transfer Head tube and stem sizes

mankybianchi

My bikes are steel 80s and 90s standard frames but unfortunately my main ride is really showing its age. Many rust spots and the like so I'm looking to replace with a new frame.

My problem is transferring the size of the head tube and stem extension above the head tube plus height of headset above the head tube with the modern equivalent ie. how tall are headsets these days and what diameter are extensions. Knowing this will help me find the corresponding head tube length.

Many frames have varying headtube lengths whilst having similar effective top tube lengths. It's this head tube length that's causing me a bit of a problem. I can work out reach fine.

Thanks

M

sungod

headset stack can range from a few mm to >30mm, depends on the type of headset accepted by the head tube and the model of headset used

are you getting a custom frame or off the shelf? if it's custom talk with the make about it and they'll tell you what info they need

or you can measure the saddle height/setback, and the axis of the handlebars relative to the bb axis and then look for size/geometry that allows you to match it

off the shelf, if the frame is the right size for you, you'll be able to replicate position by suitable combination of spacers and stem length/angle

mankybianchi

It'll be an off-the-peg frame. Head tube size was something that was never thought about years ago due to the quill stems ability to be raised or lowered.

Having looked at a few frame dimensions, there are many variations. My current top tube length is 57cm c-c with 120mm extension and this works great for me. One frame's figures which I was studying had a 56.6 cm TT and 16.5 cm HT or a 57cm TT with a 19.5cm HT. Quite a large jump I thought and it's this that led me to ask the original question.

I see it'll be a bit of back and forward measuring and researching.

Thanks

ai_1

Have you measured the stack of your current bike?
This will be the vertical distance from the centre of the bottom bracket to the top of the head tube.
Many brands provide a stack measurement as part of their bike geometry. If you can find this for the bikes you are considering you are a large part of the way there.
Now you just need to compare the differences between your bike and those you're considering from the top of the headtube to the centre of the bars.

For yours you can just take a vertical measurement.
For an off the shelf bike you may be able to find the measurement or you can go to a bike shop and see how it's configured or ask owners of similar bikes here. Typically if the stack is measured to the top of the headtube you will then have a headset collar and spaceers and then the stem.
Some bikes have very high tapered collars 25mm or more in height, others don't. This is the only thing you might have trouble figuring out. After that, most bikes will accomodate at least 25mm of spacers and often more. the stem clamp is usually about 40mm high, I think. That means the stem centreline will be approx 20mm above the spacers. The bike specs will usually give you the stem length and angle so you can determine the drop or rise this will give from that stem centreline. Add it all up and your sorted.

mankybianchi

Yep, I have measured the stack along with many other combinations of dimensions so I think as AI_1 says, the collar height will be the tricky variable.

Thanks for all the help.