AASQ #143: Gravel Bike Geo – How handling relates to wheelbase, stem length and fork offset

AASQ #143: Gravel Bike Geo – How handling relates to wheelbase, stem length and fork offset


We know, there’s no such thing as a stupid question. But there are some questions you might not want to ask your local shop or riding buddies. AASQ is our weekly series where we get to the bottom of your questions – serious or otherwise. Hit the link at the bottom of the post to submit your own question.

Welcome back to the Bikerumor Ask A Stupid Question series. This week, we’re tacking gravel bike geometry, and how wheelbase, stem length, and fork offset contribute to handling properties like stability and agility. Joining us this week are the following experts:

Would a Gravel Bike with a short wheelbase, low trail but long stem behave similarly to a bike with a long wheelbase, high trail, and short stem? Does the length of the wheelbase and/or trail have the same impact on stability as the length of the stem? If not, which is more important for stability and how would I feel this difference during a ride? 

Marin Bikes: In our experience, a longer wheelbase is always going to feel more stable than a shorter wheelbase, but head tube angle and stem length will still very much affect the steering feel. The two cases given (short wheelbase, low trail, long stem vs. long wheelbase, high trail, short stem) are exactly the differences between what we used to see on MTBs all the way to the 2010s, and what we’re seeing on MTBs now.

2020 Marin gravel and all-road commuter bikes, carbon alloy steel

Marin spec a 60mm stem on the size 56 Headlands Gravel Bike; 420mm stays, a 386.4mm reach, 71.5° HA with a 50mm fork offset gives a 1028.5mm wheelbase

The benefits of the modern geometry are undeniable with handling, comfort, and safety on the bike at most speeds in most conditions, and this is the same on a gravel bike, albeit with less “extreme” geometry numbers than what’s being pushed in the Enduro MTB category.

marin headlands

From Size 58 upwards, Marin increase bar width to 440mm and increase stem length to 70mm

To summarize the feeling of the bike with a longer wheelbase, more slack head tube, and shorter stem (preferably with a wider handlebar too!), there is a less twitchy, more planted feel to the front end. The bike is still easy to steer, but the feeling that the front end would require so much effort and focus to keep pointed in the desired direction is pushed aside and allows the rider to focus more on what’s coming further down the path. That predictability means the rider can ride faster and still have the feeling of having more time to react to obstacles, and also feel more comfortable keeping the bike in the desired path when they’re tired.

Ritchey: In answer to your question, “Would a Gravel Bike with a short wheelbase, low trail but long stem behave similarly to a bike with a long wheelbase, high trail, and short stem?”, our answer is… These are two things that don’t really have anything to do with each other. So, no, these two bikes would not behave the same. The ride characteristics of longer chainstays cannot be replicated with a longer stem or even a low trail. 

ritchey swiss cross

The Ritchey Swiss Cross has been in their lineup for over 25 years, first raced by multi-time Swiss CX & World MTB champ Thomas Frischknecht in 1994

The first sounds like a cross bike. Most drop bar bikes with shorter wheelbases (like the Ritchey Road Logic and Swiss Cross) are designed with an optimal range of stem length in mind, usually 90-110mm. These bikes are meant to be agile and quick handling in tight, race-like scenarios, whereas gravel and off-road specific bikes, like the Ritchey Outback and Ascent are designed for a shorter stem, usually 70-90mm, and are meant for long, smooth travel over rough surfaces. Stem length and trail have to do with handling more than the ride quality of a longer chainstay.

ritchey outback gravel adventure bike steel

The Ritchey Outback Gravel Bike runs a 50mm offset fork at a 71° HA in Size Large; on 700c wheels there is sufficient clearance for 48mm wide tires

In answer to your question, “Does the length of the wheelbase and/or trail have the same impact on stability as the length of the stem?”, again, the answer is, No. The stability that comes with longer chainstays is built into the DNA of the frame. The way it feels going into, and coming out of, a turn would be different. A longer stem would slow down the reaction of the front of the bike, yes, but the way the whole bike stays stable in straight lines and in turns is defined by its wheelbase and chainstay length.

Which is more important for stability and how would I feel this difference during a ride? Well, a bike is more stable and reliable because of its built-in geometry. A longer or shorter stem will certainly dial in a fit, thereby adding some stability, but a longer stem is no match for a well-designed frame. There are elements of the bike that are individualized, such as stem length, trail, chainstay length, seat tube angle, etc. that are important to consider…but it’s most important to consider all of this as a whole.

ritchey swiss cross racing

This all makes the bike complete – how and what it was designed for and with what components that inform the ride quality. It’s silly to say only the chainstay makes a difference with the handling when it’s inherently tied into the trail of the front end, the length of the head tube, the length of the top tube, and even the choice of tires. This is why when we look at warranties, we want to see the whole bike and how it was used because that informs how something failed. Think of a bicycle as a spider web: you cannot tug on one string and not shake the entire structure.

Scott: In answer to your question, “Would a Gravel Bike with a short wheelbase, low trail but long stem behave similarly to a bike with a long wheelbase, high trail, and short stem?”, my answer is, No. This is because the wheelbase and trail influence the agility and steering characteristics of the bike while the stem length (and bar width) influence the translation of the rider’s input to the rotation of the front wheel.

2022 Scott Addict Gravel aero integrated carbon gravel bike_Tuned.jpgdescending

The 2022 Scott Addict Carbon Gavel Bike gets a 71° HA in Size Large, spec’d with a 103mm handlebar-integrated stem

If you translate this to cars it might become more obvious: A long wheelbase and a small steering angle of the front wheels results in a very high turning radius of the vehicle. This is the characteristic of the chassis that you can’t compensate for by simply increasing the transmission ratio of your steering gearbox.

2022 Scott Addict Gravel aero integrated carbon gravel bike, integrated Syncros X gravel bar

A frame geometry with a long trail and a long wheelbase will result in a rather sluggishly handling frame. Combining this with a shorter stem will only result in a harder-to-steer bike. As the leverage between the rider’s hands and the steering axis decreases, one needs to produce a much higher force to turn the bar.

In answer to the question, Does the length of the wheelbase and/or trail have the same impact on stability as the length of the stem?”, again, my answer is, No. This is because the wheelbase and trail influence the agility/stability of the bike’s chassis while the length of the stem influences the leverage of the rider’s steering movements and so it acts as a transmission.

Imagine riding a bike with no hands just by leaning your body weight in the direction you want to go. A too stable frame geometry with a long wheelbase and trail will be harder to steer around corners while a geometry with a short wheelbase and short trail will be nervous and difficult to ride in a straight line. The stem length has almost zero influence on the steering characteristics once you take your hands off the bar.

custom Scott Addict Gravel Tuned Dangerholm edition lightweight carbon prototype gravel bike project, complete

The Dangerholm edition of the Scott Addict Gravel Bike weighs 7.13kg, including pedals, a full 1kg lighter than Scott’s lightest 8700€ complete Tuned build without pedals

Finally, in answer to the final question, “Which is more important for stability and how would I feel this difference during a ride?”, I would suggest the following.

The frame geometry is the most critical factor for the stability of a bike. You will feel this during your ride when you take your hands off the bar or when you ride in squally crosswinds and at higher speeds. On a bike with high directional stability, it will be easier to hold a straight line.

But, this stability comes to the detriment of agility. If a bike is too stable it will feel sluggish and hard to lean into corners. High-speed switchbacks or tight roundabouts may be challenging as well as quick directional changes. So, choosing the right geometry for a bike is always a trade-off between agility and stability.

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