I have never ridden back to back offsets on the same bike, but suspect that it's a subtle difference. A recent article somewhere did that test and they seemed to feel that way.

The increased offset will give a slight reduction in trail, so less high speed stability, but easier steering.

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I have never ridden different forks on the same bike, but color me extremely skeptical that anyone can tell a 5mm difference in trail.

 

I'd put in a similar category to handling differences with a change in stem length. It's not going to drastically alter a bike's feel overall, but it is a minor difference that definitely changes feel.

I recently went from a 51 mm to 44 mm offset CSU on my Chromag Rootdown (64 degree head angle). The long offset felt a bit lighter when turning the bars, and the front wheel felt more out in front, which meant I had to be a bit more forward to keep the front end under control. With short offset, the steering feel is a bit heavier, and my weight is more over the contact patch, and it no longer feels like I'm riding a chopper.

I think short offset works well with very slack head angles, where there is plenty of front centre. But my Devinci Troy 29 (65 degree head angle) came with a short offset Lyrik and I felt like the front wheel was tucked under the bike, leading to an unstable feeling in fast corners. A 1 degree angleset solved the issue.

Given the steeper head angle on your Rockhopper, I think 51 mm offset would be preferable.

 

I'd put in a similar category to handling differences with a change in stem length. It's not going to drastically alter a bike's feel overall, but it is a minor difference that definitely changes feel.

That's actually the best description I've heard of how the different offsets feel in my experience. I've never ridden both offsets on the same bike, but I have demoed and owned several bikes with both longer and shorter offsets. I'd say the shorter offset makes the stem feel maybe 10mm longer in terms of the steering and head angle feeling. Obviously it doesn't affect how long the cockpit feels like changing the stem length.

I wonder if we should really be matching offset to stem length. You could choose a stem length to dial in the sizing, and then choose a fork offset to help balance out the steering feel and weight distribution a little. E.g. if your stem is 40mm or less, get the short offset to keep the steering from feeling too twitchy, and if your stem is 50mm or more, get the longer offset to keep the steering from feeling too slow or heavy.

 

I went from a 51mm offset to a 44mm offset on a 69 degree HTA xc hardtail. I think it works fantastic on steep bikes with short travel. I did the same on my long slack enduro bike, and it works great there too.

I think its a big difference and I have ran multiple forks of different offset on the same bike. I wouldnt buy a 51 today for any reason on any style of bike. They're more twitchy going slow, more twitchy going fast.

 

I went from a 51mm offset to a 44mm offset on a 69 degree HTA xc hardtail. I think it works fantastic on steep bikes with short travel. I did the same on my long slack enduro bike, and it works great there too.

I think its a big difference and I have ran multiple forks of different offset on the same bike. I wouldnt buy a 51 today for any reason on any style of bike. They're more twitchy going slow, more twitchy going fast.

This...I feel 51° wonders on climbs and flat trails as well.

 

Haven't tested it back to back on the same bike but I think it makes a significant difference (changing anything else related to the steering 10mm makes a significant difference).

 

As a reminder, 51mm offset was introduced to compensate for the increased trail of 29" wheels compared to smaller wheels, which slows steering. 44 offset increases trail over 51mm. Increasing HTA also increases trail.

 

Numerically increasing head tube angle reduces trail.

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this purely depends on the bike it's going on, the type of riding you do, and the type of terrain you have. For me in socal, with steep ups and steep downs, it has been a pretty big improvement. It's easier to keep weight on the front while getting off the back in super steeps (-16 to -20%). The bike also wanders less on steep climbs and is easier to manage in steep uphill switchbacks as it's easier for me to keep traction in the front.

However, on my xc marathon bike, I've noticed that the shorter offset does seem to make steering while seated and pedaling a bit more difficult. It also makes navigating technical sections where you don't have momentum a bit of a chore since you can't lean the bike much. Think relatively flat janky rock gardens where you have to pedal and bob/weave.

You give up a little to gain a little in either direction. The only way you can make the decision to is read up on the effects of each and make the judgement for your bike, riding style and terrain.

 

I’ve run both.

The statements here are pretty accurate. I generally prefer 44mm. The exception being flat twisty trails, where the quickness of the 51 is nice, and it almost cams itself into the ground for grip, right on the edge of knifing over.

The 44 is better whenever it is rough. It’s easier to hold on line, especially chunky tight corners, where I found the 51mm more likely to get caught up and twist the bars. It’s also seems less likely to deflect off line in straight rough sections.

 

I went back to back on the same bike with the same pike 140, just changing the uppers from a 51 to a 42. I think its a big difference, and so far I havent noticed any drawbacks. The changes to steering geometry more than make up for the shorter wheelbase/front center. and that shorter front center is an improvement in tight situations, with no drawbacks i can feel from the steering gemoetry side. hard to imagine a bike i wouldnt like this on.

In terms of climbing, the 51 would feel twitchy in a way that made it hard to be accurate, had to focus a lot on keeping the front wheel straight and not letting it wander, tight switchbacks if anything felt easier, i dont notice it being "harder" to turn the wheel, effort wise its a small difference if anything, but it feels more controlled and accurate, Im wondering if the contact patch being that 9mm closer is helping to get around tight stuff as well.

As far as descending this is where it made a huge difference, the bike doesnt feel vastly different in any way, you could hop on either not knowing what the offset is and immediately feel comfortable, even riding hard 10/10ths, theres no one huge change. its a lot of small changes though that add up to a big improvement.

Straight line point and pray style stuff, it tracks much better, you dont have to worry as much about a rock taking your front wheel and sending you off line, the fork wants to track straight through that stuff. so if your line is less than ideal, or you dont have a good option, the front remains mostly composed and predictable. On the same fast, straight, chunky sections of trail with the 51 offset, if I felt myself straying off line and heading for a stray rock, id go for the brakes or half panic because i knew it'd likely throw me off line in a sketchy way.

