Best lightweight bikes 2025: a buyer's guide to climbers' bikes
Looking for the best lightweight, hill-flattening, mountain-conquering machine? We’ve tested the lightest and fastest climbing road bikes on the market.
While many of today's road bikes can be deemed as lightweight, it’s the dedicated climbing machine that really pushes the boundaries. Making one's bike as light as possible has long been a fixation for many cyclists but the advent of carbon fibre has allowed frame and component designers to produce exceptional light bikes without compromising strength and stiffness.
If you’re considering buying a climbing bike you might be asking if they are compromised on flat and rolling terrain? While they might not be as fast as the best aero bikes, today’s offerings typically incorporate aerodynamic enhancements that make them very efficient across a range of terrain, with the added bonus of being exceptionally responsive when the road points up.
We’ve tested many lightweight road bikes and have selected our favourites here. They’ve been chosen after many hours of riding, testing them in varying conditions to assess their ride quality and ultimately help you make an informed choice; we also have a guide to the best carbon road bikes should you want to look at other options.
The Quick List
Best overall
1. Cervélo R5
Best overall
The S5 manages to balance stiffness and compliance in a lightweight package that's a joy to ride.
Groupset: SRAM Force eTap AXS 12 speed with power meter
Wheels: Reserve 34/37 tubeless ready
Weight: 7.4kg
Reasons to buy
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Perfectly balanced handling
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Lightweight
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Rear end comfort
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Huge pedalling stiffness
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Traditional, clean looks
Reasons to avoid
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High price
The updated R5 frame is a claimed 130g lighter than the older model, weighing just 703g in a size 56cm (painted). The proprietary seatpost and stem are also lighter. There's a new carbon layup to help achieve this alongside fresh tube shapes that help give the bike its sublime ride quality
We loved how plush the rear of the bike feels, thanks in part to the flexible D-shaped seatpost, which works with help from a top tube/seat tube junction that has been dropped by 15mm. As for the front end, it delivers a connected ride with all the feedback you'd want from what is a top-tier road bike with pro peleton credentials.
It's light, and when combined with the stiff bottom bracket, surges uphill. Of course, you have to come down, and the R5 descends beautifully. As for the flat sections of a ride, the new aero tube shapes appear to do their job with aplomb.
Now in its fourth generation, the SuperSix has become a little more aero but also a little lighter too; both enhance it's reputation as true lightweight all-rounder. Little wonder it's raced at the top level by the EF Education team among others.
Recent trends for wider tire clearances and threaded bottom brackets feature in the update. Th SuperSix can now fit tires up to 34mm in width, while the BSA 68mm standard has been adopted - a win for any home mechanic.
As for the ride, we loved how fast the bike it, aided in part by the deep section wheels. When the road pointed up the bike's low weight and smart geometry really came into play, aiding our out-of-saddle efforts. Descending is equally magical.
If you're looking for a more affordable SuperSix than one reviewed here, there are a number of option in the range.
If you're after the lightest climbing bike, your search might well end at the Aethos. In the S-Works guise the frame weighs a claimed 585g, which makes it the lightest of all the bikes featured here. When we reviewed this model our size 52 tipped the scales at under 6kg!
We loved the look of the traditional tube shapes and they helped to deliver a ride quality that is quite sublime. The rear end isn't quite as stiff as an out and out racer, but that's not to say you can't race this bike - in fact it's been used in the professional peloton before. However, that greater compliance really shines through on longer rides. We also found that it's nicely balanced with a 'stiff enough' front end that really delivers a connected feel. And of course it feels right at home when climbing.
The S-Works models are incredibly expensive, whether you opt for Shimano or SRAM electronic shifting. There are 'cheaper' options however, which use a different grade of carbon. They're still incredibly light and we loved how the Comp version of the Aethos rode too when we tested it.
The TCR Advanced is designed as an all-rounder rather than and out-and-out climbing machine. However, given it's low weight it comfortably fits it the lightweight category too. While the compact race bike can be found in the pricer Advanced SL guise, it's the Advanced Pro that we love.
Why? It delivers a sublime ride quality with a spec that's really hard to beat. At this price range to get an Ultegra Di2 groupset with a power meter is rare. The SLR 1 42 Disc Carbon tubeless-ready wheels are sub-1,500g and feature a 42mm rim depth front and rear. In short, they're high end and ride accordingly.
And of course there's the frameset itself. We found it to be a really nuanced ride. The stiffness is noticeable but never to the point where it feels overly rigid. Rather the bike feels lively under foot; it's fast and smooth on the flats, handles with confidence and at a tad over 7kg climbs with great efficiency.
