Sam Song Posted October 7, 2022 Report Share Posted October 7, 2022 I am in the process of setting up a dirtjump fork for trials riding. I don't have much experience with suspension forks. What do you recommend to set the forks? Is it as simple as as firm as possible to feel like a rigid fork? Travel is 80mm. 1 Quote Link to comment Share on other sites More sharing options...
aener Posted October 7, 2022 Report Share Posted October 7, 2022 I think it would be easiest to recommend setting them... ...back in the box On a serious note: no idea, but curious as to your motives for wanting to run them? (Not saying you shouldn't - just unusual.) Is it wrist problems or something? Quote Link to comment Share on other sites More sharing options...
Mark W Posted October 7, 2022 Report Share Posted October 7, 2022 2 hours ago, aener said: I think it would be easiest to recommend setting them... ...back in the box Would agree with that, but otherwise it'll come down to the specific fork and what options you have with it. If you can add volume spacers, you'll probably want to add the max amount. Rebound you'll probably want open/fast, and compression closed/firm. In terms of pressure, going higher would be better. There's no real hard and fast rule though, it's different for 'actual' riding where you'd need suspension to work well. For trials you're pretty much trying to get it to not work well or as intended, so just try it out and see how it feels. It's easy enough to play with rebound and compression on the fly, so it would be worth finding a simple spot and just repeating the same move with rebound fully open, rebound fully closed, compression fully open, compression fully closed, etc. to see how it affects how your bike rides, and what feels better to you. 1 Quote Link to comment Share on other sites More sharing options...
La Bourde Posted October 8, 2022 Report Share Posted October 8, 2022 (edited) It is a though question, hope I can help. First of all, a fork has two purposes: to delay energy of an impact to absorb energy of an impact The first purpose is achieved through a spring function and is the most important: without a good spring function, nothing can improve the fork overall function. The second is achieved using for example a hydraulic cartridge. The compression adjustments are NOT position related (how much you are in travel) but related to the wheel displacement speed. 3 domains are defined: low speed, mid speed, high speed Mid speed setting cannot be externally adjusted (only a few exceptions on the market) Most compression adjustments affect low and high speed simultaneously or only low speed. The rebound adjustments are more position sensitive. There are only a few suspensions on the market that allow to adjust high speed rebound - and 99.9% of the riders do not need it. Almost all forks allow only to adjust low speed rebound. Movements from you body like to push in a flat turn are mostly considered as low speed displacements. So I guess most load transfers like a pivot on the front wheel or some placement hops/maneuvers are low speed displacements. Getting an impulse for a bunny hop shall be mid speed/high speed (for sure high speed if you use a brick edge for example to kick higher) Dropping from a high wall will generates high speed wheel displacement. Hitting edges like to tap against a wall with the front wheel will be controlled by the high speed compression. You want to use all of your travel on the biggest hits so that a lot of energy is delayed/dissipated and the landings are not harsh. Most forks do not offer a high speed adjustment, this is done internally in the shim stack. But it is not a problem, most of the energy of a drop shall not be dissipated but delayed, i.e. will be temporary accumulated by the spring and released so that the fork can extend back fast enough (the end of the extension is controlled by the low speed rebound damping - this is the rebound adjustment on most fork, the high speed rebound is determined again by the shim stack). So the first and most important setting will be the spring function (either with a coil spring or air spring). When the compression adjustment of your fork is fully open (I.e. the oil can flow easily) it should be able to remove most of the harshness of the biggest impact. This can be achieved by changing the coil spring rate or the volume of the positive air chamber. Preload of a coil spring will NOT really affect this! Modifying the high speed shim stack will also have almost a negligible impact on this. Changing oil viscosity too. As a trial rider, you want your fork to transmit the energy when doing a tap. But it does not come for free: the comfort will be affected, hits will be more noticeable. It means the high speed compression setting is a compromise (I think one can rely on the energy delayed by the spring, but I don't know if a rider can really benefit from this) Now regarding the low speed compression: I guess a trial rider wants his/her forces to be transmitted to the ground and does not want the geometry to be too easily affected. So closing the low speed compression adjustment seems to be right. This implies here again less comfort, but not on impact directly more arm fatigue (arm pump), cause more forces act against your muscles/body. Regarding the low speed rebound: this difficult to say. I guess because there are no succession of impacts (at least in street), the rebound could be slow. But having it faster might help to get more energy on a tap for example. The preload (case of a coil spring) defines his much forces has to be applied to displace the fork. It means it can remove completely the small bumps compliance. This is not great, use the right spring rate. The sag shall be adjusted to obtain the wished geometry. Ideally, a trial fork should have a dial to adjust how much damping the high speed compression shall have. It will be nice to adjust slightly the low speed compression to match the current fitness of the rider. Maybe the low speed rebound shall be adjusted by the same dial as the high speed compression, but the opposite way. Unfortunately, on most dirt forks the adjustment are basic: low speed rebound, spring preload or sag. Sometimes there is a sort of lockout that impacts low and high speed compression (and rebound). Edited October 8, 2022 by La Bourde 1 Quote Link to comment Share on other sites More sharing options...
cwtrials Posted October 8, 2022 Report Share Posted October 8, 2022 As someone who sucks at doing proper taps, a suspension fork can make them way more forgiving. Quote Link to comment Share on other sites More sharing options...
Sam Song Posted October 10, 2022 Author Report Share Posted October 10, 2022 On 10/7/2022 at 5:36 PM, La Bourde said: It is a though question, hope I can help.. Wow thank you for your lengthy reply. This is way beyond what I was thinking of! Quote Link to comment Share on other sites More sharing options...
Sam Song Posted October 10, 2022 Author Report Share Posted October 10, 2022 (edited) On 10/7/2022 at 12:37 AM, aener said: I think it would be easiest to recommend setting them... ...back in the box On a serious note: no idea, but curious as to your motives for wanting to run them? (Not saying you shouldn't - just unusual.) Is it wrist problems or something? I already have a high BB Echo for pure trials. The second bike I have built is for street trials, street/DJ, light trail/city cruising bike, so I wanted a suspension fork to have that flexibility. https://www.trials-forum.co.uk/topic/201894-norco-manifesto-project-bike/ Edited October 10, 2022 by Sam Song Quote Link to comment Share on other sites More sharing options...
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