How to stifffen ski boots?

Stiffening boots is a semi-permanent procedure as it involves drilling holes through the boot where the cuff & shell overlap and locking the cuff/shell shut with screws & t-nuts. SPKs already have the sides done, so you would be adding screws to the middle of the rear spine. You could also add a cuff shim to the front of the cuff. This is less invasive but also less effctive as you are simply adding material to the front of the boot.

Both ways would not weaken the boot or reduce the structural integrity of the boot when done properly. If things got too stiff, you could just remove the screws or shim.

ok. so if you have it done and then remove the screw are you left with a hole? say i wanted to ski park all day one day, taking the screws out, then go hike some lines the next day with screws in. Would there be any worries on the park day? Is it easily interchangeable?

You can take them out but you will have holes in your boot, and you will want to plug them up or duct tape them. Stiffening or softening a boot is done because it should be a better match for you biomechanically, so that is why it's usually a semi-permanent thing. It's not something you would want to go back and forth between.

hmm i always thought of flex as a preference. Is this not the case?

Yes, sort of. First it depends on how much you weigh, then your ankle flexibility, then what you are used to.

Weight is crucial because a 130 might be "flexy" for someone who weighs 200 pounds but way to stiff for someone who weighs 100 pounds who skis the same way, same terrain. Ankle flexibility is crucial because you might want a softer boot but because of a limited range of motion (for example) you need a stiffer flex to keep your heel from lifting. These 2 factors count more than personal preference because if not taken into consideration they can lead to painful skiing.

lol i weigh 230 and im in an spk 90. Though i do have very good ankle flexibility. I also read that saloman flex scale runs up to 120 whereas others use a larger scale going up to 140 (?) so a 90 is actually compareable to around maybe 100-110 in other boots. For example i tried on an atomic boot (cant remember which) with a flex of 100-110 (cant remember which again) and it felt as soft... maybe thats just my weight.

Don't let numbers confuse you, just forget about them. A 95 in one Sally boot can be stiffer than a 110 in another Salomon boot.

I second the earlier opinion, boot flex should match you as a skier. The idea that you would want a softer boot for skiing park is ridiculous. Just get the boot that is right for you, and use it every where.

Ways of stiffining a boot can (as allready stated) involve riveting the cuff to the lower, I have played with doing this on closer to the front with good results.
You can also add a driver plate to the front of the cuff. I tend to ustilize these with more emphisis on pressure distribution, but they will stiffen the boot. A pair of Nordica driver plates will be about $20-$25. Once installed it is easy to play with location for various effects. Note*

The third option is by altering or swapping the liner. A standard foam injected liner will boost the stiffness of your boot my more than either of the options above. Price is around $500... An intuition power wrap or luxury liner will also stiffen the boot up quite a bit, and can be had at $250. I like to use the wrap in cabrio shells and the lux (or other tung liners) in 2 piece over wrap, but have done a bunch of combinations for customers (most common liner is power wrap regardless of shell). Intuition also now makes several drop in liners that are really nice, and should stiffen up your spks. There are plenty of liner options out there, I am just the most familiar with intuition, comformable foam injected and head foam injected. I recently played around with a nordica foam liner that was impressive as well. Note**

*Driver plates are not going to be as useful on your cabrio boots such as Krypton, Full Tilt, Nordica Fire Arrow. They can be used, and I have, but only in certain circumstances.

**Foam injected liners are not for everyone, and more pain than their worth for most people. I ditest that Surefoot blindly puts tons of rec. skiers in them every year. Intuitions can also cause issues for some people, but these cases are rare, and the person should probably see a doctor anyway.

The best way to stiffen an spk is drill a hole about 2.5cm above the rivots in the cuff. You cant easily do it in the center of the cuff as it already has a v cut out of the upper clog. If you use a t bolt and a screw you can alter the flex for differnt skiing.