Think motorcycle-style counter-steering that's what you want the bike to want to do. This is key when turning on loose surfaces, because you want the wheel to be able to slide a bit without actually turning under. Really soft surfaces are best ridden on a bike with low trail, which means the front wheel doesn't tend to want to flop over when leaned. The 'right' amount of trail you're looking for in a bike has a lot to do with how fast you'll ride it, and what the surfaces will be like that you'll ride on. I don't think this is the time to get deep into trail, I'll try to keep my advice simple here. What does it depend on? Tire diameter and volume, primarily. In practical terms, what sort of trail is good for gravel? Well, it depends.sorry.
( UPDATE: Two manufacturers either read this when I originally posted it in 2017, or came to the same conclusion independently: Columbus and Cervelo) I hope we see one of the leading carbon fork brands come out with such a design soon. We're only talking about a difference of millimetres. Yes, they are heavier, but handling should trump weight.Ī proposed solution I submit to the industry, would be a fork that uses a thru-axle design that accepts eccentric insert to offset the axle front to back, thus adjusting rake. This is why small riders are often best served going with bikes made by custom builders who can build them custom forks in the rakes required. Spoiler, the small bike won't ride as well as the bigger bike. The result is two very different trail values, and thus two bikes that ride rather differently. However, in general, the bikes are being designed so that the most common sizes, 55-58cm have the 'ideal' geometry, while the extremes - x-small and x-large - wind up with less than ideal geometry.įor example, the smallest size offered in a given model will use a very raked out head angle (slack, perhaps 69 degrees), but the same fork rake as a bike with a 73 -degree head angle in a common size. Some companies, if they are doing enough volume, will use two rakes, which will improve things. This is because it's too costly to source more than one fork for use across sizes. If you look at geometry charts across the industry, you'll see that some companies use the same fork rake for each of their sizes in a given model. From a handling perspective, however, being able to spec the best of two rakes has its benefits, andI can attest that their forks ride very well. However, Wound Up has far less market penetration than ENVE, and their bonded, modular design lends a more old-school look to their forks than a lot of riders are interested in, particularly when matched with oversized head-tubes. Wound Up, in contrast, offers two rakes for their gravel fork, and three for their 'commuter' fork (which is good for road bikes with large tires). Many custom frame builders spec ENVE forks because they are so good, but they have to work around the one rake offered for each format (road, cyclocross, gravel, mtb). In the case of their gravel fork, rake is 47mm. However, if we look at ENVE, for example, who produce perhaps the best carbon forks on the market, we'll see that each fork comes in one rake alone. This is where builders who have the ability to either make or source forks with different rakes for each of their sizes will have the edge in terms of handling. Most of the constraints discussed above don't manifest as issues for the average rider, because they tend to be dealt with in similar ways across the board, with the exception of fork geometry.
Front-end Geometry: Forks, Rake and Trail 420mm tends to be the shortest stay length we see on gravel bikes these days. Cervelo has pushed about as far as typical drivetrains can handle, 415mm chainstays. The introduction of single-ring drivetrains has enticed many builders to ditch the front derailleur, and use shorter chainstays.ĥ) Drivetrain function - simply, if chainstays get too short, drivetrains don't work well. If you want to use a road crank on a cyclocross frame (as is standard), the arms will hit the chainstays if you place them too wide in an effort to fit a 50mm tire.ģ) Each bike is constrained by the rear hub spacing dimensions available, which influence the angle of the chainstays into the bottom-bracket shell, and thus crank clearance.Ĥ) Front derailleur clearance to the back tire affects chainstay lengths. Custom forks in carbon are very rare.Ģ) Each bike is constrained by bottom bracket and crank standards, which determine how wide the bottom-bracket shell can be (or narrow), which affects tire clearance. Both parties are constrained by a few aspects of the overall system:ġ) Forks are mass produced in a small variety of lengths for a given wheel size, and with a small range of rakes (more on rake below). Meanwhile, custom builders will build bikes in dimensions tailored to their clients. Bike companies that produce stock geometry bikes tend to make a range of sizes for each of their models.
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