tow vehicle gear ratio

[redlion7]

Hi All,
I'm asking for some guidance in regards to a tow vehicle I am about to purchase. I have a 31' excella II which I need to tow from Los Angeles to Seattle. Once I get it there it will be towed pretty infrequently and mostly only on the west side of the cascades. I am looking at purchasing a 1986 Chevy Silverado C2500 Gas 5.7L V8.
As far as I can figure the gear ratio is 3.73.
Will that work?
What is the relationship between that number and towing power?

Any help would be appreciated.

Mark V.
Los Angeles
redlion7@earthlink.net

[wahoonc]

Mark,
The bigger the number the lower the ratio and the better for towing. You would not want to tow with a 3.05 but a 3.73 is good and 4.10 is better yet. As long as you stay out of the mountains you should be okay with that rig, but....
What year is your Excella and what is the weight on it? That comes into play too. I am currently towing with a F-150 4.6 but I have the 3.73 limit slip with the factory tow package. I WILL NOT tow in the mountains with this rig, it does okay on the flat ground between here and the coast, also won't use for trips of more than a couple of hours. A new vehicle is in the works.

Aaron

[CanoeStream]

It's a trade-off. Do an airstreamforums search on the numbers 3.73 and 4.10.

General statement: http://www.dodge.com/towing/D/basics/axle_ratio.html

You might need to slow down a bit but 3.73 should do okay on hills if your tow vehicle isn't overmatched in other ways: More on tow ratings

The grandfather (mother?) of compilations: FAQ's about towing

I see too many folks having trouble with GCWR, 1/2-ton trucks, and new 25' Safaris (6300# GVWR). Hope you get lots of opinions.

[David Morgan]

Hi Mark


I tow a 2002 28 ft. classic with a1997-F250 7.3 turbo diesel 4:10 rearend. It pulls fine on flat land as well as in the mountains. It also does good on fuel mileage. 18 to 20 solo & about 14 pulling the trailer. I like to have more truck than trailer because you never know where you might want to go.

Good Luck on Your Choice

David Morgan

Weirsdale Fla

WBCCI # 3451

[davidz71]

I pulled a '77 Excella 500 31' from AZ. to TN. with a '92 Chevy Z71 350 V8 5 sp. manual trans and 3.42 rear end. It was also a 4X4. The 40 lb. aluminum tanks were empty as well as fresh/black/graywater tanks. Hills were rough and mountains were absolutely terrible when I had to downshift all the way to 2nd gear. Trailer sway was nonexistent with the Reese equalizer hitch until an 18 wheeler passed by then it was "whiteknuckle time". A 3.73 rear end would have been better but the 4.10 would have been the winner hands down. Keep in mind that I also was running LT265-75-16 tires which are around 31" tall and standard for that model truck. My 2500hd with 8.1, auto trans and 3.73 rear end handles the trailer like a dream but the tires are shorter LT245-75-16 and the engine is more powerful. The vehicle you are thinking about using will bring the trailer home but I would be concerned about a fully loaded trailer and lack of power from the 5.7 litre engine. Flat roads should not be a problem.

[overlander64]

Greetings Mark!

Welcom to the Forums!

I suspect that the 31' Excella II will exceed the factory trailer tow rating of the truck that you mention when it is loaded for travel - - empty, it might be within the rating. The 2500 series GMC that I had from that time period had a maximum trailer tow rating of 7,500 pounds with 3.73 gears and the heavy duty trailering package. The literature that I have indicates the following trailer towing capacities when equipped with the trailer tow package:

350 V8 2500 series 3.73 differential 7,500 pounds maximum trailer 2 WD or 7,000 pounds maximum 4 WD.

350 V8 2500 series 4.10 differential 8,500 pounds maximum trailer 2 WD or 8,000 pounds maximum 4 WD.

Realistically, my truck had the 350 and 3.73 and it struggled with a 6,000 pound trailer in the rolling hills of Southern Illinois and Western Kentucky. This was before my Airstream so the trailer being towed was a box-type. My truck was an '83, so there may have been a few improvements in emission control technology that might have improved the performance by '86.

Good luck with your Excella II!

Kevin

[markjoandall]

mark,

We are towing a 2001 30ft Classic. I believe the length and weight of your trailer is very similar to ours. When we purchased our tow vehicle, we originally ordered it with the 3:73. After about 12,000 of serious towing the rear end began to give us some trouble. Additionally we were only able to tow in 3rd gear.

Last spring I changed the rear end to a 4:10. I purchased the gear and pinion on line and had a local mechanic install them. What a difference. We are now able to tow in drive. The engine just seems to work less while towing. FWIW, the total cost to change out the rear end was about $750.

In my opinion, you would be much happier with a 4:10 rear end.

Mark

[George Jr.]

Transmission....straight-auto makes big difference.

