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thechriswebb
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Greetings, this is my first post on MTBR. I have lurked here for ages and post regularly on RBR, but this is my debut here.

I have a simple question. I feel like this issue has certainly been discussed at some time, but I cannot seem to find it by searching. So, please humor me.

Over in the road bike forums, the issue of carbon fiber vs. aluminum has been discussed a million times. The same arguments come out: carbon explodes, aluminum is too harsh, and so forth. It is pretty much universally accepted and has been for years that carbon fiber is capable of absorbing more shock than aluminum. However, there is quite a constituent of riders (and I mean good, experienced riders who have the resources for and own expensive carbon fiber bicycles) that will vehemently argue that the difference in the compliance between carbon and aluminum bikes can be virtually eliminated by slightly lowering the tire pressure in the bike with an aluminum frame. Now, this may or may not be true, and it has been argued into the ground. Take into consideration however, that this is in reference to fully rigid road bicycles with no suspension whatsoever.

My question arises from some reviews that I have read on mountain bikes. I have read multiple reviews on mountain bikes with aluminum frames that claim that the bikes are overall pretty good, but feature some of the harsh "feel" of aluminum bicycles. Now, whether or not it is completely true, it seems to me that if it can be legitimately argued that the harshness of aluminum can be significantly dampened by a reduction in tire pressure on a super stiff rigid road bike, that arguing that the ride of a modern $3000+ fully suspended mountain bike with fat tires set to 45 psi is somehow notably more harsh because the frame is made out of aluminum seems a bit bogus to me. Perhaps I just don't have the special sensitivity claimed by the experts to detect such things, but it seems like just a bunch of rhetoric to me, perhaps brought on by the preconceived notion that the ride would turn out a certain way. I'm curious to hear other perspectives on this.

-Chris-
 

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Since I have acually sat on a carbon bike once several years ago, I feel qualifyed to respond.
I feel that several things go into the feel of a bike. Resonant frequency, give or deflection during an event, damping of the vibrations, and getting those resonant frequencies started in the first place are the promanant ones. A ridged bike sets up these vibrations easier than a fully. Same with soft tires. I feel carbon quells the vibrations best which is why I still use fiberglass fishpoles. Never seen a carbon bell either.
 

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I'll take a stab.

Its how the material is used, not just what material is used. Alu frame tubes are seriously oversized, and cf bikes are designed to flex a bit because people expect them to. Also, the impacts going into the frame are much larger on a mtb. A pebble on the road is a branch on a mtb, and the fork is a big lever on the frame. Riders tend to be sloppier pedalling an mtb too, they have trail features to focus on, instantaneous power output is higher, and the geo doesn't work as well for standing. It all adds up, especially if you are a discriminating mtb'er, and it helps if you're large. Granted, it's not as significant as tire pressure or fork choice, but it's definitely perceptible.

If you're running 45psi, you're doing something wrong.
 

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I have an Al and cf road bike. For the first 1.5 hrs, not much significant difference. Certainly not to justify double/triple the cost. Lowere tire pressure? Meh... I guess. Y cf bike feels almost the same at 80psi or 110psi. But I do notice rolling resistance and handling. After 2hrs of riding the Al bike, I wanna quit. On the cf bike, I still feel very fresh. That's where the difference is really noticed.

For mtb, there's argument for Al vs Steel on Hardtails. The feel of steel and all. On an fs bike, the suspension impacts the ride way more. Stiffness of the frame allows the suspension to do it's work properly.

Cf really allows you to Taylor where and how stiff you want to make your frame.
 
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