Head Tube Gussets

I’m working on my 3rd bike and first TIG frame. It’s an aggressive hardtail MTB so I want to put some gussets on the HT.

So far looking at others I see two general styles:

The “Side Plate” style that connects DT, HT, and TT together on each side. I see this style from REEB Bikes and others.

The “BMX Gusset” style where a shield shaped plate is welded on the top of the TT and bottom of the DT.

I’m wondering, what are people’s opinions on each?

Also, for each style, what thickness is generally used?

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How aggressive are we talking? In many instances gussets can cause more problems than they solve or at least create a 1 for 1 type of scenario. My suggestion on your first TIG frame is forgo the extra welding and associated heat input and just use tubes with sufficient wall thicknesses

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Geo is similar to a Kona Honzo ESD.

I have been worried that I didn’t go thick enough with my tubing but it was all bought during COVID and was really the only stuff available.

My TT and DT are:

TBE-MTQ317B501 31.7MM Ø ZERO UNO DOWN TUBE .8/.5/.8 X 650MM MTQ317B501 1
TBE-MTQ380B806 38MM Ø ZERO UNO DOWN TUBE 1.0/.6/.8 X 780MM MTQ380B806

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I’m a fan of gussets but you don’t need one for that downtube with the 1mm wall - assuming there’s enough butt length on both tubes (which is in itself subjective). The top tube takes less abuse but as long as you have a good amount of butt at the head tube end it’ll be fine IMO.

The hardest part about gussets is making them unless you design in CAD and send out to get cut.
Getting the right fitup is a pain, but when done right should act like you used a thicker wall tube butt at that end and therefore add “insurance” to your frame. They’re hard to prove that they work and easy to prove that they don’t (frame cracks).
Butted tubes with >=1mm at the head tube should have reduced the need for using them. There are a ton of mtb frames out there still going strong with 9/6/9 wall downtubes.

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I’ve used those tubes a bunch, I think you’ll be fine without the gussets. Again, since this is your first tig welded frame I would leave them off, the extra welding and heat input is likely to cause more issues than anything at this point

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I can speak of titanium experiences I had over the years. When forks were short and headtubes smaller we had very few issues at Moots using lightweight tubes 0.035" and 0.039" mostly 1.500" diameter as well as 1.640". When forks got longer and headtubes bigger diameter for tapered forks for 29" wheels with 100mm travel we had issues with cracks under the toptube in the HAZ. We tested several front triangles with someone that was excellent at testing for ISO standards, with gussets in various places and with different tubing, got pretty much the same result. He described watching the downtubes on the frames in testing as “flexing like a beer can”. I also worked with the guys at Sotto Design and they were not into gussets as a solution; quote “you will chase your tail”. Again this is with US made CWSR 3/2.5 tubing in the sizes mentioned above.
I took a trip to Taiwan to work with our fork manufacturer and while there visited Oro Engineering which produced a lot of frames for a variety of companies. They were using a 1.750" diameter down tube that they butted in house and is now what Moots uses on the Womble. The wall on that thing is 1.4mm at the head tube, 1mm in the middle and 1.2mm at the bb shell. No problem, but weighs a lot.
The lesson I learned from this was if the downtube is stiff enough either through diameter and wall or by using a second “top tube” which supports the downtube, we did this on the Divide with the split top tube, others do a double top tube landing on top of the down tube, then there is no problem.
Ti is definitely not nearly as stiff and high quality ChroMoly. Just my experience.

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Thanks to this thread I now realise that I need a thickness gauge!

I really wanna know the TT and DT wall and butt lengths of the Sunday Park BMX frame

On the other more fancy frames they do a DT gusset with a sectioned bit of tubing.

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I’ve been lusting after a 45MG for non-destructive test on carbon fiber frames and to use as an overkill tube butt measurer. They occasionally pop up on eBay for a good price, but you gotta be careful that all the software features are unlocked.

What’s a good price? I truely have no clue!

I would say in the ~$1000 range is a “good price” but that is very much in the eye of the beholder

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