Ask the experts

[toast2266]

How the fuck to do calculate the spring rate for an Ohlins rear shock? I can't find shit online unless I'm just not looking well enough.

Depends more on the frame than the shock. You can get a very ballpark figure on a site like this: https://www.tftuned.com/spring-calculator. There are assorted other online rate calculators that will all give varied results. You can try a few of them and then take an average. And then probably end up buying a sprindex that covers roughly the correct range.

[Andeh]

How the fuck to do calculate the spring rate for an Ohlins rear shock? I can't find shit online unless I'm just not looking well enough.

A year or two ago, Seb Stott had an article on PB explaining how to calculate it. I made a quick GSheet to do this:
https://docs.google.com/spreadsheets...it?usp=sharing

Most of the fields should be pretty self explanatory. The rear bias one is kinda a personal preference tweak. I find 0.64 was giving me results that lined up with actual sag measurements, but maybe try a little bit higher if you ride really, really steep stuff or really hang off the back. Seb suggested doing: 1-(RC/WB), which for my bikes usually gives 0.64. I imagine if you rode a size XL without proportionate CS this would change.

[jamal]

very roughly, I would start by taking the ratio of rear suspension travel to shock travel, weight of rider and bike, and an approx f/r weight distribution.

For simplicity so I don't have to like use a calculator, lets say a 150mm bike has a 50mm stroke shock, and the bike and rider are 200lbs, and the weight distribution is 50:50. So there's 100lbs on the rear wheel, 3:1 ratio between travel and shock means a 300lb spring would compress 1" with the rider on the bike. Aaaand we mixed units but anyway that's like 50% sag (also motion ratio calcs are not quite that simple). To get, say, 25% sag, we'd want a 600lb spring. I think with accurate weight and weight distribution numbers you could get pretty close that way although it does ignore the shape of the leverage curve and you'd actually want the unsprung weight of the bike (ie subract the weight of the wheels, tires, cassette, rotors, calipers, some of the suspension parts). So I'm sure one of the above calculators/spreadsheelts does it slightly better.

[toast2266]

Ultimately, the answer is guess and check. There's a reason that anyone who runs coil shocks has a pile of coils lying around their garage.

And it all gets messier once you realize that most coils aren't particularly accurate for their stated value. And to make it worse, different brand's coils feel different, so you can't always switch between different brand coils and get a consistent effect.

[XXX-er]

well I got a bunch of air just sitting around

[Whiteroom_Guardian]

Wireless droppers? Building up a new frame soon and want to clean up the cockpit. Is sram the only really tested one?

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[Andeh]

I've got 2 of the AXS Reverbs, and they've been great. They do need a basic service about once a year just to get clean bushings and fresh lube, but that's it. That's mostly me being picky about them feeling super smooth though. I bought both mine used on PB (one for relatively cheap because it had a stanchion scratch that I repaired).

From what I've heard the KS one is the only one that is a legit competitor (has good return speed, 200mm drop version). The Magura one is mega slow. The TransX one is also apparently pretty slow. But check the reviews on them.

Edit: if you are going to drop a bunch of coin on a wireless dropper, I'd suggest getting one in 30.9 dia then getting shims as necessary for whatever bike you ride. The Problem Solvers one are junk in my experience (creak) but the Cane Creek ones work well.

[Roxtar]

Crown race question:

Bike A has a Chris King Inset 3 headset. According to CK the baseplate (crown race) has a 45 degree bearing seat angle. The fork (cane creek helm if it matters) has the King baseplate.

Bike B has a an FSA Orbit 1.5 ZS headset and the fork (Fox 36) has the associated crown race. FSA says the bottom bearing is 36/45 degrees which I think means the crown race is 45 degrees?

My question is can I swap the forks between these two bikes without messing with the crown races/baseplates? I want to do this to experiment with travel on bike B since the Helm can be travel adjusted without an air shaft swap.


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No,
A 36/45 bearing has a 45* OD taper and a 36* ID taper. It's the ID taper that mates with the crown race, hence, the FSA crown race would be 36*

[Whiteroom_Guardian]

I've got 2 of the AXS Reverbs, and they've been great. They do need a basic service about once a year just to get clean bushings and fresh lube, but that's it. That's mostly me being picky about them feeling super smooth though. I bought both mine used on PB (one for relatively cheap because it had a stanchion scratch that I repaired).

