[Keith Seymore]

Originally Posted by kipps

There's two things you need to worry about. What's legal to tow, and what's safe to tow.

Legally, you can't exceed the truck's GVWR. That's the weight on the two axles of the truck, including trailer tongue weight, but not including weight on the trailer axles. I'm almost certain you're good to go there.

Safe towing capacity is based largely on how the rig feels when driving it. If you're comfortable doing what you're doing, that's the most important thing.

Originally Posted by Dead Parrot

As long as everything is in good shape and you don't bust the GVWR, the truck is doing what it was designed to do.

While I appreciate the sentiment(s), please be reminded we are talking about GCW (Gross Combined Weight), not GVW (Gross Vehicle Weight). The GVW is highly visible, whether on the SPID label or on the placard, but the GCW is a bit more nebulous since it varies by rear axle ratio.

Originally Posted by Blake_496

I ended up putting in 5.13 gears in the stock D70HD (on stock tires) and that really helped getting loads of water and materials up here.

Now here is my question based upon this rig '75 GMC C35 2wd with an 8.1 /gearstar 4L80E / 5.13 gears and detroit. Otherwise stock truck on stock springs.

On one hand, you are in uncharted territory since the factory did not offer the 5.13 rear gear. On the other hand, you are inside the 17,000 lb chassis limit (the highest rating shown on the chart) so you should be ok.

Having been the one that established the trailering rating for some of these vehicles I can say the limiting factor was the ability to launch the vehicle at GCW up the 16% grade. There were a number of combinations that would have been rated higher if it were not for this particular requirement.

K