Geometry Primer

Tight cornering and turning is based much more around trail, handlebar width and individual rider skill than wheelbase, IME/O.

I think this is partially due to mis-attribution due to a lack of understanding how small changes in the first two variables have more outsize effects on the feel of a bike much more so than wheelbase. Especially during high speed and aggressive movement of the bike/rider. Something like ~7mm of trail and corresponding ~2-3mm of flop can have a very large effect on how a bike feels as it begins to lean over. Conversely, when riding blind I’ve found most riders have a hard time differentiating less than 20-40mm of wheelbase change, especially if it’s balanced on both the front and rear end.

Looking at the bikes that finish DK is interesting but most people do not understand geometry well enough to have had it be a defining factor in what bike they choose to purchase/ride in comparison to all the other variables involved. It takes quite a bit of $$$/experience to really suss out the small changes and their effects.

I will also say that the terms relaxed and aggressive are poor descriptors and do not describe how a bike rides. It would be better to describe bikes along a spectrum as:

Use steering to turn or maintain a straight course, leaning and body english produce much less reaction and are much less necessary. Also has less stability at the front end as the speed increases.


Use leaning the bike at an angle, counter-steering (push handlebars inside of the turn) and body english to turn or maintain a straight course, steering with the handlebars produces much less reaction and is much less necessary. Also has more stability at the front end as the speed increases.

Low Trail 35mm
Steering, less stable at speed

Mid Trail 55mm
Balanced steer/lean, stable at speed

High Trail 70mm
Leaning/countersteer, very stable at speed

Note: larger tires, more aggressive tread and lower pressure all increase trail for a given geometry. Wider handlebars provide more leverage and increase feedback on low trail, too wide creates a nervous descending bike that is overly sensitive to small corrections – oversteer condition. Narrower handlebars do not have enough leverage and decrease feedback for high trail, the bike is hard to maneuver during descending and resists cornering – understeer condition.

Personally I find high trail bikes extremely hard to corner with handlebars less than 52cm wide. Even then they require a significant amount of leaning and benefit from very aggressive side knobs to prevent sliding at lower speeds than lower trail bikes. Conversely I find low trail to be much too nervous descending – compared to mid/high trail, smaller rocks and road features tend to wrench the front end around requiring significant focus to make corrections to track the preferred line. Mid trail is my preferred front end geometry as it has a good balance of steering/leaning and although it lacks the stability of high trail on rough descents at very high speed it is still acceptable for the additional ease of cornering.



Why ride gravel?

I found it humorous that was posted in the fixed gear forum. If anyone understands doing something just because it’s fun it should be posters there.

Anyway; compared to gravel, road riding is intensely boring. The depth of gravel is a huge pull. Learning to ride different surfaces in different conditions, at speed is a satisfying skill to learn and develop. Nothing on pavement can compare to winding down a twisty gravel descent at the edge of traction, deep in the woods alone as the winter wind rattles the bare forest around you. The more technical and deeper into gravel you go the more serene pavement seems. Pavement is the bright suburban grocery store to hunting your dinner in the woods with a knife on gravel.

Hyperbolic to the extreme? Of course, but that’s how it feels.

Often I’ll spend 2 hours riding a flat, straight, paved rail trail to some gravel. The more I’m on the trail the more my bike seems to bog down and my legs get heavier and heavier. Once I get off the trail and gravel starts crunching under my tires the bike seems to come alive, my legs feel light and efforts come easy as I rumble along in the dust. It’s a wonderful feeling and I find it sad some people haven’t felt the pull and don’t know what they’re missing.

Banditing short sections of hiking trail in a tiny city park surrounded by urban sprawl is nothing. Fast food for a soul that needs full nourishment.

All this is to say nothing of the technical aspects. Compare two road slicks, are they different? Who cares, they’ll both get you down the road and around the corner just fine.

Ah now compare two gravel tires. Are you riding in the wet? Is the course muddy or dry? Hardpack or loose railroad ballast? How much climbing do you expect? Do these knobs give enough traction while leaning to go down that switchback at the speed you need? Does having a front tire more aggressive than the rear give you more capability of just the ability to outride your skill level?

How are you handlebars? Flared? How much? What width?

Stem length? Too long and you’re over the front end on any descent and getting squirrely over the bars. Too short and that rock you didn’t see is wrenching the bars from your hands and tossing you to the ground.

There’s a ton of things to learn and observe. As they say the core loop is enjoyable, it reinforces continuing the activity in a way that road riding does not once there’s a taste of the chalky dust in the air.