170mm 36 vs 38 fork: which would you prefer?

What's your weight and how do you like the 38’s? What are you trying to gain going to the 36's, just a lighter front end? I'm not sure which will have less sticktion, but if your servicing them regularly it should be so minimal you wouldn't notice a difference.

I really don't think a 6.3mm decrease in seal circumference is going to be a game changer for you, or even noticeable, but you're right that the 36 is lighter. I think there are riders for whom the increased flex of a smaller fork can be good. Probably riders under 150 pounds/68 kg. I'm not one of them, and I'm so glad the bigger forks are available. It was an immediately noticeable effect for me and an instant upgrade as a big tall guy with heavy tires and big brake rotors. If you're a lighter rider and bike weight is important for you, go for it. There was a long time before 38mm forks and most people got along just fine.

The larger bushing area and tube diameter of the 38 reduces friction, especially under load which everyone benefits from. The air spring is also more optimised for things like less pressure build up in the lowers from the twin tube air spring while retaining a large negative chamber. The 36 platform needed to extend the lowers and stanchion tubes to increase the neg chamber in the latest generation.

Personally I don't see the point of going for a 36 at 170mm, I think the visual difference will make people think it feels "lighter" in the front end but I can't see a practical benefit to it

It's a conundrum for sure. You really have to decide what your prioritys are. I have moved from a Fox 38, Zeb and Fox 40 to a Fox 36, RXF 36 and DH38. as a 185lb former powerlifter, I don't consider myself a light weight, however, I have worked for years on becoming a rider who uses more finesse and less brute strength on the bike. If you are riding with attitude and pushing the edge of survival, the larger chassis forks certainly offer more confidence. Personally, if I am riding clean and smart, I can use the extra traction and compliance of the smaller forks to carry more speed. Disclaimer, I ride Pisgah area high speed, often awkward, natural terrain without many of the big hits you may find elsewhere. 

I've ridden Fox 36's, 38's and now I'm on a Zeb. I'm around 150 pounds so I'm probably relatively similar in size to you. I tend to think the newer 38mm forks are really good, regardless of what brand. I think I tend to ride relatively centered on the bike, maybe a little forward and the burlier forks seem to respond better. I don't think you would gain much by going to a Fox 36. Fox 36 is an amazing fork, but if you're riding an enduro bike with a decent amount of rear travel, I think the 38 is probably a better match to the rear suspension on the bike. If you know someone who has a 36 or a Lyric who would let you borrow it for a ride, always worth a shot. 

There is also the 36 ebike version but I think it only is compatible with a 160 mm air shaft max if I'm not mistaken. But maybe marzzochi could be an option. I'm using the 36 ebike on a mid-weight ebike where it doesn't look too burly like the 38 and its perfect for my terrain. Only the Grip2 seems a bit underdamped considering that I only weigh 67 kg and even I have to close the compression fully when its really warm and steep.

The decision for me has more to do with the air springs and the air trapped in the lowers and associated ramp up effect.  Are you able to use full travel easily on a 160mm 36, requiring the usage of volume reducers?  I find that many light weight riders have a lot of issues getting a 36 setup properly for full travel.  I digress, the 38 will technically have less friction as noted above... but that's not likely to be what you notice.  

As for torsional stiffness... I'm 180lbs and ride relatively hard for a 42 year old dude.  I can feel the stiffness difference of a 36 vs 38.  I'm not going to say that I require it or it's always a huge benefit... that really depends on the bike, trail and how I'm riding at the moment.  I would say that for me, the 36 tops out at 160mm because the flex in the fork starts to get a bit detrimental in certain situations.  Mostly limited to off camber rock gardens or janky trails in laguna in general.. this manifests itself with a bit of inaccuracy in holding a line in the front end of the bike.  In contrast, I have a zeb on the front of my nomad at 170mm... there are times when I'm not riding at mach chicken, where I notice that the fork is a bit stiffer then necessary... however once I'm in a bike park landing sketchy drops and slamming into rock gardens where I'm beyond stoked with it.

The short answer to the question is yes, you could toss a 170 air spring in a 36, but I'd think the compliance and control that many (myself included) like about the 36 chassis might pass a tipping point where it becomes too flexy at 170mm. I haven't tried this setup to know for sure, but I even find a 160mm 36 starts to feel vague when you're really moving.  

It's definitely a toss up. Since you're a lighter rider, you might not have a problem overriding the fork. I'd just think about how you ride, and if it feels worth it to give up the rigidity of your 38 for the sake of having less weight under your hands with a 36.  