Built-in computer mount sits at an angle, which might not suit all users
Now in it's fifth iteration, the Ultimate is certainly lightweight - Canyon has a claimed weight of just 6.3kg for the top-tier Ultimate CFR Di2, excluding pedals and accessories, in a size M.
As for the sizing, the Ultimate is offered in eight sizes, from 3XS to 3XL. The new version now shares the Canyon Aeroad’s geometry, which means no women’s specific geometry - the previous WMN models have gone. The two smallest sizes in the SL model come with 650B wheels while just the 3XS gets smaller wheels in the SLX version.
Canyon says the new version is five per cent stiffer and some 10 watts faster. While we can't claimed to have noticed this directly, the adopted Aeroad geometry does translate to a direct front end and a pretty aggressive riding position. Our CF SLX 8 model felt really planted, even at high speeds.
The bike also felt especially smooth too. There's room for 32mm tires too, which would likely only add to the ride quality. As you'd hope from a bike this light, it climbs very well. We also appreciated just how stable it felt when coming down the other side - it made for a confidence-inspiring ride.
As well as the range of frame sizes, the Ultimate also come's with Canyon's CP18 cockpit, which is adjustable.This allows you to play around with the width to find the optimum position for you. We did find however that the built-in computer mount sits at an angle, rather than lying flat, which wasn't to our liking.
Lightweight frame allows for UCI rule-breaking builds
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Improved head tube stiffness gives the bike a confident feel on descents and climbs alike
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A stellar-looking frameset
Reasons to avoid
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Not quite as fast as the competition when gliding along the flat
When redesigning its climbing bike, Factor leaned heavily on computational fluid dynamics (CFD), enabling it to test many more iterations of the new frameset in the design phase. It's resulted in a claimed 35% increase in stiffness, and 12-watt aerodynamic improvement over the previous generation model - and the frame weighs just 730 grams.
We found that the low weight and increased stiffness lead to a delightful ride quality. Our review bike tipped the scales at just 6.3kg and as a result it felt incredibly responsive. The improved front end stiffness was tangible; it felt more assertive and handled descents with greater assurance than the previous model.
However, all this stiffness is balanced by plenty of compliance too. On long rides in hilly terrain we didn't feel overly fatigued, with the low seat stays and narrow tube profiles delivering just the right amount of comfort.
Of course no bike is perfect, and the 02 VAM doesn't quite roll along the flats like a true aero bike does. That said, it's still plenty fast. And boy does it look good, too!
As the name states, it’s a road bike that’s designed primarily for hilly and mountainous terrain. By keeping the bike’s overall weight down it accelerates and climbs faster than an all-rounder or aero bike. But because what goes up, must come down, well-designed climbing bikes will also provide the rider with confidence on the descents.
Typically a climbing bike will have a more traditional look than a modern aero bike - think slimmer oval or round tubing rather than deep section shapes. It’s commonplace for climbing bikes to have a traditional two-piece cockpit as well.
The other component of note is the wheels. While an aero bike might use a deep rim wheel, say 50mm in depth, a climbing bike will stick to something shallower in depth and, as a result, lighter in weight.
What is considered lightweight for a road bike?
While there is a certain amount of subjectivity here, a modern lightweight climbing bike will certainly weigh less than 8kg or 17.6 lbs, with many coming in under 7kg or 15.4 lbs.
With the array of lightweight components on offer there’s also an opportunity to go lighter still; while there aren’t too many off-the-peg bikes that fall under the UCI limit of 6.8kg or 15 lbs, there are plenty of custom builds that do.
The size of the bike obviously is a major factor here too. When we tested the Specialized Aethos in a size 52 it weighed less than 6kg.
How we test
We have a dedicated team of testers here at Cycling Weekly, whose job is to review a whole range of cycling products and to write objective reviews of their experience of using them day in day out in a whole range of conditions.
With huge experience, they're really well placed to compare products, identify their strengths and weaknesses and bring you an honest, unbiased assessment of how they perform.
When it comes to testing road bikes we log hundreds of miles, looking at a number of factors as we assess their overall performance. Given that these bikes are designed to be lightweight we place importance on their ability to climb without overlooking other important attributes, including speed on the flat, the handling and comfort over distance. We also look at more general considerations such as build and spec quality, durability and value for money.
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After winning the 2019 National Single-Speed Cross-Country Mountain Biking Championships and claiming the plushie unicorn (true story), Stefan swapped the flat-bars for drop-bars and has never looked back.
But his favourite rides are multiday bikepacking trips, with all the huge amount of cycling tech and long days spent exploring new roads and trails - as well as histories and cultures. Most recently, he’s spent two weeks riding from Budapest into the mountains of Slovakia.
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