In corners, similar deal, you lean the bike over and it wants to track through the corner, mid corner bumps dont upset it nearly as much, and the harder you work the front end into the surface, the better it hooks up. With the 51 offset, same corners, Id have to alter my line to avoid rocks mid corner that could potentially grab the wheel and turn it, which might tuck the front and throw you over the bars or wash out the front. When getting up over the front, trying to force the front tire into the ground, it felt like a guess if it was going to give you more traction, or wash out, tuck the front, etc.

I also noticed with the 42 offset its easier to lean the bike and keep it leaned, which i wasnt expecting, from an article i read on offset, I thought lower offset would be more "self correcting" and want to right the bike up to straight. Which might technically be true, and if it is, it wasnt in a way that i couldnt overpower physically. but it feels much more composed and easy to be confident just throwing the bike into a corner with a lot of lean and knowing it'll hook up, the bike doesnt do anything funky. With higher offset you can get this kind of uncertain feel from the bike, even if you lean it with confidence and throw it into a corner like you should. Its so much more sensitive to things like steering input, shifting weight, mid corner bumps, etc. it can throw the bike off, thus throwing you off, you get slightly hesitant, you're more likely to commit less.

Similar deal with off-camber lines, you can demand more from the front and have confidence it'll take it. where with the 51 you'd have to get a little defensive and not ask too much, or hit it a little slower.

In terms of steering quickness, I dont notice it being "slower" in any negative way. if i want to make a quick direction change, move the bike around, weave through some awkward line i can easily do it, I'd almost say its easier because you can do it with more confidence and "tell" the bike what to do. where those same situations with a 51 offset, it was so twitchy id constantly be worried about asking too much, it almost took more mental/physical effort making sure i wasnt going to ask too much of a steering input.

Downhill tight switchbacks, again only an improvement, but not as noticeable, its slightly less likely to tuck and throw you forward, and i've noticed i've been cleaning some tight switchbacks easier than i had before, which could also be due to the shorter front center/wheelbase.

 

I went back to back on the same bike with the same pike 140, just changing the uppers from a 51 to a 42. I think its a big difference, and so far I havent noticed any drawbacks. The changes to steering geometry more than make up for the shorter wheelbase/front center. and that shorter front center is an improvement in tight situations, with no drawbacks i can feel from the steering gemoetry side. hard to imagine a bike i wouldnt like this on.

In terms of climbing, the 51 would feel twitchy in a way that made it hard to be accurate, had to focus a lot on keeping the front wheel straight and not letting it wander, tight switchbacks if anything felt easier, i dont notice it being "harder" to turn the wheel, effort wise its a small difference if anything, but it feels more controlled and accurate, Im wondering if the contact patch being that 9mm closer is helping to get around tight stuff as well.

As far as descending this is where it made a huge difference, the bike doesnt feel vastly different in any way, you could hop on either not knowing what the offset is and immediately feel comfortable, even riding hard 10/10ths, theres no one huge change. its a lot of small changes though that add up to a big improvement.

Straight line point and pray style stuff, it tracks much better, you dont have to worry as much about a rock taking your front wheel and sending you off line, the fork wants to track straight through that stuff. so if your line is less than ideal, or you dont have a good option, the front remains mostly composed and predictable. On the same fast, straight, chunky sections of trail with the 51 offset, if I felt myself straying off line and heading for a stray rock, id go for the brakes or half panic because i knew it'd likely throw me off line in a sketchy way.

In corners, similar deal, you lean the bike over and it wants to track through the corner, mid corner bumps dont upset it nearly as much, and the harder you work the front end into the surface, the better it hooks up. With the 51 offset, same corners, Id have to alter my line to avoid rocks mid corner that could potentially grab the wheel and turn it, which might tuck the front and throw you over the bars or wash out the front. When getting up over the front, trying to force the front tire into the ground, it felt like a guess if it was going to give you more traction, or wash out, tuck the front, etc.

I also noticed with the 42 offset its easier to lean the bike and keep it leaned, which i wasnt expecting, from an article i read on offset, I thought lower offset would be more "self correcting" and want to right the bike up to straight. Which might technically be true, and if it is, it wasnt in a way that i couldnt overpower physically. but it feels much more composed and easy to be confident just throwing the bike into a corner with a lot of lean and knowing it'll hook up, the bike doesnt do anything funky. With higher offset you can get this kind of uncertain feel from the bike, even if you lean it with confidence and throw it into a corner like you should. Its so much more sensitive to things like steering input, shifting weight, mid corner bumps, etc. it can throw the bike off, thus throwing you off, you get slightly hesitant, you're more likely to commit less.

Similar deal with off-camber lines, you can demand more from the front and have confidence it'll take it. where with the 51 you'd have to get a little defensive and not ask too much, or hit it a little slower.

In terms of steering quickness, I dont notice it being "slower" in any negative way. if i want to make a quick direction change, move the bike around, weave through some awkward line i can easily do it, I'd almost say its easier because you can do it with more confidence and "tell" the bike what to do. where those same situations with a 51 offset, it was so twitchy id constantly be worried about asking too much, it almost took more mental/physical effort making sure i wasnt going to ask too much of a steering input.

Downhill tight switchbacks, again only an improvement, but not as noticeable, its slightly less likely to tuck and throw you forward, and i've noticed i've been cleaning some tight switchbacks easier than i had before, which could also be due to the shorter front center/wheelbase.

this is actually very good analysis, well done! When it comes to self centering effect it is under heavy braking that it feels like your bars are harder to keep turned, but we all know you shouldn´t be braking mid corner right? Hard to do sometimes though haha.