Jason-
Mathews design engineers are no dummies, to say so would be ludicrous. However I really feel they may have simply "bonked" on this one,(we all do on occasion, no-one is perfect) much like they did some years ago when they called the original straightline cam "straight". It wasn't, and they had to design the straightline 2 to get there a couple of years later. (That is another story! <img src=icon_smile_wink.gif border=0 align=middle>) If say we go with your theory that the Legacy was "designed" for the roller guide and extra prestress, then what about the Icon? Certainly it has a different geometry and does not have the same parallel design of the Legacy, yet still offers the roller guide also? This alone arouses my suspicion when the same product is offered on two different bows with different geometries/designs. I would thus have to assume that they do not go to great lengths to match up this limb and that limb and individual deflections with each and every model, but rather they more than likely have a few specific limb blank lengths and deflection values that they choose from same as everyone else in the industry. They simply install the designated length limb from the stockpile to reach the poundage rating they are looking for on each model, same as any other manufacturer. If so then the excess prestress issue has merit IMHO.(grabbing a 60lb limb to reach 70 in the Legacy's case) Let me strongly state that if you are happy with your bow and are confident in it, that's fine by me, by all means enjoy your bow!<img src=icon_smile_wink.gif border=0 align=middle> I do lots of testing on alot of different brands of bows and feel that people should know about issues that COULD possibly affect the bows themselves or COULD be potentially susceptable to failure later down the road. I do this type of testing with all bows, and I don't "pick" on Mathews exclusively.(read the Hoyt cam and a half posts on various boards where I found an interesting issue as well for instance) I feel Mathews makes fine products,(in fact my son still shoots an MQ1) but to summarize this is the reasoning behind my "peeve" on the roller guard system and why I would not choose one, myself. Whatever floats your boat, we are all individuals and have different likes and dislikes.
WWAG-
You've been thinking!<img src=icon_smile_wink.gif border=0 align=middle> Currently I know of no such specific "formula", however there are factors involved as you have mentioned above. A shorter-draw archer has a shorter power stroke, yes, therefore any reduced brace height will not have as much effect as it would on a longer draw archer you are correct, this is good thinking and basically common sense. However, there are many variables that come into play here and it becomes highly technical, as it is not as simple as differeing brace heights itself that determines a bows' overall forgiveness. ATA, overall bow geometry,(riser design and relation to the shooter, limb angle, cam design, letoff, and dynamic spine of the individual arrow used) all play a part in forgiveness. (and performance!) I always recommend a bow with at least 7" brace height at all drawlengths for best accuracy in a given application. Lately we see a multitude of bows in the 28" -34" ATA categories being sought after for hunting and 3D applications, but we must be realistic about their ultimate accuracy. Some use them for 3D, but take notice of what the Pros are shooting in the same format. (38-40" or more with decent brace heights) There is a reason why they are shooting what they are shooting! I shoot a 31" bow myself for treestand hunting as this is what these shorter ATA bows were primarily designed for-- (short, liteweight bows for use in thicker cover and limited shot distances) but I also know I wouldn't be shooting it at say the Redding Tournament with distances out to 100 yds. I also wouldn't shoot it more than just occasionally and locally at 3D shoots even, as it just does not offer the same accuracy as a longer bow with deeper brace.
The bottom line here is application and individual accuracy and what you can expect from a setup in relation to your individual skill level. What do you expect out of yourself as an archer? If you expect to hit a golfball consistently at 40 yds as I do, well you simply are not going to get that with a short brace and ATA bow, no matter what the drawlength. But if you want to shoot hunting shots at say 20-30yds and keep them in an 8" circle, yes, you can do that with some of the shorter ATA and brace bows, but I still recommend a decent (over 7"
brace height regardless. If quite proficent you can even shrink that size and stretch the distance a little should you feel you can. Each individual is different, as are their shooting skills, proficency, and preferred application(s). We must be very aware of our individual skill levels and not try and fool ourselves on this or one can end up missing or wounding alot of game and/or watching scores plummet. If one keeps the 7" brace height limitation in their minds as a "standard" no matter what their drawlength or ATA, I feel they are in much better shape than those who run less. I have yet to see anyone who runs a shorter brace height NOT have at least some contact with heavier clothing at some point also, and that alone can be the difference between harvesting that 10 pointer and either missing him or worse yet wounding him and never recovering him. Now that the twins are seemingly "back", there is no need to run super-low brace heights anymore to gain the speed which the solos needed to be competitive, and I'd personally like to see more bows go back into the 8" brace range myself. Just my own thoughts, Pinwheel 12