First you need to install imwheel using whatever package manager you use.
Ubuntu users should be able to use the software centre apt://imwheel
Or command line:
sudo apt-get install imwheel
Put imwheel in your Preferences -> Startup Applications list.
Download the code below https://nicknorton.net/mousewheel.zip
Unzip it into your home folder. Run it and enjoy.
#!/bin/bash
# Version 0.1 Tuesday, 07 May 2013
# Comments and complaints https://www.nicknorton.net
# GUI for mouse wheel speed using imwheel in Gnome
# imwheel needs to be installed for this script to work
# sudo apt-get install imwheel
# Pretty much hard wired to only use a mouse with
# left, right and wheel in the middle.
# If you have a mouse with complications or special needs,
# use the command xev to find what your wheel does.
#
### see if imwheel config exists, if not create it ###
if [ ! -f ~/.imwheelrc ]
then
cat >~/.imwheelrc<<EOF
".*"
None, Up, Button4, 1
None, Down, Button5, 1
Control_L, Up, Control_L|Button4
Control_L, Down, Control_L|Button5
Shift_L, Up, Shift_L|Button4
Shift_L, Down, Shift_L|Button5
EOF
fi
##########################################################
CURRENT_VALUE=$(awk -F 'Button4,' '{print $2}' ~/.imwheelrc)
NEW_VALUE=$(zenity --scale --window-icon=info --ok-label=Apply --title="Wheelies" --text "Mouse wheel speed:" --min-value=1 --max-value=100 --value="$CURRENT_VALUE" --step 1)
if [ "$NEW_VALUE" == "" ];
then exit 0
fi
sed -i "s/\($TARGET_KEY *Button4, *\).*/\1$NEW_VALUE/" ~/.imwheelrc # find the string Button4, and write new value.
sed -i "s/\($TARGET_KEY *Button5, *\).*/\1$NEW_VALUE/" ~/.imwheelrc # find the string Button5, and write new value.
cat ~/.imwheelrc
imwheel -kill