[Sandwich]

I'm looking for help building/choosing a shock for a regressive frame.

I really like my cannondale rush. It has a low bb, relatively slack ha, short chainstays, and is cheap. I'm thinking of picking up a second one to use as a mini park bike to compliment the one I have set up as an xc/trail bike.

The problem is that it has a pretty regressive shock rate. That's not a huge deal on a 4" travel xc bike running a boost valve vorsprung tuned rp23, but if I'm looking for something more comfortable at highland, what are my shock options? Dhx air? Manitou isx? Presumably something position sensitive would be better than something truly speed sensitive. The other challenge is that I would need to shorten the stroke of the shock to 1.75" from a normal 7.5 by 2.0.

Any ideas?

 

[johnbryanpeters]

Try a piece of billet stock.

 

[StiHacka]

Shortening the stroke is easy with Fox shocks. DHX 5.0 Coil

I am sure you could do the same thing with the air version, just remove the air sleeve and install a few spacers below the bottom out bumper.

 

[Lelandjt]

I'd be concerned about durability using an xc frame for jumping. Having said that a DHX Air with small air can and travel spacer should fit your needs, and they're cheap and easy to find.

 

[4130biker]

I cut and put a coil bottom out bumper into an rp23 in a frame (kona howler) that seemed overly regressive. the bike was too harsh off the top, and flew through the travel and bottomed hard. Problem solved with the bottom out bumper (small air can).

 

[Jm_]

Too bad you can't fit a Stratos Helix Expert on there, not only did it have a progressively wound coil spring, but it also had an air-spring incorporated into it, so it was like 2x the progressiveness...so you knew it was good. Rode like a jackhammer on a non-regressive bike. Maybe you can set up the IFP depth for even more over-the-top progressiveness. Oh yeah, it used ATF fluid and supposedly you could refill/bleed it by submerging it in a tank and cycling it, but it didn't work for me.

 

[Jm_]

(and goddamn if that doesn't look EXACTLY like my old one...like my pic was floating around on the net...I hope not)

 

[weedkilla]

Didn't giant run 1.75 stroke shocks on the 4" travel trances?
When I've short shocked stuff in the past I've had issues covering ports with an extended top out bumper and needed to use the shorter shafts from other size shocks.
I can't remember doing it on an air shock - but memory says there is a bleed port for the negative spring in some of them.

 

[Sandwich]

I'd be concerned about durability using an xc frame for jumping. Having said that a DHX Air with small air can and travel spacer should fit your needs, and they're cheap and easy to find.

Fair point, how about for a prophet, 7.875 x 2.0?

 

[Muddy]

Fair point, how about for a prophet, 7.875 x 2.0?

Wouldn't Avalanche in Colchester have something close for you? An 8" shock?

 

[slimshady]

I'm currently running a 200x50 Roco Air TST in my Prophet, and couldn't be more happy with it. Being a heavy guy living in Argentina, my options for custom tuning were non-existent. So I ditched the floppy Fox RP2 and picked this one used form eBay for almost nothing (82 bucks shipped, and in need of a service). Changed the oil, greased the thing and changed some o-rings. Also stuck a rectangular piece of plastic (cut from a Tupperware's lid) inside the outer air chamber of the Roco to reduce the air volume and cope with the frame's regressive rate.

I was running 210 PSI in the Fox to simply keep it running at 40-50% of its travel while pedaling, bottoming it just with 1.5-2 ft drops. Now with the Roco I'm using 140-150 and 180 in the bottom out chamber. It feels bottomless in 4ft+ drops, even when I'm a total hack with less park skill/technique than a drunk snail.

 

[Jm_]

And the old 1st generation RP3 was super progressive, before they came up with the big can. I remember that normal-sag on my Turner 6pack resulted in about 3" of travel. Sagging it to nearly halfway also resulted in about 3" of travel, but softer initial and still no bottoming.

 

[Sandwich]

Wouldn't Avalanche in Colchester have something close for you? An 8" shock?

Most of what Craig does is make shocks speed sensitive rather than position ñ like I need

 

[4130biker]

There's a good selection of manitou swingers, air and coil on PB for dirt cheap. Will Manitou rebuild them anymore? If so, that could work. On the right bike, they work pretty well IMO.

 

[HAB]

I've got a 7.5x2 Swinger 4 way air I'd let go for not much.

