Best Hardtail Mountain Bike Review – Top Rated Models with Buying Guide
With summer nearly here and so many plans for riding adventures, getting the best hardtail mountain bike must be on your mind right now. Going through the trouble of finding the right bike with just the right components might be worth it, but then again, you’d probably be better off riding as soon as possible and leaving research to us. We’ve done the homework for you and analyzed some of the most popular bike models available on the market. Our first choice is the Diamondback Bicycles Overdrive Hardtail Mountain Bike. It comes with a sturdy frame, a 100mm RockShox Recon Gold RL fork, 29-inch tires, 1×11 drivetrain, and other components that will enable you to ride on any terrain. In case this model is out of stock right now, you might want to take a look at the SAVADECK DECK300 Carbon Fiber Mountain Bike 27.5″/29″ as well.
The Overdrive from Diamondback has a sleek and strong aluminum frame, 29-inch wheelsets, and a RockShox Recon Gold RL fork with 100mm of travel for good shock absorption. The SRAM NX/GX 1x11 drivetrain makes it a good candidate for XC-style riding.
The Shimano M315 brakes aren’t exactly the greatest, and the drivetrain doesn’t make this bike very versatile.
This bike has decent components, comes at a good price, and is suitable for many types of cycling. The hardtail frame is great for both off- and on-road riding, while the 29-inch tires help with speed and power.
The DECK300 from Savadeck is made with a TORAY T800 carbon frame so it’s very light but durable and strong. You get 100mm worth of suspension with the Suntour fork, while the 3x10-speed Deore shifters and derailleurs allow for seamless gear transition.
The Shimano MT200 hydraulic disc brakes are entry-level, as opposed to many other components on the bike.
If you’re looking for a bike with quality components and a carbon frame, you probably won’t find anything cheaper than this. You can also choose between 27.5" and 29" wheelsets to ensure they’re the right size.
Also To Consider
Just as its smaller DECK300 cousin, this bike comes with a TORAY T800 carbon frame that keeps the entire rig light (24.69lb). You get a Shimano M8000 2x11 drivetrain, DEORE XT front and rear derailleurs, a Manitou M30 suspension fork, and other goodies.
The bike comes without pedals so you’ll need to get these yourself. The suspension fork could have had more travel.
While this bike isn’t the cheapest, its Shimano Deore XT drivetrain, derailleurs, and other similar-level components make it an amazing value for the money. The frame is light and strong, and the overall design is attractive.
10 Best Hardtail Mountain Bikes (Updated Reviews) in 2021
Are you searching for an affordable hardtail mountain bike but don’t have the time to look through countless models flooding the market? Then read our hardtail mountain bike reviews below, as we’ve put in the effort to present all their specs as well as pros and cons so that you can make the right decision and pick the one that’s fit for your needs.
- 1. Diamondback Bicycles Overdrive Hardtail Mountain Bike
- 2. SAVADECK DECK300 Carbon Fiber Mountain Bike 27.5″/29″
- 3. SAVADECK 700 Carbon Fiber Mountain Bike 26″/27.5″/29″
- 4. Steppenwolf Tundra Carbon Race/Pro/LTD Hardtail 29er MTB
- 5. SAVADECK Carbon Fiber Mountain Bike DECK2.0
- 6. Diamondback Bicycles Sync’r Carbon Hardtail Mountain Bike
- 7. Diamondback Bicycles Lux Women’s Hardtail Mountain Bike
- 8. Mongoose Men’s Meteore Comp Mountain Bicycle
- 9. Diamondback Bicycles Hook 27.5 Hardtail Mountain Bike
- 10. Diamondback Bikes Line Hardtail Mountain Bike
- Our Comprehensive Buying Guide
- Frequently Asked Questions:
1. Diamondback Bicycles Overdrive Hardtail Mountain Bike
This model from Diamondback Bicycles comes with a sturdy build and quite a few components that are pretty good for the price. The frame has a sleek design, with a tried-and-true geometry and aluminum tubing that offer the right strength and rigidity to enjoy rides both on- and off-road.
The RockShox Recon Gold RL fork has 100mm of travel which should be able to soak small-to-medium bumps and is good enough for most trail rides. Thanks to the SRAM NX/GX 1×11 drivetrain, you can shift efficiently and avoid losing momentum and power when the riding gets tough.
