The Dentist's Enduro
- Thread starter ianjenn
- Start date
Now you've said too much!
Have you learned nothing? The only way forward to keep people happy is through new standards. Search your feelings, you know it to be true.
Orthodontist?
With 25% sag (43mm of 170) would put you @12.07" bb height.
Um, no.
1) Are you really running 25% front sag? That's a lot.
2) Even if you are, the line of action of your fork isn't vertical (and more so once you're sagged into the rear).
Your math isn't wrong, but it's not a good approximation of how a bike actually behaves.
Are you talking about front or rear travel/sag?
Technically, I was speaking of the rear 170mm cause I was thinking of it being static on both wheels and subtracting 25% of 170mm. But it's just a basic way of measuring it. I'm not the mathlete trying to be that precise really, just giving an approximation.
Btw, why would 25% sag be too much? Most DH calculators say 33%. I think 25 for a bike like this is a good starting point.
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because he's probably not measuring front sag while in the 'attack' position. when i measure this way, 25% is usually spot on and causes zero issues with ride height or front/rear suspension balance.
HAB is correct, but I'm glad someone brought it up.
While I had my spreadsheet open I noticed a lot of the front sag numbers people were typing in were quite high (eg. 15-30%). These numbers shouldn't be that high, because a) weight distribution over the rear of the bike is higher (keep in mind this is *static* sag) given the typical CS to WB ratio, and b) static sag recommendations are supposed to account for the dynamic scenario of the bike pointing downhill and thus biasing the weight distribution forward heavily.
I edited in some "default" values of 9% F (to 29% R) for DH and 11% F (to 27%R) for spenduro. The 33% comes from a long time ago (over a decade) and since then we've improved kinematics, improved dampers, and even changed wheel sizes, so bump absorption has improved dramatically. More sag means less dynamic stability, so the currently (way) superior bump absorption means we can now run a little less sag than in the past and still have superior bump absorption overall while improving stability. Correlating the way Gwin rides, his suspension setup, and his results are a good practical example of this - not to say we are all him - but I think a 30% rear / 10% front static sag setup for a DH bike is a good average these days. Very fast riders might be around 28/8.
Setup Sidenotes:
- it's pretty hard to measure front sag, just set your fork up so it provides the support you need and realise your measurements might be way off. Generally if you set it up well (or it's setup by someone who knows what they're doing) the number will be somewhere around that 10% mark,15% absolute max. Static bushing friction and the angle of force action on the fork affect its movement on flat ground so measurements tend to be inaccurate and inconsistent.
- I don't buy the "attack position" thing, just stand on your bike - the numbers already account for the fact that static sag isn't a real world scenario measurement. The 30/10 example I gave considers that you have more mass on the rear of the bike, and that you're on flat ground. That's why those numbers are so different! If you're actually measuring 25% on the front then you shouldn't have 30% on the rear - it's a distribution.
- The static bias should vary depending on the "DH" component of your riding, so if you're riding very flat trails then you should subtract from the ideal rear sag number and add to the front. Given this is the DH forum though I think we can skip that (I used a 2% difference for enduro).
- Finally: sag is an approximation, and not a good one. Since the front measurement is so unreliable we can only measure the rear, and even that isn't incredibly precise. Given this, when using sag as an input to calculate something else like ideal BB heights (in this case), it can be more reliable to use an analytic input value (which is close to corect) rather than an experimental / measured input value which might be way off. Aside from this, it's just a rough starting point for new setups.
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maybe you're looking at it back-ass-wards?
You talking air springs or coil springs for the forks? I can still get 15-20% sag out of a freely moving set of forks with the stiffest coil springs available while sitting or standing upright on the pedals, and I'm 185# or so. Figure 0.95kg/mm with just enough preload to keep things quiet. Feels well balanced with 25% rear sag.
Well that's what I mean - it varies with air/coil spring, friction variations (can be huge), and actually varies substantially with head angle... so it's hard to take a reliable/comparable measurement for front sag (for the purposes of giving a general recommendation). That's why I think it's better to base fork setup less on a sag measurement and more on actual riding, whereas on the rear measuring sag is less prone to error.
Not saying there's a right or wrong way to do things, just some general notes. Obviously if you've measured 25R, 15F it still fits within my total, my concern was more for people who typed in 30R/25F (but maybe they just like a lot of sag - if so fair enough!).
Has anyone seen what the frame only MSRP is?
I thought fork sag was a starting point. then you add/substract air based on feel. I find it's not hard to determine "feel" for the fork. I usually look for a substantial dip in the trail, like a smooth creek crossing. If the bike dives forward through the dip, add air until it stays relatively stable. (this should be done with no LSC). then, I find a long hill, and gently apply the front brake, and dial in the LSC to an appropriate level. last thing I do is keep an eye on achieved travel throughout a ride (with the o-ring). I'm consistently not getting full travel at the moment (with two tokens in my Pike). I suppose I could remove a token and add a bit of air to the spring, but I'm pretty satisfied with the level of support I'm getting through fast, rough and chundery sections of trail.
With all that, I've found I have just under 20% sag. But, I also find sag varies a lot depending on how recently I've changed the bath oil and lubed the dust wipers. When freshly serviced I tend to run less sag. It seems to wind up closer to 15% or so.
Honey Badger Dentist don't care. He gets paid either way. : )