Want to know if the bottom race the On-one Smoothie (?) headset that is fitted to my On one c456 would fit a straight 1.5″ headtube. This headset is a 1 1/8th in – 1.5in but has a reducer crown race so that I can fit a 1 1/8th straight steerer.

Its just that I want to fit a 1 1/8th steerer fork through a 1.5″ head tube on another bike. Curently it takes a tapered fork, so I’m just looking for a lower race with a 1 1/8th reducer crown race.

My C456 has one but is it the same dimensions to fit the cup in the frame? (Are all 1.5″ headtube lower sections the same? Regardless of straight or tapered top end?)

I have the same headset on my ti456 and I would say no as it is made with the smoothie dimensions in mind but you could always try as its not that difficult a job. Unless of course you a planning to remove and fit the whole lower cup,bearing and crown race to the new frame.

1.5 in is 1.5 in , whether it’s in a tapered headtube or straight . Should fit if all else is equal . If it doesn’t Hope do all sorts of headsets that you can by in modular form so you could buy the bottom half of a 1.5 headset or a 1.5 to 1.125 reducer .

Wanted to fit the whole lower assembly, so would need to remove cup, bearing and crown race.

Might have a look at the Hope ones…

1.5 in is 1.5 in , whether it’s in a tapered headtube or straight

Sadly, you would think that, but it’s not.

A straight 1.5″ is a different diameter from a tapered headtube.

Even at the 1.5″ end???

1.5 to 1.5 will have a straight inside edge, 1.5 to 1.25 won’t, as it tapers

Yes, a tapered headtube isn’t actually a 1.5″ lower cup, its a slightly smaller inner diameter.

Have a look on the Cane Creek website, it has all the different sizes in MM on there for all the various different standards.

So, could I fit a 1.5″ zero stack headset in place of an external cup 1.5″ headset?

Or are 1.5″ headtubes for zero stack headsets even bigger?

Check out the Hope site for details on dimensions. It is a right pain with the different sizes but this makes it clearer.

Thanks Colin, thats excellent!

I’m just doing a similar exercise. It seems to me that On One have bucked the trend on Headtubes. The industry standard seems to be 44mm top/56mm bottom for a tapered headtube internal diameter and 49.6mm top/49.6mm bottom for straight 1.5 headtube inner diameter. So, On One design a frame with 44mm top/49.6mm bottom, just to be a bunch of twonks?