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Hmmm, I can see how there would be little point in having a seatpost extending down past a shim. But would it have no impact? I don't have the engineering to answer that but I was thinking that a deeper insertion would be marginally better unless it allowed seatpost movement.
The Qoroz looks good and if the builder is prepared to stand by the design then I'd be happy. If you have 508mm of ST then you're looking at closer to 50% of the post inserted rather than the nearer 25% mark of the Lynskey, that's a huge difference.
I hadn't realised the GF Rig you broke had such a small seat tube. I know others are saying Ti breaks a lot etc but that's not the impression I have. There are a lot of repeat postings of the same frame breakage and there's a lot of unsubstantiated opinion. Most of the problems I've been able to find, Ti or otherwise, seem to share similar attributes:-
quality control - a known or recognised poor batch or builder
really short seat tubes - being of the larger persuasion I'm happier with at least 150mm of a 410mm post in the frame, preferably more. The 100mm min insertion is a seatpost limit it isn't a frame limit.
long seat tube extensions above the TT without additional support - this makes me nervous, though I have no technical support for that feeling, it just looks vulnerable. By long I'm thinking anything over about 40mm. I do seem to remember reading something about that being a recommended limitation from XCAD.
shimming, butting and manipulation - a lot of this looks like workarounds to me. Trying to get a given framesize to cover a broader range of rider sizes. Almost as if they start with aiming for clearances around the shortest/smallest recommended rider rather than the midsize in the range. This would put the riders at the upper limit of the size range at the extremes of the design.
rider/user error - treating an XC frame as a freeride or similar, crash damage not being investigated properly and otherwise exceeding design parameters.
I hope you post up plenty of pics of the new frame, looks like it'll be great.
One more thing that may be relevant, I've been told that there is a very limited range of titanium tubes available to make bike frames from.
Whereas aluminium can be tapered, butted and hydroformed to almost any shape the frame builder wants, all the titanium frame builders are working with essentially the same tubes.
I don't know how true that is, but apart from a few variations like Lynskey's twisted helix frames and the squared top tube and down tube on the Ridgeline, there does seem to be a lot less variety of Ti than Alu frames available.
That would be my understanding as well, it's not like there's a ti smelting plant and mill in every town.
I was looking further at the Lynskey geometry for the Ridgeline-29 SL. They have the Large as covering 5'11" to 6'2" and the XL as 6'3" to 6'6". I know that you can size up or down to suit but you've got a 1" gap there. Running down the list the only big difference is in the ST, it jumps from 470mm to 520mm. Yet the ETT only jumps by 12mm, part of which is acounted for by a half degree increase in HT angle, and the HT jumps by 6mm. Everything else stays the same.
The 7" height range from 5/11 to 6/6 is quite a jump to be covered by such minor changes.
Ahh; Qoroz have their frames made by XACD hence the confusion - I can see why you'd want to keep things local given your current luck with frames!
Definitely interested in seeing how it turns out 🙂
Have to say titanium is looking like a pretty poor frame material, stories of them breaking seem quite frequent.
more likely incorrect use of frame material and sizes for the job.
One more thing that may be relevant, I've been told that there is a very limited range of titanium tubes available to make bike frames from.
again likely to lead the use of tubes etc that are not quite suited to the job
those cracks are from that whole joint rotating backwards and putting the middle under tension (why the crack is wide in the middle and not the ends - they would be better putting the joint for the seatstays/ST higher up than the ST/TT joint
and/or sleeving the ST (if external butted tube is not available)
"...again likely to lead the use of tubes etc that are not quite suited to the job..."
I don't know much about the world titanium tube manufacturing industry, but I would have thought bicycle frame builders were their biggest customer, so the tubes would be made for the job.
Do titanium road bikes have the same reputation for breaking ?
Do mountain bikes use bigger diameter and/or thicker walled tube ?
If all bikes use the same tubes, then either road bikes are over engineered or mountain bikes are inevitably going to fail.
Graham, looking at your CAD drawing again and noted you've gone for 73/71 angles based on a 475 AtoC with 45mm rake. I'm trying to get my head round exactly what this means. I'm considering some squishy forks and it's all rather confusing. For rigid geo it seems straight forward, 71 HA, 45 rake, 2.2" tyre = 79mm trail.
But I've been looking at geometry charts, thinking Salsa and Niner here, that show the numbers for frames based on 80mm or 100mm geometry. For 80mm they're using approx a 470mm AtoC, 72 HA and 45 rake, which brings up a trail number around the 72mm mark. For 100mm forks they show the angles slacking by approx 1 degree and that bumps it up to nearer the 80mm trail mark. Is the 475mm AtoC you have on your drawing meant to be reflective of an 80mm or 100mm fork? I seem to get varying answers when looking for AtoC info and level of sag to allow etc.
I'm musing about trying to design something that would work with 80-120mm forks. I was thinking a tweaked Niner geo starting point would be about right. So 74/72 at 80mm, 73/71 at 100mm and 72/70 at 120mm, if my understanding is correct. This would give me trail numbers of 72mm, 79mm and 86mm, or touring/light trail, XC and trail just by changing the forks. The main tweak being a bigger BB drop so that the BB doesn't get too high as the forks change. Coupled with moveable dropouts to tighten up the back end as the front lengthens, keeping the wheelbase roughly the same. Beef the frame up enough to cope with 120mm travel.
I don't know much about the world titanium tube manufacturing industry, but I would have thought bicycle frame builders were their biggest customer, so the tubes would be made for the job.
