ok, had to do this last week for my IForged wheels... it's pretty simple but I took a few shots to be able to give a quick guide to doing this... the biggest problem or fear for most is that they'll drill a hole & then it won't work, thereby ruining there rim. well, if you follow the procedures I used you won't have to worry all that much, as it's the best way to properly locate & drill this one simple, but oh so intimidating hole...
many aftermarket rims, especially 3 piece wheels & rims with wide lips, will usually load the tire from the back of the wheel instead of the front like the OEM wheels. this will mean that the recessed channel that creates a step in the lip will be in the back of the wheel instead of the front. this recessed step is usually where the tire valve is located, but since the recessed lip is in the back of these aftermarket rims, they usually use some other sort of way to allow a tire valve to be used & accessed from the front. usually it's some sort of proprietary design & accesses the air fill from somewhere in the center of the rim & this valve fill location is usually unusable for the tpms sensor, as it's designed to sit in the stepped lip area that is now on the back of the wheel.
in many cases it can be as simple as just drilling your own valve stem hole in the correct spot on the rear stepped lip & walla, instant tpms compatibility. it is up to you to determine if your lip looks suitable for this, & not all will always be on exactly the right angle, but even a little off the tpms can still be mounted... these pictures are from my fronts & the tpms fits perfectly, but the rear lips were a little different & the tpms sat a bit off the rim, still works fine though & is still protected somewhat in case of a flat, but it is always ideal that they sit like shown in these pictures, all the way up into the channel...
first step, once you sure that the tpms will sit in the rim is to determine exactly where to drill the hole. if you drill it in the wrong spot then not only will the sensor not sit right in the wheel, but it is possible it won't even seal... if you drill on the edge of a flat or off on a curve then the sensor will not seal... the sensor needs to sit on a relatively flat area to seal properly.... the correct spot for this hole is very critical, you shouldn't just eyeball it or wing it, the best way to properly find the exact spot is to use the tpms tightening nut/collar to locate a flat area for it to sit on
place the collar on the flat part of the step, determine a spot that it can sit flat, this is where you want it to sit on final tightening. use the 23/64th's bit to locate the precise center of this spot. the sensor should be located directly opposite the factory valve stem for balancing, actually counterbalancing against the original valve... if you placed it at the same spot on the rim as the other fill valve you will be creating a heavy area that will need much wheel weights to make up for, always space them 180% opposite each other...
the bit will fit in the collar snug enough to be perfectly straight & centered, but not tight enough that you can't spin the bit... it'll glide on the inner surfaces of the collar nut & not damage it at all... use this bit to drill into the wheel just enough to give you the center point. you don't want to go all the way through with this bit, drill enough to get a good point
& then remove the bit & switch it out for a small bit. use the small bit to drill your pilot hole. 1/8th" is good, little bigger or smaller is also ok, nothing 1/4" or larger though. a small bit will go through straight & not walk... run the bit through the center of the collar nut,
use the collar nut as a guide to drill straight & at the same angle as the nut will sit on the flat part of the step... drill straight through
now the pilot hole will make drilling the large hole easy... the large bit will always follow the pilot hole(hence the reason it's called a pilot hole) & be in the precise spot it needs to be. you cannot drill through the center of the collar nut with your last bit, cause the final hole is larger than the center of the collar nut, but you should still hold the collar nut right along side the hole you will be drilling, still using it as a guide to your angle & straightness relative to how the collar sits on the rim
the final bit I use is 7/16... this is the size of the final hole for all normal car valve stems... actually 7/16th's is a little tight, I rather run the drill through a few times to clean it up till it fits snug than stare at a hole that's too loose. after running it through with the 7/16, clean up & debur the inner side of the hole, as it's the sealing surface for the sensor.
try to wiggle the sensor in, if it goes in great, if not, run the bit through the hole a few times & try again... it won't need much... once the sensor is in, tighten till the seal bulges, you don't need to necessarily crank them till they bottom, just tighten them till you have nice rubber compression & it's good to go...
of course you could just ignore all of this, just chuck up a 7/16'th bit & wing it, eyeball it straight & centered & bang, poke the hole... I've done that before but this method is def the safest way to get it right & worth the trouble... a pilot hole is always a good idea for any large hole drilling & helps the large bit go through like butter rather than burning out & walking all over the place..
See More: HOW TO: drill aftermarket rims for tpms