I see many different types of Ti bikes with different materials and had some questions which I'm hoping framebuilders gurus can chime in on.
Regardless of brand, which type would be stiffer and why?
i'm looking to get a Ti road bike frame and wasn't sure which material would be better as i don't want it to end up riding like a noodle. comfort is one thing, but i'll be putting her through some climbs, so would prefer the overall frame and BB to be stiff.
I'm no Ti expert or guru, but here's my take based on the materials data sheets and what I've read in various framebuilders forums. Take this for the $.02 it's worth.
3Al-2.5V has a "stiffness" modulus (E) of 100 GPa, while 6Al-4V has a "stiffness" modulus (E) of 113.8 GPa, so the latter is about 14% stiffer, but frankly the wall thickness and diameters of the tubes are going to have a much greater effect of the frame stiffness than the alloy.
The density of both 3Al-2.5V and 6Al-4V is close to the same. 3Al-2.5V has a density of 4.48 g/cc, while 6Al-4V has a density of 4.43 g/cc, so 6Al-4V weighs a hair less for the same volume of material.
There is a significant difference in ultimate tensile strength (UTS) and yield strength (YS) between the two. 3Al-2.5V UTS=620 MPa and YS=500 MPa. 6Al-4V UTS=970 MPa and YS=880 MPa, so 6Al-4V is about 50% stronger than 3Al-2.5V.
Hardness (Brinell) for 3Al-2.5V is 256, while 6Al-4V is 334.
I believe most builders who work with titanium will tell you that 3Al-2.5V is easier to work with.
There are trade-offs, but if I were considering a Ti frame I would go with 3Al-2.5V personally.
3/2.5 is easier to work worth, Scooper...further the aerospace and military industry has been gobbling up most all of the 6/4 supply there is in the USA. And most builders no longer can source enough for a semi-reasonable price to bother marketing whole framesets anymore. Even the Lynskey Scooper cites is not entirely 6/4, only the front triangle.
Originally Posted by Lynskey
[snip] sheets are rolled into tubing and seam welded together by Lynskey. These newly-formed tubes are then welded together to create the R450’s front triangle. [snip]
6al-4v titanium front triangle for maximum stiffness and power transfer
Now as with any material, a builder can make any frame so stiff that you will not want to ride it...as it will rattle your fillings out. The question is how much it would weigh. Unless you OP weigh 300+lbs (or badly lie bout your weight to the builders) it would be hard for a reputable framebuilder who knows what they are doing to make a custom Ti frame a noodle. And material would factor in, but in and of itself 3/2.5 does not make a frame noodly. It is what you do with the material.
OMG... if you guys are not Ti gurus.. I don't know of any others that is as informative as you all.
My buddy recently bought a Litespeed T1 frame, which is listed with 6/4. Not bad for $2K on a 2014 model from fleabay.
I on the other hand don't have that much and looking at the Motobecane Le Champion Ti w/ 3/2.5. I weigh about 148lbs and like to hard sprint on flats and occasional standing attack on climbs.
I use to have an aluminum frame and that flexed a lot, but it probably cuz it's a cheap frame. But would hate to have that flexy feel on the bb part when sprinting or out of saddle climb.
Your buddy's Litespeed is not entirely 6/4. It too is most likely half-n-half, if that
Originally Posted by Litespeed
The frame is made of a proprietary blend of 6/4 and 3/2.5 titanium and has innovative features that include PF30 bottom bracket and oversized head tube for more fork-tuning capabilities and precision handling.
Premium 6Al/4V radically shaped top tube shaped for maximum stiffness
Now I am not personally familiar with this frameset...but given the very specific way the above marketing is phrased, it is very possible it is not even half-and-half 6/4 and 3/2.5. It reads in legalese like the top tube is 6/4 and everything else is 3/2.5. That being said it doesn't matter a whole lot aside from impressing people with marketing and trying to justify a higher price. Now older Litespeeds, as well as older Moots/Sevens/etc back half-a-dozen years or so were available in full 6/4
Buying a cheapo (relatively) online and sight unseen is a crapshoot, especially for someone concerned with sprinting/climbing stiffness. I certainly wouldn't do it. Better to spend the money on a ride I can test in person, than be out $3000 on a bike I couldn't try and is no better than what I have.
thanks marcus, yea i was a bit weary when he asked me about litespeed.. sure they make good bikes, but since he never rode one before, it was too late for him as he had already won the auction. i saw it last sunday and it looks used, but seller said it was a demo at a bike shop.. so who knows.
as for the motobecane Ti, i've only read positive reviews on it from here and RBR. wish i can test ride one, but dont know of anyone that owns that Ti nearby. but for $1K, guess it's not too bad as long as it doesn't ride like aluminum.
Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder
The concerns I have with low cost TI frames is what was taken out of the manufacturing (or is it only the distribution chain that gives up the costs) to allow selling so cheaply. Was the frame well welded? Properly back purged? How well aligned is it? How well chased and faced is it (or reamed too)?
TI does crack and warp with the stress of manufacturing. It does corrode/react galvanicly. It is a pain/expensive to correct once made.
Given all that if I were starting my building again I'd learn to weld TI and find a facility that has the tooling to make frames with. Andy.
thanks Andy. i've read in the past that their lineup of motobecanne le champion Ti is made by Ora Engineering Co. in Taiwan. they've been around for a very long time welding Ti frame and doing OEM for many other companies, one of which is Rikulau.
i've emailed bikesdirect.com and waiting to get their confirmation on whether or not the frame is stil made by ORA. if so, then i'm pretty confident in their welds, as i have friends in the cycling industry in Taiwan that told me they are reputable. the strange part is, if i were to source the frame through friends from ORA in Taiwan, it would cost more than getting the frame from bikesdirect.com, because ORA said bikesdirect.com buys in bulk to get the discounts.