Both have thier place, as people have said rider weight plays a big factor, i can see why burly forks are prefered by bigger riders but as a lighter rider (around 70kg) i have had a Zeb and a 36, both in 170mm and i've stuck with the 36, partially due to weight (saves 2-300g) but mostly due to the stack height which nobody seems to talk about, part of the stiffness of the Zeb / 38 comes from a bigger steerer to crown join which makes the Zeb around 12mm taller for the same travel, that makes it more like a 180mm fork which is a bit tall for my frame really and made the BB heigher so decided against it, i will say the Zeb was probably the nicer feeling fork and did smooth the trail better but that is a whole different conversation and could just be setup or fox vs rockshox rather than 36 vs 38.

I’m pretty sure The Suspension Lab response is the most scientific you’re going to get so I’ll just throw my $.02 in as a heavier rider. I’m 225lb and noticed the 38 felt more precise compared to the 36 at 170mm of travel. The 36 seemed to flex under heavy braking and I felt like no matter how I adjusted the air spring and damper I felt like I was lunging forward and spent more time towards the front of the bike trying to get backwards towards the middle. When I put the 38 on it felt more sturdy and kept me in the middle of my bike easier. It also feels more capable of “point and shoot” if that makes sense. Now all of this could be placebo but for me if I’m putting a fork on a bike that’s 160 or greater I’m probably using a 38mm diameter stanchion. My riding style is also much more plow through stuff than finesse around and over stuff so I’m sure that plays a part in the capabilities as well. 

I've been running a 2020 Fox 36 with a 2023 Grip 2 Damper at 170mm with zero tokens and a Luftkappe to enlarge the negative air chamber, and while the fork isn't as stiff as some of the burlier forks I have on my other bikes, the 36 chassis is still stiff enough for big rock gardens and hard work in general.  The weight also makes it a nice prospect in comparison to the 38mm forks.  I weigh 175 lbs (79.3 Kgs) with full kit.  I think it is important for a 36 @170mm to have the top end of the stroke be as light and smooth as possible to keep away from any fork flex.  Just my 2 cents.

I would say this really depends on your weight, riding style, and terrain. I have ridden 170mm 36's/Lyrik's on a couple of enduro bikes (2016 Trek Slash and 2022 Knolly Chilcotin 167) and have rarely felt held back as a 150-160 lb rider. I will say the front end tends to have a "light" or "vague" feeling on especially fast trails, mainly in the park. If you plan on mainly riding mediumish speed blues and blacks at your local trail center and you're not especially heavy you probably won't notice anything. The main bonus, besides the weight, I have noticed with the smaller fork is how less rigid the bike feels in slower-speed trails, that little extra flex can be nice if you want that feeling. 

I have a 2019 Fox 36 at 170mm with a vorsprung smashpot. While I am only 64 kg and not that quick, I can feel quite a lot of flex in rock gardens and rougher situations. Granted I am comparing this to my 37mm BOS dual crowns, but I can't see a situation where you would need a 170mm enduro bike and want more flex.  300 grams on the forks is a relatively small difference and certainly not worth compromising on suspension performance for. I couldn't notice the ~500 grams added by the smashpot conversion after the second ride.

I always felt like the pre-21 (square arch) Fox 36 at 170mm was fine on my old Pivot Firebird until I got a Trail 429 with the same fork at 140mm travel. Riding the two back to back made it pretty apparent how susceptible the 36 is to binding at a longer travel, especially when combined with the headtube angle most 150-170mm travel bikes will have. The 140mm fork felt infinitely smoother and more consistent over bumps of all sizes where the 170mm version felt like I couldn't trust it for the lack of small bump sensitivity.

The MY21 (round arch) 36 mounted to my Stumpjumper Evo at 160mm travel felt okay but still had a bit of that sticky feeling. What was more apparent was the front wheel tucking in one particular section I ride every day, which is a super tight turn that requires heavy braking to navigate. I never noticed any of these drawbacks from the same fork on my old Pivot Switchblade, which makes me think most of the drawbacks of going over 150mm on a 36 are related to the headtube angle of the bike.

What bike are you thinking of mounting the 36 to?

Im wondering if i should go in the opposite direction.  I have a 2023 bronson with the 36 grip damper.  Either going grip 2 damper same fork or move to the 38.  I weigh 200 ride new england tech; anyone have good results with the 160 38?

Big fan of the 160mm Zeb for Phoenix tech at 230lbs, I imagine a 38 would be sweet too.

PSA:  Be careful when you are changing travel on a fork that it can run that travel.

I know for a fact that the new Lyrik (charger 3/buttercup version) can NOT run 170 travel.  That would push the stanchions up in the lower bushing and have less than designed/tested amount of bushing overlap on the stanchion at top-out.  The older generation Lyrik (the red one) had longer stanchions/less bushing overlap and could run up to 170 or 180 travel.  BE CAREFUL.

I am not sure about Fox 36 travel limitations or if they have changed recently but be careful and check with the manufacturer.

