What Gear/Tire Size & How much Do You Tow?

[Billman]

This Question is for the guys with Automatics & tow Heavy? Over 7500 lbs.

I'm considering changing my ratio from 4.10 to 3.73. I run 235/85 tires. Approx. 32" tall.

I've been noticing everyone's signatures and seeing more 3.73's.

What have you got? Are you happy with it?

[rjschoolcraft]

I tow between 8,000 and 12,000 lbs. with my Suburban. I have the factory 4.10 gears and factory 245LT75 tires. Now that I have adequate power, 3.73's would probably be better for me for fuel economy. My uncle ordered his '96 with 3.73's and his truck is still bone stock. He's been happy. I will probably never change the gear ratio, though, because of the four wheel drive and the cost associated. An aux OD box would be a nice addition, however.

[eracers999]

Billy;

I have a taller tire than you, but have the 3:73. If i tow heavy 10,000 + or even lighter i have found that it is a real struggle to tow at 68 to 72 mph. It likes to tow at 74 to 80 mph and i can hold that pretty darn good. I would say what ever speed that you feel your rig pulls its best at you will have to figure on towing 5 mph faster to have that same grunt from the motor. I have often wished that i either had the same size tires as you, or, had a 4:10 so i had the grunt at a slower speed. However, If the loads you are towing that you find yourself in direct or 3rd a lot of the time that a 3:73 could help you out. Able to maintain a higher road speed.

I have to admit somthing here, i assumed for a while that i had 4:10"s. Till one day i was reading thru all the stuff that i had on my truck. When it came to the window stickers i carefully read it and there it was, 3:73 gear. Hmmm , that explained the things i was thinkin.

Kent

[rjschoolcraft]

Check the codes in your glove box. There is a code that will tell you what your truck was manufactured with.

[Turbine Doc]

3.73 ratio,and 265/75-16 same size as came with the truck; in addition to mods in sig, I upgraded rims to 3300# rated and 7" wide to 8". With mods on mostly flat land I've had no problem maintaining 70-75 mph occasional towing 18K, long grades & bridges have posed no problem, my normal tow is 10K or less once load is rolling no problems maintaining any speed even in cruise control.

In heavy traffic or rolling hills I have to come out of cruise control the way CC adds and removes fule is too agressive for me it's basically max fuel to get to speed up a hill, and fule off coasting down the hill, and max on while climbing back up other side of hill.

With me on APP vs CC I can drive by load and feel, where CC is just looking to satisfy speed request. 3.73 is tall enough for most IMO especially if you don't tow much or very heavy.

[MikeC]

I run 235/85 on steel rally wheels in the winter and 245/75 on 2002 alloys off of a sierra/silverado. Diff is a 3.73

My camper weighs 9500# and with all of us packed and ready to go the combined weight is 17.5K

We know the weight is there but with the mods it is very manageable.

Mike

[tanker]

Hi Billy, I've been towing a 30'Jayco for a number of years with 3:73's and 265/75's I weighed in at just under 14,000lbs with four adults and trailer. Crossed the Rockies several times without an issue. Howie E also has 3:73's but w/245/75's and he tows heavy as well with a tri-axle air stream. He's been almost everywhere with his as well, without a hitch, well I mean with out a problem :D . Go for it. Our new trailer, has put us at 18,000lbs, and that is almost too much for any serious mountains, so we avoided the Rockies this year. Several others that have attened the past Rendezvous' have also towed various size trailers. Hope this helps. smile.gif

[ace58]

I would try a tire with a larger circumference before making such a slight, and complicated, gear change.

[Billman]

RJ - I knew you had 4.10's, wasn't sure of the tire. Surprised to hear you say you could got to 3.73.

Tim - I've read the posts about your heavy loads and also surprised you don't want 4.10.

Kent - Your tire is over an inch taller. I'd be looking to tow about 70.

Tanker - Your ad was what really got me thinking. I knew you towed a Heavy Holiday Rambler. I also realized you had a highly modded 18 to 1 motor. Didn't know you had 3.73.

Thanks Mike. I'll probably be in the 11-12k load.

Hey Ace. It would be more complicated to put a bigger tire diameter on this truck. I would have to buy spacers like Kent did. I have a 2 wheel drive. 1 gear change. I could probably complete the gear change in 2-3 hrs.

