Best mountain bike frames: Upgrade your chassis

If you're browsing through mountain bike frame listings looking to upgrade your current bike, here's everything you should know before hitting that 'buy' button.

Even with the sheer variety and high quality of complete bikes available in the modern era, there is still something to be said for cherry picking a frame to build up into the best mountain bike for you and your particular sets of requirements and preferences.

It could also save you some bucks too, by letting you transfer parts off your old bike (providing they fit). Compatibility is a bit of a minefield – we’ll go into more detail later – but big ticket items such as forks and wheels should transfer across if the frame fits into a similar travel and application category.

As we don’t test frames on their own, this buyer’s guide represents some of our favourite (and highest scoring) models from each category that happen to be available as a frame only.

Hardcore hardtail

Nukeproof Scout 290 Alloy frame

1. Nukeproof Scout

Light weight with sharp handling

Reasons to buy: Stellar specification. Compliant ride.

Reasons to avoid: Care needed with sizing. Tall seat tube. Only three frame sizes.

Although it doesn’t boast the most up-to-date sizing and fit, we can’t fault the ride quality of Nukeproof’s Scout. When we last reviewed the Scout it was the smaller wheeled 270 and we praised the compliance of its frame. It’s no different with this 290 Comp either – smooth, comfortable and quiet, allowing your mind to stay focused on the trail ahead.

Yes, the XL Scout would certainly benefit from a shorter seat tube and a longer head tube, or at the very least and adjustable stroke dropper to get the best from the frame and as it’s very much at home on the descents.

Read our full review of the Nukeproof Scout 290 Comp

XC race bike

specialized s-works epic evo frame

2. Specialized Epic Evo

Dialled option from the Big ‘S’

Reasons to buy: Ditching the chainstay pivot has only improved its speed. No more Brain makes suspension set-up easier.

Reasons to avoid: Seat tube lengths are still more in tune with road bikes than modern trail bikes

The Epic Evo takes the quintessential XC bike and puts it through boot camp to emerge faster and more capable than ever. There’s an extra 20mm travel up front compared to the Epic, which helps slacken the razor-sharp steering to make it less twitchy at high speeds.

At the back there’s 10mm more travel, which helps with comfort and traction. The carbon frame is sleek with a classic shape and an excellent choice of sizes, so you can be sure to get the right fit.

You’ll need tighter reins compared to a true down-country bike, but the Epic Evo is more than capable of winning on Sunday, shredding on Monday.

Read our full test review of the Specialized Epic Comp Evo

Down-country

Santa Cruz Tallboy frame

3. Santa Cruz Tallboy

Blends big bike geometry with small bike travel

Reasons to buy: Still one of the longest-feeling 120mm travel bikes

Reasons to avoid: Needs a pretty skilled rider to avoid prat-falls

Despite its desirability level forever being premium, Santa Cruz is often ever so slightly behind the cutting edge. Not so with the Santa Cruz Tallboy. In fact, the very first version of the Tallboy way-back-when in 2009 was probably the bike that tipped a lot of bike media journos into a love affair with 29in wheels that has held sway ever since.

More than any other bike name, the Tallboy is to blame for down-country. The new version continues to lead the way.

Read our first ride review of the Santa Cruz Tallboy

Transition Spur frame

4. Transition Spur

Hilarious speed freak

Reasons to buy: Perfect speed/capability ratio.

Reasons to avoid: Business-like way it keeps wheels on the ground.

Did someone say down-country? The Spur is so on trend it hurts. Transition as a brand is typically a leader rather than a follower and this short travel, progressive geometry ripper is right at the forefront of modern mountain biking. The Spur is not designed for hitting chunky enduro tracks blind at warp speed; the Spur is all about maxing out the fun on trails that are more familiar and/or calmer.

It’s not cheap, but that’s the price you pay for being on the cutting edge of speed and handling.

Read our full review of the Transition Spur

Trail/Enduro

nukeproof reactor carbon frame

5. Nukeproof Reactor

Devours the roughest tracks yet climbs with poise and efficiency

Reasons to buy: Fast, fluid suspension, never feel over-biked.

Reasons to avoid: Fairly steep compared to some modern trail bikes. Could do with a shorter seat tube and more standover clearance.