Been riding and racing for 30 years BMX and mountain bikes. Went to an RXF 36 2 years ago and don't see myself going back to non Ohlins suspension anytime soon

The Mezzer weighs the same as the Fox 36, with the rigidity of the F38.

That's what I'd go with.

The answer for me is, frustratingly, it depends. Bigger = better, unless it doesn't, but it probably does. Forgoing any comparisons between fork brands, I found a 170mm 36 to be workable and even preferable (and I ran one for along time) on mellower more playful terrain - so long as I wasn't not pushing too hard - but soon as things are in the realms of speed, big hits, gnarly lumpy tech descents, and I want to make a good go of it, 38 all day.

So much of it will depend on you physically, your technique, where/what you ride and how you want to ride it - for me at least (95kg/210lb RTR), now if I'm riding something that justifies 170mm, it justifies a 38 generally. In those scenarios the burliness of the fork adds to my sense of stability, directness, confidence and being able to push - and generally, I have the sense that the bigger fork is doing more forking and less flexing.

For reference after many fork swaps & travel adjusts over the last few years (which included 36's in 150,160,170 and 38's in 160,170,180) I've settled on the following preferences across my fleet currently, purely based on the "science" of feel:
 - 180mm Zeb (Enduro - previously: 36, 38)
 - 150mm RXF 36 m.2 (Trail - previously: 34, 36, Zeb)
 - 160mm Zeb (Eeb - previously: 38, 36)

You'll see across the board, I've ultimately err'd away from Fox after a LOT of km's on them, and this pretty much came down to frustrations with how the damping felt, and my ability to find the sweet spot, which I always struggled with across the range (even across several MY's & dampers). So there's probably some interplay there with my fork length/size pref's too, but who knows!? For now, I've run out of money... send help.

To the OP's original question: Going to such great lengths to save ~300-400 grams of non rotating weight seems very much not worth it to me, at least on an enduro bike. If you really want to make your enduro bike feel more sprightly, look at tires, wheels, anything that rotates, really. This is where you'll really notice a change in weight. 

As to the 38mm vs 36mm stanction thing, I have my thoughts but I do think its important we start thinking of stiffness more holistically across the bike, not just in the fork, the cranks, the rear triangle, the wheels etc. 

There was this time where every engineer seemed to simply be aiming at building the stiffest thing possible. Stiffer = better, because it felt more precise, robust and responded to inputs "better". 

Now we're starting to see the pendulum swing the opposite way. For instance, 31.8mm bars are more in vogue than 35mm, many riders trying to find more compliant wheels, frames are being built with some flex in mind (sometimes anyway) etc. 

Moto has long been ahead of the curve here. Engineers tune the entire motorcycle, not just a part, for a rider experience balances flex, grip and precision. They tweak every part to offer the blend they are seeking, usually backed by rider feedback and lap timers. I really believe this is where mtb needs to go to offer the best performance. I'd like product managers to think more as if the bike is an entire system working together, not just a collection of parts you can swap out. Tune the bike for a purpose, and for a distinct feel, not for "riding on the internet". 

With this caveat aside, I have been really liking the way my 160mm 36 is performing on my Stumpy Evo. It tends to deflect a little less (according to my placebo affected brain), seems to help with hand fatigue a tiny bit and finds a line a little easier. That said, the 38 it was replacing was far from perfect when I was done with it, so this really screws up any comparison. 

Ultimately, we're splitting hairs, and most of what I'm saying here pertains to the smallest of perceived change. We're chasing tiny percentage points, not massive noteworthy changes. If you could ride a bike blindfolded, I'd wager most riders couldn't tell the difference between a 38 and 36 at the same travel. 

I only weigh about 63kg/138pounds at 5'10 and I find my Zeb to not feel too laterally stiff. I think the width of stanchions has less to do with lateral stiffness and more to do with the lower legs or the crown of the fork.

I have a question to the flex pros itt:

Why does a 180 mm zeb a scott ransom eride feel flexier than the 2023er e-optimized (thicker walled steerer and stanctions) 36 in another ebike (conway ewme 2019)?

Is it mostly due to the 20mm more travel or is the scott frame that much flexier? Its looking burlier tho than the conway frame but is an intube design while the conway has external battery.

It's a controverse discussion here. Interestingly, in all the tests I have read the bigger stanchions were not perceived to be an andvantage in terms of comfort, rather the opposite. So, one thing is what you think should happen based on the tech numbers and the other thing is what you can feel during testing. Also interestingly, Isabeau Courdourier has been using a zeb despite having the lyrik option and she is like 55 kg. But she had some custom stuff going on there for sure.

Having said that, in all of these discussion you need to consider the serial dispersion and the service condition, general technical condition as well as setup. Because the difference felt on the trail is rather small, so the the factors mentioned above can play a huge role. For example, if a fork is "sticky", then it relies heavily on the chassis stiffness for comfort, so the flexier fork wins in this case. Also, due to the stiffer nature of thicker forks, the production tolerances can be compensated less with elasticity, so this can be more of a production/production cost issue.

