The bike rolled out of the shop wearing fat, chunky off-road tires, and somewhere along the way its life turned into roads, bike paths and the long way home through the park.
You hear it first. That low hum from the knobs on smooth pavement, like the bike is quietly telling you it’s working harder than it should on a ride this easy.
Slick tires on a mountain bike change that.
A swap, and the same bike rolls easier, rides quieter and picks up speed on the pavement it actually sees. Here’s what those knobs cost you, how to pick the right replacement, the checks that make sure it all fits before you spend a cent, and when the knobs are still worth keeping.
What Those Knobs Cost You On Pavement
Knobby tires are built to dig into dirt. On pavement, that tread just costs you.
Bicycle Rolling Resistance runs every tire in its mountain bike tests on the same drum at 18 mph with a 94-pound load per tire. A near-slick MTB tire with tiny 0.5 mm knobs tested at about 12 watts per tire.
Proper knobbies stacked up badly. A Schwalbe Nobby Nic used 30.8 watts per tire, a Kenda Small Block Eight 33.9, and a Schwalbe Hans Dampf TrailStar 42.2 watts per tire.
You have two tires, so double everything. The knobby is burning roughly 2.5 to 3.5 times the power just to roll.
A 2013 field study in the Journal of Sports Sciences put the same question on real ground.
Tested on road, sand and grass, a smooth tire averaged 21% less rolling resistance than a knobby.
Worked out from those test numbers, a 188-pound rider and bike going from a typical knobby to a puncture-resistant city slick gains roughly 1 mph at the same effort.
A fast near-slick roughly doubles that to about 2 mph. Call it an estimate from the drum, not a road measurement. Riders who make the swap commonly describe a 1-2 mph gain at cruising speed and a bike that feels easier right away.
Some riders say the gain is small in stop-start city riding. Riders also say the hum from the knobs goes away and the bike feels quieter.
The swap itself is cheap, as long as the new tire fits. The next five steps make sure it does.
Step 1: Find Your Wheel Size On The Sidewall
Before you browse a single tire, read the sidewall of the one you own. The number with the dash is the one that matters.
It looks like “50-622”, the tire’s ISO size, also called ETRTO. The first number is the tire width in millimeters, the second is the bead seat diameter, and that one has to match the rim it sits on.
A 26-inch mountain bike is 559, a 27.5-inch is 584, and a 29-inch and 700c are both 622.
That last one is worth knowing, because a 29er and a 700c hybrid can take the same road and hybrid tires. Several different “26-inch” sizes exist, including 571 and 590, so match the number, not the inch label.
The rim comes next, because the tire has to sit properly on the wheel you already own before you buy anything new.
Step 2: Check Your Rim Width Before You Buy
The rim under your tire decides which widths will actually fit. Measure the inside width of the rim first, then check a tire maker’s chart.
Schwalbe’s rim-width chart, built on the 2024 ETRTO standard, puts 35-46 mm tires on rims with a 17-27 mm inside width.
Wider tires, 47-57 mm, need rims from 17-30 mm inside. So a modern trail mountain bike rim around 30 mm inside takes a tire about 47 mm (about 1.85 inches) wide or wider.
Skinny 700c tires suit narrower hybrid and older 29er rims instead. Sheldon Brown’s sizing guidance warns that a tire too narrow for the rim raises the risk of tire and rim damage from road hazards.
Hookless (straight-sided) rims may only take tubeless-ready tires, marked TLE or TLR, even with a tube inside. If that pushes you toward tubeless, first weigh whether tubeless is worth it.
The full measuring method, including how to read the rim decal, lives in our rim width guide.
Step 3: Choose A Width And Tread For How You Ride
Mostly pavement and bike paths: a slick or near-slick. Pavement plus regular gravel paths, towpaths or hard-packed trails: a semi-slick, smooth down the middle with small side knobs, or a low-knob tire.
Whatever you pick, keep the volume. A 2015 field test on hard-packed ground pointed to less tread area and depth, with volume kept high, as the way to roll better. So swap the knobs, not the width.
Go very narrow and you give back the comfort, so keep enough width for your kind of bike.
Riders say skinny slicks feel nervous on sand patches and loose gravel.
One trade to know is that heavy puncture-resistant slicks roll slower than the fastest near-slicks. You’re trading some speed for fewer flats.
On wet roads, Schwalbe, which makes both kinds, says a bike tire can’t hydroplane below about 124 mph (200 km/h). It also says a slick grips better than a treaded tire on smooth wet pavement, because more rubber touches the road.
On smooth roads, grip comes almost entirely from the rubber compound. That compound differs between tires.
Once you’ve swapped, a few habits make riding in the rain safer.
Four examples, with typical list prices:
| Tire | Tread | Fits | US list price |
|---|---|---|---|
| Schwalbe Road Cruiser | Budget city tread | 26″, 27.5″, 700c | $25-29 |
| Schwalbe Motion Big Apple | Balloon slick, light pattern | 26″, 27.5″, 29″ (2.0-2.6″) | $38-59 |
| Specialized Nimbus 2 Armadillo Reflect | City slick, puncture belt | 26″, 27.5″, 700c | $59.99 |
| Schwalbe Marathon Plus | Puncture-resistant touring, heavy | 26″, 27.5″, 700c | $69 |
Check that the exact size you need is offered, and remember prices change.
For a wider choice, compare more commuter bike tires.
Step 4: Make Sure It Clears Your Frame And Fork
A tire that fits your rim still has to fit the bike around it. Frame and fork clearance is the final check.
Giant’s owner’s manual says to leave at least 6 mm (about 1/4 inch) between the inflated tire and any part of the bike. Follow your own bike maker’s figure if it differs.
Check it with the tire mounted and inflated, because the same labeled size can measure differently once it’s on and pumped. On a suspension fork, compress it fully and check the crown.
One more point if you run rim brakes. Sheldon Brown also notes that a tire too wide for the rim raises sidewall wear from the brake pads.
Clearance checked? Then it’s time for the boring bits that make the swap stick.
Step 5: Tubes, Fitting And What It Costs
A big width change can need a new tube.
Schwalbe’s standard Tube 15 for 28-inch (622) wheels covers 23-30 mm road widths only, so a tire outside that range needs a different one.
Match the tube to the new tire’s size range and the valve type.
Budget check: a pair of mid-range slicks plus two tubes runs roughly $120-140 at Schwalbe list prices. A budget pair like the Road Cruiser comes in well under that, and tubes are about $9-12 each.
If you’d rather hand the job over, REI’s bike shop in San Diego, California, lists a flat fix at $24 for members and $30 for non-members. Ask what your shop charges to fit tires you bring.
Once the new tire is on, set the pressure within the range printed on its sidewall.
Check it weekly, because tires lose air every week.
If the old knobs are already worn down, that’s a good moment to swap anyway.
When The Knobs Should Stay
None of this means the knobs were a mistake. On the right ground, they earn their keep.
On soft ground like loose sand and grass, the same test lab notes that almost all grip comes from the knobs digging in. Schwalbe’s own guidance says a slick’s control on rough roads and dirt is extremely limited.
Slicks are out on real trails too. For snow and ice, Schwalbe says that once roads and paths are covered, studded tires are indispensable, and all-season tires don’t give secure grip on ice.
Riding through winter? Make tires part of your winter commuting prep.
The middle path for mixed riders: run a semi-slick with small side knobs, or keep the old knobby pair for trail days and swap back for the week.
Tonight, walk out to the bike and read the number on the sidewall, then the decal on the rim. Write them both down.
That’s the whole shopping list: tire width, bead seat diameter and inside rim width. The rest is picking a tread for your riding and checking the clearance.
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