I’ve not had a chance to read this yet, but the article was hinted at in an early one by the same author and is one I’ve been excited to finally see.
1 Like
Good article - very articulate in relating geometry numbers to handling characteristics. It still comes down to rider preference, though (or, said another way, “it depends”). Thanks for sharing!!
2 Likes
Is “fork flop” a common term?
I’ve only ever head it referred to as wheel flop.
Otherwise good article, it could have been three times longer and still barely given a high level overview but it’s interesting to read thoughts from a renowned builder and rider.
I’m not convinced short stems are inherently more reactive. I have two gravel bikes that are set-up almost exactly the same (same handlebars, tires, trail/hta/sta/offset, etc) but one is designed around a 35-55mm stem and one around the more common 80-100mm stem lengths. Basically they have the same measurements except one has a top tube 55mm longer than the other.
They steer and handle front tire impacts and obstacles very similar. I can go ride singletrack for an hour on one, get on the other and it feels very similar in the front. I think that the short stem->reactive thought comes from the effects observed, historically, when using short stems to brace riders onto bikes that are not designed for such stems and do not fit the rider (as well with narrow handlebars). As opposed to short stems in modern designs that are designed specifically for that length stem as well as accounting for handlebar width and tire width/design.
James Johnson of Analog cycles and Peter Verdone are two of the only designers/builders I’m familiar with that are really iterating very short stems and drop bars. I think gravel bikes should be pushing out the front center a lot further without necessarily going to higher trail numbers. Expressing to riders that a off-road big tire drop-bar bike can be good for gravel racing and fun to ride in general with a 40mm stem (and 46-50cm handlebars) is a big challenge, especially given the crossover now weights mostly towards road racers and road cyclists and their concerns.
Flop is not something I discuss frequently, but I have seen a mix of fork vs wheel if it’s mentioned at all. Otherwise 'flop" has been tossed around solo for the small amount I’ve used it.
-
This can get confusing since most people discussing it leave out details or make assumptions in the discusison.
-
All else being equal, a shorter stem means the rider’s hands are closer to the center of rotation (headset and such). As a result, moving the hands a given distance in the handlebar turning arc (NOT angle) will give more steering angle input compared to the longer stem.
-
That distance vs angle aspect is what often gets lost in translation. If we think about it more like a person’s range of motion, it makes sense to think about the distance along the arc (arc length) over pure angle. If we reverse consideration and hold input angle constant, the output is also the same. What changes it the distance the rider’s hands move in that arc. So, same issue just a different way to look at it.
Here is a super quick sketch, top view of a handlebar & stem setup with a pivot at the headset:
-
Top is setup with 100mm stem, bottom is 80mm stem with the same 2" [50mm] movement distance at the hand (along the arc) using the same handlebar width and reach. Stem length is the only changed variable.
-
See how the shorter stem version gives about 0.5* more angle into the fork vs the longer one.
-
That is where the statement, “shorter stem = faster steering” is correct in the broad sense.
4 Likes
Great to see Rob putting his opinions to paper like this. When I had my English built 7 years ago, Rob and I discussed these details quite extensively. We were both on the same page in terms of geo for fat tire road bikes. I came to the conversation wanting a 58mm trail as from my experience this feels right - especially when coupled with wider tires (pneumatic trail comes into play here). It may seem aggressive or ‘twitchy’, based on the numbers, but I don’t find that at all.
We also designed the bike around 165mm cranks as an input - this drives the reach and toe overlap considerations and how much BB drop we could get away with (I wanted as much BB drop without risk of pedal strikes) We settled on a 90mm stem to achieve no toe overlap using 35mm tires, and just a bit at 40mm tires.
Another geo preference we built in was short chain stays compared to traditional gravel bikes - most seem to be around 425 to 430, and we went with 415 to keep the road bike feel and balance.
60,000km later, I’m still loving this bike!
Edit: Forgot to add that I’m only 5’8, so toe overlap is more of a concern for shorter riders in terms of getting the geo dialed
3 Likes
Good discussion on geometry considerations starting around minute 42.
2 Likes
Im only 24 mins in but had hopes for this cast from the description. Glad to hear it’s worth the wait. 