The Shimano M315 hydraulic disc brakes offer plenty of stopping power so you can ride safely no matter the terrain or the weather conditions. The 29-inch Blanchard 25 wheelset allows you to cover a lot of terrain with few pedal strokes, even if you do lose some handling abilities. The all-terrain WTB tires do a good job offering grip on various surfaces.
This bike comes at a decent price and with a modern-looking design that’s bound to please riders.
The 100mm RockShox Recon Gold RL fork will help you negotiate rough terrain while saving your hands and behind from the punishment.
The 29-inch wheels are great for going over tree roots, rock gardens, and they make for great riding on the road.
The WTB all-terrain tires are an added plus, as they’re great on a variety of surfaces, even if they don’t truly shine on any of them.
The frame looks sturdy and it’s made of aluminum which means it’s light but strong and relatively stiff.
The 1×11 drivetrain is nice for XC riding but doesn’t offer nearly enough flexibility for touring, road riding, and other activities.
For the price, the hydraulic disc brakes could have been a bit better. Some other components could have been a bit better, as well.Buy from Amazon.com
2. SAVADECK DECK300 Carbon Fiber Mountain Bike 27.5″/29″
If you’re looking for a bike with a carbon fiber frame that doesn’t cost an arm and a leg, then the DECK300 from SAVADECK is certainly one choice you can’t overlook. The TORAY T800 carbon frame makes the bike very light but retains amazing strength. Thanks to the SR Suntour fork that has 100mm of suspension travel, you can ride over bumps and potholes like a true pro.
The M6000 DEORE 3×10-speed derailleur system is awesome considering the low price of the bike. The shifters are also Shimano Deore M6000 series so you’ll get smooth gear transition for even power shifting wherever you are. The Shimano MT200 hydraulic disc brakes are nothing to write home about but they do their job well.
You can choose between 27.5” and 29” wheelsets so that the bike offers the right combination of power and speed for your size and riding style.
This bike is quite cheap, considering that you get Shimano Deore components such as shifters and derailleurs. Combined with the TORAY T800 carbon fiber frame, this rig comes at a price that’s hard to beat.
You can choose between 27.5-inch and 29-inch wheelsets so you can get the right size for your height and specific needs.
The Shimano M6000 DEORE 3×10-speed shifters and derailleurs will lead to ultra-smooth shifting so you’ll have no problem no matter if you’re slaying trails or riding on pavement.
The SR Suntour fork has 100mm of travel which is enough for most off-road adventures so you should enjoy all of them while minimizing fatigue.
While you get Shimano Deore-level shifters and similar components, something had to give, and that was the MT200 disc brakes, which aren’t exactly outstanding.
The tire selection isn’t the greatest either, so you might want to get a new set after a while.Buy from Amazon.com
3. SAVADECK 700 Carbon Fiber Mountain Bike 26″/27.5″/29″
While a bit more expensive than its DECK300 cousin, the 700 from Savadeck is a rig that will certainly attract more than a few riders. It comes with a TORAY T800 carbon fiber frame so you know you get an ultra-light bike that you can count on when things get rough. The bike weighs just 24.69lb which makes it ideal for cross-country and not only.
The 2×11 drivetrain is complemented by the Shimano Deore XT M8000 shifters and derailleurs which should ensure superb shifting in any conditions. Thanks to the fully internal routing of the cables, there’s no risk of snagging any in thick vegetation or during transportation. The Manitou M30 air suspension fork will soak up shocks so you don’t have to.
You can choose between 27.5” and 29” wheelsets, where the former gives you enough speed and good handling while the latter helps with higher speed while sacrificing some handling.
This bike has a carbon fiber frame that doesn’t just look awesome, but it is also very light and strong as well. The entire bike weighs only 24.69lb which is pretty good.
The 2×11 drivetrain is excellent for climbing those steep inclines, but also for riding downhill or negotiating tricky terrain.
You can choose the wheelset size so it fits your height and riding style. Pick 27.5” for enhanced handling, or 29” for superior speed.
Thanks to the Shimano Deore XT M8000 derailleurs and shifters, gear shifting will be so smooth that you won’t believe it.
The Shimano hydraulic brakes will give you all the stopping power you need to ride aggressively but also safely.
The bike doesn’t come with pedals, so you’ll need to purchase these on your own.