From what I've heard the KS one is the only one that is a legit competitor (has good return speed, 200mm drop version). The Magura one is mega slow. The TransX one is also apparently pretty slow. But check the reviews on them.

Edit: if you are going to drop a bunch of coin on a wireless dropper, I'd suggest getting one in 30.9 dia then getting shims as necessary for whatever bike you ride. The Problem Solvers one are junk in my experience (creak) but the Cane Creek ones work well.

What is the rationale behind that? My new frame will be 31.6. I feel like shims will just add another place creaks could come from.

Are the 30.9 stronger/better posts?

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[Abies]

No,
A 36/45 bearing has a 45* OD taper and a 36* ID taper. It's the ID taper that mates with the crown race, hence, the FSA crown race would be 36*

Capiche, glad I asked


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[Dantheman]

Are the 30.9 stronger/better posts?

Universally compatible with any new frame you get in the future.

[Andeh]

What is the rationale behind that? My new frame will be 31.6. I feel like shims will just add another place creaks could come from.

Are the 30.9 stronger/better posts?

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You can always size up with shims but can't size down. When I buy a gratuitously expensive component like a wireless dropper (or eeWings), I want to be able to use it on every other frame I get down the line.

[Roxtar]

Capiche, glad I asked


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No problem. I had to learn this stuff when trying to upgrade the cheap-azz bearings from my Works Component angleset.
For info sake, both Cane Creek and Enduro offer 45/45 lower headset bearings that should directly replace your FSA lower. Combine that with a 45* crown race (also avail from Cane Creek) and you can swap forks to your heart's content.

[Canada1]

Anyone made the switch between xt four buckets and SLX? I’ve ridden both, and could not feel a difference. One of my kids is considering this switch, and it has me wondering.

[El Chupacabra]

Anyone made the switch between xt four buckets and SLX? I’ve ridden both, and could not feel a difference. One of my kids is considering this switch, and it has me wondering.

I don't think there's any meaningful difference. Why switch?

[XXX-er]

I think having the 4pot calipers might make a difference if you are 240 and/or ride very long steep trails

[El Chupacabra]

My comment was directed at changing from 4-piston XT to 4-piston SLX, or vice versa. No reason to do so.

[XXX-er]

i just assumed 2 pot vs upgrading to 4 pot in any case do you really need more power or do you think you need more power ??

[Canada1]

He had some overheating on the SLX and never had on his xt. I think it is that he grew and is on a bigger (significantly more travel) enduro bike. I went from a four bucket xt on my altitude to a four bucket SLX on my new specialized, and feel zero difference.

[grskier]

i just assumed 2 pot vs upgrading to 4 pot in any case do you really need more power or do you think you need more power ??

If you don't notice a significant difference between the two, you are either very light, or not asking a lot of your brakes.

[tellybele]

4 pot in front and 2 in the rear, just like moto and it makes hella sense. I can feel a diff having 4 up front.

[toast2266]

2 pots are for XC bikes. I honestly can't remember the last time I ran a 2 pot brake on my own bike. Probably some Juicys ~15 years ago.

[smmokan]

But why bother with a 2-piston in the rear unless it's for a full-on XC bike? Just go with 4-piston F&R... other than Magura, I can't think of a company that sells a complete set that's split like that.

[Andeh]

I ran those Magura MT Trails (4 front 2 rear) on a trail bike ~5 years ago and it was dumb. You burn through pads so fast, and it's so hard to modulate speed with the rear like you're used to because it just doesn't have enough power. Chasing grams on trail and enduro bikes is bad, mmmk?

[Sandbox]

I ran those Magura MT Trails (4 front 2 rear) on a trail bike ~5 years ago and it was dumb. You burn through pads so fast, and it's so hard to modulate speed with the rear like you're used to because it just doesn't have enough power. Chasing grams on trail and enduro bikes is bad, mmmk?

I echo this statement. Had the trails on last year and I just wanted sooooo much more. Switched out to MT7 this year.


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