Sonnie I've done a couple threads on the topics of measuring and comparing, so let me try to take a stab at this, and I will say that the best I can do is TRY simply because the manufacturers make it hard for the buyers to compare APPLES TO APPLES.
First let me deal with this, you wrote <font color="blue"> As I understand, the lift capacity is rated in different ways so it's not exactly a true comparison unless it states how it's measured. I'd like to know how serious of an issue this is and how to compensate. </font>
MY OPINION is that this is a very serious issue because if someone wants to lift a 900# generator (a thread that was recently posted here on TBN) and they buy a tractor that is "rated" for 1100# and they buy that tractor specifically to lift the 900# generators thinking they have 200# of extra capacity then they MAY OR MAY NOT actually be able to lift what they want to lift!
So lets move on to 3 real life examples, these numbers were pulled from the manufacturers MARKETING data, that is the data that people like you & I typically see when we go shopping.
FOR EXAMPLE, I just pulled up tractor specs for 3 small frame compacts. One from a Big 3 company, 2 from popular minor brand companies. This EXAMPLE just to show how the numbers APPEAR on the surface!
Big 3 Stats in their MARKETING stuff:
FEL capacity = 750#
Breakout = 1220#
3pt capacity = 1265#
Minor Brand #1 stats in their MARKETING stuff:
FEL capacity = 1074#
Breakout = 1511#
3pt capacity = 1109#
Minor Brand #2 stats in their MARKETING stuff:
FEL capacity = 915#
Breakout = 1828#
3pt capacity = 1400#
NOW IF WE EQUALIZE ALL THESE NUMBERS to the SAME MEASURING POINTS, the numbers look something like this:
Big 3 brand capacities =
FEL capacity = 1090# @ the pivot point . <font color="green">340# MORE than their "marketing" claims</font>
Breakout = 1720# @ the pivot point . <font color="green">500# MORE than their "marketing" claims</font>
3pt capacity = 1265 @ 24" behind the ball eyes
Minor Brand #1 capacities =
FEL capacity = 1074# @ the pivot point
Breakout = 1511# @ the pivot point
3pt capacity = 1109# @ 24" behind the ball eyes
Minor brand #2 capacities =
FEL capacity = 915# @ the pivot point
Breakout = 1828 @ the pivot point
3pt capacity = 980# at 24" behind the ball eyes. <font color="red">420# LESS than their "marketing" claims </font>
The above "Marketing" numbers are based on the marketing materials I was able to find on the various websites (the 980# capacity was listed on a competitive site, it is not a calculated number).
Now if we want to make the FEL numbers HONEST and we can calculte them DOWN. Doing so will make the numbers look like these (these are calculated so all the capacities drop the same % with the same distances)
FEL capacities @ 500mm forward of the pivot point (calculated if not claimed)
Big 3 FEL capacities =
FEL capacity = 750# as claimed in their marketing material
Breakout force = 1220# as claimed in their marketing material
Minor Brand #1 capacities =
FEL capacity = 739# <font color="red">335# less than their marketing material</font>
Breakout force = 1072# <font color="red">439# less than their marketing material</font>
Minor Brand #2 capacities =
FEL capacity = 630# <font color="red">285# less than their marketing material</font>
Breakout force = 1296# <font color="red">532# less than their marketing material</font>
--- My point with all of this is that this is DECEPTIVE and ANTI-CONSUMER. ---
While I pulled an example of 1 "Big 3" brand and showed it against 2 similar tractors from "Minor" brands in this particular example, that is only to illustrate my point. I think there has been ample evidence to suggest that at least 1 "Big 3" brand uses confusing data in at least SOME of its marketing stuff. And this example also shows that the "Minor" brands do not agree on how to measure 3pt capacity because Minor Brand #1 measured at 24" behind, while Minor Brand #2 measured at the ball eyes. So it just further illustrates the confusion.
Now to address your question of HOW to calculate it, the absolute best answer is NOT to calculate it at all but to find the actual numbers. Sometimes those are VERY elusive indeed. So if you have to calculate it, it is safe to reduce capacity by 30% to 35% as you go from the PIVOT POINT to the center of the FEL bucket. It is also safe to reduce capacity by roughly the same amount as you go from the ball eyes to 24" behind the ball eyes on the 3pt hitch. The ACTUAL decrease will vary slightly from manufacturer to manufacturer, but 30% puts you in the ball park, 35% may give you some safety margin. When calculating BREAKOUT FORCE, again, figure 30%.
Now if you ask where these 30+% numbers came from that I keep throwing out, then go back to the DETAILED spec sheets that SOME of the manufacturers provide. I looked over several different brands, I did the math myself (subject to my error) but when I used the manufactuer's numbers, the capacity drops were roughly 30% some were higher, occasionally some were as low as 29%! And it varied with tractor models and loader models and 3pt hitches within any given manufacturer and I did not calculate every tractor by every manufacturer, I simply picked a couple popular models dug until I could find what I was looking for ---which was occasionally difficult and I thank other TBN members for providing me some operating manuals via email--- and that is where the roughly 30% to 35% capacity drops come from.
Then you asked this: <font color="blue"> What about HP? Can you compare these when they are rated at different RPM's? Is there a way to compensate or is it needed to make it a fair comparison?
</font>
Again MY OPINION is that you can make a fair comparison between models that operate at different RPMs simply because each engine's power band is different does not mean that they will necessarily perform differently in real terms on a given task. For example, take an engine from brand A, and one from brand B. For the sake of this illustration assume both are HST transmissions. Assume their torque curves are maximized when they achieve 540 PTO RPM and those are equal. Assume brand A spins at 2600 RPMs to achieve 540 PTO RPMs and maximum HP. Assume brand B spins at 2800 RPMs to achive 540 PTO RPMs and maximum HP. Both are going to run a Bush Hog with equal power assuming they both have the same rated PTO HP and same rated Engine HP and they have the same efficiency drop in the HST system. Now one will be spinning a bit faster, one may assume that by spinning fast it might wear out in 40 years instead of 45 years, but generally these things are going to run for as long as we are alive.
Now to your charts, you show the 2 Mahindra models with lift capacities on the 3pt hitches at 3969#. Mahindra posts their specs at the ball eyes in most of their literature from what I can find. So assuming that you got those capacities from their marketing material, then the "calculated" capacity at 24" behind the ball eyes, to equalize the measuring points would actually drop the Mahindra capacities to 2778# capacity. (3969 multiplied by .70 = 2778) That may not be 100% accurate, but it is going to be darn close in the real world. That means the 2 Mahindras have roughly 500# to 550# pounds LESS capacity than the other two brands posted, BUT their marketing materials would have a typical consumer believe that the Mahindra models selected for the charts are actually stronger. This may or may not be true for other models or other brands. This assumes the Mahindra numbers are ball eye capacities in your charts.