I really didn't think 3.73 was an option for me. You guys are making me think different though. I'm not doing it so much for the mileage. I'm also hoping to lower the engine noise at cruising speed. That's my biggest complaint with this truck. I'm hoping by reducing rpm by a couple hundred, and loading the engine more, by making more boost at cruise, it will quiet down some. I have noticed when towing that when your foot is in it, turbo whine is up a little and engine/diesel noise is lowered a bit.

Thanks guys.

[Turbine Doc]

If I was towing heavy often I'd go 4.10, also would probably be in a 3/4T or 1T single wheel; the LD frame is okay for infrequent tow, but if heavy towing regular like, I'd feel better with a beefier frame and axle under me.

[99gmccrew]

Billman,

I have the same dilemma as you. I've got the 4:10's and I'm getting tired of the engine rpm's at 2200 cruising at 65mph. (It is noisier and puts more wear on the engine) I would like to cruise at 70mph with the flow of traffic, but when I do now my fuel milage goes down quickly. I do have a 33' fifth wheel that weighs in at 8600lbs empty. With the 4:10's it tows really well, but with the mods I've made I'm thinking It might be ok to switch. I'm really interested in going to 3:73's. Good luck with this project I hope it works for you, keep us posted please! I may be right behind you! smile.gif

[Keith Richards]

Kent,I wasn't aware that 3500's came with the option of a 3.73 gear ratio.I wonder if thats a diesel specific option? In my owners manual thats not listed as an option.Maybe the difference in years?mines 98 and yours 95

[eracers999]

Keith:

With the 3:73 and the tall tire it"s more like a 3:55. With the converter locked up in OD i really dont like to tow at 65 or under, it"s too close to the point were the converter will unlock. Somone who knows the 4l80 trans will tell you that it"s a no no to hold full tork to this unit in OD at or below 2000 rpm.

Kent

[Scottpearce]

Last Year I had a slideout that weighed 3100 lbs in ready-to-use form, and towed a 4 place jetski trailer that weighed 4100 lbs. My truck weighs 6600 lbs empty. With people and gear in the truck, we weigh somewhere around 14.5k lbs.

I had 4.10's in my truck but hated having the rpm's so high and having to go so slow on the interstate. I switched the gearing out to 3.42's and have been happy ever since smile.gif . The turbo master is able to build boost better now, my empty mileage has gone from 12-13 to 15-16 around town (20mpg highway) Towing mileage has improved from 9-9.5 to 12-13 pulling similar loads.

I too have 235/85 r16 balonies.

[99gmccrew]

Scott,

What are your rpm's at 65mph with the 3.42's.

Steve

[Scottpearce]

Steve

My Tach reads approximately 1900 rpm at 65mph in its current configuration. It reads about 8% high, however. It used to be about 15% high until I changed out the drive pulley on the alternator. When I get a chance I am going to make a pulley that is 8% bigger yet so that the tachometer reads accurately. The actual rpm at 65mph should be about 1775 rpm with 3.42 gears and 31.7" tires

Scott

[JohnC]

I used to tow about 5000# with 3.42 gears, stock tires and a 5 speed. I think this would have been great with an automatic, but with the 5 speed I sometinmes found the gears a little too far apart. (This setup gave 72 MPH at 2000 RPM in 5th) The 3.73 would have been a better choice. So, IMHO, the 3.73 with stock tires and the auto would probably work well for 7500#, but with the 32" tires you may be pushing your luck. Unless you live in Kansas...

[Billman]

After reading everyone's input, I'm goin' for it.

It's just gears and a couple of hours. Well, VSSB calibration, too.

Anyone have 3:73's layin' around?

[JohnC]

Originally posted by Billman:

Anyone have 3:73's layin' around? They show up on E-bay all the time, from folks going to 4:10's... ;)

What size? Here's a 10 1/2 ending today. (look a little rusty...)
Ring and Pinion on E-bay (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33731&item=7944856888&rd=1)

[ 01-06-2005, 08:32 AM: Message edited by: JohnC ]

[Billman]

Yes. 10 1/2.

I saw that set already. Used as a door stop for most of its life.

I'll keep watching...