Limbs come in short, medium and long. Medium limbs that are rated 28 lbs on a 25 inch riser will have an AMO of 68 inches and will be 28 lbs. at a draw length of 28 inches. Long limbs will be 70 inches using the same 25 inch riser and will be 26 lbs. at a 28 inch draw. The longer the limbs the lower the draw weight for the same rating. The limbs usually have a label giving you the specs.

There are draw weight tools you can order from Lancaster or Amazon that hook onto the string. Using the tool, you draw the bow to your draw length, hold for a second or two and then let down. The tool will give you a precise draw weight measurement at your draw length.

 

Thanks for your reply but it doesn't answer the question. If the poundage goes up by two as the riser length goes down by two.... is it that linear? If the riser length goes down by 4" to 21" will the poundage go up by 4lbs to 32lbs?

Thanks again - C

 

Usually, but not always. Make sure you are able to be OK with a pound or 2 either way.

 

Assuming the same geometry the rule of thumb is that for every inch the riser is shorter than 25", the weight goes up by a pound; and for every inch longer than 25", the weight goes down by a pound. Like most rules of thumb, they tend to be linear (because the human brain doesn't naturally understand exponential or geometric scale).

In another thread where someone was shopping for 27" riser, someone noted that Mybo has a different geometry for their 27" riser of the same model family so that the rule of thumb didn't apply. A 34# limb in on their 25" riser would still be 34# on their 27" riser. I'd like to say it was the Wave model family, but I need to find that thread to verify.

 

Thank you!

 

Note the “assuming the same geometry”. Different riser models from different manufacturers may have different limb pocket angles.

 

This can be a can of worms. So many variables to contend with. Limb pocket angles and even the way a limb manufacturer weighs their limbs. Hoyt measures their limbs with the tiller bolts turned 1/2 way in between maximum and minimum where as Win&Win measure at the minimum setting for their limbs. My 34 pound Hoyt limbs make 34 pounds on my Hoyt riser , With everything being equal my W&W 34 pound limbs make almost 36 on the same riser. But for the sake of this thread I have found that if the limb weight is given as 28 pounds on a 25 inch riser it will make 30 pounds on a 23 inch riser and 32 pounds on a 21 inch riser. Going the other way it will lose 2 pounds and be 26 pounds on a 27 inch riser.

 

Just a general curiosity since I don't shoot that many risers from different companies, but don't limb manufacturers generally measure their limbs on their own risers, and as such a Hoyt limb is measured on a Hoyt riser at the midpoint of the adjustment range, and a W&W limb on a W&W riser set at the minimum of the range... Is it not that it's the riser design that determines where to measure the rated limb weight... I.e. a Hoyt limb on a Hoyt riser measures it's rating at the midrange, but on a W&W riser hits it rating at the low end of the range?

I just don't have two risers of the same length or two sets of limbs from different companies of the same weight to compare

 

What riser are you planning on…I’ve tried a bunch…and what limbs. But it’s pretty close formula 1 pound for 1 inch. It’s worked out perfectly for me on several risers.

 

The riser unless it’s a very neutral riser like the just recently passed Hoyt HP geometry…most geometric difference in the risers from multiple manufacturers are close enough…fractions of a pound…mix or match however you will…most importantly is how correctly they are rated as a few people complained a year or so ago about mk limbs. Most limbs are in 2 pound increments and I have had Hoyt limbs that were on the high or low end of their weight rating…a low 40 pound limb that would barely make the 40 pound maxed out…the plus minus system has a flaw when quality control isn’t doing its job correctly. Uukha has a weight calculator and it’s pretty accurate amongst their limbs on about all standard geometry risers…the uukha I have had were rated in the middle tiller setting just like Hoyt. Every win win limb I have owned (several) have been 2 pounds heavier than their weight rating when in the middle of the tiller setting…or basically a 40 pound win win limb is about 40 pounds at the lightest/safest tiller setting of most standard 25 inch risers…might as well include my experience with Hoyt HP geometry and say that the few HP formula risers I’ve owned made 40 pound limbs 42 in the middle setting…give or take again a fraction of a pound…