It's important that you find a ski boot with a suitable flex for you. If your boots too stiff you will be leaning back seat like the terror squad! Too soft and you'll have thighs more jacked than Arnold!
First of all, the flex numbers that can be found printed on the ski boots cannot be compared between different models of boots. For example, you can compare a 90 to 120, but only if they are in the same line of boot. Otherwise, they are meaningless numbers. There are no standardized tests for flex ratings, so regard them as just a guide to select a boot in your ability range.
How do boots flex?
-An overlap boot flexes by moving the top cuff forward towards the lower shell. It can go as forward as there’s clearance for the cuff to move but is also restricted by the rear section of the shell.
-A three piece boot offers flex from its front tongue. With a more limited flex from the rear cuff
The actual amount of flex in your boot will depend on design, the pivot point and density of the plastics used.
What Flex is Right for You?
The best way to judge the flex of a boot when your first standing in them. And that you can flex the cuff of the boot quite freely. (A major thing to note is that the boot will flex differently in colder temperatures, by being a little stiffer.) So what you’re looking for from your boots is to give you perfect amount of travel while your skiing. When you flex your knees forward, they should be able to reach over the top of your toes. Once you reach that far forward, the boot should give you some rebound. It should also feel quite even on your shins as you go forward.
Most of the adjustments that can be done in a three piece boot is with an interchangeable tongue or a restrictor. However not all three piece boots allow this.
Any boot that allows you to take off the cuff completely, you can soften the flex by removing the cuff at the top. Once you have the shell trimmed either at the back or sides you will have softened the flex. You can soften even further by cutting some of the front of the plastic off the front cuff. It will give you more clearance in the front of the cuff to move before it touches the lower shell.
Rarer is the need to increase the flex of your boots. You can stiffen up the boots by putting attaching plate to the front part of the cuff. Attach it in place with a couple of screw rivets.
Another option is to put an extra bolt in the back of the cuff through the shell. This will give you the extra rigidity that you are looking for.
Good skiing is hugely reliant on having the appropriate flex of boot.
This topic can go much deeper and I plan to revisit this subject with greater detail.
For more information on the subject, send me a message :)