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8/21/2022
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Tacoma, WA
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Is there a standard length for the head tube on downhill and enduro bikes?
Or, is there a standard bearing to bearing distance with the crown race and upper seal-cap installed?
Searching the internet I found nothing to indicate any standards for 1.5", 1-1/8" or tapered head tube length. I understand the different bearing cups and all of that, but if there's no height standard, what are some common numbers for that total length of the tube and bearings?
I'm about to machine a few bottom brackets and head tubes for some frames I'll be building this summer.
The bottom brackets are easy, I have 83mm stuff. I can do anything I want for head tubes, but I'd like to be within the range of normalcy.
Maybe take a look at what PMW makes? They're a pretty popular supplier...
https://www.paragonmachineworks.com/headtubes/steel.html
Thanks, I had no idea the range was so wide on that dimension...
They offer 90mm all the way up into 200mm.
It would be nice to know what is typical on a modern mountain bike.
There is no standard length, per se. Head tube lengths often vary by frame size. For example, on the Forbidden Dreadnought V2, head tube length is 90mm on a small and 135mm on an XL frame. The Commencal Supreme V5 has a HT length of 112mm across all sizes of frame. This info is listed in the geometry chart for each bike model.
To make it more entertaining, the stack height [distance from crown race to the headset top cover varies with the type of headset. Pressed-in bearing cups with the bearings outside the frame create the tallest stack, and bearing cups that are part of the headset provide the lowest stack.
^^^^ This explains why you weren't able to find a standard bearing to bearing dimension. If you're looking for numbers, 90-160mm will capture most of the enduro/DH frames out there. Probably.
This site has a lot of bikes but I don't know if you can get it to list just head tubes; you can however, compare a bunch of bikes like this: https://www.bike-stats.de/en/geometrie_vergleich?Bike1=Canyon_Torque%20…
Edit: what @pinkrobe said
There is no standard but for trail/enduro bikes head tubes in the 100-130mm range in 10mm to increments are the most common. For metal bikes head tubes under 100mm can start to be harder to pass testing with. It's typical to increase ~10mm/size so something like 100/110/120/130mm for a S/M/L/Xl is a starting point.
If you are building a standard large frame for yourself I probably wouldn't go under 110mm. You can correct with bars and stems spacers a bit but it's nice to not have too much under there.
Thanks to everyone who posted suggestions.
My eyes have been telling me over 100mm and under 150mm, but you guys are helping put some practical experience behind the numbers. I've only owned one mountain bike and have been riding it for about a year and a half. I come from motocross, so my two wheel skill is fairly high, but my experience with bicycle components and standards is minimal.
I have a Cane Creek IS41 short headset here which adds 9mm on top and 1mm bottom to the stack height.
My current plan is to machine a head tube similar to the straight 1.5" steerer on my old Transition Gran Mal and then machine a few eccentrics that allow me to vary the geometry of the bike a small amount.
I believe I can stay within the 110mm to 130mm range and still be able to suit the dual crown fork with appropriate axle to crown dimensions. I'll lay it all out in CAD to see where the constraints are.
My current bike has the straight 1.5" steerer setup with a 120mm head tube length and external Cane Creek headset which measures 150mm top to bottom when installed.
As a tall person, the one headtube standard is for them to be too short. I've never needed less than a 135mm headtube, and even with that I'm often running a healthy dose of spacers under my stem. And if I haven't convinced you yet, taller headtubes tend to be safer because there's more distance between the top and bottom welds on the headtube, meaning less leverage acting on them. You're more likely to see a short headtube ripped off.
Came here to say the same thing about 130mm+ being a great number to see when looking at a size XL geo chart. Also seems to eliminate a bit of flex from the steertube with less spacers under the stem.
I'm about 5'9", so the tall rider concerns don't apply to me personally.
The structural concerns at the welded interface are foremost on my mind for safety, especially in a frame I'll fabricate in my own shop. It's not the only constraint, though. I do want to be within the useful range of available forks and accessories, so I decided it was a good idea to ask all of you guys who no doubt have far more experience with bicycles than I do.
As far as handlebar height goes, I'll get that from the bar mounts and the handlebars since I'm building for a dual crown fork.
I don't want to go too high at the upper headset bearing for fear of building a bike I can't optimize for myself.
I've tried playing with stack height on my Transition. I machined a few spacers of various heights and brought them to my local trails with a 5mm hex key. I found that taller was slower (lap times) for me with vague feel at turn in and reduced cornering stability. Lower didn't change cornering performance, but it moved my body position slightly forward which would likely be a disadvantage on some of the steep technical downhill trails around here.
My intention is to build a few frames. The first frame will be a big learning experience to confirm or bust some of my ideas on geometry and the second frame will incorporate what I learned testing the first frame and so-on.
That sounds sick! If you can get the stack dimension close to where you want it, going slightly shorter on the headtube can be pretty helpful for a dual crown fork by allowing a wider range of adjustment.
My size R3 (XL) Trek Session has a 117mm headtube length, the same 9mm upper / 1mm of lower headset stack, and 634mm on the geometry chart which is shared acoss all sizes. While the stock configuration felt super low to me, that could be somewhere around what you're looking for. I played with bar height a lot to get things dialed in and the freedom to go up or down was really nice, I ended up slightly lower than I anticipated.
Headtube length is just an arbitrary number, if you are starting your design with a tube dimension you are kinda doing it backwards.
Figure out where your hands, your feet, and the wheels are all going to be relative to each other to achieve the fit and handling dynamics you want, then the tube lengths are just things connecting the dots.
Production bikes are trying to fit a range of people and have to make a compromise on this stuff. They also need to cut costs and increase efficiency so they do stupid things like use the same headtube length on all sizes.
Most DH bikes I’ve tested are 110-120mm head tube length.
If you can fit a straight tube 56mm head tube, you have tons of room for reach and angle adjust headsets.
I realize all the constraints and have narrowed down the dimensions to a range I want to land within. Nothing is backward.
This question is my attempt to avoid building a bike that suffers from potential blind spots I might have for industry standards or common practices. I don't want to build something that doesn't accept common parts; that would be creating a big pain in the ass.
That's my plan for the larger diameter on at least my first frame.
I want to try moving the bottom bracket forward relative to what the MTB industry trends seem to be.
To facilitate that I've considered an eccentric in the bottom bracket, or a removable bottom bracket.
Later, I can save weight and complexity by eliminating all the adjustability once I discover my preferred setting.
Moving the BB forward in geometry terms is just lengthening the chainstay and shortening the reach. This does not require any eccentric BB options.
Mechanically there might be reasons for tube butts you might want but the geo can be independent of this.
Within the range of adjustment possible you are better off with an axle flip chip and a reach adjust headset to play around with Front/Rear centre proportion (which is what sliding the BB forward or aft would do).
From an opinionated perspective I probably would not even bother with a reach adjust headset. People spend a lot of time worrying about a few mm in reach when there are a thousand other parameters that effect fit and balance more. Chainstay and head tube angle adjustments are significantly more impactful.
Post a reply to: Head tube dimensions - Downhill, Enduro, Etc.