KirkB wrote:That .... It could hamper their technique to the point that they just can't use the pole.
Kirk
Great advice by Kirk - this one sentence should have grabbed you, it did me.
With only the info you have provided:
Vaulter 1: Heavier than 155#, using a 12'6"-155, griping not higher than 12'6 (and not able to grip high enough to use the 13-155 - which is similar to a 12'6"-165)
Vaulter 2: Weighs less than or equal to 155#, using a 13-155, griping no higher than 13' (and wants to grip higher)
Your choice of a 14-170 is a poor one, in my opinion, which is not based on seeing either of these vaulters in action.
If you put vaulter 1 on the 14-170, using his current grip, it will feel like a 12'6"-200. OMG!!!! If he suddenly raised his grip to 13' , it would feel like a 13-190. But if he could raise his grip to 13', why wasn't he using the 13-155 rather than the 12'6"-155? I suspect that his technique is not good enough yet. So what make you think he could use a 14-170 anytime soon?
If vaulter 2, uses the 14-170, at a 13' grip, it would feel like a 13-190 a 35# increase is stiffness!!!! That's huge - like moving up 7 poles in a series - unheard of!
Both of these vaulters are going to have bad experiences going up that much in pole (to a 14-170)!!! I think you are expecting too much from these vaulters to make that big of a jump in poles without having a series/progression of smaller increases in pole sizes to help them get there step-by-step. If a pole is too stiff - the vaulter can get rejected and not land in the pit. This is a big safety concern and should be a coaches #1 priority!
A better choice, would be a 13'6"-160. That is still a big jump for both vaulters (it will feel like a 12'6"-180 for vaulter 1 - a 25# or 5 pole increase, and feel like a 13-170 for vaulter 2 - a 15# or 3-pole increase in stiffness). If vaulter 1 needs a 165# pole, then maybe you should consider a 13-165 instead. Even though vaulter 2 can't go above 13' in grip on a 13-165 pole, it will be 10# stiffer than what he's using today - it will have the same "feel" as a 13'6"-155 - like going up two poles for vaulter 2. Vaulter 2 should be able to jump higher on a stiffer pole without raising his grip because it will throw him higher - if he has good technique.
A even better choice is to look at more economical pole brands (PacerOne, Altius, Rocket) and get two poles - one for each vaulter. Remember, going up 6' in pole length, adds 10# of stiffness if all else is kept the same (grip and weight rating). That's what Jan's chart illustrates so very well.
Another rule of thumb a lot of coaches use with pole progression is that, until the vaulter is using a pole 20#'s above their body weight - don't go up in pole length (assuming you have all poles at your disposal). So if a 150# vaulter is holding at the top of his 13' pole, he stays on 13' poles until the 13-170 is too small, then he/she can move to a 13'6"-165 (which is equal in stiffness to a 13-175).