55.2-59 Gas Tank to road dimension?

[hotrod1]

Question for everyone.

What distance should I maintain from the very rear of the tank to the road? The rest of the truck will have a ride height of about 5 1/2" or so on coil overs. Don't want to chronically drag going up driveways, etc. By the way, this is not my truck but it is very cool.

Thanks in advance for your answers.

[3drburb]

That would be pretty low and a nice ride height. I think about an inch or so above the lowest section of the rear of the bed and several inches forward of the very rear of the bed and you should be good. Tape a string across from side to side at install to make sure so in the worst-case scenario the bed or bumper will hit the ground, sidewalk or parking curb first if you back into a parking spot or something like that.

[dsraven]

when I was certified to do propane conversions waaay back in the day, we were taught to draw an imaginary line from the contact patch under the rear tires to the lowest point on the rear bumper and to keep the lowest part of the tank higher than that line. also it needs to be higher than the lowest part of the wheel, so if you were to take the ties off the wheels and had just the wheels on the truck, no tires, the tanks would be higher than that. this is to compensate for a blown tire, the lowest hard point is what should be used. if you were to look into the highway traffic act in your local area you ight see mention of this where it says something like no part of the vehicle suspension or body is allowed to hang lower than the lowest part of the metal wheel. this is o that should a tire blow out your vehicle will ride on the rim and not a body or suspension part-or a fuel tank, engine oil pan, etc. allow for suspension travel worst case scenario, like when the axle bottoms out on the suspension snubbers and keep the tank higher than that imaginary line from the tire contact to the bumper .
in other words, imagine your truck with just the bare wheels on, with the suspsension bottomed out, and then draw a line from the wheel contact on the ground to the lowest point on the rear bumper. I say bumper but if you dont have a bumper then use the hard points on the rear of the frame. if you use the body sheet metal you will be disappointed because it will crush easily up to the point where the frame hits the road or curb or whatever. placing the tank closer to the axle will help, having a tank that is tapered at the rear will also help. if your tank is large and does hang down then placing some guards under it at the rear may help. on some really low cars, like corvette, they used sacrificial wear bars on the "frame" so that the wear bars would bottom and make a terrible racket before major body parts were damaged. a lot of the body that is low to the ground uses "soft" plastic parts that clip on or are screwed on with light duty retainers so that the air dam, or whatever that part is, will tear away rather than damage a larger, more expensive, body part.

[leegreen]

I'd prefer not to see the tank when standing behind or beside the vehicle, so tucked in behind bedsides / bumper. but that is just an opinion

Functionally it's more of a question for the area you want to drive your truck. You could measure tallest speedbump, steepest driveway by driving something with a similar wheelbase and rear over hang onto it then measuring different points.

5 1/2 sounds a little low for a vehicle with a long flat rear overhang, depends where you drive. Check your municipal definition of speed bump/hump height, but assume the guys shoveling the asphalt will pile it higher. Locally speed humps are supposed to be only 3" but in reality they are probably 6
Dips in the highway can bottom you out harder than bumps on local roads

[dsraven]

if the truck in post 1 is your truck, I think you may want to reconsider the fuel tank size, shape or location. it's your truck and you can do what you want, within local laws and logic, but if you were to have a rupture with a full tank of fuel it becomes a pretty large fire and hazmat issue for you and everything/everyone around you.

[mr48chev]

With that wheel/tire combo you are well aboce the scrub line. In truth you could look under the back of a lot of 50's / 70's cars at the next local car event and see a number with more exposed and lower to the ground tanks sitting at stock height.

[fauXGT]

I think the worst case scenario is when you run over the spike strips that LEO's have set to stop you and all tires go.... set the tank a couple of inches above that.

[dsraven]

did anything in the posts help you decide on a plan of action?

[hotrod1]

Yep, everyone had great insightful comments. Here is what I decided to do - Measure the back of the tank at ride height the way it sits now - lets say that is 5 1/2". Take a long piece of 1x1 square tube and weld on two 5 1/2 pieces perpendicular to the long piece which would equate where the tires would contact the ground. Make sure the overhang on one side equates to the length of where the tank would possibly hit the ground. Then it is off to find common traveled driveways and place the "device" on the driveways to see if the long overhang side contacts the ground (with the small 5 1/2" pieces acting as tire contact patches) as it is traversed up the driveway (or speed bump - I don't think they will be a problem though). Hope this makes sense? Obviously the truck is not running and is at the end of the chassis stage and want to make sure its correct now so if tank/chassis needs changing, its easier now than later.