In the Reactor 290c Elite, Nukeproof has delivered a 29er trail bike that easily meets the demands of modern trail riding. It has a buttery smooth suspension response, where its reactive 130mm travel never feels too soft or lacks the support needed for hard charging. And charging hard is what this bike actively encourages.

The full carbon frame makes for a precision instrument that can be used to slice through any trail, but the Reactor is not so stiff as to make it a double-edged sword. Balance is the key, and Nukeproof has delivered on all fronts.

Read our full review of the Nukeproof Reactor 290C

Vitus Sommet frame

6. Vitus Sommet

Race-ready 29er enduro bike that blows the doors off everything else at this price point

Reasons to buy: Neutral handling, killer build.

Reasons to avoid: No low-speed adjuster on rear shock.

In the same vein as the Trek Slash or Yeti SB150, the Vitus Sommet CRS is a 29er enduro bike that is designed for big days in the saddle, not just sitting on your ass on a ski lift. And by simply swapping the sticky Maxxis MaxxGrip front tyre for a faster rolling MaxxTerra, it can easily serve double duty as a fast, efficient big-hitting trail bike.

The fact that the complete bike costs less than the Yeti or Trek frame and weighs under 16kg, goes to show that you don’t need to sell your car to have a really nice bike.

Read our full review of the Vitus Sommet CRS

Giga MX: the new frame-only mullet option

7. Nukeproof Giga

Devours the roughest tracks yet climbs with poise and efficiency

Reasons to buy: All of the travel, none of the drawback.

Reasons to avoid: Nothing we can think of.

The Giga is testament to the adage that you can have your pudding and eat it. You can all of the all-ness all of the time. Loads of travel. Slack AF head angle. The biggest of wheel sizes. And the most remarkable thing? It rides just like a normal mountain bike when the gradient tips up.

The Giga really is a race-worthy enduro bike that doesn’t feel like a chore to pedal around on your Sunday Social rides. Poppy and playful, the Giga is no passive plough.

Read our full review of the Nukeproof Giga 290 Carbon Factory

Electric mountain bike frames

Specialized Turbo Kenevo SL frame

8. Specialized Turbo Kenevo SL

All the agility of an enduro bike with helping hand on the climbs

Reasons to buy: Can descend with the best enduro bikes and leave them for dead on the climbs. Unobtrusive motor.

Reasons to avoid: Battery can’t be removed easily. Seat tube lacks insertion depth. Price.

Yes, it’s an e-bike, but the Kenevo is the e-bike of the future, available now. Specialized’s highly regarded Enduro gets a lightweight motor and battery and the result is more than the sum of its (not inconsiderable) parts. Agile and powerful, every turn, every jump, every drift, every burst of acceleration – and they come thick and fast – felt natural and familiar on the Kenevo SL, yet also somehow more intense and satisfying than either a pure analogue bike or a full power e-bike could deliver. It inspired us to give more and it gave me more back in return.

Every joule of energy we invested turned to profit – more speed, more control, more engagement, more fun. We really don’t want to be this gushing about a push bike that costs twelve and a half grand, but it’s everything we hoped for and more.

Read our full review of the Specialized Turbo Kenevo SL

Specialized S-Works Turbo Levo frame

9. Specialized Turbo Levo

State of the full-power art

Reason to buy: Specialized takes the e-bike to another level in terms of engineering and ride quality. Adaptable geometry. Dynamic handling. No major motor issues in nine months riding.

Reasons to avoid: Specialized takes the e-bike to another level in terms of price. Shock yoke caused issues with shock leaking air after nine months (we’d also avoid using most coil shocks on this bike).

Totally updated with aggressive, adjustable geometry and a broad 6-frame size range, the new Turbo Levo raises the e-bike bar another couple of notches. There have also been updates to the motor (sturdier belt and different software), better water sealing around the battery connection and a new display screen located in the top tube. The first two are aimed at improving the old bike’s notorious Achilles heel – its reliability – while the final update just extends Specialized’s lead over the competition in terms of its interface and user experience.

If you hadn’t clocked it already, we’re totally smitten by the new Turbo Levo. It’s a completely different beast – and beast is the right word – from the previous generation. It’s insanely capable, addictively dynamic, beautifully designed, masterfully integrated, completely adaptable and brilliantly easy to live with.