If you have 4 speed straight shft, you have decent tow.

my 2 cents

[davidz71]

If you like the truck and it seems to run well then try it out with your trailer. As mentioned on a previous post you can have a ring and pinion set put in. Labor can be as much as $500 for the job unless you can find someone with the correct measuring equipment for proper setup.

[minkus]

Along these lines, I am thinking about putting on some tires and rims that are a lot bigger than the original. I'll bet there is some fancy math formula to equate rear ene ratio and tire diameter, and I am no good at math.

Any math whizes there?

[davidz71]

Check the search forum for my search a few minutes ago on tire diameter ratio and you will find a thread on tow vehicle by paul k. Click on the third page and scroll down. You will find info on tire diameter and gear ratio. Sorry I haven't figured out how to copy the material and paste it back to a reply. I mess it up every time.

[Tarheel]

Mark, once a year Trailer Life puts out an issue that shows the towing capacity of all the major trucks and suv's. You can get the data from trailerlife.com.
I pull a 34' limited that I call 9,000 lbs with a 92 dodge cummins. The first pull for us was from the coast of NC to Chicago. A nice long (6% grade 3 miles) crossing the Virginia mountains ( Afton Mtn.) had me all the way back to 3rd gear and 42 mph. I am running an 3.54 gear in a 5 spd 4x4. When I got home I put on a banks kit with a pac brake and some much need instrumentation, tach, pyro, and turbo boost. The next trip out crossing the same mountain my wife noticed the difference made it in 4th at 50+. Since then I have added an intercooler and it has made even more difference. Pulling long grades takes a lot of power and I have just made up my mind that if I have to pull in a lower gear thats just how it is. The next truck will have at least a 3.73 and it will be a cummings 6spd 325 hp 600 ft/lbs. I don't remember the last time that I heard someone complain about having too much horsepower. But I have heard the cry of the 454 "don't you need to stop for fuel". Do your shopping and match up your truck to fit your trailer. Don't trust the salesman to do it for you. Most of these guys have never pulled before and don't have a clue.

[Silvertwinkie]

3.73s should be fine.

[CanoeStream]

Craig -- Ask the forum or ask a kid -- the kid would have the answer right away! A real basic way to insert a website URL in Internet Explorer:

Move the cursor arrow up to the Address window in the top menu bars. Right-click and two things will happen; the URL will highlight and a short menu will drop down. Select 'Copy' from the menu. It is now stored on your computer's 'Clipboard.'

What happens next works the same whether you are in a word processing document or ASForums Reply window.

Check the search forum for my search a few minutes ago on tire diameter ratio and you will find a thread on tow vehicle by paul k. Click on the third page and scroll down. You will find info on tire diameter and gear ratio.

The insertion point as you type is represented by a vertical flashing bar. When you want to enter the thread address, right-click again and select 'Paste.' It happens automatically -- http://www.airforums.com/forum...o&pagenumber=2

[uwe]

Mark,
the 3:73's in your truck will get you home.
If you stay nearby, you won't have a lot of problems. You will be slowing down considerably on the uphills, and you will have the motor floored quite a bit while accelerating, but you will get by for a while. 4:10 gears would be my recommendation, or just get a 3/4ton with a 454 and 4:10's.
I tow a lighter trailer with a Suburban, Vortec 5.7l, 3:73 gears. It works to my satisfaction, but i don't tow at much of an altitude, either.
You will not be very happy if you try and go over 5000ft.

[dinoburb]

Red Lion,

The truck you mention is a good work truck but probably a weak tow vehicle as the 5.7 (350) installed has but 210hp and torque to match. Very low. I have a 454 of the same vintage an its original rating was 230hp! A bit more torque but still rather anemic. The tow on flat land would be OK in all liklehood but hills, let alone mountains would be a killer. A 4.10 rear would be better by far and replacing it would be easy with a complete salvage yard donor. Just swap axles. Quicker and cheaper. Make sure you get the correct 14 bolt rear (there are two). There should be a tag on the rear, yours too, that indicates installed ratio.

Minkus: Be careful bigger tires reduce the numeric ratio. I too have forgotten the formula but a search on Google should bring you to a tire mfg site with the info you need.

Hope this helps,

[davidz71]

Lets see if I learned right from Bob:

Jeanarlene asked sometime ago about tire size and how it effects power and towing. In a nut shell, a larger tire will rotate (circumference) slower than the smaller stock tire there-by effectively reducing power to the ground. Changing to a lower gear with a larger tire will bring that tire back to factory specs at a given RPM and speed. I finally found my formulas so I could share with all.

To find:
Gear Ratio= (RPM x Tire Dia.) divided by (MPH x 336);

RPM= (MPH x Gear Ratio x 336) divided by (Tire Dia.);

MPH= (RPM x Tire Dia) divided by (Gear Ratio x 336);

Tire Dia.= (MPH x Gear Ratio x 336) divided by (RPM)

Silver Bullet gets credit for this previous post.