Fork ATC

[Vanquisher]

So, I know what the axle-to-crown measurement is.

Is it just as straightforward as the longer the ATC the slightly higher your front end, or is there more to it??

There seems to be very little ATC difference between forks of the same category. Like if you took the standard 180 29er fork off your bike and put another 180 29er on that you preferred, is a few mm's reduction in ATC significant?? If so, at what point does the ATC difference become significant so that it changes the bike geo / feel you had before you changed the fork??

 

[Bones]

You won't notice anything different with the geometry when it's only a few mm.
You could get that with different tyres.
I don't know the answer about what amount of mm starts to affect the handling. I think it depends on what angles you have to start with wether 10 mm or so makes it unrideable.

 

[Shjay]

ATC does seem to be more of a thing now. Used to be when buying a bike could run a fork at 150mm as recommended for bike or 10mm longer. My Rise the ATC is 567mm which is 150mm Fox 36. A 150mm Zeb would be around 577mm. Some are running 170mm Zeb so around 597mm ATC quite a lot more than recommended amount. I am running 160 Yari on my Rise

 

[Tooks]

Anybody remember when travel adjust forks were a thing?

I’ve still got a pair of 26” RS Pikes on a Cove hardtail that adjust from 95-140mm.

Does the bike handle differently over that 45mm of axle to crown adjustment? Yes, of course, but it doesn’t make it unrideable, just different.

Potential warranty issues aside, I wouldn’t consider even a 20mm change in axle to crown that significant, but then I seem to worry less about a lot of things than some folks!

 

[steve_sordy]

Anybody remember when travel adjust forks were a thing?

Yep, I had a 110/140 Fox Factory FIT CTD TALAS from 2103 to 2017. Dropping to 110 was great for climbing, but adjusting on the fly was a recipe for disaster. After the first few months, I stopped using it. The BIG negative on the TALAS fork was you couldn't use spacers in the air leg.

NOTE: TALAS I seem to recall stands for Travel Adjustable Linear Air Spring

 

[Vanquisher]

You won't notice anything different with the geometry when it's only a few mm.
You could get that with different tyres.
I don't know the answer about what amount of mm starts to affect the handling. I think it depends on what angles you have to start with wether 10 mm or so makes it unrideable.

Good point on the tyre comparison ...... there's only 4mm in the fork difference I'm considering

 

[Vanquisher]

ATC does seem to be more of a thing now. Used to be when buying a bike could run a fork at 150mm as recommended for bike or 10mm longer. My Rise the ATC is 567mm which is 150mm Fox 36. A 150mm Zeb would be around 577mm. Some are running 170mm Zeb so around 597mm ATC quite a lot more than recommended amount. I am running 160 Yari on my Rise

Yeah ... I think if you are changing the travel of your fork rather than going like-for-like on travel, everything gets much more complex on Geo.

 

[Vanquisher]

Anybody remember when travel adjust forks were a thing?

I’ve still got a pair of 26” RS Pikes on a Cove hardtail that adjust from 95-140mm.

Does the bike handle differently over that 45mm of axle to crown adjustment? Yes, of course, but it doesn’t make it unrideable, just different.

Potential warranty issues aside, I wouldn’t consider even a 20mm change in axle to crown that significant, but then I seem to worry less about a lot of things than some folks!

That's a fair point. I'm not technical enough to know if the new designs of today are more sensitive to these changes than a 26" hardtail

I'm building up a frameset and I don't want to make any mistakes that end up costing me, or impacting how good the bike could be

 

[Bones]

I screwed up my geometry by mulleting it. Although when I posted on here and showed a video of me hitting the deck, the general consensus was my crap riding, but I'm having none of it

 

[Tooks]

That's a fair point. I'm not technical enough to know if the new designs of today are more sensitive to these changes than a 26" hardtail

I'm building up a frameset and I don't want to make any mistakes that end up costing me, or impacting how good the bike could be

A lot of it is down to riding style and preferences, I like a light ‘poppy’ front end as I like to be able to lift the front wheel to change lines in my riding.

Mulleting my Focus Jam2 made it much more to my liking, but that was a 27.5” from the start so it effectively raised the axle to crown height.

If the bike you want to change is already a slack 29” with a big travel rear, then it might not be ideal to make it higher, but the fact is that geometry is constantly changing on a full suss frame. I like my front end to be soft and grippy, so sometimes more axle to crown just means being able to run more sag, which I like.

It’s often a case of just trying it and seeing how it feels. Most decent forks can have travel adjusted relatively inexpensively with a change of air spring anyway, or adding/removing some spacers, so it’s all reversible should the experiment not be to your liking.