Read our full review of the Specialized Turbo Levo

How to choose the best mountain bike frame – a question of compatibility

There are some questions that are easier to answer than others.

There are questions about compatibility that have definite yes and no answers. These are relatively simple things to get right.

But then there are questions that are less black and white. Questions about suitability. Questions about value for money. Questions that have “well, it depends” as the answer.

Let’s deal with the easier compatibility questions first.

Frame compatibility with your existing components

Starting at the front of the bike and working backwards, here are the vital standards to get right.

Don’t you love choice eh?

Wheel size

You’ll need to make sure any new frame accepts the wheel size of your existing wheels. There are two main wheel sizes out there: 27.5in and 29in.

Even if some wheels will technically fit into the wrong wheel size-d frame (27.5in wheels will usually fit into 29in frames for example) you shouldn’t do this as it will almost certainly mess up the handling and possibly cause other issues.

What travel fork do you have?

Fork travel

Assuming your existing fork is a suspension fork, it’s important to match any new frame to the amount of travel that your suspension fork has. In other words, if you have a 140mm travel fork then you need to get a frame designed around a 140mm travel fork.

Having said that, there is a bit of leeway here. It’s generally okay to running a fork that’s slightly longer in travel than the frame is technically designed for i.e. running a 160mm fork in a frame designed for a 140mm fork. We’d advise that you don’t want to run more than 20mm over the intended amount and always check with the frame manufacturer to make sure it is built to withstand the extra leverage of a longer fork. If the fork gets too tall it raises the front end, shortens the reach, slackens the head angle (not always a good thing) and jacks up the BB height.

But we wouldn’t recommend AT ALL getting a frame that’s designed around a longer fork than your existing fork i.e. getting a 140mm travel frame and running a 120mm fork in it. Running a shorter fork in a frame will make the bike really sketchy to ride.

Headsets are a minefield

Head tube

This is again related to your fork. Most modern mountain bikes run tapered steerer tubes, running from 1.5in at the base to 1.125in (1 1/8in) at the top. As a result, you shouldn’t have to worry too much about fork compatibility unless your current bike is very old. But (there’s always a but…) there is a newer standard developed mostly for e-bikes that tapers from 1.8in at the base to 1.125in at the top.

If your current fork runs a straight 1.125in steerer tube, we’d suggest it’ll be worth upgrading the fork at the same time as buying a new frame for a multitude of reasons including geometry, metal fatigue, damping, air spring and stiffness improvements.

A headset pile, yesterday

Headsets

Speaking of headsets. This is the worst part of any bike build project due to the number of different standards out there!

Even sticking with the same general design – say, tapered – there are loads of non-interchangeable standards. Internal, external, integrated, integral.

Unless you’re really strapped for cash, we’d always recommend being prepared to buy a new headset with any new frame. Although, some frames come with headsets included, as brands know it’s a minefield to get the right one. Research the new frame’s headset type and/or contact your chosen retailer to find out what headset to get.

We certainly wouldn’t base any frame choice around what your existing headset is. It’s not worth it. If you have a really expensive existing headset – bung it on eBay and flog it.

A standard – if slightly battered – threaded BB

Bottom bracket

This is a bit like the headset problem above but not quite as bad. There are two main types of bottom bracket: threaded or press-fit.

Check your new potential frame’s spec to see what bottom bracket standard it has. Hopefully it’ll be the same as your existing bike and you can just swap it over. If it’s not the same, don’t worry. You can still probably get that new frame. There are very few chainsets that won’t fit in a variety of bottom bracket designs.

For example, it is possible to run your existing press-fit chainset in a new frame that has a threaded bottom bracket shell. You just need to buy a ‘conversion’ bottom bracket. Similarly, you can have a chainset that used to plumb into a threaded BB and you can run it in a press-fit BB frame. Again, just get the required ‘conversion’ bottom bracket.

What diameter seatpost will fit in here?

Seatpost size

Seatposts come in three main diameter sizes: 27.2mm, 30.9mm and 31.6mm. If you have a look at your existing seatpost shaft, somewhere on it (usually near the bottom) it will say one of the numbers.

