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Trek Bonded CF frames "flexy"?

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Trek Bonded CF frames "flexy"?

Old 03-04-22, 10:21 AM
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Smokinapankake
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Trek Bonded CF frames "flexy"?

So I've got a 1995 Trek 7900 Multitrack, the one with the main tubes of carbon fiber, bonded onto aluminum lugs and aluminum rear triangle. Think of a Trek 2300, but with fatter tires, cantilevers, and flat bars. Bought it used last summer and have been enjoying it mostly, but it's always felt like it had a low rear tire. You know how it feels when your tire is low and the bike tends to "wander" around, won't track real straight.... Sitting on the bike with the handlebars rested against the wall, I can move my weight through the saddle side to side, and the seat tube (whole frame, really) flexes alarmingly far side to side. Maybe an inch to inch and a half. My other aluminum (and steel frames, for that matter) when subjected to the same "test" don't flex side to side near as much. Feels weird, like the rear end is coming apart or the back tire is low. I've investigated every joint and tube, every junction and connecting point and found nothing. I don't hear any creaking or cracking, nothing. So my question is this: Are these frames known to be more flexy than other, non bonded frames? I have a Raleigh Technium mountain bike (Bonded E9 main tubes to steel lugs/rear triangle) that doesn't behave like this. Am I in danger of imminent failure? Any insight you can give is greatly appreciated.






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Old 03-04-22, 10:32 AM
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Unfortunately I have no experience with these frames so I can't speak to their flex. I didn't even know Trek had bonded CF frames in the hybrid/mtb line! Interesting seat pillar clamp/brake straddle combo
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Old 03-04-22, 10:51 AM
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Yes, you hear "noodley" with them often. I've owned a couple of the road bikes and will confirm. It really shows up at higher speeds. I just couldn't get used to that.
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Old 03-04-22, 11:15 AM
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Thank you Curbtender for your comments. It's been like this since I bought it (used) but not knowing its history I was afraid I had missed some clue somewhere that would key me into its imminent failure, leaving me broken and battered on the side of the road. But if that's just how they are then I guess I'll just keep wobbling my way down the road.

Anybody else with experience with these frames please feel free to chime in. Thanks!
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Old 03-04-22, 01:07 PM
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I rode a 2300 for a few months and was pleasantly surprised at the solid feel, comfortable ride and good handling. This was with the original aluminum fork. I weighed ~200 lb at the time FWIW.

Scott Peterson
Newport, OR
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Old 03-04-22, 05:08 PM
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I had a 2100 and never objected to the softness of the frame. I raced steel frames that were nice and stiff in the corners and in sprints, but the 2100 was never raced, just LSD because it rode really nice. I believe that under regular riding conditions without stop sign sprints and killer hill repeats, one will find the frame likeable.
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Old 03-04-22, 10:52 PM
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my boy had an alloy framed Trek hybrid machine .
He complained about it wallowing while at speed downhill .
Frame was fine but the tension on the rear wheel spokes was completely out of whack .
Rode like a totally different machine after spoke tension fixed.
I figure the wheel was on the edge of collapse before I got to it .
Just a thought!

That frame is really nice !
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Old 03-04-22, 11:10 PM
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I had a Specialized Epic bonded carbon frame, and it always felt like I was riding on a flat tire. I didn't like it.
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Old 03-04-22, 11:15 PM
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Flexy or not, that thing is CLEAN.
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Old 03-05-22, 12:00 PM
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I don't know about flexy, but they are mighty sexy...
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Old 03-05-22, 02:52 PM
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Flexy? Nope, these bonded alu/carbon frames have a dampened, dull ride quality - the opposite of a lively steel frame, for example.

I remember doing something really stupid once - attempting to spread the rear triangle of an alu/carbon 2300 with Park dropout tools. Long story short, it couldn't be done without ruining the frame -- that alu rear triangle wasn't moving at all. So if you're getting flex out of these babies, something else is going on.
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Old 03-05-22, 08:00 PM
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Thanks for all the input; Iíve done a bit of sniffing around and the results Iím seeing in the few places Iíve found folks discussing these bonded frames reflects what you fine folks are saying - some say theyíre flexy, some say not so much. Iíve been through the wheels; they are trued and properly tensioned so Iím not ready to blame them. I am looking suspiciously at the tires, Specialized Nimbus sport 700 x 45c. Maybe Iíll try something a but stiffer like some Schwalbe Marathons in 35c just to see what that doesÖ

And you are right, they are sexy!
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Old 03-05-22, 11:57 PM
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I was looking to buy a carbon fiber road bike about 1995/96.

