# Gear ratio vs. Line retrieve



## Bantam1

I was asked by my boss to explain this as it seems some people to do not quite understand the difference between gear ratio and line retrieve. This is better known as inches per turn (IPT). I realize many of you know this so go ahead and skip this post unless you want to brush up on your math skills.

The Chronarch 50MG has 25 IPT with a 6.2:1 gear ratio.

The Core 50MG7 has 28 inches IPT with a 7:1 gear ratio.

The Core 100MG is 26 IPT with a 6.2:1 gear ratio.

The Core 100MGFV is 30 IPT with a 7:1 gear ratio

When comparing the Core 50MG7 to the Core 100MGFV the 100 picks up 2 inches more per turn.

How does this reel pick up more line even though it has the same gear ratio? 

The spool circumference is what determines this. If you have a taller spool it will pick up line faster, even with a slower gear ratio. Its simple math really. If you wrap something around a spool such as line, a taller spool (greater circumference) will pick up more line per revolution than a shorter spool (less circumference). Gear ratio still affects this number but not as greatly as the actual dimensions of the spool.










Above we can see two spools. One has a slighter greater diameter than the other. This means that the taller spool will have a greater circumference. You take pi (3.14) X diameter. On spool A (CH50MG and Core 50MG7) the circumference is 79.80 mm. Spool B (Core 100MG/MGFV) is 86.39 mm. I know its been a while since most of us have taken Algebra and Geometry so here's a refresher picture to define the difference between diameter and circumference.










You need to calculate the gear ratio (which has laready been done on our reels) by dividing the number of teeth in the main gear by the number of teeth in the pinion gear.

_*Gm/Gp x Circumference*_

Using the CH50MG we have 50 teeth on the main gear and 8 on the pinion gear which gives us 6.25:1 or 6.2:1. You now measure the diameter of the spool which is 32.34mm or 1.27". We can calculate the circumference using this number which ends up being 101.60mm (4"). Now you multiply the gear ratio by the circumference which gives you 25. This is the IPT for this reel.

_*50/8 = 6.25*_

_*6.25 x 4 = 25*_

The Core 50Mg has the same spool circumference of 4". Using the 7:1 gear ratio we acheive 28 IPT.

Now using a Core 100MGFV with the same gear ratio as the Core 50 we then realize that the spool is slightly taller. The circumference of the spool on this reel is 4.29". With the same formula it shows we have 30 IPT.

_*7 x 4.29 = 30.03 *_

Subsiitute the 6.2 gear ratio from the Core 100:

_*6.2 x 4.29 = 26.59*_

This probably confused more than it helped but this is the exact way to figure out what the true speed of the reel is. Every angler needs to determine what fits the application and the way that they fish. Two different reels that have the same gear ratio will fish completely different from each other due to the IPT difference.

As an example the Trinidad 12 has the same gear ratio as the Trinidad 16. However, these reels have very different speeds and dimensions. The TN12 has 36 IPT and the TN16 has 46 IPT. That is a HUGE difference!

OK now that my head officially hurts from doing math :spineyes: I think its much easier and faster to just check our catalog or website for the specs. We have engineers do all the math for us. That leaves more time for fishing and :cheers:


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## Bantam1

Oops I forgot to change the numbers in my spool diagram. Anyways you will all get the idea I hope.


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## jboogerfinger

I'm sorry, I wasn't listening. Can you repeat that? LOL


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## Bantam1

Yeah I know it was a little technical and over the top, but I was asked to post this.


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## Fishwish

Bantam1, I realize you posted the method to determine IPT of a reel, but I see that Shimano includes this information in the "specifications" for current reels on the Shimano web site. Can it be found anywhere for the discontinued low profile reels?


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## MattK

Good post Bantam!

Now for your next assignment. 

A) Calculate the IPT on a Core 50Mg7 when I have 58.6 yards of line out and the line I'm using Power Pro which has a diameter of .011 inches. 

B) Apply answer from part A to a graph and show at the IPT at four points (15, 30, 58.6, 75). Connect the points to show diminished IPT in comparison to current line amount on the spool and in comparison to amount of line out.

