Gravel Cyclist's Tire Dilemma: Knobbies or Slicks? 5/8

Read this, if you are a critical thinking gravel or allroad cyclist

Cornering on Dry and Wet Forest Soil and Grass

Dry forest soil is more compressed and softer than dry gravel. For this reason, traction on dry forest soil is better than on dry gravel. Slicks' cornering traction on dry forest soil was very good, obviously also due to the fact that cycling speed in forest is on average lower than on gravel. Cornering was also good when riding big knobbed knobbies: the annoying bouncing effect of big knobs was less noticeable, obviously due to knobb's partial digging into soil. With small soft knobs, cornering was wobbly due to squirm felt almost as strongly as on tarmac.

Cornering on dry grass caused no traction problems for knobbies and slightly serrated slicks or semi slicks (Maxxis Re-Fuse). On slicks (Vittoria Voyager Hyper, Compass Snoqualmie Pass), cornering was slippery.

When forest soil was wet, cornering on big knobbed tires was relatively good, on small knobbed tires and semi slicks poor, and on slicks very poor. Why? Forest soil particles are smaller than that of gravel, which makes them more water soluble. Consequently, wet forest soil is less dense and stickier than wet gravel. For that reason, only big knobbs worked well in wet forest soil (mud). With small knobbs, on the other hand, poor mud shedding was often an issue.

On wet grass, cornering was clearly the best with big knobbed tires, decent with small knobbed tires, and very bad with slicks.

Northern forest path of the Halls of Heaven S hike is full of roots, winding, occasionally very steep, leaning to one side or another, and usually damp or wet. Slicks don't provide traction in such conditions. The terrain calls for big sized side knobs.

To sum up, if forest soil or grass is dry, semi slicks slightly outperform knobbies, and if forest soil or grass is wet, knobbies perform much better than (semi) slicks.

Cycling in dry and wet sand

I noticed that in deep dry sand, the tread or its absence didn't play any role. Both slicks and knobbies sunk in. The sinking in, not the traction, was the main issue (the 28 mm Michelin Pro 4 Endurance v2 run at 5 bars (72 PSI) was totally useless in sand). The solutions were two. The tire pressure as low as possible, and the tire volume as big as possible.

In this not too deep dry sand, slicks (Vittoria Voyager Hyper, 40 mm) with latex inner tube inflated to 2.0 bar (29 PSI) performed very well.

Water in wet sand holds sand particles together, providing significantly less sinking of tires into sand, as well as better traction. But the sinking into sand also occured in wet conditions, to a lesser extent, though. I also noticed that sand had higher water retaining capacity than gravel. It ment that in very wet conditions I got better traction on sand than on gravel. Apart from that, what I said about riding in wet gravel, also applies to riding in wet sand.

Winding forest descent from the Uniküla hill (Surprise the Edelweiss M route). I bombed down this descent, and Maxxis Re-Fuse 40 mm offered superb traction with only slight slow draft through the corners of damp sand.

Cycling Uphill

When cycling uphill, traction was noticeably improved by transferring onto my rear wheel as much of my body weigth as possible. This was done by sitting on the rear part of my saddle in the most upright position. Using this technique, traction was not an issue when I rode slicks on gravel roads with up to approx. 15% incline. On the other hand, cycling uphill in standing position with my body leaned forward resulted in lessened traction of my rear wheel even with big knobbed tires.

When using the proper uphill technique, traction was only deminished in the following occasions:

On up to moderately wet gravel roads with inclinations 10% or more, slicks (Vittoria Voyager Hyper, Compass Snoqualmie Pass) on my rear wheel started slipping a bit every here and there. Under the same conditions, my semi slicks (Maxxis Re-Fuse) on the rear wheel didn't slip at all.

In very wet forest soil (mud) traction was already very poor at slight inclinations, except for big knobbs. As a matter of fact, when riding on slicks (Compass Snoqualmie Pass) through sections with most watery and slippery forest mud (which usually encircle puddles), the slicks didn't offer any traction even on pancake flat terrain. On the other hand, my semi slicks (Maxxis Re-Fuse) performed surprisingly well even at inclinations as big as 10%, under the condition that forest soil was no more than moderately wet. The semi slicks' traction was only significantly deminished in watery mud (already at inclination as slight as about 5%), and moderately wet forest paths / singletracks / field lanes with inclination above 15%.

Crossing muddy harvested field in late autumn. Traction was no problem for the Maxxis Re-Fuse 40 mm as long as the terrain was more or less flat. But as soon as I hit cca. 10% climb, the tires grasped in vain for their grip. I had to step off my bike and walk.

To sum up, with proper climbing technique, semi slicks' climbing traction is surprisingly good both on gravel and forest soil, whereas the steepest and muddiest climbs should only be reserved for big knobbed knobbies.


Credibility of the Article

The author of the article is Matej Goršič [Matey Gorshich], 41, male, PhD, who has been an active sportive cyclist for 28 years. In his youth, he trained, and competed in, road cycling and athletics. Once finally out of the competitive waters, he started consciously re-defining his understanding and practice of cycling. Today, he feels most at home in a creative mixture of non-competitive, electronic-devices-free, self-exploring, adventurous allroad cycling. During last 3 years, he spent over 25.000 km mostly on tiny gravel roads of South Estonia.

The tires tested for the article were bought by its author at normal market prices from different cycling shops in Europe. There have been no sponsors or donations for writing the article nor for mentioning brands and items in the article and showing them in its photos.

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