Carbon rear triangles (MTB)

Curious if anyone has an answer.

Why do some companies, (Salsa for example) have a carbon bike with everything carbon except the chain stays?

Can they not spec a full carbon bike?

Hump

Probably fall under 2 reasons:

  1. Cost - aluminum is likely cheaper and may have a VERY small weight penalty compared to a similar carbon piece. Look at carbon stems - most are the same or heavier than a good lightweight aluminum one.

  2. Complexity of build/strength needed - certain bikes may require a complex shape that is better suited to the properties of aluminum. Either due to the strength needed or cost to build the shape out of carbon(see #1)

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Because they break. I’ve had several carbon XC frames that have had chainstays break. I think aluminum is just a better material for the stresses put on chainstays. Like mentioned above…they could probably make carbon stays that were better but they might be too heavy or expensive to serve the purpose.

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Off topic….I really wish more companies sold complete aluminum bikes with higher end component specs. Carbon frames are great but expensive and aluminum frames are really good these days. I see more benefit in higher end suspension, brakes, hubs, etc. on aluminum frames than low end components on a carbon frame.

I know I can build up my own bike but I prefer to buy completes.

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That would be nice, like pick between a similar spec, but aluminum or carbon.

Hump

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I couldn’t agree more. My current XC bike is a 2020 Giant Anthem 29 2…all aluminum frame. I swapped out everything to Shimano XT, swapped out all the aluminum components to carbon…bars, stem, seat, seatpost, & wheels. Its a large and weighs 24.5 lbs, not too bad but I don’t have to constantly look for cracks on the rear triangle. My previous bike was a Felt Edict, broke the rear triangle three times, Felt replaced it the first time, the second time they said they only had a few left and had to save them for “team” riders, so I had it repaired and it failed again. Picture is of the stock Anthem.

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I think it’s weight/cost. The previous Spark, and several other brands over the years, had a Carbon main triangle, aluminium rear triangle option.

That was a super appealing option to me having had seat stay damage on my aluminium anthem that never caused issue.

I agree nice aluminium options would be cool. I’m super into the 2022 Trek Top Fuel 8. Good spec, great colour, and an aluminium frame which should be recyclable and more hardy/less precious.

It is heavy though. Medium is 14.5kg so that’s nearly 2kg more than carbon equivalent

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That’s a great weight for an aluminum framed bike.

Hump

@KonaSS is bang on the money.

An additional factor is that companies would like to offer cheap(er) bikes that they can advertise as carbon. Even though @mtbjones makes a good point about aluminum, I think in practice this puts many companies at a disadvantage. A lot of customers buy bikes according to specs, because you can’t tell how they ride from the stats. So if you have a $4k bike with very good components and an aluminum frame at a “mediocre” weight, I don’t think it’ll sell all that well.

Even on the road bike end of things, the only two aluminum bikes with some cachet are Cannondale’s CAAD-series and Specialized’s Allez. On the MTB side, I would like to have a BMC Twostroke AL frame to replace my current (old) carbon frame.

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Salsa’s tagline for years has been “Adventure by bike”. They don’t try to compete on lowest build weight, they‘ve always marketed towards bike packing, adventure touring, backcountry riding and similar.

I’ve personally never had a problem with carbon rear triangles on a MTB, but if you’re not racing XC against weight weenies I can buy the idea of an aluminum rear triangle being a simpler, more durable and dependable option for those who want most of the advantages of a carbon frame but with less risk of being stranded in the backcountry.

For what it’s worth, I have a 2014 Spark 930 with an alloy rear triangle, and the rear triangle still broke and was replaced under warranty (by the previous owner).

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