Fork offset. 44mm vs 51mm and does it really matter.

[Steady Spin]

So... my fiance is upgrading from a Stumpjumper ST to a Forbidden Druid and I believe the Stumpy is a 51mm offset while the Druid is a 44mm. 

We are building the parts from the Stumpy across and my only concern is the fork now. Currently it is at 130mm and will be changed to 150mm which is what the frame needs. But now this offset thing. I understand it changes the handling but a lot of research suggests that it doesn't make that much of a difference. 

Anyone with real world experience? Will a 51mm offset fork ruin the experience on a frame designed for a 44mm fork?

[TheoG]

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Edited February 1, 2022 by TheoG

[100Tours]

I'm sure the experts will weigh in.. but it is hard to really know until you measure the trail for the new geometry. Also with a bigger offset you are reducing trail so your handling will be a bit more aggressive.

Trail is the distance on the ground between a plumb line through the front axle vs. the line of the steerer tube. if that makes sense

I think I contradicted the previous reply.. but greater offset does not mean greater trail.

Edited February 1, 2022 by 100Tours

[Steady Spin]

3 minutes ago, TheoG said:

Unfortunately I cant offer you any real world experience, only some theoretical knowledge.

The 44 and 51 is the "caster offset distance".  The main difference is going to be if you let go off the handlebar, the 51 will be a bit more stable to ride "handsfree".

As far as handling is concerned I don't think you would feel the difference.  Maybe there is someone that had both and can confirm or deny this .... .

Thank you. 

My understanding is that the 44mm offset increases the trail and makes for a more stable platform in theory. 

I can't fathom how Joe Average will notice this.  

[TheoG]

1 minute ago, Steady Spin said:

Thank you. 

My understanding is that the 44mm offset increases the trail and makes for a more stable platform in theory. 

I can't fathom how Joe Average will notice this.  

I had it wrong, so please ignore.

[100Tours]

diagram below helps understand. increasing the offset moves the tire patch forward, increases the wheelbase, and shortens trail. Not intuitive at all.

Increasing the fork length lifts the head tube (slacker angle), and increases trail again. 

Apparently the 'ideal' trail is something like 57mm

Edit - 150mm is a lot of travel. probably worth having a look at the geometry before you change the fork? Shorter travel will also reduce the trail.

If you end up with a number outside of 50mm-63mm you're probably too far off of reasonable numbers

Edited February 1, 2022 by 100Tours

[Steady Spin]

Thanks. 

Went through this whole process when I built my Evil and now it is that time again with the Forbidden. 

On paper it appears that 44mm is what is right according to the manufacturer. 

In my wallet the existing 51mm offset fork is the one that makes sense.

Budget doesn't allow for a new fork right now. 

[Steady Spin]

9 minutes ago, 100Tours said:

If you end up with a number outside of 50mm-63mm you're probably too far off of reasonable numbers

The Stumpy is 67.5deg with 51mm offset. 130mm travel. 

The Druid is 66deg with 44mm offset. 150mm travel. 

1.5deg is quite a lot and pushing another 7mm on the offset adds up. I can try and draw this out on paper and calculate the trail. 

[Chadvdw67]

I really doubt she or you for that matter will notice much of a difference, my bike had a 44 offset fork and I replaced it with a 51mm offset, albeit 10mm more travel, and I really didnt notice much of a change in handling, the actual fork upgrade made a MUCH bigger difference, I would just put the 51 offset on, and if/when you can and budget allows, then get the 44 offset, that is what I am doing

 

https://www.bikeradar.com/features/pushing-the-limits-of-fork-offset-an-experiment/

[Steady Spin]

34 minutes ago, Chadvdw67 said:

I really doubt she or you for that matter will notice much of a difference, my bike had a 44 offset fork and I replaced it with a 51mm offset, albeit 10mm more travel, and I really didnt notice much of a change in handling, the actual fork upgrade made a MUCH bigger difference, I would just put the 51 offset on, and if/when you can and budget allows, then get the 44 offset, that is what I am doing

 

https://www.bikeradar.com/features/pushing-the-limits-of-fork-offset-an-experiment/

The slacker HA and 20mm extra travel will be more noticeable indeed.

 

[Grease_Monkey]

Yes, makes a big difference. I built my Sentinel up with a 51mm offset instead of the 44mm suggested. It handled like a bus. When I changed to shorter offset it felt like a different bike. 

A couple of mm on long and slack bikes makes a big difference when it's on the front wheel. 

If you are going to stick with the longer offset for just counter it with a longer stem so you can weight the front wheel. Will still not handle as intended, but will be better than short stem + long offset. 

[Chadvdw67]

2 minutes ago, Grease_Monkey said:

Yes, makes a big difference. I built my Sentinel up with a 51mm offset instead of the 44mm suggested. It handled like a bus. When I changed to shorter offset it felt like a different bike. 

A couple of mm on long and slack bikes makes a big difference when it's on the front wheel. 

If you are going to stick with the longer offset for just counter it with a longer stem so you can weight the front wheel. Will still not handle as intended, but will be better than short stem + long offset. 

So the longer offset made it steer slowly? Funny, that is exactly the opposite of what every article I have read says when they test different offsets...

[Grease_Monkey]

Just now, Chadvdw67 said:

So the longer offset made it steer slowly? Funny, that is exactly the opposite of what every article I have read says when they test different offsets...

Of course, your front wheel is further away from you. It's like riding a superbike vs riding a chopper (exaggerated example, but you get the idea). Short offset forks were introduced to counter the front wheel getting further and further in front of you with bikes becoming more and more slack...

[Steady Spin]

That was my understanding as well. Longer offset = shorter trail = faster handling. 

[Chadvdw67]

Just now, Grease_Monkey said:

Of course, your front wheel is further away from you. It's like riding a superbike vs riding a chopper (exaggerated example, but you get the idea). Short offset forks were introduced to counter the front wheel getting further and further in front of you with bikes becoming more and more slack...

Read the article I posted above, Long offset makes the bike steer quicker, short offsets make it more stable

 

Yes, longer offset will increase the wheelbase, but it decreases the trail, which has a greater effect on the steering than the wheelbase does

[droo]

1 hour ago, Steady Spin said:

Thanks. 

Went through this whole process when I built my Evil and now it is that time again with the Forbidden. 

On paper it appears that 44mm is what is right according to the manufacturer. 

In my wallet the existing 51mm offset fork is the one that makes sense.

Budget doesn't allow for a new fork right now. 

You don't necessarily need a new fork, just a new CSU. Still not cheap, but better.