Following my recent search for replacement forks for my Roadrat, I think I’ve got it down to a pair of 26″ 420mm A-C eXotic carbon forks.

Cotic Roadhog fork: 400mm a-c, 45mm offset
eXotic 26″ carbon fork: 425mm a-c, 42mm offset

I’m a bit worried about what effect longer fork length (and resulting slacker head angle) combined with 3mm less fork offset will have on handling. Basically I don’t full understand the topic and hence don’t know what effect this combo will have. Added to this is if I go ahead with this fork I’ll also be swapping from a 700×42 (29×1.6) tyre to something chunkier like a 29×1.75 or 29×1.90, effectively further slackening the head angle a tad.

T’internet searching so far thrown up conflicting info which has just confused me further TBH, hence over to STWers to either set me right or utterly bamboozle me:

What effect will slackening the head angle have when combined with a reduction from 45 to 42mm of fork offset? Or am I simply worrying too much?

Thanks.

You’re slackening the head angle by approx. 1 degree, which on its own will increase the trail and reducing the offset will increase it slightly more.
I think it’ll fall within the “a few minutes into the ride and you won’t even notice” category.

In theory, slightly heavier steering and more self centering effect, slightly floppier at low speeds.

Agree, after a few minutes you’ll probably not notice – the bigger tyre and offset will speed-up trail and possibly compensate for the effect of the longer fork. I’ve put 50mm shorter forks on a bike to see what it felt like and didn’t die.

If the bike rides well as it is I think it’d be beyond ‘not notice after a few mins’, at least for me. That’s quite a change esp combined with the tyre swap. Try it, only way to find out – some people like geometries that others don’t.

the bigger tyre and offset will speed-up trail

The new fork offset reduction and tyre OD increase will both add trail and add wheel flop / slackness. That’ll feel slower, not speed it up in any way.