Hiya MTG
no biggest customer for ti tubes is the aerospace industry - bike industry is just picking up the crumbs/using what is available...
alu and composites (and steel) is always going to be better for the bike industry due to the flexible of design even in limited runs, alu tubing for its hydroform possibilities and composites for complete flexibility even for short production runs...
doubt due to the limit Ti tube manufacturers and manipulation options this is going to be the case for Ti
Si
Surely the amount of seatpost length is irrelevant if your frame has a shim?
If your seatpost shim is say 100mm long, then as long as you have 100mm of seatpost inserted you will get maximum strength. If you have 150mm inserted then the extra 50mm will extend below the shim and not add any extra strength.
macb, I really didn't go in to the geometry in that much depth.
I told Chris at Qoroz that I liked the handling on my large Lynskey and asked him to copy the geometry.
I'll be using a Lefty fork, which is 500mm AtoC, the same as the 100mm Fox F29 I've got on the Lynskey, so I'm hoping it all works out OK.
The only significant difference is the 454mm chainstays. This was dictated by the belt drive as I will be using 50x28 single speed and 50x20 with the Rohloff.
There's a very limited choice of sprockets and belt lengths for Centre Track and this was the closest I could get to my two current 32x18 & 32x13 chain & sprocket ratios, both using the same chainstay length. I was lucky that they both use the same front pulley which means less parts to buy and easier swapping between the two.
Independant Fabrication say:
http://www.ifbikes.com/?id=40&keepThis=true&TB_iframe=true&height=400&width=500
"Shot peening is a cold working process in which the frame is bombarded with small spherical metal balls called shot at a precise angle. Shot act like tiny ball peen hammers and create a uniform dimpled texture on the surface of the frame. This compacts the outer layer of the material.
The processes of butting and welding titanium tubes to make a bike frame are known to create tensile stresses in the frame material. Tensile stresses make the area in question want to pull itself apart. This is a bad property to impart to a bicycle frame as any minor notch or micro crack in the frame will want to propagate and further compromise the material. The induced tensile stresses are most concentrated in the heat affected zone — the area of the welds. Thus, strength is compromised precisely where you would like it to be greatest.
Shot peening of a welded titanium joint substantially increases both fatigue strength and fatigue life as compared to the same joint which is not shot peened. Shot peening imparts what is called residual compressive stress which counteracts the residual tensile stress, which is created in the process of cutting, grinding and welding. Typically, fatigue strength of a welded titanium joint after shot peening is double that without shot peening. Fatigue life is enhanced by shot peening to an even greater degree.
By shot peening the frame after it is welded together, we are able to relieve the stresses in the material providing compressive qualities, which are known to reduce micro cracking and enhance fatigue life. Without stress relieving, each of the tubes will retain tensile stresses which tend to conflict with one another. Stress relieving allows the component tubes of the frame to work together as designed, acting as a unified structure rather than a collection of competing parts.
The shot peening process work hardens the surface of the tube, while giving it a finely textured surface. These two properties together create an attractive finish that is highly resistant to scratches. If scratched, the scratch is harder to see because the surface is textured. The textured surface glitters in the sun in a manner similar to that of a pearl paint job.
Some people may confuse shot peening with sand blasting or bead blasting. At IF, we use sand blasting on our steel frames to remove contaminants. We also use it impart a microscopic tooth to the surface of the metal to provide a mechanical bond with the paint. Bead blasting is used for cosmetic purposes to provide a uniform finish to the surface of the metal. Neither sand blasting nor bead blasting improve the mechanical properties of the metal.
Shot peening is used precisely because it improves the performance characteristics of the finished parts. It is used in the aerospace industry, in high performance cars and motorcycles, and in light weight bicycle stems and bars where light weight and high strength are performance imperatives.
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What's the big deal? Don't a lot of frame builders shot peen their frames?
To the best of our knowledge we are the only titanium frame builder using the shot peening process. This process should not be confused with bead blasting, which is used to provide a cosmetic finish to ti bikes. Any company that claims to bead blast over a shot peened finish does not understand shot peening. Any type of finish polishing brushing or bead blasting applied after shot peening negates the benefits of shot peening.
See www.shotpeening.com for more info.
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Who does the shot peening of IF frames?
We do not do the shot peening in house. We use Metal Improvement Company in Wakefield, MA, which specializes in shot peening high performance parts for the aerospace industry. At Metal Improvement our frames are peened along side of parts for the space shuttle and F14 jet engine rotors.
See www.metalimprovement.com for more info.
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Why can't IF do its own shot peening?
To shot peen properly requires the use of very large, sophisticated, and expensive computer-controlled equipment, and trained personel. Shot Peening really is high-tech stuff, and it's tough to get right. We decided to leave it to the specialists. In addition, we are confident in the established leadership, reputation, and quality of Metal Improvement."
Here it is.
This is not the final build spec. The biggest omission is the belt drive, I'm still waiting for the belts and pulleys.
There's a few other odds and ends I'll be changing, but nothing major.
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Nice, Graham! I'd love a belt drive frame one day.
From those pics above, it looks like your saddle is at an extreme angle, meaning that when you're pedalling in the saddle, you are puttling a lot of stress on the post, thus the frame int eh place it has cracked. Just a thought. try flattening the saddle a bit, it might help things?
edit: posts double.
Is that an I9 front wheel? Need a matching rear!
Yes, I9 on the front, Rohloff on the back.
Flat blade spokes on the back too. I bought the spokes and rim off a guy who had sold his hub, I wouldn't normally put aero spokes on a Rohloff hub on a mountain bike. 😀
I'll be swapping the seat soon for a Gobi. I'll do something about the angle then too.
Sweet ride. Love it. :jealous: