Changing the horizontal scroll speed on a corded Apple mouse I have the latest MacBook Pro running the latest version of OS X and I am using the corded mouse. 

The horizontal scroll speed using the mouse wheel is dead slow. The vertical scroll speed is OK for scrolling regular websites, etc., but when I try to scroll something like a Trello board, the horizontal scroll speed is unbearable and I have to tilt the mouse wheel multiple times to get from one card to the other.

Is there a way to increase the horizontal scroll speed, or am I stuck with a single speed for both axes?

Hacking system files or config files is OK with me if that's what it takes!
You mention that you have the latest MacBook Pro and a mouse with a 'wheel'? Is it an Apple corded mouse? There are two current models available - Magic and Corded with a 'tracking ball', so my immediate thought is you haven't got a Mac branded mouse (dont think Apple have ever made a wheel mouse) and there in lies your issue. If its the latest tracking ball corded mouse then you should be able to set tracking speed in the preferences. Note: the System Preferences / Mouse panel on Mac 'changes' dependent on which mouse it detects to reflect the capabilities of that particular mouse... if it isn't detecting horizontal scroll capability you wont see this in the preferences panel and it may be running on a default preset coming from the mouse itself. 

Here is a screen grab of mine (running a magic mouse) - the tracking preference is universal vertical / horizontal so only one is shown. 



Apple have built the scroll speed control into OSX so its odd that your mouse is reacting this way. I would be thinking broken mouse*, 3rd party mouse driver issue. The way to check that is to 'borrow' a colleagues working Mac mouse (see if it behaves differently on your Mac) or get on eBay and buy a used one for $20. Could be with you in 2 days.


Apple mice can part fail. I have two currently with issues - one over sensitive and clicks when I don't want it, one with intermittent random scroll speed issues (which might be the laser failing). 


Link to help:

Apple Mice Variations over time on Wikipedia.

Tip: I work on Mac everyday to deadlines so part of my support kit is a bog standard Apple Pro Mouse (M5769) circa 2003 which I have used on multiple Macs to keep me working - its on my MacBookPro OS 10.8 right now for Photoshop as I prefer scrolling OFF in that programme. The Pro Mouse has no scroll function and I don't need a system hack, just plug it in. Two mice on the same Mac works fine and does not affect the Magic Mouse performance at all.