27.2mm isn’t very common on new frames – although it is still out there, particularly on XC hardtail frames, so watch out as 27.2mm seat tube frames won’t be able to run very many types of dropper posts.

If your existing seatpost is 30.9mm then it will fit any new frame with a 30.9mm seat tube (obviously!) but it will also fit into any new frame that has a 31.6mm seat tube too. You just need to buy a 30.9-31.6mm seatpost shim to convert it.

If your existing seatpost is 31.6mm then it will fit any new frame with a 31.6mm seat tube but it won’t fit any new frame that has a 30.9mm seat tube. Sorry, it’s new seatpost buying time.

Still on QR rear wheels?

Rear dropouts

This is a biggie. There are various types of rear axle design out there and your existing rear wheel may well have a strong influence in what new frames end up on your shortlist. Having to buy a whole new rear wheel is not a small amount of money.

Most dropouts (and axles) are Boost standard. So 12mm x 148mm rear. Super Boost is the other, less common, rear axle standard on full-suspension frames. This is 12mm x 157mm. If you have an older frame, you may also have 12mm x 142mm or even 135mm QR. If your old frame and new frame don’t have the same axle standards, it’s very likely you will have to buy new wheels to go in one or both ends of the bike.

You can purchase Boost conversion kits for certain hubs. These add a 6mm longer axle spacer to take up the extra space between the dropouts and a further spacer between the disc mount and the disc to space that across to meet the repositioned caliper. But, you will need to redish your wheel (so that it is centred and aligned with the frame) and you won’t benefit from the wider spoke bracing angle (and stronger wheel) that inspired the development of Boost in the first place.

Bracing allows thin driveside chainstay for extra clearance

Tyre clearance

Will your desired new frame accept the volume of tyre you want it to? Does it have enough space at the back to run 2.35in tyres covered in a layer of your local sticky mud?

Some frames – especially 29ers – can be compromised for wide-tyre and/or heavy-mud clearance at the back. Check the new frame’s description to see what tyre volume it can accept up to. In the UK you really want to be running clearance up to a 2.5in tyre (AKA a 2.35in tyre covered in muck!)

Size matters

What size mountain bike frame do I need?

We see far too many people out there on bikes that are wrong size for them. People who’ve been seduced by a ‘bargain’ only to end up with an ill-fitting bike that harms their riding and limits their fun. Don’t be one of those people.

It can be really, really easy to convince yourself into buying a frame that you know isn’t the right size for you. “I’ll just run a different length stem” or “I can re-adjust my saddle position” or “small bikes handle better” etc etc. All of this is wrong. Don’t do it.

The problem here is that frame sizing – and frame sizing theory – is a bit all over the place. You’ll hear conflicting advice. You’ll read about experienced riders ‘upsizing’ to a larger frame size. You’ll have mates who ride bikes that are too small for them extolling the virtues of small bikes.

Frame sizing based on seat tube length doesn’t help things either. Seat tube length doesn’t really matter with the advent of longer dropper posts. It’s top tube length (and ‘reach’) and standover that are what you need to look out for.

So don’t browse for a new frame based on its stated frame size. It’ll potentially be misleading. A lot of riders think they’re a Medium/18in size when in actual fact they’re a Large/20in, for example. You should be browsing for a type of frame first, drawing up a shortlist and THEN inspecting its sizing dimensions.

Standover: just make sure any new frame has enough standover for your leg inseam length. Simple.

Length/reach: this is a bit more complicated. We’re generally fans of longer reach bikes paired with short (35-50mm) stems. If the standover is still acceptable, go for a large a frame as you can. Smaller is not better. Smaller is sketchier and slower. Larger is faster, more stable, more controllable, and actually more nimble as it turns out.

Questions of suitability and value for money

Now we’re going to discuss the more tricky aspects of choosing a new frame. The questions where there is no obvious right or wrong answer. Questions that are all about “well, it depends”.

Should I choose a full-suspension or hardtail mountain bike?

A common thing is to go from a hardtail frame to a full-suspension frame. In our opinion the main reason not to go to full-suspension is money. Although this is only a single issue, money is a big thing for everyone so it’s a big issue nonetheless.