For bike touring, a 3×11-speed drivetrain would have been a better choice. However, for other types of riding, it’s quite good.Buy from Amazon.com
4. Steppenwolf Tundra Carbon Race/Pro/LTD Hardtail 29er MTB
While not the cheapest around, you actually get a lot of bike for the money. This one comes with a carbon composite frame that’s going to keep the overall weight low without sacrificing strength or sensitivity. The RockShox SID RLT has 100 mm of travel and it will absorb most shocks both on and off the road so you’ll feel comfy even after hours of riding.
The rig is equipped with Shimano XT shifters and derailleurs so you can expect gear shifting to be smooth and just like clockwork. The 10-speed cassette and chain are also Shimano XT, so you get high-grade components across the board.
The DT Swiss X 1900 Spline wheels come with Schwalbe Rocket Ron 29×2.25 Evo tires so you get decent performance on various types of terrain. Great stopping power is ensured by the Avid Elixir 5 disc brakes, that will keep you safe and enable you to ride more aggressively.
The frame is made of carbon composite so you know you get a lightweight rig that’s also strong and stiff.
The 29-inch wheels are great for speed and jumping over large obstacles such as rock gardens, and they are also ideal for bigger individuals.
You get Shimano XT shifters and derailleurs for superb shifting capabilities and enhanced performance.
The 29-inch DT Swiss X 1900 Spline and Schwalbe Rocket Ron 2.25-inch tires give you better handling and grip even on tough terrain.
The FSA Afterburner 175 mm crankset, with 42/34/24t specs combined with the 11-36t cassette, is perfect for both touring and off-road riding.
You might need to change the FSA Afterburner Flat 685 mm handlebars for two reasons: they’ll most likely be too narrow for you, and you might want some riser handlebars instead.
The bike is surely not cheap, although the components such as Shimano XT-level ones more than make up for it.Buy from Amazon.com
5. SAVADECK Carbon Fiber Mountain Bike DECK2.0
Are you looking for a cheaper bike but aren’t willing to compromise on quality? Then the DECK2.0 is just the model you need. It has a TORAY T800 carbon fiber frame that’s stiff and lightweight yet strong enough to handle all the use and abuse you can put it through.
The SAVA Hydraulic suspension fork can handle the shock absorption so your arms and posterior don’t suffer even when riding on rugged terrain. The lockout helps when you’re trying to pedal more efficiently on the road. You can choose between three wheel sizes: 26”, 27.5”, and 29”.
The bike comes equipped with Shimano Altus shifters and derailleurs which should translate into decent shifting performance. You get 3×9 speeds to play with. Braking power is ensured by the SHIMANO BD-MT200 hydraulic disc brakes which will allow you to ride worry-free. The handlebars vary from 630mm to 720mm so you can get the right width for your needs.
The bike’s carbon frame is good-looking and it keeps the weight low while offering superior strength and vibration response.
Thanks to the SHIMANO BD-MT200 hydraulic brakes, you’ll be able to control and stop the bike whenever you need to and even if these are entry-level, they still do their job well.
You get a 3×9-speed drivetrain for extra flexibility so you can ride on any kind of terrain without the feeling that you’d need more gears.
The KMC Z9 is a nice addition as it’s strong and the power link also makes cleaning and repairs (especially those annoying ones on the roadside) much easier than with normal chains.
The fork isn’t this bike’s strong point, and a basic RockShox or SunTour fork would have been much better.
The Shimano Altus shifters and derailleurs are entry-level and somewhat weaker than what you’d expect on a bike in this price range.Buy from Amazon.com
6. Diamondback Bicycles Sync’r Carbon Hardtail Mountain Bike
Want a high-end bike and have the money to spend on one? Why not have a look at the Sync’r from Diamondback? This beautiful rig comes with a Monocoque carbon frame which offers high strength and enhanced stiffness for comfortable rides, and that in addition to keeping the weight low. The Fox 34 Float Performance fork gives you 140mm of travel for superb shock absorption.
The SRAM GX Eagle 1×12 drivetrain with a 32T Eagle chainring and 10-50T cassette gives you flexibility when shifting gears so you can power-shift when cranking up the power uphill but also ride smoothly on flats without a problem.
