What effect do bicycle tire sizes have on riding?

Hi all. I'm getting back into cycling after a long time "off the saddle" and I have a question for beginners that I can't find an answer to. What are the advantages and disadvantages of bigger and smaller, thin and wide tires on a bike? For example, small 20" or even 16" tires vs. 26" and larger. Similarly, narrow tires less than 2" versus the thick 2.5" or 4" tires you see. Why prefer one of these options over the other? What are the good and bad of each? Thanks.

Comments

  • singleton
    singleton Posts: 2,523
    Hi Arthur,
    There has been a lot of research and a lot written about this topic, so it's hard to boil it all down to 2 sentences or so.
    Smaller 16" or 20" wheels are easier to turn, but the downside is that makes them less stable at speed.
    Off road tyres are generally wider, and road tyres narrower - but that trend has altered a bit over recent years as road tyre have gone up from 23mm to 30mm.
    The best tyres for you will depend on what type of bike you buy and for what reason.
  • andrew_s-2
    andrew_s-2 Posts: 51
    a)
    For any given size of wheel/tyre, some tyres roll faster than others. In general, a flexible tyre is faster than a stiff one, and a slick tyre is faster than one with a pronounced tread or knobbles.
    bicyclerollingresistance.com has rolling resistance figures for many tyres of interest to the roadie community.

    b)
    Tyre pressure and surface roughness are interrelated. High pressures roll faster, but if the pressure is high enough that the rider starts to get vibrated about (i.e. is uncomfortable), the rolling resistance goes up pretty fast, and can reach very high values if it's really rough, like cobbles. Tyres roll fastest on a smooth road at high pressures, but as the road gets rougher, the fastest-rolling pressure decreases, so on something really smooth like velodrome boarding, 200 psi is fastest, but on your average British road with chippings all over, something like 50 psi may be fastest.

    c)
    Effective surface roughness is related to wheel size, with a half-inch bump affecting a small wheel more than a larger one.

    d)
    Tyre pressures are limited at the upper bound by blow-off, with wide tyres blowing off the rim at a lower pressure than narrow tyres, and at the lower bound by either pinch punctures (snakebites), or by the tyre deforming sideways on corners giving dodgy handling. The narrower the tyre, the higher the pressure needed to avoid pinches.

    In general, bicycle wheels/tyres are the size they are for a reason, and something like 700x32 at 60 psi or so (depending on rider weight) is the best compromise for an "average road".

    Off-road is different, as the surface is very much rougher than any normal road, and the soft surfaces mean that tyre tread is useful (on-road, the road surface digs into the tyre rubber, rather than vice-versa). This means that considerably wider tyres at a pretty low pressure are best.
    Harder tyres being bounced off the track also wrecks bike control, so suspension is useful.