[Closed] Understanding fork offset

Shorter should make your steering slower.

I think.

Shorter offset means longer trail. Longer trail means more stability/slower handling. Shorter trail means livelier/twitchy handling depending on your point of view.

In reality, people are very adaptable and most likely, unless you understand it and have a preference, you'll be riding quite happily by the end of the first ride, whichever one you choose.

Right, so currently have 120mm forks with a 42 offset, in theory if i go 130mm with a 51 offset im going to be a smidge slacker with 'faster' steering?

Yes

Hmm, just have to figure out import duty then and decide if its worth the purchase. Thanks

If you like how your bike handles now, stick with the short offset.

I've just moved from 51mm to 42mm on one of my bikes, same length travel just a newer version of the lyrik.

I much prefer the way the bike handles with the new one. And I wasn't really expecting to notice much difference, so I don't think it's placebo effect.

I currently have a 42mm offset 120 RS Judy silver, cant say i have any problems with how it handles steering wise. Just want to put a burlier one on there as I'm not sure how much more of my lardy arse it will take 😂. It was great when i was just riding through the countryside and running down mildly challenging trails. But now i have the confidence back in jumping and dropping, I'm just not sure i have the confidence in the fork for those kind of duties

What was the difference with Fisher's Genesis offset? <10mm iirc?

So the main difference I've noticed is the bike handles much better at speed with the shorter offset fork.

Makes the steering feel calmer and more intuitive. Also slightly more composed on steeps, especially ones with corners.

Not really any different on jumps and drops.

Cy at Cotic has this take on offset

Genesis G2 29er forks were 51mm offset. It was only available on Fisher/Trek bikes initially, then offered to all OEM and aftermarket.
So same differences as we’re talking about now 7-9mm depending on the brand.

If there isn't a great difference in 10mm shorter offset, why aren't fork manufacuters making much shorter offset forks? Doesn't seem (to me) like it would cost much to do a run of 20mm offset forks.

Possibly so we end up buying another new fork in a couple of years?

More SKUs, more cost. No demand (yet).

20mm offset would require backward facing crowns or new lower castings as there’s more than 20mm offset in the lowers. Neither would be popular as backwards crowns would be ugly, and new lower castings are expensive. Offset changes are done by crowns as they’re cheaper.

20mm would be pretty extreme. The difference between 51 and 42/44 offset is pretty distinct.. increasing trail figures by around 30mm would be a huge change. Maybe things will get there for some, but it would be too big a change to move from circa 50mm to 20mm.

one point to note is that if the fork has a different length then it will change the head angle which will affect the trail calculation...

i use these 2 sites to help me understand affects of any changes i’m thinking about

https://bikegeo.muha.cc/ - for geometry changes

http://yojimg.net/bike/web_tools/trailcalc.php - from trail calculations

This was a good article about it some years back:

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

Bike steering is really weird because it’s so three dimensional and definitely depends on how you ride, body position, leaning, etc.

I’ve had 42mm offset 160mm fork on my Levo from the start - it was meant to have a 51mm offset 150mm fork. The new version comes with a 42mm offset 160mm fork as standard and although the geometry can be adjusted even slacker, in the middling positions it’s essentially the same geometry as my bike (a Gen 2 large is between a Gen 3 S3 and S4).

Is it a fear of making too big a change and riders not liking it or is it deliberately making progress more incremental so they can keep people upgrading?

it would be too big a change to move from circa 50mm to 20mm.

I'm not sure about that, in fact nothing seems to faze the bike industry. 135mm/142mm/148mm etc or 26"/27'5"/29" all requiring new tooling, new designs and the last lot, or previous models consigned to the dustbin.
Sure as fate, some mag or other or some rider will promote it and 'All Change Please'

I hope you've kept your 135mm 26" with the 1.95" tyres, cos 5 years from now they'll be back in 😕

I meant from a handling perspective rather than tooling. Reducing offset by ~30mm is equivalent to approx 3.5deg reduction in HA in terms of resultant trail figure. Big step change assuming it’s being applied to a modern, already slack bike. On a shorter, steeper bike that could arguably benefit more from a trail figure increase, such a big reduction in offset could introduce toe overlap issues, and the reduction in wheelbase would make OTBs more likely.
Porter has done plenty of custom offset experimentation, but don’t think he ever went as far as 20mm?

Is it a fear of making too big a change and riders not liking it or is it deliberately making progress more incremental so they can keep people upgrading?

The former, I think. Effectively both though. Muscle memory and habits. If it takes 3-6 months for us non-Pro riding time types to really get used to a radical change and a model year is compressed into a 6-9 month launch>sales period you'd need to be sure why you were making such a big change rather than heading in the right general direction.

Is it a fear of making too big a change and riders not liking it or is it deliberately making progress more incremental so they can keep people upgrading?

As stated above can take time, although also check out pinkbikes youtube video around the grim doughnut, they went radical on the geo with surprising results. Not sure on climbing ability but downhill it looked okay, despite looking like the fork would snap with a bad landing.

Understanding fork offset
or not

https://www.ebay.co.uk/itm/cotic-bike/294103175594?hash=item4479ea51aa:g:qdgAAOSw9A9gagA8

or which way to offset?

https://motochassis.com/articles/experiments-with-steering-geometry/

https://crosscountrycycle.wordpress.com/2015/09/17/castoration/

WTF is with that Cotic. At first I thought it was just someone put the forks on backwards, but the brake is on the left. Is it supposed to be like that or did they run into the back of a car at full speed?

Fork is surely on backwards. Mudguard mounts are pictured facing the wrong way. No idea what’s going on with the disc mount though.

I have seen the Burrows video before and he explains it well. You could have a 90 degree angle but then the bars would be further away and the front wheel would be too near the pedals. Not a problem on a recumbent and why they can have 90 degree.

Fork is surely on backwards. Mudguard mounts are pictured facing the wrong way. No idea what’s going on with the disc mount though.

Must be backwards but yes disc mount is hard to explain. It may actually steer okay but it looks like it has pedal overlap rather than even toe overlap.

Caliper mount is reversed because it reverses the brake reaction forces that can eject a wheel. I can't remember which manufacturer did this but its a good reason to have the caliper mount in front of the fork

I [i]think[/i] the fork might actually be backwards there - look at the orientation of the brake disc, the studs for rim brakes, and the mudguard eyelet location. Not seen a fork with a forward facing disc mount though!

the fork IS backwards. Calliper mount is in front of the fork leg for brake force reasons

the fork IS backwards. Calliper mount is in front of the fork leg for brake force reasons

So it's meant to have asymmetric brakes? Great for RH corners, with the bike crabbing under brakes, but won't the tyres wear unevenly?

As per my post above - its so that the reaction force pushes the wheel into the dropout not out of the dropout.

I have the same fork in the shed, it's the original Cotic roadrat fork, which had the disc mount reversed - to prevent it pushing the axle out, and for mudguard clearance. It's fitted backwards in the pic.