To buy a decent full suspension frame costs significantly more than buying a decent hardtail frame. Cheap full-suspension frames will weigh a lot, may have durability issues and will usually sport outdated geometry. Full-suspension frames can often have more compatibility conflicts (than a hardtail) with your existing stuff, which necessitates you having to buy a significant amount of new bits (forks and wheels mainly). The debate around full-sus versus hardtail has been around for decades. To put it bluntly, if you have more than £1,000 to spend on a frame, get a full-susser. If you have less than £1,000, get a hardtail frame.

Black magic? Or just another frame material?

Which is a better bike frame material : carbon versus aluminium?

Often you can find the same frame available in either aluminium or carbon fibre versions. The carbon fibre version will be significantly more expensive. The general idea is that the carbon frame will be lighter than the aluminium. And it will be. But often the weight difference isn’t actually very much. Often there’s less than a pound between them.

What is often misleading about comparing carbon v alloy bikes is that the rest of the stuff on the bike isn’t the same. Alloy bikes often get built up with lower spec, cheaper, heavier build kits. Carbon bikes inevitably get build up with top end, expensive, lighter build kits. This gives the illusion that carbon is significantly lighter than aluminium. It often isn’t really. An aluminium frame built up with high end parts will typically end up being lighter than a carbon frame built up with low end parts. Remember this.

Perhaps the more obtuse debate here is ‘ride feel’. Carbon bikes feel different to aluminium bikes. They can be made to feel stiff, flexy, compliant, wooden – you name it, carbon can be engineered to feel completely different depending on the type of carbon used, the tube profiles and the lay-up of the carbon sheets. It’s a lot harder to control the wall thickness and tube profiles of aluminium frames, so engineers tend not to have quite as much control over how an alloy bike will feel on the trail. Having said that, alloy tech and knowledge of frame properties is improving all the time, and the best alloy frames are really sophisticated bits of kit with excellent ride qualities.

A significant development of late has been the introduction of steel into full-suspension frames. These steel full sussers can be almost as expensive as carbon frames and yet they weigh more than even aluminium frames. So why make a steel full-suspension frame then? Because of how they feel to ride. Chassis feel. That particular blend of give-and-go that makes some bikes more fun to rid then others.

Online temptations

Is it better to buy a mountain bike over the internet or via a bike shop?

We’re not going to debate the whole ‘mail order direct sales versus high street local bike shop’ thing here. But we are going to highlight something practical and financially relevant.

Namely, if you buy a frame via your local bike shop, chances are the whole process will go through without hitch or any stress on your part. They’ll make sure your existing parts fit, or will sort out the correct parts to make it all work. They will also have all the right tools – and decent quality tools too – suitable for the latest standards. Whereas you might be thinking of doing it all with your ‘trusty’ multi-tool and a hammer.

And if you’re going to be approaching your local bike shop anyway to help with building up your new frame, then the grand total of what it will cost won’t be as more expensive as you might think. Any decent independent local bike shop will always help you out and leave you happy.

But we do live in the 21st century. Online mail order bargains are a fact of life. If you’ve got the tools and know-how to build up a new frame on your own, go for it.

Even if you’re going to end up taking your new frame (and your old bike) to your local bike shop and paying the subsequent workshop fee, it will probably still be cheaper overall if the new frame was a significant bargain deal. Local bike shops know this more than anyone and you needn’t worry about offending them by presenting them with a frame bought elsewhere. They’ll be used to it and will welcome the workshop job.

Some classics are best left in the shed

Is it better to buy a new bike frame or a whole new bike?

Although this whole guide is about how to choose a new frame, we should also point out that it may not be the best option for some people.

Basically, if you’re going to end up shelling out a load of money because you need to buy loads of bits to successfully build up a new frame, you should think long and hard about just getting a whole new bike.

If you’re still riding on old standards – 26in wheels, QR wheels and forks, 1-1/8th head tubes and so on – it’s time to cut your losses and get a whole new bike. Keep your existing bike a spare bike or a ‘winter bike’ or a ‘bike for the kids’ or a ‘loaner bike’. Don’t try and make a 2012 bike into a 2022 bike, it doesn’t really work like that.

But if you’re not having to shell out for loads of extra stuff – or if you want a frame that isn’t available as a complete bike or as a complete bike in the spec you’d like – we hope you’ve found this buyer’s guide helpful.