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Towing Capacity After Modifications
Q: As I understand it, a vehicle’s tow rating is dependent on multiple factors (axles, springs, engine and trans, and tires, to name a few). The question I have is how to go about determining a vehicle’s tow rating after modifications have been made. I currently drive a ’09 Jeep Unlimited Rubicon (manual trans) with the following modifications: supercharger (approximately 240 hp and 245 lb-ft torque), Dynatrac 60 rear and 44 front with 5.13 gearing, an AEV 4.5-inch suspension system and 37-inch tires. How can I determine my tow rating? Have I improved it or lowered it? Thank you.
A: Vestal, your Jeep’s towing capacity/rating is still the same as listed in your owner’s manual. There isn’t really a way to “increase” a vehicle’s tow rating; you can only “improve” it by decreasing the stress on related components, such as brakes, suspension, and engine performance/cooling system.
I assume that your rear Dana 60 included bigger brakes, which will help in towing. Adding a hydro-boost system would be another step toward better braking while towing (electric trailer brakes are also a great aid). The 5.13 gear ratio will also help but mainly in turning the much-larger-than-stock 37-inch tires. The 4.5-inch suspension and new shocks are likely a bit softer than stock, so this might affect ride height while towing, but all are still as strong or stronger than stock in regards to towing capacity. If you tow frequently I would also suggest use of air bags in the rear springs to add stability and decrease rear spring sag resulting from the weight of the trailer tongue. The supercharger will also help, especially during hill climbs, but I would certainly suggest a larger radiator if one is not already in place. Though you have a manual trans, those with automatic transmissions would benefit from a transmission cooler.
As far as determining whether you’ve improved or lowered your towing capacity, I would say that is up to how the vehicle handles towing similar capacities before and after the upgrades were installed. Does it feel like it tows easier or not? I would think that you’d feel some improvement simply from the supercharger, but the increased tire size and additional weight (bumpers, armor, etc.) may offset any improvement. This being the case, I would avoid towing anything close to the indicated maximum capacity and stick with smaller utility and tent trailers. This will help ensure against parts failure and put less stress on your Wrangler JK during the long hauls. Thanks for writing. ’Wheel on.