This will be due at the beginning of class on Monday.


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## Zimbass

Always did well at Math at school but have had no use for me it my business life since. This post helps me remember so many things I knew and forgot !

Now class is resumed.

Your marks Bantam.................10/10 :cheers:


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## Smackdaddy53

I loke ta fi ish...(in forest gump voice)
Thanks for the info, it makes sense but never really crossed my mind about the spool diameter effecting IPT as well as gear ratio.

http://www.fishingscout.com/anglers/SmackDaddy


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## Aggelos

So why theres a reference to Gear ratio when the IPT seems more realistic? especially on the spinning reels which i only use.
Maybe im wrong but at the current point gear ratios are above IPT on the reels marketing whilst it should happen the oposite.

(sorry for my poor english,im european)


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## MattK

lol I just looked at the original post date 08-19-2009

I'm going to have to deduct 10 points for it being late


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## Bantam1

Yep this was a serios necro-post haha 

I can look up the older reels info. It just depends on the age. Some of the IPT info is not there, but gear ratio is. 

And just an FYI on the formula. I had to do serious research to figure it out. I had to use another formula for a similar calculation and modify it to work for the info I was asked to post. I hate math and it is not my strong subject, so imagine my frustration when figuring out the formula and creating this post. One of my true personal accomplishments :rotfl:


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## MattK

You get a gold star for participation :rotfl:


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## Bantam1

That would be my first one :slimer:


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## CoralSeas

Well, as pretty much this is the only thread of it's kind props to Dan.

Something that is also very useful however is that not all reel's "IPT" is created equally. Spool height in proportion to Drive Gear and Handle Length all affect "cranking power" so one reel's 36 IPT is not the same as the other. Some reels may bring in 36" per crank, but have short handles and small drive gears and a tall spool that all increase angler effort.

The great increase in the size of Drive Gears on many reels has improved their cranking power tremendously even though we have seen a general increase in IPT in most company's offerings. Combine this with extra long power handles (for those who find they suit their fishing) and we have seen a tremendous revolution in small reels and their power to handle big fish.

best regards


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## Basswhippa

Thanks for the cool info on IPT Bantam!


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## CharlieA

Ok. Help me out here. I understand about how spool dia. effects IPT. I also understand how Gear ratio effect not only retrieve speed but the effort it takes to reel in the fish. My question is knowing that all this changes as line is reeled in (the more line on the reel the greater the dia.) Other than just a reference number to compare reels does all this really matter considering that it is a constantly changing rate. Charlie


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## Smackdaddy53

CharlieA said:


> Ok. Help me out here. I understand about how spool dia. effects IPT. I also understand how Gear ratio effect not only retrieve speed but the effort it takes to reel in the fish. My question is knowing that all this changes as line is reeled in (the more line on the reel the greater the dia.) Other than just a reference number to compare reels does all this really matter considering that it is a constantly changing rate. Charlie


Yes it matters because the rate may change but it will start and stop at different rates depending on the ratio.

http://www.fishingscout.com/anglers/SmackDaddy


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## RB II

It can/does change throughout the day depending on how the reef gods are treating you and the associated break offs and loss of line. It really is just a good starting point/reference, it constantly changes, even each time you respool unless you actually measure the line.


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## Bantam1

The only thing that matters is if you change ratios from what you are used to your fishing cadence may be off until you adjust. The more important thing to worry about is that your drag pressure will go up when you have less line on the spool. Typically it's not much difference on a low profile reel, but on a larger lever drag reel it could cost you a fish.


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## merle

I've gone through this tread and understand how it all pieces together, but if I'm trying to determine the best IPT for my style of fishing (slow to very slow retrieve winter fishing). Am I better going with the lesser IPT? For example, the Metanium has IPTs of 26, 31 & 36. I know the slack will be picked up quicker, but it seems to me a greater IPT will also pull a lure in quicker....unless I seriously reduce the crank. Input appreciated.


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## MattK

You are correct sir


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