Gear ratios?

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FleetProwl

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Aug 4, 2006
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Central Louisiana
I just joined this RV Forum, and I have a question.  About 3 months ago I purchased a Chevy Silverado 1500 Ext. Cab w/6.5' bed.  The truck has the 5300 V8 and the towing pkg. (hooking up the brake controller was a breeze).  I found a web site that list the towing capacity of this truck at 7,100 lbs. with a 3.42 gear ratio and at 8,100 lbs with a 3.73 gear ratio.  But my truck list the gear ratio as 3.23.  With these figures, I used a ratio formula to calculate approx. 6,600 towing capacity with my truck.  Does this sound about right.  The GVWR of the truck is 6,200 lbs. if that makes any difference.  Also the truck has the trailer towing button on the shift lever to make the transmission accomodate towing a trailer.  Thanks for any info.
 

OldSoldier

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Sierra Vista, Arizona
Your calculation if not right is very close.  Your low ratio rear end is a fuel economy accommodation, and as you've noticed will affect your towing capability.

The tow button is used exclusively to control transmission shift points.  If you notice in the tow position your truck will shift significantly later than normal requiring you to achieve higher RPM rates between shifts than in the off position.  This is actually good for your transmission and engine as it will prevent you from up-shifting too early resulting in lugging the engine and requiring immediate down-shifting.

It is not necessary to have the tow button on all the time.  My best advice is to control your gear selection to achieve maximum time in the peak area of your power curve.  In my 6.0 gasser that is between 2500 and 3500 RPMs.  I don't know where your power peak is on the 5.3 engine.

Good luck.
 

Carl L

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Trailer Life tow ratings for 2006 list the truck tow rating at, 6900 lbs conventional, 6800 lbs for 5th wheel.  Discount those 10% for safety, 20% in the mountain and Pacific west.
 

FleetProwl

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Aug 4, 2006
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Location
Central Louisiana
Thanks for the info guys.  OldSoldier, I noticed your Jay Flight in your signiture.  My wife and I were looking to upgrade to a 5th wheel with a slide for the additional interior room.  Just yesterday looked over an '06 Jay Flight 24.5 RBS at a local RV dealer.  I really liked it, but the brochure list the dry weight at 6,195 lbs.  Don't you agree that this is probably a little too much for my truck though?
 

OldSoldier

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Sierra Vista, Arizona
I have that exact trailer and I love it, but I pull it with a 2500 with 4.10 gears.  It's an excellent fit.  The actual dry weight of my 5'er was 6350 with, I believe a 1500 or 1800 lb carry weight.

At 6100 dry and your current vehicle's configuration you are VERY close to the limit and will have to manage weight to the oz.  I think you'd be pushing your truck's limit under the most controlled conditions.  the 24.5RBS is labels 1/2 ton series but it's a tight fit with a 1/2 ton truck.  It's an excellent trailer with an excellent floor plan.

Good luck what ever your decision is.

Also consider
Carl's advice, he is VERY experienced.
 

jgallego

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Aug 5, 2006
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1
You can have the gear ratio changed on your truck to 3.73.  I had this done on my Tahoe to get the extra 1,000 lbs.  It cost me approximately $1,400 for this change.  It does seem like the fuel mileage is less than with the previous ratio.

Jaime Gallego
 

2006F350

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Memphis TN
jgallego said:
You can have the gear ratio changed on your truck to 3.73.? I had this done on my Tahoe to get the extra 1,000 lbs.? It cost me approximately $1,400 for this change.? It does seem like the fuel mileage is less than with the previous ratio.

Jaime Gallego

Change gear ratios does not change your GVWR. That is unless you take it back to the Mfg and have them run the numbers, etc and put a corrected capacities plate on your vehicle. The GVWR is based on frame strenght, tire / wheel size / brake size / engine / transmission / and rear end. There may be more factors, but I believe the ones I mentions are the primary factors. Yup, the engine has to run a little faster to get you to the same speed with the 4.10 ast it did to get you to the same speed as the 3.73 so you have a bit more pulling power, but again, it DID NOT increase your GVWR.

Larry
 

Carl L

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2006F350 said:
Change gear ratios does not change your GVWR. That is unless you take it back to the Mfg and have them run the numbers, etc and put a corrected capacities plate on your vehicle. The GVWR is based on frame strenght, tire / wheel size / brake size / engine / transmission / and rear end. There may be more factors, but I believe the ones I mentions are the primary factors. Yup, the engine has to run a little faster to get you to the same speed with the 4.10 ast it did to get you to the same speed as the 3.73 so you have a bit more pulling power, but again, it DID NOT increase your GVWR.

Larry

I generally agree with you on that.  Changing the rear end ratio can change the tow rating but you never know how much.  It could be a lot, it could be zero.  The transmission or brakes could be the criitical factor not ratios.  There may be one limited exception.  If a truck mfr has a specified model and version with a range of ratios available, changing from one ratio to another in that range could effect the indicated tow rating change.  But if that limited exception does not exist -- you are dead on right.
 

FleetProwl

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Aug 4, 2006
Posts
12
Location
Central Louisiana
Maybe in the future, the manufactures will install quick change rear ends (like they use in race cars) in trucks, where you could use a lower ratio for everyday driving, and put in a higher ratio for towing.  Race cars use this because they might run a 1/2 mi. track one weekend, and then run a 1/4 mi. track the next.  They just unbolt the differrential "chunk", take it out, bolt in another one and fill it up with 90 wt. grease.
 

2006F350

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Memphis TN
There sort-of is something like a quick change rear-end type benefit avaliable - it's Gear Vendors Over/Underdrive that bolts to the output of the tranny. I like the overdrive side as my 4.30 gears kill me on non-towing driving, but underdrive would be essentially useless, unless I had a need to go 3 MPH with the engine screaming at 3000 RPM. The existing gear ratios in Ford Torque Shift (5 speed) keep your RPM up to where you don't lug the engine on shifts. The flip side is that for the $2500 or so, I would have to use somewhere in the neighborhood of 10,000 gallons of diesel to pay for it.

Larry
 

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