I've seen manufacturers a couple of times put suspension forks on gravel bikes instead of rigid carbon forks. Yes, this fork was not in the top price category from RochShox or Fox, but still, is it possible to replace a rigid fork on a gravel bike with a suspension one? I plan on getting a RockShox Reba fork with 100mm of travel. And no, I'm not going to ride trails or use gravel for downhill, it's just that in my area there are a huge number of bumps, holes, and the quality of the roads itself leaves much to be desired. (While maintaining the same wheel dimensions, including diameter, I can also reduce the travel of the fork by pumping less pressure into the fork to offset the difference in geometry of the previous fork that was in stock)
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1Gravel forks often have 30-50mm of travel so as to preserve neutral handling. Cheap forks for hybrid bikes exist with this range of travel like Suntour Nex, but whether that cheap fork is worth having, I don’t know– NoiseCommented Mar 21, 2022 at 19:49
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Suntour has gravel specific products (GVX, with 40-60mm travel) in 400-500€ price range. 100mm is for sure too much. But if your frame is still under warranty (some brands offer lifetime warranty for the initial owner), that is the kind of upgrade that will likely void it.– RеnаudCommented Mar 21, 2022 at 20:55
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RockShox now makes the Rudy, and Fox the 32AX for gravel usage. Check those out.– MaplePandaCommented Mar 21, 2022 at 21:49
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2Alternatives to getting a suspension fork for the purposes of better "cushioning": 1) Get the widest tires that fit and run them at the lowest pressure that is safe; 2) Get a steel or carbon rigid fork if you are currently running an aluminum one.– Grigory RechistovCommented Mar 22, 2022 at 8:42
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2I would add to @GrigoryRechistov's suggestion adding thicker bar tape or a second layer. Iv'e had success doing that when riding rigid aluminum forks and straight handlebars (MTB fame hybrid), specially considering that the most riding I do is with suspension forks. The second layer saves me from some wrist pain when riding my hybrid.– JahazielCommented Mar 24, 2022 at 0:15
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2 Answers
Swapping a fork (rigid/suspended, suspended/rigid or even rigid to another rigid) is subject to the following considerations. I would assume that the wheel diameter is not changing.
Geometry changes. Putting a longer fork (and suspension forks are generally, although not necessarily, longer) changes many bicycle dimensions, such as reach, headtube angle, bottom bracket height. This also changes the so called mechanical trail of the front. Unless your calculations show that the changes are minimal, you should be prepared for the fact that the feel of steering, and general frame fit, will change, and not necessarily for the better. To answer this question, find out and compare the values of A-C (axle to crown) and wheel offset of the two forks. You would need to compare these numbers even if you do a rigid/rigid swap.
Clearance issues. As a suspension fork compresses, the wheel comes closer to the down tube of the frame. Toe overlap may become real or worsen. While the toe overlap is undesirable and dangerous, the wheel touching the downtube is catastrophic. Also, suspension forks have wider crowns, which may touch the frame when the fork is rotated about 90°. You should experiment with the new fork at its maximum compression to see if the clearances are big enough.
Then there are generic issues of parts compatibility such as steerer dimensions, braking system, wheel axle length and diameter etc. I assume you've ensured that there will be no problems with them.
As for you suggestion:
I plan on getting a RockShox Reba fork with 100mm of travel.
Unless you can shorten its travel by opening up the fork and moving some spacers around (not a common feature for RockShox products), this fork will generally be too long. Lowering the air pressure will still keep it at 100 mm of dynamic travel. The increased static sag will only visually hide some of the travel but won't make it go away.
answered Mar 22, 2022 at 8:30
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Nicely phrased answer. Clearance is probably not going to be an issue because the suspensions fork mostly puts the wheel further away from toes and downtube, but it's definitely important to check that it's still safe in full compression. Commented Mar 22, 2022 at 10:29
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@leftaroundabout I agree. Still, there are bike frames with crazy curved or wide downtubes. the only way to be sure is to test it. Commented Mar 22, 2022 at 10:30
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1Yes. In addition to the tyre, one should also consider that a suspension fork has a much burlier crown, which may not fit under the down tube in 360° rotation. In that case steering range would be limited, the bike can't be stored as easily in particular in a car, and it's easy to damage the frame if a crash smashes the fork crown into it. Commented Mar 22, 2022 at 10:59
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1@MaplePanda simply locking the steering in center position should do the trick... Commented Mar 22, 2022 at 20:27
A small answer to the last part of your question.
I do not recommend trying to adjust the travel of a fork by reducing the air pressure, this will have a number of undesirable side effects.
If you run a pressure so low that you have ~50% sag you will find it blows through its travel and bottoms out on even moderate impacts. You will also find it bobs whenever you put power down which is inefficient. Most importantly, you will also introduce a phenomenon known as brake dive - when your weight shifts forward during braking, the fork will compress and alter the geometry of the bike. In extreme cases such as emergency braking, this could throw you over the handlebars.
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2All of this is true, but a) forks are designed so bottoming out is not a big problem b) there shouldn't be much bob on the front, even with a very soft fork, as long as one stays in the saddle; standing up it's a different story but can still be minimised by good coordination between arms and legs c) brake dive is inevitable with any standard fork (unless you pump it so hard it becomes basically useless), but can be anticipated and countered by moving the body weight back and down (a dropper seatpost is enormously helpful for this). Commented Mar 22, 2022 at 10:35
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2Also, with better forks there's the possibility of inserting volume spacers that make it more progressive: that means you can make the pressure so low that it sags a lot, but still gets firm on the bottom half of its travel. Commented Mar 22, 2022 at 10:41
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Great point about the volume spacers - they'd be a decent compromise.– Andy PCommented Mar 22, 2022 at 10:56
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@leftaroundabout: Yes, all of those disadvantages/problems also exist at high pressure, but they get much worse and more pronounced at the extremely low pressure OP is considering.– MichaelCommented Mar 24, 2022 at 8:15