Why is frame weight important?

Discuss light weight issues concerning road bikes & parts.
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vinuneuro
Posts: 103
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Location: Chicago

by vinuneuro

I live in a particularly flat area so I'm a bit naive about climbing. Generally there seems to be a sentiment that lighter bikes are better for climbing. I can understand wheels making a massive difference due to the physics. But I've lost 1kg of water in long hard workouts and weight among riders will vary 10s of kg's. So when light vs. heavy carbon frames is only in the range of 200-300g difference, why is so much importance given to frame weight?

I realize the forum I'm asking this in, and just to be clear the question is posed out of genuinely wanting to know, not to be provocative.
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Kayrehn
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by Kayrehn

It feels good to accelerate and roll off on a light bike. If you race, you'll like to feel fast. If you don't, you'll like to enjoy the experience of riding something light. Overall bike weight is probably more important than just the frame weight in contributing to the feel of lightness, imo.

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by Weenie


claus
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Joined: Fri Oct 31, 2008 10:04 pm

by claus

vinuneuro wrote:
Mon Mar 26, 2018 1:30 am
weight among riders will vary 10s of kg's.
How is the weight of other riders relevant?

It's simple physics: with the same power output less weight gets you uphill in less time.
Whether that matters to someone is up to them to decide...

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Lewn777
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by Lewn777

Simple answer is 'light bikes are more fun to ride'. They accelerate quicker, decelerate quicker, are more 'flickable', 'hoppable' and climb quicker. The only thing they don't do better is descend, but they are probably equal to any other bike with the same geo in that regard.

If you look at a range of bikes made by the same manufacturer at different levels lets say Giant TCR, Trek Emonda, Fuji SL etc the difference is up to 3-500g from lower to higher end frame-set. All other things being equal I'd rather have a lighter bike. If we said the frame cost for a low end carbon bike (if you could get it as a frame-set only but you almost never can) was say $500-$750 and the high end frame-sets cost $1,500 to $2000+ dollars then you can see the difference is 50c a gram or so. For many people that's worth it, even if we don't take into account that the higher end frame could have better ride qualities.

Although I ride in mountainous areas. Maybe if I rode in flat areas I'd be more interested in being an aero weenie, although I'd still be interested in keeping weight lower when possible.

stormur
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by stormur

Generally not true ;) assuming same "shape" of frame, just thicker ( cheaper ) layers heavier bikes will be more comfortable ( more thicker material equals to better vibration dampening ). Will be more sturdy as well, and much more damage resistant. Chance for voids ( reliability over time ) are much lower with less layers. Due to better dampening it will feel more "planted", some call it "dead" , but just in comparison to lighter frame transferring road much more directly to contact points . Lighter frame will vibrate ( resonate ) much easier than heavier one.

Lets say that everything went very ok with process ( no voids, wrinkles, resin issues ... ) - so all is exactly as engineered ( dream on ;) ) - lighter bike should ride better. Not because it's lighter, but because of used material characteristic. Thinner fibers allow for more complex layup. That's major difference.

Agility & co.... so if you throw away water bottle your bike characteristic will change ? ( 700g difference approx ) . Nope. It's not that easy.

Another factor is non relative stiffness. heavier bikes are stiffer. That's why we're feed with crap called "stiffness to weight" .

If I have to choose from uber-light bike and 2nd tier which is 200-300g heavier .... I'll choose lighter for climbing and heavier for descending ;)

overall... so long as someone pays for own equipment... 300g is irrelevant for performance ( half water bottle ) . If it start to matter for someone... then someone else will pay for his/hers equipment.

For the sake of "having the lightest" - here every gram counts :)
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TLN
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Joined: Wed Jul 12, 2017 4:50 pm

by TLN

Hi. I'm in Chicago as well. I got an Allez Sprint and Tarmac bikes. (overkill, but getting rid of one this spring).
To me, weight does't matter. I realize that Tarmac should be more comfy and it is. It's also lighter, even though it have discs. OTOH Allez have wider and deeper wheels, and after several days on Tarmac I'm not sure which one is faster and more fun.
Btw, I got single chainring (50T) and you can shave that 300gm by removing front der, chainring and cabling easily.

Kaboom
Posts: 118
Joined: Wed Mar 22, 2017 3:53 pm

by Kaboom

lighter bikes are definately more fun to ride and the difference of a full to half empty or empty water bottle hanging on the frame can definately be felt when flicking the bike into corners, hopping, swaying it fom side to side etc.

Is it faster? Yeah, but only veeeeeery marginally so. But it just feels more exciting to ride.

bilwit
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Location: Seattle, WA

by bilwit

claus wrote:
Mon Mar 26, 2018 12:59 pm
It's simple physics: with the same power output less weight gets you uphill in less time.
Whether that matters to someone is up to them to decide...
This. If you never or rarely go uphill, then as far as you're concerned, it doesn't matter. If you enjoy flying up climbs with as little effort as possible for the same amount of speed, those 300g "feels" tangible.

It's the same as people who never ever ride in the rain and/or go down unavoidably brake-laden downhill roads asking why in the world ANYONE would EVER want disc brakes :lol:

MyM3Coupe
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Joined: Thu Nov 24, 2016 10:32 pm

by MyM3Coupe

It’s not. Rims/wheels are way more noticeable. A frame is the last place to “save weight.” Unsprung weight is what u wanna kill. A frame is not that.

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Calnago
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by Calnago

I think discerning between "sprung and unsprung" weight is only relevant when you're talking about suspension. When battling gravity going uphill, everything counts... sprung, unpsrung, everthing. If you go uphill long enough you start looking for any and everything that you can ditch. Having done some significant long distance fully loaded touring, it's funny how you start off your journeys thinking "this will come in handy, I can't leave without this, etc.". After a few weeks and some mountainous terrain, you're either tossing everything you don't need or sending it back home, or looking for the same utility in a lighter package. Every extra ounce seems a burden when climbing.

On the flats... not so much... takes a bit longer to get up to speed, but not much extra effort to hold it once youre there.
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Vermu
Posts: 235
Joined: Wed Dec 22, 2010 6:39 am

by Vermu

MyM3Coupe wrote:
Tue Mar 27, 2018 5:49 am
It’s not. Rims/wheels are way more noticeable. A frame is the last place to “save weight.” Unsprung weight is what u wanna kill. A frame is not that.
Unsprung mass is mainly used in automobile sector and for a reason. On roadbike unsprung mass doesn't have real effect. As everything is unsprung :roll:
But still wheels have biggest impact as it has inertia on them are thus are easily detected.

I think that on frames it's not just the weight that matters. Some really light frames have properties that cannot be achieved on heavier.
All super light are not as comfortable as heavier ones, but then again at the same time carbon frames lay-ups have gone forward by a ton.
Some 800ish bikes are on lighter side but still have aero properties and are comfortable.

More or less you're comparing apples to oranges as the ride feel is created by other properties than weight.
IMO weight gives some info but frame weight isn't something you should keenly stare unless you're Godzuki and better half needs a new bike.

by Weenie


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