As short and light rider, I am happy riding the previous gen lyrik with 170 mm with b1 air spring and torque caps. The fork is so smooth and having 200g less on the front of my bike is noticeable. It's great out of the box, and with burnished bushings it's silky smooth. I can't feel any flex being a quicker rider at 65 kg.

I have just recently moved from a well maintained Lyrik to a new 38 (both 170mm), weighing 75kg. I don't think stiffness of the fork means less comfort, on the contrary, more stiffness means less binding. If anything, I can hold offcamber lines a bit better since it has less torsional flex and you get more comfort when braking. For sure comparing different forks, especially from different brands, is very, very hard, there are lots of other variables and most people do not control them. So internet discussions about that are a bit pointless.

A lot of the mtb marketing is driven by the bigger=better. However, Even if I want to give credit to the theory that a compliant fork might help to hold a better line, my feeling is that I can be more precise with a stiffer fork such as a Zeb or 38. I still remember the aha moment I had when I first ride  a Zeb. BTW, I could never get the Zeb charger2 then charger3 to perform as well as I expected then I got blown away again when I started to ride a 38 grip2. A great suspension in a great chassis

I run a 36 170mm on a Deviate Claymore coming off a Zeb 180mm. I can definitely feel the difference but I wanted to keep the weight down on the build. I ride the same stuff and there's times Id want a 38mm stancion fork but i dont regret it. The option to get a 38 is there but I have no urge too. I found the Zeb more stable and the 36 needing a bit more muscle when it gets super dicey. It's my daily driver so I wanted it not to be a total pig on the climb and shits me. 

I'm 175lbs kitted and fairly aggressive rider. Drops, jumps and tech are dailys 

I've had all 4 forks; Lyrik Ult 160, 36 Fact 160, Zeb Ult 170 and 38 Fact 170. 

I'm 220 lbs kitted up, and the torsional stiffness of the 38 and Zeb chassis is definitely noticeable but with a significant weight penalty. An extra pound and some change up front certainly is palpable on mellow undulating trails. I prefer the smaller Lyrik and 36 on my trail bikes and the Zeb and 38 on my Enduro. In some conditions you want a bit of flex and deflection; where the trail bike pairs well with the smaller diameter forks, they tend to ramp up quicker and are a bit less supple, which is just fine when you need to have support going up and down on more mellow trails. The harder hitting gravity oriented trails, the larger Zeb and 38 are fantastic, they have a much more supple initial stroke and ramp up a bit less harsh at full squish. 

All in all, if you are on a 170 + travel Enduro bike, get the 38, it pairs well with what the bike intends to excel at. For all other all mountain or trail, go with 36 or Lyrik .  

You guys need to stop worrying about weight ofvforks, it's nonsense, especially if you are over 200 lbs. Say your 235 lbs with the bike, you really think half a pound or half a pound of unsprung weight makes any difference or you would notice it is laughable l. That's less than a   0.5% increase in weight.

I have some custom 36's at 170mm with an old fit damper, low friction seals etc and are buttery smooth on my old patrol.,

then went to select plus zebs on trek rail which were appalling (over damped).  Currently got base level 38' on my trek ebike which are much better than the zeb but not as plush as the 36's, feel stiffer but not as smooth.

Then my new build patrol has 38 grip 2 cos building this with intention of some DH races and Alps trips, but  I'm yet to test bike due to illness, should be back on it next week.

but concerned I should have gone for 36' s or lyric ultimate instead, tbc....

I'll chime in with my opinion, which seems to differ a bit from most. Some background on me, I am 150lbs but I would say I ride harder than most. I spent 2 years beating the crap out of a 170mm Fox 36, including many park days, enduros, and DH races. I never felt like that fork held me back at all; I never noticed excessive flex. It was a solid, comfortable, fairly lightweight fork. I just moved to a new bike with a 170mm Zeb Ultimate, and wow the torsional stiffness was very noticeable for me. It's hard to describe, but I do not like how it deflects off of rocks/roots which I steer into in slow speed tech. It is much less forgiving, and I find myself focusing much harder on keeping a precise line. I very much wish for my 36 back in the slow speed tech. 

The flip side of this is that it does feel better in high-speed smashing. There were a few moments in Sedona and out here in CO where I sent harder/faster than I wanted into a rock garden (they had me bracing for impact and gritting my teeth), and the fork handled them beautifully. It could just be that I'm going to a more recently serviced fork, but it does feel smoother in high speed rough sections. I feel like it gives me slightly more confidence to push that *little* bit harder. 

So overall, the 38mm fork has its positives and negatives. I am glad that I have it for the upcoming enduro/DH season, however in slow-speed tech I would far rather have a 35/36mm fork.