As often is the case, I think the flexy answer is = maybe; especially, given tire width (as you have pointed out). For 'on-th-road' situations, loaded weight, torque applied to drivetrain, how that torque is applied (out of saddle climbing in harder gear or seated and high cadence smooth spin), lateral stiffnes of frame, other input forces from rider (handlebar width/stiffness?).

My impression was that the 2100/2300 were quite flexy in size 60cm with a 200# rider.
The OCLV 5200 that I tested was stiff, but had no road feel which I attributed to the large BB area and tube sizes. So called "wooden feel". Aegis was similar. Kestrel was better. Look the best. A few years later, 1999, I bought a Calfee, made in Santa Cruz, CA. By then Parlee was getting started, too.

Degradation of the bonded carbon with aluminum lugs was often due to 'galvanic corrosion' as much as any other bonding concern. Not sure if that design&manufacturing challenge was solved 100% in their 1995 models.

Make it the recovery day bike.
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Old 03-07-22, 12:07 AM
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Originally Posted by Smokinapankake View Post
Feels weird, like the rear end is coming apart or the back tire is low. I've investigated every joint and tube, every junction and connecting point and found nothing. I don't hear any creaking or cracking, nothing. So my question is this: Are these frames known to be more flexy than other, non bonded frames?
Have you checked your rear wheel? Maybe a broken axle?

That frame appears to be in incredible condition for its age, and as such I think you would be able to spot an issue with the bonding relatively quickly.

To be fair, the seated flex you feel is dependent on some bits being stationary whereas there may be room to slide/skew/move while actually rolling. I can make various parts of a bike flex on their own while stationary (eg crank arm, fork) but in concert, while moving, it's a different song.
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Old 03-07-22, 08:40 AM
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Rear wheel is good, axle is not broken. I just trued it Satuday and discovered it is sporting butted spokes (brass nipples), a feature I was unaware of previously. I haven't been able to find anything suspicious about it, other than my fat a$$ sitting on it. I weigh right under 200 pounds some days, just over on other days. Maybe this has something to do with it? At any rate, the next thing I'll try is a tire swap, then if that doesn't produce any noticeable change I'll go for a wheel swap. It's too nice not to ride, and the wiggly feeling doesn't bother me too much, so it'd be foolish to shelve the frame. Until it does separate on me, that is. Thanks for all your input folks, this forum is amazing!
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Old 03-07-22, 10:33 AM
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Second pic: What is that vertical line along the seat tube, left side just above the BB?

Since the gloss finish carbon is shiny, it could be a reflection of something on the ground, like a floor pump, but if it isn't - hairline crack?
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Old 03-07-22, 11:36 AM
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https://www.wisconsinhistory.org/Records/Article/CS2777
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Old 03-07-22, 10:09 PM
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Trek 2120 owner here. 200#, not massive wattage. I definitely don't describe it as flexy. And I'll ride it with 15# of picnic lunch and family layers in some panniers

The prior description as somewhat "wooden" is closer to my feeling about the ride.
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Old 03-07-22, 10:10 PM
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OP, how is the spoke tension on the wheels, check it on both again?
My friend had a similar situation as the one that you are describing and it turned out to be that he had several spokes that were really loose. I tensioned the wheel and all was good.
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Old 03-08-22, 03:40 PM
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Spoke tension is good - the bike hasn't been ridden since last week; been cold outside and I don't like the cold one bit. I rechecked the seat tube at the BB; no cracks so that must have been a reflection or something. Looked at it from all angles with a flashlight to highlight any funkiness and found only smooth contiguous finish. Maybe I'm making too much of it. I've yet to swap out tires.... I'm quite confident the frame is sound.
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Old 03-21-22, 01:31 PM
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So I did finally get a chance to swap tires out. Went from Specialized Nimbus Sports labelled to be 700 x45c to Schwalbe Marathon Plus labeled to be 700 x 40c because that's what I had on hand. A 15 mile ride should have revealed any funkiness but I'm quite pleased to report no funkiness was encountered. It appears that the culprit was the tires. In thinking about it, I got to looking at a copy of the 1995 Trek Catalog where it lists the rims and their measurements (pg. 42, if anyone is asking). The Journey rim, which my bike has, measures only 13mm between the bead seats. That seems really narrow to mount a flexy, wide tire on. Or am I thinking wrong? What is the recommended practice with regards to how wide a rim vs. how wide a tire is appropriate? Any thoughts, as always, are welcome.
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Old 03-21-22, 02:01 PM
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That does seem like a pretty narrow rim for a 40 mm tire. Sheldon Brown's page (which has always seemed a bit conservative to me) suggests a max 25 mm tires with a rim that narrow.

https://www.sheldonbrown.com/tyre-sizing.html
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