Condensed Answer: There’s nothing wrong with using different tires for the front and back of the bike. In some cases, people follow this strategy deliberately to improve performance or save money. The choice should take into consideration the terrain and the rider’s style.
The Most Common Combinations
- Grippy Front Tire + Slick Rear Tire
The front wheel is heavily responsible for the stability of the bike. If the rear wheel slips, the rider has a decent chance to recover, but if the front wheel gets out of control, a fall is almost guaranteed.
For that reason, people who ride off-road and mix tires, often put a wider and grippier tire at the front.
Meanwhile, the rear wheel has a far greater rolling resistance because most of the rider’s weight is on it. The higher the rolling resistance, the more energy is required to spin the wheel.
To lower the rolling resistance, some cyclists use a rear tire with a less aggressive tread.
The combination of a grippy front tire and а slicker fast rolling rear one is often seen on touring bikes too. The goal is to acquire a decent grip on less-than-ideal terrain but also a lower rolling resistance reducing the effort needed to keep the bike rolling.
- Wider Front Tire + Slim Rear Tire
Another combination is a wider front tire and а slimmer one at the back. The wider front tire provides more grip and cushioning thanks to the extra contact surface. The slimmer tire in the rear has lower rolling resistance and saves weight.
Note: By putting a wider tire at the front and a slimmer one at the back, you will also slacken the head tube angle of the bike (elevate the front).
The head tube angle is the angle between the head tube and the ground. A slacker headtube angle makes it easier to descend on uneven terrain and lift the front wheel. Hence why modern MTBs come with much slacker head tube angles than their predecessors.
The downside of slacker head tube angle is the increased drag (the rider has a more vertical back angle) and poorer maneuverability at low speed.
- New Tire At The Front + Old Tire At The Back
The rear tire wears faster because it supports more weight (more friction) and is more likely to experience punctures.
To save money, some cyclists buy only one new tire for the front and place the old front tire at the back.
The new tire goes to the front because the front wheel is crucial for stability. The new tire has more grip and is less likely to experience a puncture thanks to its better health and greater thickness.
Meanwhile, by placing the old front tire at the back, the cyclist not only saves money but gets a tire with a lower rolling resistance for “free” because the tread of the tire is already worn/slicker.
That said, if the front tire has experienced a massive puncture, it’s recommended to get a new tire for the rear too because the weak spot could be a frequent source of punctures. (It’s more difficult to fix a puncture at the rear because the rear wheel is harder to remove and install.)
What Are The Downsides of Using Different Tires For The Front and Back?
As long as the combination of tires respects the terrain that the bicycle is designed for, there aren’t notable downsides from a performance standpoint, and the choice boils down to personal preferences.
That said, it’s worth mentioning once again that a notably larger front or rear wheel will change the geometry of the bicycle.
Note: If you have full fenders and intend to use a front tire of a larger size, make sure that the fender is big enough to cover it.
- Putting an old rear tire at the front
Due to misinformation or unawareness, some people may conclude that it makes more sense to put a newer tire at the back of the bike and an old one at the front, but this is incorrect.
As already mentioned, the front tire is crucial for stability. If you put an old rear tire that has suffered multiple punctures at the front, you’re increasing your chances of a tire blowout and unwanted skidding.
Furthermore, the front wheel has greater friction during braking. Hence why the front brake is more effective than the rear. By putting an old tire with reduced traction at the front, the braking capabilities of the bike will suffer too.
- Large Tire Width Discrepancies
While it’s ok to have tires of varying widths, the difference shouldn’t be large. For example, it makes little sense to put a massive front tire on an MTB and a super-thin tire at the back. Such large discrepancies make up for a weird ride and will require you to carry inner tubes of different sizes.
- Excessively Large Rear tire
If the rear tire is much larger than the front, then the head tube angle will become too steep. If the HTA of the bike is already steep, the new geometry will be dangerous due to the increased chances of going over the handlebars during an emergency stop or when hitting an object.