Do frames “wear out” ?

The guys who send their suspension out for a revalve before touching a clicker are going to tell you they can feel a worn out frame.  They can also feel different motor mount flex while running mid pack +40-C.

no.

I don't know from personal experience, as far as the feel of a frame as it accumulates hours. I do remember back when I had my 350 (the '16-18 gen) that Keefer mentioned that those frames get sort of noodley as they age. I have no idea if that means that they are worn out or just they set-in after a certain point. I could feel the difference of that frame compared to the YZF I also had, at the time, but I didn't really noticed it getting flexier, as I put hours on it (granted, it wasn't several hundred.) And then I believe it was 1 of the next 2 KTM gens after that all the media said you needed to run it for at least 10hrs for it to break in, for it to feel right. It's an interesting question, but I don't know the answer.

As far as the comment above, yes I know some guys can be ridiculous and claim they "need" certain things to run Vet C, I don't think you need to be pro speed to feel things on a bike. Plenty of fast riders don't know how to set up a bike or aren't detail oriented, in that manner. And plenty of slower guys are good at feeling little things and putting it into words. 

Steel frames do...they used to stretch...and break. Never had an aluminum one do squat. 

To me they don’t wear out the wear in. Frames feel so stiff at first. Get 20-30 hours and they feel better. Or hell maybe that’s just how long it takes me to get use to the bike. 

The older Jap bikes. You could measure when new from the pivot point to the rear axle and there was def stretch over a year or 3. This was dependant on how many hours and if you rode hard obviously...casing constantly never helped. I found that out on my 1992 KX 125. Snapped that bitch on both side near the pivot area. Tore the bike down to the frame and squeezed it back with ratchet straps and welded it. Never had an issue. I forgot about how we'd measure the head tube to the footpeg and pivot areas also. The frames back then def would kinda bow if that makes sense...actually increasing the wheelbase over time. We just lived with it. 

If have no basis for this but I would assume modern Austrian frames have better metallurgy and engineering and don't stretch like older steel frames. The old ones would stretch and slacken the head tube angle over time. 

Back in the day a guy I know would measure the distance between the foot peg and front axle on his steel frame yz250’s. They would grow an inch in 1 year. He was a fast A rider. 

Yes.

When I raced an XR650R regularly (primarily desert with some moto just because it was my only bike at the time) I would change out the aluminum frame every other year. The lower frame rails would spread apart.

Have seen lots and lots of frame stretch in older Japanese steel frames. Pull a motor of an older bike and it may not go back in all that easily once the tension is off the frame and it relaxes to its "new" dimensions. 

Are more modern frames built better? Yes, they are. Hard use such as big jumps and constant g-outs will still stretch and wear the metal. Just not as obvious with aluminum frames as aluminum isn't as elastic as steel. I would expect the average individual to see cracking in an aluminum frame before it noticeably stretched. Genuinely curious what a high hour frame would look like if magnafluxed.

Once a bike gets a couple years old the frames are genuinely dangerous and should be replaced with a new bike. At least that is what wives across the nation are told.

“Babe, frames are like a helmet…”

. The only way you will notice a worn out frame is if you can push it hard enough to flex or distort it in the first place. The fast guys however push frames to their limits and can absolutely feel them wearing out. They will start to twist more in turns causing them to track differently and they will give to much feedback hitting hard bumps. The frames soften so they give off energy differently, more harshly. 

Ask Chase

KTM frames are chromoly. Japanese steel frames are generally high-tensile steel.

This topic comes up every so often. My responses in this thread are applicable if you want more info, but short answers here:

Does a frame wear out as-in the stiffness/flex/feel changes? - No. If will feel the same from day 10 to day 1000000. But the chassis as a whole will break in and change feel (suspension bushings break in, parts settle into their "preferred" location due to slop in bolted joints, seat foam softens, etc.)

Is there an initial break-in on a new bike that changes stiffness/flex/feel? - Yes for the chassis as explained above. The frame itself will "break in" in a few tiny spots initially, but that difference is likely unnoticeable to anyone.

Does a frame wear out as-in it's more likely to break when it's older? - Yes, fatigue starts to build up and the frame will eventually crack with enough use. This should take A LONG time if the frame was well engineered. More likely to be a problem in aluminum frames than steel frames.

Can a frame wear out as-in it's bent/broken/etc.? - Yes, of course. If it takes a hit hard enough, it will fail/break/bend/stretch

I'm no metalurgist, but steel becoming more flexible over time doesn't make sense to me.

Depends on who is riding the bike.

I stretched a CR500 so much it wouldn’t fit in the van. 

Well, ‘broke’ would be better word.

IIRC race teams junk a frame around 200 hours, so for most of us they'll last the life of the bike.

I'm no engineer but I've always kind of side eyed the notion that the steel will change it's elasticity for a short while when "new" then plateau somehow. Bushings, springs, and slop in bolts/holes finding their home after consistent use makes much more sense. 

To me the frame itself will feel exactly the same from new until it finally deforms from enough force, at which point that is the new baseline until it deforms further.

IIRC Reed absolutely could feel it and switched within a presribed # of hours in the TwoTwo days on Honda. Also clear anodized the frame and I thought he could even feel that, which makes no sense to me. 

Yes they do!

even based off current yz models

We just had a subframe welded up on one of our bikes from "wearing" through.

When we tear bikes down for inspection youll find where the frame has worn where boots rub and very visibly too. also youll see where any thing like rubber vent tubes rub the frame down from vibrations.

It would take me 2 laps to realize if one of my tires was flat

Well I just so happen to be an internet certified metallurgist and, not only does steel become more elastic overtime, but it also cannot be melted with jet fuel.

I’ve heard they do on road bikes (cycles), but you gotta think those are thin wall aluminum frames with zero suspension, supporting a rider that weighs 4-8x the bike. I’m sure our bikes do but it’s gotta be such small degree and even then 99% of us don’t have the feel to actually tell.

All anodizing amounts to is a thin oxide layer grown on the surface of the aluminum and filled with a colorant of your choosing.  Anodizing can absolutely change the friction coefficient of the surface for dynamic parts, but claiming that anodizing can change the mechanical properties of the frame itself just isn’t realistic.  

Steel, when bent, becomes harder at the point of the bending which results in the metal becoming brittle and more prone to cracking. I would expect the miniscule flexing over time will cause the frame to become brittle in some spots and eventually break. Not so much "wear out."

My 1st mx bike 87 cr125 I jumped up & down  a ski flying ramp. The wood was removed. Jumped it sideways too that was like cliff jumping. Get air hang in the air pancake the bike then turn it left . Still hanging take a deep breath & drop 700 ft.  That frame was trashed when I sold it . Lol   I broke the shock in 4 ft whoops too.