I wish you could toggle the sag amount without having to have a “custom fork” and without having to toggle the “frame lock”.
Is there possible to code the sag variable such that it is not a “permanent” geometry change or a fork parameter? It would be great if it would just toggle the geometry change.
To clarify, I’m not suggesting that hardtail designs shouldn’t consider sag, I just think it would be nice to easily toggle and adjust the sag without accidentally changing the frame or fork geometry.
I know my thinking goes against the established framebuilder wisdom, but these are the reasons why I design without sag:
Sag is subjective to the user: 20, 25, 30%? I have no idea what the sag is on my fork. I would argue that most mountain bikers do not look at the sag when they set up their fork. They adjust the spring rate, damping, and air volume to get the proper grip and feeling of support.
All full suspensions and all major frame manufacturers list their geometries unsagged. I feel like this is the industry convention, and it leads to customer confusion when I show sagged geo.
I feel that designing around sag puts too much confidence in a parameter that is subjective, fork-dependent, and terrain-dependent.
In light of all those reasons, I prefer to design based on a nominal static parameter (unsagged), knowing that the bike will sag.
In addition to what Daniel said, here’s another reason why:
If you spend any non-negligible amount of time climbing a hardtail on a relatively smooth (paved or otherwise) surface, you will do yourself a service by locking out your fork. In my experience, through motion of the rider the fork creeps upwards over time (because the lockout prevents it from returning to the sag point) until it is essentially topped out. In this configuration (because the rider is on a hardtail), the head tube angle is at its slackest possible configuration. This corresponds to the longest trail and flop height. If you’re at all like me, you find that climbing (at low speeds in particular) is where any unwanted effects of long trail and flop height are the most salient. As such, I want to design around these factors where they are the most important, i.e. when the fork is unsagged. Hope my wording makes sense.
It sounds like things would be easier if I made it so that when you select a standard fork, the input field for sag would be left enabled. I’ll plan to implement this change in the next update.
Not 100% BikeCAD specific but this site is handy if you’re comparing geo between sagged and unsagged bikes. Defo helps if you’re buying off the shelf or trying to wrap ya head around industry geo trends since most manufactures seem to list unsagged geo for hardails.
Dredging this back up for a related question: When you/the industry generally are designing a hardtail are you typically displaying unsagged geometry on the geometry chart, assuming a 1-2 degree change in HT/ST angles when sagged?
I guess Esker is doing what I’m talking about by listing all their geometry based around a 120 fork with 30% sag (491 A-C) which to me makes the most sense, although it introduces the confusion of the cycling industry speaking in static terms for “ideal” geometry and sagged geometry not comporting or requiring some math to extrapolate. Hayduke 2024 – Esker Cycles
This is my opinion: the correct way is to design unsagged and accommodate the 1-2 degrees. It is the most clear and reduces the chances of miscommunication. Why?
This is the industry standard (every major manufacturer lists unsagged geo for FS, HT, road, etc…)
People run different levels of sag in their forks
When climbing, the fork has zero sag, and the STA matters more; when descending, the fork has a lot more sag, and HTA matters more. There is no “nominal” mode in which the hardtail operates.
From what I see, framebuilders and framebuilding adjacent companies (Salsa, Esker, etc…) design and list bikes sagged. I have seen this lead to manufacturing mistakes and riders getting the wrong size bike.
That makes sense just from the perspective of individual preference/bike set up. I guess it’s easier for a manufacturer to run some numbers on different set-ups to determine an ideal number that will accomodate most of their consumer base (one would hope they understand them well enough).
I feel like I’d personally account for some sag when climbing as I never use lock-out and will be pretty frequently standing or navigating an obstacle, although I understand it will be less than the sag when pointed DH.
Daniel is correct in that most companies list unsagged geo. However there are a few who go against this trend. Cotic also lists their geo the same way as Esker. And not only do they state sag percentage and A-C but also show multiple options for fork length.
Like you I prefer to work with sagged numbers for fit/handling reasons. I wish this was industry standard but as long as you known if the geo listed is sagged or unsagged it’s easy enough to compare. The only time I come unstuck is when a geo sheet doesn’t say either way.
Rewinding a bit, I will amend my advice: if you are designing a bike for yourself, it does not matter what convention you use as long as you are consistent! Whatever method gets you to where you need to be.
It’s bike industry convention to send engineering drawings unsagged, but that only applies if you are manufacturing stuff.
I like to use unsagged because then the bike is easily measured in real life, and easy to compare to other bikes I have in front of me.
I was comparing two hardtail frames from one manufacturer- they had the geo of one frame listed sagged, and the other frame unsagged. The only way to tell was to look at the fork a-c, and then find what fork they had spec’ed on the bike.
Technically… all the horizontal dropouts should be designed rolled clockwise, parallel with the chainstay (not parallel with the ground). But the sliders never have enough hoodspace to do this, nor does it look good, so everyone makes them horizontal. Everyone’s sliding dropout hanger is off 3-4deg with sliders…
I run mine parallel with the ground so any adjustment doesn’t impact the geo. Probably not significant, but with a low BB the CS angle is greater, and mine have 40mm of adjustment, so something.
This!
A detail that is very easy to overlook. All the frames I’ve built with sliding droputs have had the slot horizontal, but they were all also specifically built as singlespeeds, so it doesn’t matter.
When designing some sliding dropouts and inserts for my day job, I made sure that the design works with the slot in line with the chainstay, and the hanger position has been clocked accordingly since we won’t sell exclusively singlespeeds. We’ve actually got them included in the latest release of BikeCAD.
My take is for trail/enduro bikes etc. I just lay it all out unsagged. Im used to seeing those numbers and can quickly design and know what I’m getting. Even a trail orientated hard tail I would do that. It’s not like road where we are in a fixed position for hours on end need that mm perfect fit. You could argue that in a enduro racing environment that bar height and reach is important though and should be considered. Fortunately as builders we can offer that to our customers.
Where I would be looking at the sagged geometry is for rider fit from a XC/marathon racing perspective where they have put time into getting their position dialled and looking at the racing performance aspect. ie. climbing and driving it hard in the seated position.
