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Distinguishing Aluminum from Titanium?

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Distinguishing Aluminum from Titanium?

Old 03-19-21, 01:13 PM
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pstock
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Distinguishing Aluminum from Titanium?

this cannot be a new question, but I have searched the archives and haven't immediate found anything related.

given that frame stickers can be had cheaply that say anything you want (and so you can slap an SLX or Titanium sticker on anything), how could you tell if a painted (paint preventing you from easily tell the color of the material) frame - assumiing it's not one of the top Titanium brands - is Aluminum or Titanium?

weight doesn't seem to be an obvious differentiator - I see an aluminum Colnago is listed as 1308g vs a L LItespeed at 1344g, almost the same.

Last edited by pstock; 03-19-21 at 01:18 PM.
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Old 03-19-21, 01:31 PM
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The welds on aluminum will be bigger/more evident; also the tubes on aluminum will be much fatter than titanium.
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Old 03-19-21, 01:33 PM
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Tough question. Perhaps verify the serial number with the manufacturer to determine model. Another way is to look for oxidation around areas where the paint may have been scraped. Al may show white blooms while Ti will not. Bottom bracket or rear dropouts perhaps.

Polishing raw alum will turn a light cloth black so you could pull the bottom bracket and rub some polish around the shell lip, which may have been machined (or possibly the shell threads). Of course, you'd have to clean all the gunk before you did this

The definitive non-destructive way would be to have it tested by X-Ray Fluorescence. XRF analyzers are expensive so you won't want to run out and buy one. Best bet is to look for engineering lab companies in your area if you want to go that route.
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Old 03-19-21, 01:36 PM
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Also, but maybe this is just the difference between my Bianchi titanium and Klein aluminum mtb, but if you flick the titanium with your fingernail, it makes a "ping" sound, whereas the aluminum is a "plink" sound.
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Old 03-19-21, 01:38 PM
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Titanium is also very springy. If you could take the rear wheel out and try to flex the rear triangle, aluminum would be very stiff, while titanium would move quite a bit (and spring back). Again, the aluminum chainstays and seatstays would have a bit beefier tubing as well.
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Old 03-19-21, 01:39 PM
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+1 for ridelikeaturtle. Al welds are generally about 3-4 times wider then that of TIs. Ti's welds are around the same size as steel's (at least TiG'ed steel) but steel is magnetic so that difference is easy to discern. Andy
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Old 03-19-21, 02:57 PM
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Originally Posted by ridelikeaturtle View Post
Titanium is also very springy. If you could take the rear wheel out and try to flex the rear triangle, aluminum would be very stiff, while titanium would move quite a bit (and spring back). Again, the aluminum chainstays and seatstays would have a bit beefier tubing as well.
This is often (usually?) not true. When Damon Rinard did his frame stiffness testing, a Cannondale 2.8 showed one of the most flexible rears of all (over 60 frames tested).

The problem is alu needs to be oversized to have decent stiffness, because it's about half the inherent stiffness (Young's Modulus) of Ti. But chainstays are constrained by chainring and tire clearance, so alu will almost always lose to an optimized chainstay in Ti.

Many early Ti frames had undersized chainstays, due to the lack of commercially-available tapered tubing, so they went with a 3/4" tube that was too big at the dropout and too small at the bottom bracket. Stiffness at the BB is almost all that matters in a test like Rinard, or in the ride feel. The tiny 3/4" chainstays is the reason for any Ti frames in the Rinard list that showed a flexy rear. At least with undersized chainstays you get the advantage of better tire/chainring clearance. No such advantage on a Cannondale.

Ti chainstays should be a bit larger than steel, due to Ti having a lower modulus than steel. Not as oversized as Al, but around 1" is good in Ti, vs 7/8" on classic steel. (Now of course there is also OS steel, a bad idea IMHO.) Back when Rinard did his testing I think there were zero commercially-available Ti frames with 1" chainstays. Maybe on the custom Merlin track frame made for professional sprinter Ken Carpenter — which I happen to know he didn't race on, because it was too flexy for him. I know this because I made the steel frame that he kept on riding when he was sponsored by Merlin. They made him a second frame (supposedly "twice as stiff") after his review of the first one was unprintable, but even the second was called "an abortion" by Ken. They painted my frame to look like Ti, and put Merlin decals on it! But I digress... Sorry I know steel is off-topic for this discussion.

Anyway, most any welder can tell at a glance whether a frame is Ti or Al, so maybe that's the way to tell — bring it to a welder or bike frame builder. The ability to tell by looking can't be taught over the internet unfortunately.

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Old 03-19-21, 07:15 PM
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Take a grinder to it and see what color the sparks are.

But really, the welds. You can usually tell from the inside of the bb shell as well.

I would be surprised if there were any frames where there is much confusion.
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Old 03-20-21, 08:19 AM
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I agree that in most cases titanium is obvious.
but take the example of this Aquila bike. Aquila is the private label brand of a local bike shop here and they imported and labelled everything over the years.
they have a Lot of aluminum bikes out in the world too.
would you think this one (attached) was Aluminum or Titanium?

but turn the situation around. imagine someone not very familiar with bikes were selling a bike with what they assumed was an aluminum frame (maybe having tested with a magnet). and you were buying and supected it was titanium. that is a situation where it would be handy to be able to tell the difference between the two.

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Old 03-20-21, 09:37 AM
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I think the most difficult frames to tell would be if they had cosmetic welds like a Cannondale and some Ti builders that were ground, post-weld.
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Old 03-20-21, 10:58 AM
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Originally Posted by pstock View Post
I agree that in most cases titanium is obvious.
but take the example of this Aquila bike. Aquila is the private label brand of a local bike shop here and they imported and labelled everything over the years.
they have a Lot of aluminum bikes out in the world too.
would you think this one (attached) was Aluminum or Titanium?

but turn the situation around. imagine someone not very familiar with bikes were selling a bike with what they assumed was an aluminum frame (maybe having tested with a magnet). and you were buying and supected it was titanium. that is a situation where it would be handy to be able to tell the difference between the two.

I'm going to go with aluminium for that one. But it does look like the welds on the main triangle have been cleaned up so it's not so obvious.
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Old 03-20-21, 02:09 PM
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Definitely looks like aluminum welds to me, although as guy153 says, they are smaller than normal for aluminum. I think the shape of the welds says aluminum too. Even production Ti bikes I have seen have a concave shape to the welds.

The thing that really gives it away is the shaped headtube. Very few production builders are going to the expense of such a headtube on a Ti bike
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Old 05-29-21, 09:17 PM
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1. I'm assuming this is mainly academic because there are accessible non-painted surfaces on most frames even without paint chips. The inside of the seat tube is an easy one to get to, but the insides of any threaded surfaces such as the BB or derailer hanger are others.
2. I'm leaning aluminum on the pictured bike above for the reasons already stated.
3. You could probably figure it out by how fast an ice cube makes a given section farther away cold, but you would need an aluminum or ti bike to compare to.
4. If you can't tell by sight and ride, does it matter?
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Old 05-29-21, 11:15 PM
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I'm going to assume he figured it out back in March
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Old 05-30-21, 02:43 AM
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Sorry, that’s what I get for wandering into a different section of the forum at the end of the week and not looking at dates. I am curious what the answer is though.
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