 

[Muddy]

Most of what Craig does is make shocks speed sensitive rather than position ñ like I need

Avy's site gives an impression there is much in the way of sourcing nearly any shock - seems like a good guy too.

 

[StiHacka]

You need this bike: http://canfieldbrothers.com/frames/balance

Or my Mojo HD frame, 'coz I am getting the Balance.

 

[Sandwich]

Avy's site gives an impression there is much in the way of sourcing nearly any shock - seems like a good guy too.

Craig knows what he's doing, and he's honest too. What I've got/am looking at is a bike with a ****ty shock rate. He doesn't make bandaid shocks, he makes good quality dampers, but they can't fix bad suspension. I've had a conversation with him in the past and he was pretty blunt, the shock can do what the shock can do, but it can't do what it can't...which is where boost valves and SPF comes in.

He might be able to revolve the main piston though, which might work in combo with some weirdness.

You need this bike: http://canfieldbrothers.com/frames/balance

Or my Mojo HD frame, 'coz I am getting the Balance.

I probably can't afford it...pm with a price?

 

[Muddy]

Craig knows what he's doing, and he's honest too. What I've got/am looking at is a bike with a ****ty shock rate. He doesn't make bandaid shocks, he makes good quality dampers, but they can't fix bad suspension. I've had a conversation with him in the past and he was pretty blunt, the shock can do what the shock can do, but it can't do what it can't...which is where boost valves and SPF comes in.

He might be able to revolve the main piston though, which might work in combo with some weirdness.



I probably can't afford it...pm with a price?

Says $2100.00

...+ 4 months of wait time -- June.

 

[Sandwich]

Sorry I meant the mojor

 

[Muddy]

Sorry I meant the mojor

Yeah sorry about that. I was trying to come up w/ something clever but it wouldn't change that I can't read - sometimes.

 

[Beef Supreme]

What I've got/am looking at is a bike with a ****ty shock rate.

OK, I'll bite. Why buy a bike with a ****ty shock rate? There are lots of bikes from that era that have have a decent shock rate and would be cheap. The Norco Empire 5 was a really fun bike and would be worth next to nothing.

 

[Sandwich]

OK, I'll bite. Why buy a bike with a ****ty shock rate? There are lots of bikes from that era that have have a decent shock rate and would be cheap. The Norco Empire 5 was a really fun bike and would be worth next to nothing.

weeeeeell...

the rush/prophet has
is cheap
long effective top tubes
similar ground-breaking suspension technology also seen in the evil undead and devinci troy (aka a single pivot above the chainring)
they're cheap
relatively slack head angles, short chainstays, and relatively low bbs (the rush sits at 12.6, with a 69 HA, and a 16.7 chainstay, the prophet is slightly higher and longer)
plenty of availability, frames are super common so a breakage is easily remedied
simple, robust suspension means more time riding and less time replacing linkage bearings
73mm bbs and 135mm rear ends, cutting edge technology that are creak free and compatible with most of what's been on the market for 20 years
they're cheap
1.5" headtube makes for easy angleset compatibility
single pivot rear makes for easy short shockability
simple swingarm allows for 650b compatibility, which i've down with my current rush
they're cheap
the prophet also came in a 12mm, iscg equipped version for extended derping.
they're both extremely lightweight
shock sizes are relatively common (aside from the rush needing a spacer)
they're cheap.

So yeah, if I can overcome the regressive shock rate, I can have a frame that is really an incredible package, but overcoming the falling rate rear is a real chore. It's "ignorable" on a 4" frame used for derping in the woods over 20 miles, but for aggressive riding, it'll be more of a task to make it not suck.

 

[Jm_]

So basically, totally worth it until it snaps in half.

 

[slimshady]

So basically, totally worth it until it snaps in half.

Actually, Prophets are notorious for snapping their headtube off or getting their downtubes stripped halfway.

 

[Sandwich]

Downtubes stripped? I can only find a few reports of breakages on the intertubes, and those are all the non-MX version.

 

[slimshady]

Downtubes stripped? I can only find a few reports of breakages on the intertubes, and those are all the non-MX version.

My mistake, I sorta wrongly recalled an old thread here at RM, but the pic of the broken downtube there was from a Moto.