You get Diamondback Blanchard 32R tubeless-ready rims that are equipped with Maxxis Minion DHF and DHR 27.5×2.8″ EXO folding tires which should give you superb traction and grip as well as handling on those steep trails. The 780mm Race Face Æffect 35 handlebar, with a 20mm rise boosts handling and control.
The frame is made of carbon fiber, just as expected, for extra endurance and low weight. The internal cable routing helps improve looks while also avoiding the annoying snagged cables.
The bike boasts the Fox 34 Float Performance fork which offers 140mm worth of travel for those nasty descents.
The Face Æffect 35 handlebar is 780mm wide so perfect for downhill riding and not only. You can always shorten it a bit if you feel the need to.
The rig comes with Shimano MT501 hydraulic brakes which give plenty of stopping power without being expensive.
While this bike is perfect for cross-country and general trail riding, it’s not such a great option for road touring due to its single-chainring that can be limiting, despite its 10-50T cassette.
This model is certainly not the cheapest and some riders might be unable to afford it.Buy from Amazon.com
7. Diamondback Bicycles Lux Women’s Hardtail Mountain Bike
This bike is relatively cheap, good-looking, and it’s a perfect fit for women, so what’s not to like about it? The 6061-T6 aluminum alloy frame has a lower top tube so it’s comfortable to ride but it doesn’t sacrifice strength. The RockShox Judy Silver TK offers 120mm of travel to soak up bumps and potholes so you can enjoy any ride both on and off the road.
You get the SRAM GX 1×11 drivetrain with a GX shifter and rear derailleur, with the SRAM PG1130 11-42T cassette and a 30T chainring for flexibility and smooth gear shifting. The Shimano BR-M365 brakes will help you control the bike and stop on a dime so you stay safe and sound at all times.
The 32h Diamondback DP25 Doublewall rims are strong yet relatively light, and they come equipped with Vee Rubber Crown Gem 27.5×2.35 tires. Thanks to the Race Face Æffect 35 handlebar that’s 760mm wide, you get better handling and control.
This bike comes with a women-specific frame that offers generous stand-over clearance for extra comfort but also safety in case of unexpected events.
The RockShox Judy Silver TK suspension fork offers 120mm of travel which makes it a good candidate for many off-road riding disciplines.
The 27.5-inch wheels are great since they offer the right balance between maneuverability and speed and the 2.35”-wide tires ensure decent grip.
The full SRAM GX drivetrain provides smooth gear shifting so you can pedal on steep inclines or downhill without a problem.
The Shimano BR-M365 hydraulic disc brakes are there to make sure that you are safe and that you can stop the bike whenever you need to.
The Vee tires are kind of cheap and could have been replaced with better ones, considering the price of the bike.
There’s only one 30T chainring which means you might wish for more gears depending on the type of terrain you’re riding on.Buy from Amazon.com
8. Mongoose Men’s Meteore Comp Mountain Bicycle
This bike from Mongoose comes with some pretty good components and a price that shouldn’t scare away too many riders. The frame is made of tapered EV6 aluminum tubing which is light, strong, and gives the bike a pleasant aspect. The Manitou Marvel Comp suspension fork gives you plenty of shock absorption power to enjoy bumpy tracks without a hindrance.
The 27.5-inch Alexrims MD-21 32-hole tubeless rims are durable and relatively light, and they are equipped with Kenda Slant Six 120 TPI tires that offer adequate grip and traction on hardpack and dusty trails. Thanks to the 3×10-speed drivetrain, you get all the flexibility you need to negotiate any type of terrain like a pro. You get Shimano SLX M670 shifters and derailleurs for smooth shifting.
The Hayes Radar disc brakes and levers are a low-cost option that’s surprisingly durable, even if it’s not the most powerful one out there.
The frame is made of EV6 aluminum tubing that is strong and light but it also looks modern and sleek so it makes the bike a sure head-turner.
The Manitou Marvel Comp with 15 mm thru-axle is there to ensure no tree roots, rock gardens, and other obstacles will cause you trouble down the path.
The Shimano 30-speed drivetrain comes with Shimano M670 SLX shifters and derailleurs for seamless shifting performance in any situation.
Built with 27.5-inch Alexrims MD-21 rims and with Kenda Slant Six tires, the wheels are going to be able to handle lots of abuse without showing signs of fatigue.
The Hayes Radar disc brakes aren’t known to be very powerful or sensitive, although they do last for quite a long time.
