Hitch height math & suspension compressed on tow vehicle?

[Bubba Buoy]

Bought a boat and a truck. Lots of sites have guides for measuring for ballmount rise/drop. None mention the amount the tongue weight will compress the suspension of the tow vehicle and how to account for it.

I'm an admitted greenhorn with buying hitches, but if the trailer is measured when level, and the hitch is measured with no weight on the tow vehicle's suspension, it would seem the trailer would go below or down past level/parallel when the suspension on the truck was compressed by the weight of the trailer.

Don't I have to account for that compression, even a little, in my drop calculation?

Thanks in advance for any light you can shine on this!

 

[bruceb58]

Yes, the trailer needs to be level when it is attached to the tow vehicle.

What is your tow vehicle and what are you towing?

 

[Bubba Buoy]

Towing Sportcraft Fisherman 230 cuddy on EZ Loader roller trailer. (5000-ish lbs loaded and trailered)

When measured level, the tongue is at 17". If I measure the height of my hitch ('05 F150 FX4) when there's no load on the suspension, it'll be higher than if there was 500+ lbs. of tongue weight on it, obviously.

So my question is, wouldn't that weight reduce the height of the hitch and as a result, wouldn't that modest amount of suspension flex change the amount of drop required for my ballmount?

 

[bruceb58]

So my question is, wouldn't that weight reduce the height of the hitch and as a result, wouldn't that modest amount of suspension flex change the amount of drop required for my ballmount?

Absolutely.

For example, if your ball height is at 17" with no load and the trailer coupler is at 17" with the trailer level, you will have to increase the ball height of the vehicle to account for the suspension sag. If it sags 2", you need to increase the ball height to 19".

 

[smokeonthewater]

Don't over complicate it...

You expect 500 lbs tongue weight so get 500 lbs on the tailgate and whip out your tape measure... A couple buddies... Bags of cement.... Whatever

 

[smokeonthewater]

If you get it wrong by an inch or so it's not a huge deal.

 

[bruceb58]

Don't over complicate it...

Exactly...put the boat on the existing ball on the truck and measure the sag! Can do this all by yourself.

 

[Bubba Buoy]

Thanks one and all. My plan was to do just that. Wanted to confirm.
No ball on it, currently. Buying one. The boat isn't parked here. I know all the numbers...just gonna measure with 500+ lbs on gate. Thanks again!

 

[smokeonthewater]

Absolutely... I was assuming you didn't currently have a ball mount and ball.... If you do then do just as Bruce said and measure.. Then measure the trailer when level parrallel with the ground under it... Level IF the ground is level.... The difference will be the difference between existing and future ball mount.

 

[NYBo]

I wouldn't put the entire 500# on the tailgate. Does your owners manual have anything to say on the subject?

 

[smokeonthewater]

Probably not a terrible idea to spread out weight but he has the same tailgate as my truck and I've had over well over 500 lbs on mine with no issues...

 

[Bubba Buoy]

No worries. By "gate" I simply meant rear end, bed, bumper, etc. Not just the actual tailgate...and I appreciate the spirit of helpfulness around this forum a lot. A well-deserved friendly reputation!

 

[thumpar]

Depending on your suspension it may not drop much at all. My tow rig has factory air suspension and only drops about an inch with the trailer on it. If you don't have air suspension and it drops a lot you can add airbags.