Anyway, I still encourage you to grab a Prophet (or an MX one if you could) and put a DHX Air or a Roco TST Air in it. As you said, it's cheap, lightweight and easy/cheap to replace in case of damage.

 

[Sandwich]

That's what I thought. The motos were failures from the factory, the rushets were pretty well built, though flexy. Supposedly they designed flex into the frame per cedrac garcia's suggestions, but that might just be making excuses.

The geometry is virtually identical to the evil ugoogly, if that makes your eyes go googly. 67 HA (66.5/67.5), 13.1" BB (13.1/13.5) 17.1" stays (17.1/16.8), and I think it weighs at least a pound less.

 

[slimshady]

Mine sits at ~66.5° HA with the Roco in the FR mount hole and a 150mm RS Revelation. The BB is a bit higher for my taste to begin with, but once it sags around 30% runs like buttah.

 

[Udi]

similar ground-breaking suspension technology also seen in the evil undead and devinci troy (aka a single pivot above the chainring)

You're generalising way too much.

The pivot isn't in the same spot (and this can actually make a reasonable difference to acceleration / braking characteristics) but that aside, what makes both of those bikes IS the leverage curve combined with a safe main pivot location. They have entirely different ride characteristics to the Cannondales as a result of the LR curves.

In this day and age where geometry is either good out of the box or very easy to fix (with headset cups, shock bushings, shock lengths etc), leverage curves are actually the most critical thing for a bike that rides well - and a good one would leave you out of the mess you're describing here.

It's also super hard to blanket fix a poor leverage curve with shock tuning, there just isn't that much freedom in it. You can alleviate small flaws but you definitely aren't turning a 222 into a DHR.

If you haven't already bought one, my strong advice would be to buy something else. You're wasting your time and money. Also 69* isn't slack - combined with the awful leverage curve (primarily) you've described a terrible frame to me.

 

[Sandwich]

I know I'm generalizing. I'm just being cheeky, the pivot point on these two bikes is actually pretty distant from one another, not to mention build quality, frame material, etc. etc. that all go into how the bike rides. I'm just trying to suggest that you don't need to have a pair of links, a dogbone, a fancy acronym, and dozens more patents in order to have a bike that rides well. So many people have ruled out the single pivot, but it just keeps on trucking, no matter the suit it's wearing, be it full denim or italian wool.

Still, prophets are plentiful, and if you could make one ride decently with the appropriate shock, you could end up with a decent bike at the end. The question is whether you can make one ride decently with the appropriate shock. Of course you can pay way more and get a way better bike, I won't deny that, but there are those of us who can't afford carbon uber-bikes.

Also, 69* is for the XC/Trail Rush, 67 is what the prophet runs in "FR" mode, and with an angled headset, you can have more fun. Not trying to say either is particularly slack, but the fat headtube gives you some freedom.

 

[Udi]

Apologies if my post sounded a little harsh, my point was that there are so many good frames these days that there's no need to buy an awfully regressive one. I actually disagree that regressive linkaged SP frames ride particularly well, but it depends what you're comparing to.

However - on the off chance that you insist (or have already bought it), I think the best shock for highly regressive frames is the humble DHX5.

The two characteristics you are looking for are a freely moving beginning stroke to iron out the harshness that is common to low initial leverage ratios, and some ramp up at end of stroke so that a) you can run a reasonable amount of sag to compensate for the initial harshness and b) not bottom out excessively as a result of it. Unfortunately the first requirement somewhat rules out the old large-shaft RC4 that has desirably strong EOS damping progression - because it's a little harsh at the start due to the large shaft) - and also means that most (current) air shocks will feel less than spectacular also.

The DHX5 has a small shaft so no large air preload influence from the reservoir pressure, moves quite freely at the start like any coil shock, and will provide decent bottom out resistance if you run minimum chamber volume (adjust IFP if needed) with the boost valve. It's also easy to find them cheap, and they're easy to work on yourself.

If you want to use an air shock, I think the Vivid Air is one of the better choices for not being too harsh initially. The CCDB-A feels poor to me, and Fox is better but not spectacular.

 

[Sandwich]

Thanks Udi. I'm definitely not trying to make the statement that you can get a porsche for a prius price, but I'm just trying to explore whether you can get a bike that doesn't ride well on paper, and a shock that doesn't work on certain frames, mix them up, and get a decent, rideable bike out of the blender. I feel that the prophet and rush both have a lot going for them, but if cannondale had mounted the shock at the downtube, we really wouldn't need to have this conversation.