Some older-generation components were used, which is a bit odd considering the price of the bike isn’t exactly the lowest.Buy from Amazon.com
9. Diamondback Bicycles Hook 27.5 Hardtail Mountain Bike
This bike is a favorite among many riders and for all the right reasons. Its amazing look is backed up by quality components that can make any ride feel great. The aluminum frame has a progressive geometry that strengthens the structure while also enabling it to be lighter and behave better on the trails.
Thanks to the SR Suntour XCM 120mm suspension fork, you won’t be bothered by tree roots, rocks, gravel, and other things you normally bump into when riding off-road. The SRAM single-ring 1×8 drivetrain keeps the weight low while still giving some flexibility when it comes to gear ratios.
The Tektro Aries mechanical disc brakes are decent enough as far as braking goes but you will need to fiddle with them to ensure they’re adjusted properly at all times. The 27.5-inch tires are good for both speed and handling so you get the best of both worlds.
The frame has a modern and progressive geometry and it uses lightweight aluminum tubing for high strength and durability.
With the SR Suntour XCM fork, you get 120mm of travel so you can ride just about anywhere without tiring your arms or bottom.
The 27.5-inch wheels are great since they allow you to pedal fast and get over large obstacles while still being easier to handle compared to 29-inch wheels.
The single-chainring drivetrain helps keep the overall weight of the bike low.
You also get pedals mounted on the bike, which is a bonus, considering the fact that the bike is quite inexpensive.
The 1×8 drivetrain is pretty limiting so you won’t be able to do stuff such as cross-country or other riding styles unless you’ve got thighs of steel.
The Tektro Aries mechanical disc brakes are perhaps not the best choice for the bike, but at least they keep the overall price quite low.Buy from Amazon.com
10. Diamondback Bikes Line Hardtail Mountain Bike
If you’re looking for a bike that looks just as good as it rides, then you can’t go wrong with the Line from Diamondback. The frame’s low-slung geometry offers plenty of standover clearance so you don’t get into any accidents, and the 6061-T6 aluminum tubing is reliable in the long term. The tubing is also custom-formed and butted for extra strength and durability.
The 120mm SR SunTour XCR fork is a good choice for an inexpensive bike such as this one, and it can soak up quite a few bumps so you won’t be penalized when the riding gets rough. The Shimano 1×9 single-ring drivetrain makes things simple and eliminates extra mechanical parts so there’s less to worry about. It also comes with the added bonus of lower weight.
The Shimano Acera M3000 shifter and derailleur help keep shifting smooth so you don’t get frustrated by misses in all the wrong moments.
The Shimano Acera M3000 shifter and derailleur offer decent shifting performance so you don’t miss a second due to missed gear.
With the Shimano M315 hydraulic disc brakes, you get the peace of mind that you can stop the bike at any time without a worry.
The 6061-T6 butted aluminum frame is a strong option that will serve you for many years to come.
You don’t have to worry about bumps and other obstacles anymore as the SR SunTour XCR fork comes with 120mm of travel which is quite enough for most riding purposes.
This is an all-purpose hardtail that will allow you to ride on forest trails, climb steep inclines, pedal fast downhill, and maybe even do a few low jumps here and there.
You only get 9 speeds to play with and that could prove to be far from enough, especially for longer rides.Buy from Amazon.com
Our Comprehensive Buying Guide
Whether you’re looking for the best hardtail mountain bike under 1500 or you want something a bit cheaper, finding the right rig can be more challenging than you might expect. That is not due to a lack of options on the market, but on the contrary: there are so many of them, with so many specs and components, that it’s hard to figure out which one is the right bike for you.
Here are a few aspects to think about before deciding on the best budget hardtail mountain bike.
When it comes to top hardtail mountain bikes, you can expect the frame to be made of carbon, although that’s not necessarily true for all models. Carbon is lighter than aluminum, in general, and it’s stiffer, which is why you tend to find it on many bikes.
However, it does not mean that you need to fork over tons of cash to get a carbon build, as you can certainly find that ‘the best hardtail mountain bike under 2000’ candidates that have a carbon fiber frame.
On a cheap hardtail mountain bike, you can expect to find an aluminum frame, although that does not necessarily mean that it is of lower quality. The tubing diameter and thickness matter as much as the frame material, and so does the geometry, so don’t disconsider a bike just because it’s got an aluminum frame and you think carbon is all the rage.
