120mm fork 20-25 % sag what will the angle go to on a hardtail all other things equal

ta

Add an inch to the fork and it slackens the angle by about 1deg.

If you want more accuracy you will need to give data like the old fork length, new fork length, wheelbase etc etc etc.

You will also need a new set of friends as you will bore all your existing ones with talk of frame angles, most angles are made up to suit the designers/marketers whims at the time.

e.g. marin measure the BB height with a rider sat on the bike, a lot of companies do it unweighted, the cotic soul which everyone rides with 120-130mm forks, is listed with the angles based on a 100mm fork with 25% sag (so 395mm ish a-c length, as opposed to the 500mm ish most will run it at unweighted)

Did anyone else hear a rumour that the new 2010 commencalls werent as good as the old snaptastic ones as the QC is stricter (hence no more snapping) and Commencal never specified the angles that slack?

71.5 degrees*

*this is a joke at the silly OP

spoon has it. Rule of thumb says 1 inch = 1 degree.

It's a fair rule of thumb but the maths says that 20mm per degree is pretty exact. A 100mm fork sagged 25% is also around 450-455mm, not 395mm – most of them are about 475-480mm to start.

there's loads of rumours about commencal – don't believe them all 😉 there is something to the discussion about angle tolerances but i'd say thats more about journalistic speculation than factory reality, alu frame tolerances tend to be within 1/2 degree total so any variance they talk about is minimal. it was also about the difference between 08 and 09 frames – 2010 meta bikes feel like the 2009 (breakage issues year) versions to me, i don't ride them much tho so that's just first impressions. i know where they make commencal's sussers and they also make some of the most well respected frames around here, they're one of the most trusted factories out there. they're not known for major gaffs.

don't know where 395 came from, think I gave it 70% sag rather than 30%

the cotic soul which everyone rides with 120-130mm forks, is listed with the angles based on a 100mm fork with 25% sag

CHECK HERE FOR COTIC HARDTAIL GEOM WITH VARIOUS LENGTH FORKS: http://cotic.co.uk/geek

Are manufacturers' head angles quoted at correct fork sag?

Are manufacturers' head angles quoted at correct fork sag?

i always used to, but lots of companies are moving to static, which for long travel hardtails makes numbers look bonkers.

Brant, while your here, is an mmmbop rideable with a 130mm QR fork (say 500mm A-C)? Or is it really for 6" forks?

Wouldn't a steeper head angle but a greater fork offset result in less change of angle with travel?

yes but you'd need to change / increase the rake toward 100mm and go for an 80 degree + head angle to see more constant angles for a given change in fork length, even then it's not much more consistent.

the static / sag measurement thing seems to confuse, look at some grouptests and some rbikes are listed with sagged numbers, some static, often no mention of how they're measured.

sussers are measured static so i guess that's the more common measurement for many now, i'm more used to sagged angles on a hardtail but as long as you know whether its static or sagged, and with what fork travel, it tells you the same thing really. static is easier for most of us to measure anyway.