Suspension can be derived in two different ways for anyone on a bicycle. First is pneumatic- suspension from the tires. The other way is to use a mechanical means to absorb vibrations, either passively, by way of frame flex or component flex, or by an active, purposeful means involving some form of moving parts.
Either way, absorbing vibrations is the order of the day. Vibrations are important to consider, because if the energy causing the rider to feel vibrations is not absorbed by the tires, frame, or a passive/active mechanical means, then the rider has to absorb those vibrations which eventually can cause fatigue, numbness, and other issues.
|It's not just about width, it's about volume.|
Tires are essentially air springs. Whether you choose tubed, tubeless, or tubulars, your tires are springs that can be adjusted. Furthermore, the tire casing, tube, (if any), and tread pattern also affect the way the "spring" will work.
Springs can be stiff, soft, linear, or they can "ramp up" in spring rate quickly due to volume available and/or tire pressures used. You as a rider can greatly affect the ride quality of your bicycle in a number of ways by your tire choices and tire pressures that you choose. Go to a higher pressure and you get a stiffer spring rate. Use a lower volume/narrower tire and you may also have to move pressures higher and the volume of that tire will affect the ramping up of the spring rate as well.
Typically, you would not want to run maximum pressures as rated on a tire on rough roads because this affects how your tires can absorb vibrations. Higher pressures in tires make vibrations that the tire could normally absorb go past the tires and into the frame/rider.Likewise, the narrower/lower volume your tires are also affects the way you can adjust your spring rate, (ie; tire pressure), and this may affect your ride quality. Finally, things like frame clearances, terrain demands, rider weight, tire construction, and more will start to narrow down choices.
If you don't remember anything else though, remember this- a tire with a reasonable amount of air, but still at a point where it can conform to road irregularities, will be faster and provide more rider comfort and control than a tire at maximum, or close to that, pressures. (I would only add that a higher volume tire provides the rider with a wider range of adjustability in this respect.) A tire at higher pressures has to bounce up and over trail/road irregularities instead of conforming to, and rolling over them. Those little bounces have to be absorbed, and don't forget- overcome by- the rider. Yes, higher pressures result in more rolling resistance on rough roads.
|The smoothest line is less fatiguing|
Mechanical Suspension: Oddly enough, mountain bikers would never think twice about accepting the benefits of suspension, yet gravel/back road/rough road riders almost never consider such things. Too heavy? Too complex? Not worth the trouble? At one time, the answer to these questions was no. The proving ground was the cobbles of Europe, specifically the course of Paris-Roubaix.
|Early 90's road suspension bike|
Probably the most outlandish example of suspended road bike design has to be the Bianchi piloted by Johan Museeuw at Paris-Roubaix, which you can read all about here. Said to have cost $20,000.00 to produce, the bike did not reach the final desired result when a flat tire ended Museeuw's chances near the end of the course.
So much for road bike full suspension, right? Well, the idea has not gone away entirely. Just take a look at Trek's Domane bike which has already won events like Strade Bianchi, a stage in this year's Tour de France, and most recently won at Gravel Worlds in Lincoln, Nebraska. The Domane takes a subtler approach than the overtly suspended bikes from the early to mid-90's, and hides the suspended component for the most part at the junction of the seat tube and top tube. (Which are in fact, decoupled) The fork is made to flex more, and in so doing this, Trek has retained a traditional look to the road bike, at a fantastic light weight, without resorting to an offensive assault on the eyes and sensitivities to bicycle overall weight.
Is there a place for such a beast on the dusty gravel roads? Is it even necessary to go that far with suspension, or are voluminous tires enough? It'll be interesting to see if folks can even envision needing such a device, much less having the option.
Okay, tomorrow I will explore the opposite end of the spectrum regarding suspension with fat bikes.