[Closed] Longer Travel Forks and 40% Sag - Hardtail Ra Bikes

The faster you go the more noticeable this becomes.

I like this bit. "If you don't like it, you're not riding fast enough!"

I'm not entirely convinced that isn't marketing guff for "just run more sag". Especially as its frame only so the buyer would need to be the one doing the imaginary mod

It seems to be more than just running more sag i.e. less overall air pressure.

i was just wondering about how the 'reduced negative spring' was achieved in practice

i was just wondering about how the ‘reduced negative spring’ was achieved in practice

It’s not, it really is just sag they are discussing (I reckon anyway)

surely to achieve that much sag, you will have to run far less pressure, which in turn will just blow through travel.... unless you counter that with a truck ton of volume spacers. No idea how a fork would perform setup like this.

And why no other manufacturers are suggesting this technique?

If you run lots of sag, presumably you have reduced "positive spring" which I guess means less negative spring needed to keep it all moving right

maybe

yea so you dont get the soft start of the fork and it sits in its mid travel so its firmer.

im guessing because the ctoA length is too long for the frame.

I think that was why i was asking as not entirely sure.

I had assumed that at 40% sag the neg volume was larger than design for and perhaps to correct to do this you would reduce this volume with spacers/tokens?

Like:

[img] [/img]

If 160 forks performed better with 40% sag wouldn’t the manufacturers and users of these forks have sussed this out already. It’s not specific to any particular frame. It’s marketing bobbins.
Just fit a shorter fork. 🤷🏼‍♂️

I’m building one up. Fork doesn’t take tokens so gonna run it 150 with 30% sag, and go from there essentially.

I guess you have high sag for good small bump compliance, then add tokens so as you aren’t blowing through all your travel off a kerb.

Will report back.

was just interested in how to achieve, not the pros / cons of actually doing it.

I guess you have high sag for good small bump compliance, then add tokens so as you aren’t blowing through all your travel off a kerb.

My experience of higher sag is that you get a wallow-y mess, but then plenty of folk on here say they run 30% as standard so might not be too bad. 40% though......

rootes1
Full Member
was just interested in how to achieve

You'd just make the chamber volume smaller, but as these chambers are already pretty small (think about how much discussion theres been over Vorsprung Luftcaps and RS Debonair springs over the last few years) you'd be left with something tiny. It couldn't just be whacking in spacers though as then you'd run into issues with top-out. Also bear in mind that some brands have a coil spring involved with the negative chamber, so there's not even a one-size-fits-all solution possible

yep aware of the differences between forks, my assumption this was doe the most common air forks from RS and Fox that use a shared chamber for pos and neg.

I have asked Rafi from Ra to explain also.

Please post up the reply - should be interesting. Not sure what you mean by shared chamber though, it's very much separate as soon as the seal head moves past the dimple

The weird thing is that it looks like a nice frame and doesn't need this confusion. e.g. Ragley BigWig comes in 140 or 160 guise to suit tastes, no further explanation/fluff required

This feels like fudging the geo chart to shoehorn a 160mm fork into the "fork travel field".

I have found that I have benefited from using plenty of tokens in forks when riding hardtails so you can get a nice feel off the top without blowing through the travel when things get steeper/faster/rougher.

This sounds horrible to ride. Like, truly disgusting. I preferred running a fork firmer rather than softer to reduce the geometry change through the travel.

Not sure what you mean by shared chamber though, it’s very much separate as soon as the seal head moves past the dimple

You know what I mean i.e. solo air vs dual air. as in both springs are pressurized via one valve.

On my Ribbons as they are dual air i did play with more negative pressure than MRP recommend, could see if you started off with them in longer travel position could have some benefit - might play with them some more.

Yep if I get a reply will see about posting up.

@tomhoward

yes be good to find out, perhaps you could ask Rafi as an existing customer?

rootes1
Full Member
You know what I mean i.e. solo air vs dual air. as in both springs are pressurized via one valve.

Gotcha. Think it would still feel like a mess - lifting the front end would be a particularly soggy affair

Think it would still feel like a mess – lifting the front end would be a particularly soggy affair

I agree, the front wheel is going to drop into all the holes too.

perhaps with the change to the negative the volume of each (pos/neg) and ratio between the two would mean that it would in effect be the same as a shorter fork?

I agree, the front wheel is going to drop into all the holes too.

Perhaps that is the idea? better tracking of the ground over a wider range? also if the negative is reduced it would also mean the pressure would ramp up quicker as it un sags into a hole to control to some degree.

Might be fun to test this all out?

What I found with my Switchback is that it worked 'best'* with a 130mm or 140mm air fork with around 15-20% sag, I can't imagine a flaccid 160mm fork would be much fun at all 😐 Why would you want the front to track the ground into holes on a HT? If you're weighting the front to the point that's the case then you can't be ready to soak up the chunder from the back end with your legs and with a soft-ish fork that's just asking for an OTB moment 🤕

* YMMV, obvs.

I tried this with some Helms, that let you fiddle to your heart’s content with the negative spring, and the results were mixed. Better small bump compliance for sure, but everything else was “compromised”. If not riding hard or steep, and after comfort above all else, then it could be a good approach.

Oh, the grip claim is valid. I found that as well.

I have actually done this (by accident!) with my current bike, although that’s made me realise that their numbers don’t add up. 40% sag on a 160mm fork is quite a lot shorter A2C than the same fork @ 140mm with 20% sag. (96mm travel left at sag vs 112mm).

When I first got my Zero AM I set it up with a 130mm Pike which felt best at ~20% sag. I went through various set-ups after that and for the past few years it’s had that same Pike @ 150mm with a Luftkappe added and that feels best at ~30% sag. If you do the maths you’ll see that the former had 104mm travel left at sag and the latter 105mm.

You don’t end up plunging deep into the travel because the spring rate stays firm and doesn’t dip above sag (most air springs are U-shaped to some degree) and because the end stroke ramps up plenty. I only use the last 20-30mm of travel when landing hard to flat or having some kind of disaster. The 130mm fork with less sag but the normal Pike air spring had less grip but dived more plunder braking and steep stuff and bottomed out much more easily.

The Luftkappe increases the negative volume quite a bit and decreases the positive volume by the same amount (but it’s a smaller percentage change). I’ll try to find a graph!

had a response from Rafi from Ra Bikes and yes the reduced neg is implicated though volume reduction of the negative spring such as:

[img] [/img]

not sure of the exact detail though