I've considered the DHX5, but I was also considering the DHX air. I've seen people mod them with RP3 air cans for more progressivity. I suppose a small air can combined with a spacer, plus the boost valve cranked might make for a very progressive shock, but you still have the initial air stiction of the large shaft to overcome, and I've heard bad things regarding the DHXair's mid-stroke compression support, which I'm concerned wouldn't work on a falling rate bike.

 

[Udi]

I think the key point you can take away here is that the range of available curve compensation in a shock is very minimal. It means you can slightly improve bad characteristics, enough so to notice, but definitely nowhere near a frame that has a better leverage curve in the first place.

I don't think you need to spend big money to get good frames, but I don't want to recommend anything because it's hard to line up cheap with good suspension, good geometry, and durability all at once. Expensive definitely doesn't equate to good though, and the benefit of that is - with an open mind sometimes you can find a cheap frame that works really well. I just don't want to be responsible for something potentially bad as my experience with AM bikes is limited, but do look around.

That aside though, I think the DHX Air is probably not much better than an RP - the boost valve is handy, but I think the initial harshness in a digressive bike is a bigger problem that the EOS digression. This is because it's easier to reduce bottom outs and also to deal with them in comparison with dealing with a wheel that is reluctant to move initially.

If you don't mind running a coil shock, I'd start there assuming there is a fitting size. Even if it's a non BV shock you can always get creative with the bottom out bumper/s etc. If you must run an air shock I'd save your money and run the stock RP (or whatever is included) with as much sag as you can handle + maximum ramp up (via volume spacers or small cans).

I think mid-stroke problems pale in comparison to the issues I described anyway, but for reference, shocks that don't use a position-sensitive valve are linearly damped in compression (with respect to position, aside from damping rate changes as a result of leverage curve which are independent of shock choice) - so the mid-stroke compression falloff is a myth. What you do get in any air shock is some mid-stroke spring rate falloff, but as I said it's the least of your concerns in this case.

 

[Jm_]

so the mid-stroke compression falloff is a myth. What you do get in any air shock is some mid-stroke spring rate falloff, but as I said it's the least of your concerns in this case.

This. A graph of the curve says it all.

 

[Sandwich]

ah, I see, I've been holding it upside down this entire time!

//sarcasm

 

[slimshady]

I think the key point you can take away here is that the range of available curve compensation in a shock is very minimal. It means you can slightly improve bad characteristics, enough so to notice, but definitely nowhere near a frame that has a better leverage curve in the first place.

I don't think you need to spend big money to get good frames, but I don't want to recommend anything because it's hard to line up cheap with good suspension, good geometry, and durability all at once. Expensive definitely doesn't equate to good though, and the benefit of that is - with an open mind sometimes you can find a cheap frame that works really well. I just don't want to be responsible for something potentially bad as my experience with AM bikes is limited, but do look around.

That aside though, I think the DHX Air is probably not much better than an RP - the boost valve is handy, but I think the initial harshness in a digressive bike is a bigger problem that the EOS digression. This is because it's easier to reduce bottom outs and also to deal with them in comparison with dealing with a wheel that is reluctant to move initially.

If you don't mind running a coil shock, I'd start there assuming there is a fitting size. Even if it's a non BV shock you can always get creative with the bottom out bumper/s etc. If you must run an air shock I'd save your money and run the stock RP (or whatever is included) with as much sag as you can handle + maximum ramp up (via volume spacers or small cans).

I think mid-stroke problems pale in comparison to the issues I described anyway, but for reference, shocks that don't use a position-sensitive valve are linearly damped in compression (with respect to position, aside from damping rate changes as a result of leverage curve which are independent of shock choice) - so the mid-stroke compression falloff is a myth. What you do get in any air shock is some mid-stroke spring rate falloff, but as I said it's the least of your concerns in this case.

Udi, the stock RP2 in the Prophet already has a LV air can, a volume reducer tucked in and the highest compression setting. Add Fox's recommendation on which volume spacers you can run in LV and this lenght & stroke (200x50), and you'll find it doesn't have much to offer in terms of customization except for sending it to PUSH or something like that.