the bike even if you don't know the name / model of the forks?

larkim

This https://en.wikipedia.org/wiki/Head_tube suggests internal diameter of 1 1/8 headtube should be 33.8mm

30mm internal diameter would be a 1" steerer, assuming perhaps that your measurement of 30.1mm is 0.1 incorrect?

Richard.S

As crazy as it sounds, I actually don’t, as the frame was supplied to me, and has no details as it is totally plain.

The internal dimensions of the head tube is 30.3mm - I just re-measured it.

So I basically have an oddball Sized headtube, with normal 1 1/8” forks.
I guess it’s time to get a new frame then, even though this one is new and never used

Thanks.

larkim

Very odd indeed!

JBA

Older frames had 30mm head tubes to take 1" quill stems.
Any idea how old the frame you have is, Richard.S? It may not be used but could be very old.
It is a mountain bike frame, isn't it?

Richard.S

Yes, definitely a mountain bike frame, and new. It’s obviously some weird manufacturer using an odd sized head tube for some strange reason.

Thank you for all the help. I will just get a new frame - much easier.

Once again, thank you everyone for the advice and help, it is much appreciated.

The Rookie

As you can't buy a headset for 30.3 I suspect your measuring is out more than the actual size.

At least you'll know what it is when you're selling it.