Frame geometry is also important to take into consideration, and that especially if you’re a woman. A modern frame on a women’s bike usually has a low-slung geometry which still keeps the classic triangle shape while retaining its typical strength.
Most modern bikes come in 27.5” or 29” wheels, although you can still find 26” bikes out there, which are still a decent option if you’re low on cash or you’re shorter. The most popular option is probably the 27.5 hardtail mountain bike as it offers the right combination of speed and maneuverability.
When it comes to good hardtail mountain bikes, you will usually see that they come with suspension forks with a travel between 100mm and 120mm. You can also find models with 140mm forks, but those are quite expensive.
However, even a 100mm-travel fork should do the job if you’re a casual rider, and 120mm forks will probably be enough for many other types of rides, unless you’re into DH, in which case, you’ll need a full-suspension rig rather than a hardtail one.
Depending on what you want to do with the bike, you’ll have to think about what sort of drivetrain you need. For a trek hardtail mountain bike, an “oldie” 3×9-10 drivetrain is a good option as you get many possible gear ratios for all sorts of situations and terrains.
If you’re more into cross-country, then a single chainring drivetrain might be a good choice as you get to simplify mechanicals and shifting while also lowering weight. Double chainring drivetrains are somewhere in the middle, but the specs of the cassette sprockets are equally important.
Most bikes nowadays, hardtails included, come with hydraulic disc brakes. You may still find some mechanical disc brakes on lower-end models, which might be decent enough, especially if you’ve got a low budget.
You’ll probably want to aim higher and if you can afford them, go for higher-level brakes such as Shimano Deore or Shimano XT to benefit from reliable braking.
Frequently Asked Questions:
Q: Are hardtail mountain bikes better than full-suspension bikes?
In the never-ending hardtail vs full suspension mountain bike debate, no one seems to be winning, and the answer to the question is that one is not better than the other, and the real question is “what will you use it for?”. Hardtail bikes are excellent all-arounders as they are good on paved roads but also on off-road trails.
They have simpler mechanics than full-suspension rigs and are easier to maintain. They’re much better in terms of pedaling efficiency and speed and they are cheaper than their full-suspension counterparts. Full-suspension bikes, on the other hand, are mechanical wonders, they absorb most bumps and obstacles and they’re ideal for downhill or for riding on any tough terrain.
They’re also becoming better at pedaling efficiency as both shocks come with lockout features. The best full-suspension models are considerably more expensive than best hardtail mountain bikes, so if you don’t need rear suspension and are on a limited budget, then a hardtail rig is what you need.
Q: What are the benefits of riding a hardtail mountain bike?
Despite all the buzz and rage about full-suspension rigs out there, hardtail mountain bikes still have their advantages, which can actually be many, depending on what you are looking for. First of all, hardtail models tend to be considerably cheaper than full-suspension ones, so if budget is a factor, then a hardtail is in order.
Hardtail bikes are also lighter, and their simpler design means they’re also easier to maintain, since they don’t have a rear shock, bushings, bearings, pivots, and all sorts of other moving parts. Hardtails are much better when it comes to pedaling efficiency, and even with all the improvements in suspension bikes, the former still own when it comes to speed.
This efficiency is also applied when it comes to climbing steep hills, as there is no rear shock to rob you of energy. Of course, no hardtail mountain bike review is going to brag about downhill prowess, but you can’t have it all (or you actually can if you buy a hardtail and a full-suspension bike).
Q: How much does a hardtail mountain bike cost?
If you’re planning to get the best hardtail mountain bikes under 1000 but fear that is not enough money for a decent build, then fear not, as there are actually a few rigs that come with quality components without costing an arm and a leg.
For less than a grand, you can find bikes with aluminum frames, hydraulic brakes, and components that are usually between entry- and mid-level, such as Shimano Altus, Acera, Alivio, and so on. As for wheel sizes, you can find anything from 26” to 27.5” to 29” so you’re not limited here by the budget.
There are also quite a few choices out there when it comes to the best hardtail mountain bikes under 1500 dollars. Some of these can actually come with a carbon fiber frame, higher-grade components such as Shimano Deore and XT or SRAM NX/GX. Forks also vary and travel distance is usually between 100mm and 120mm.