My father and i is in a decusion about reargears. He's sayingthe 4:10 that comes in the 10.25 rearends on the HD packages cant really be 4.10 cause the truck sets on 17" wheels. He's idea is that for you to have the gears you would have to be setting on 15" wheels. He claims it would be alittle closer to 3.60. I thought they computed the reargears with the wheels and tire size for you to have the gearing that advertised.Can anybody shed any light on thid matter?

 

I believe you father is confusing gear ratio, with final drive ratio.

Edit: It doesnt matter what size tire you run, your gearing will not change. The gears are not made out of playdoh, and change when you stick some tall BFGs on. The final drive ratio will certainly change if you move tire sizes. You can compare the new final drive ratio, to other size tires/gear combos. I do believe this is what he is thinking about. Towing will not necessarily change when you change rims and tires. That is still dependant on the truck, and weight rating of the individual tire chosen.

 

I think where the point is being missed is that you can have 15" wheels or 17" wheels or 22" wheels and still have the same OVERALL DIAMETER. A 265/75R16 is @ 31.5" tall, a 265/70R-17 is @ 31.5" tall, and a 285/60R-18 is @ 31.5" tall. Wheel size is only one part of the equation when determining overall diameter. The WHEEL diameter will have nothing to with your rear end ratio but as the previous post pointed out, overall diameter will change your final drive ratio.

Jeff

 

[QUOTE=WheelMA1]I believe you father is confusing gear ratio, with final drive ratio.[QUOTE]

I believe your right. Bt for my sake what is the differnce. what i'm asking is, say you have a 4.10 gears and 15" wheels and a 4.10 with 17" wheels will bost truck have the same engine speed at the same mph? He made the comment that if you put the truck on a dyno that it would'nt as 4.10's but i did'nt know dyno's saw gear ratio's

I guess to make this easier. What would be the final drive be and how does that compute to towing/pulling?

 

Well you left out tire size. While rim size matters, it does not determine the overall rotating diameter...which is used in the calculation. Theoretically, you could have two different rim sizes, and have the same final drive ratio....if the overall tire diameter was the same. Typically increasing the tire size, while leaving the stock ratio gears, will reduce the tow rating. http://www.4lo.com/calc/gearratio.htm You can play around with that to figure some ratios out.

 

i left out tire size on perpose cause we where talking about factory. And coming from the factory i believe the HD package only comes with the 245's on 17" wheels. unless i'm missing something yall are sayingthe same thing that i am. Ford computes you towing with the gears with the wheels that come on the truck. And not that Ford puts 4.10's in your truck the puts tires on it leaving you the work load of say 3.60's. That would make so sence at all the me.

 

That's because Ford uses a certain tire size on each of those wheels. Ford's 18" wheel option uses a 275/65-18 while the base 4X2 uses a 235/70R-17. It's the overall tire diameter that matters, not the wheel size. Ford also uses 245/70R-17, 255/70R-17, 255/65R17 depending on how the truck is optioned. These tires have different overall diameters but the wheel size is the same.

 

But to what gear ratios? only thing i can find for the 4.10 is the 245/70/17

 

A gear ratio is calculated to the ratio of the size of the pinion to the ring gear. In a 4.10 a pinion is 1/4.10th the size of the ring gear. wheel size has nothing to do with it. Final gear ration is calculated using the diameter of the tire. Like previously said you can have 15's and 24's with the same final gear ratio, because the tire heights can be the same. The higher the gear rato "lower the number" the lower rpms and higher speeds and economy, but you lose performance and towing capabilities.

 

See we know this, and already extablished this. I've gotten my answer in that the tire diameter is same no matter what the rim size. my last post was to jhooch, and really cause we all know ford has several tire options in a few gear ratio's. my point is that in the 4:10 there is no option its going to be a 7lug 245/70/17. Now i'm not smart enough to figure out the final drive of any combo but i can see the differnce in a 3:55, 3:73,or 4:10 on the same size tire, although the 4:10 is on a smaller tire, of course i dont think theres that big of a difference between a 245 and a 255.

The thing is my dad was thinking the bigger rims changed things and the gears was based on a 15" wheel{i dont know why}. my thing is "if" it did ford would have calulated it for the bigger size.And that does'nt matter even if he was right he was wrong cause 4:10 is a percentage of 3:55 it doesnt matter what size tire that percent will stay the same.