Guesstimating Leaf Spring Travel ?

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Guesstimating Leaf Spring Travel ?

Postby Wobbly Wheels » Sun Mar 29, 2015 2:04 pm

I did a search thinking this would have been well covered in the past but came up empty and, while it doesn't answer my question, I did find this useful page.

I'm looking to make a SWAG at the travel in my leaf springs so I can lay out the curve and the mounting location for my fenders. I figure I'll allow as much 'wiggle room' as I can for when I actually install them, but I need to come up with a starting point.

Since the donor was a popup, it came with the dopey little 8" wheels. After mulling over a few options I've decided to replace the hubs when I do the bearings so it will be riding on the same 235/75/15 BFGs as the truck. Before I buy the parts, I need to approximate a compressed height for the springs and clearance between there and the fender so I can determine whether or not the forward edge will interfere with the door opening. I'm at a point now where I can still adjust the bottom corner of the door opening if I need to, but not for much longer.

The springs themselves are three-leaf and 32" eye-to-eye. The shackles are 3-1/4" long and the space between the bottom of the frame rails and the top of the spring is 7".
All those measurements are approximate since it's dumping rain out there so I didn't want to unwrap the trailer too much :rainy:
The trailer is rated at 700 kg (1440#) gross, but that's just the upper limit for any trailer without brakes so I suspect it's more regulatory than actual. The donor was a 1974 Loughheed so there's no info for it the way there might be for a StarCraft or a Jayco. I'm still on track for around 1000# sprung weight.

Image

I realize it's probably a guessing game at this point but any help in setting the height of the fenders from the axle center would be a huge help.
Last edited by Wobbly Wheels on Sun Mar 29, 2015 5:47 pm, edited 1 time in total.
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Re: Guesstimating Leaf Spring Travel ?

Postby Socal Tom » Sun Mar 29, 2015 5:15 pm

If I understand correctly, you want to know how much room to leave above the tire for the wheel well? Whats the distance between the top of the axle and the frame? That's most likely your worst case. Even if the shackle swings up and hits the frame, the leaf can bend upwards under enough load until the frame hits the axle ( though this is probably pretty tough on the spring.
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Re: Guesstimating Leaf Spring Travel ?

Postby Wobbly Wheels » Sun Mar 29, 2015 5:45 pm

Thanks for the reply Tom.

I will be flipping the axle under the springs, so theoretically I'll have that whole 7" for spring travel. The dilemma is that, with the bigger wheels (29" OD) I want to put on, I don't have 7" before they encroach on the corner of the door opening. I think that should be fine, because I don't think the shackle would allow the spring to rise that high anyway. Even if it did, I could put a jounce bumper on the underside of the frame. I'm not sure how best to estimate that travel.

I do want to get an idea of how high to set the fenders and perhaps put spacers between the axle and springs and to do that I need to know the "working range" of the springs and add a 'fudge factor' to it for the fender clearance. Once I know that, I'll be able to figure out if I need to round the bottom of the door opening to give myself more room for the fender. If I do have to block the axle up it changes other things, most importantly the counter top height. I'm about to start making stuff permanent so I need to nail it down and the axle is where it's all measured from.

My backup plan is to leave the forward end of the fender open and just have it cover the top and rear of the wheel (like a Jeep), but I'd rather not.
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Re: Guesstimating Leaf Spring Travel ?

Postby Redneck Teepee » Sun Mar 29, 2015 10:00 pm

I fear the day that technology will surpass our human interaction, the world will have a generation of idiot's.
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Re: Guesstimating Leaf Spring Travel ?

Postby Wobbly Wheels » Sun Mar 29, 2015 10:34 pm

That looks like exactly what I was looking for. Thank you !!!
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Re: Guesstimating Leaf Spring Travel ?

Postby Socal Tom » Mon Mar 30, 2015 8:24 am

Wobbly Wheels wrote:Thanks for the reply Tom.

I will be flipping the axle under the springs, so theoretically I'll have that whole 7" for spring travel. The dilemma is that, with the bigger wheels (29" OD) I want to put on, I don't have 7" before they encroach on the corner of the door opening. I think that should be fine, because I don't think the shackle would allow the spring to rise that high anyway. Even if it did, I could put a jounce bumper on the underside of the frame. I'm not sure how best to estimate that travel.

I do want to get an idea of how high to set the fenders and perhaps put spacers between the axle and springs and to do that I need to know the "working range" of the springs and add a 'fudge factor' to it for the fender clearance. Once I know that, I'll be able to figure out if I need to round the bottom of the door opening to give myself more room for the fender. If I do have to block the axle up it changes other things, most importantly the counter top height. I'm about to start making stuff permanent so I need to nail it down and the axle is where it's all measured from.

My backup plan is to leave the forward end of the fender open and just have it cover the top and rear of the wheel (like a Jeep), but I'd rather not.


If there is no evidence that the axle is hitting the frame in the current position, then you could assume that you would have similar travel with it under. So if it only had 2 inches of travel above the axle, then assume 2 with it below.
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Re: Guesstimating Leaf Spring Travel ?

Postby 48Rob » Wed Apr 01, 2015 5:15 am

Once you determine the maximum vertical travel, be sure to add another inch or two.
The reason is when one wheel is in a deep pothole, and the other wheel is on the high side of a road, the high side wheel will extend vertically further than it would if both wheels were on level pavement and were maxed out.

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Re: Guesstimating Leaf Spring Travel ?

Postby Wobbly Wheels » Wed Apr 01, 2015 9:48 pm

Thanks guys.
I probably should have put this up earlier, but this is what I'm working with:
Image

From the axle center to the bottom rear corner of the door opening is about 16". With a 29" OD wheel and tire, which doesn't leave much room for fender clearance. I can gain a little by blocking the axle off the bottom of the springs a bit, but it's still going to be tight. If I need to I can round that corner of the opening and blend the fender into that but, if I'm going to do that, now's the time.
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Re: Guesstimating Leaf Spring Travel ?

Postby KCStudly » Sun Apr 05, 2015 1:51 pm

The rounded door bottom looked good on Woodbutcher's Slowmobile.
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Re: Guesstimating Leaf Spring Travel ?

Postby Wobbly Wheels » Sun Apr 05, 2015 10:54 pm

Thanks for that, KC. I had a look at that - my concern is that it needs to look like it belongs there (at least to my eye) and his certainly does. Sometimes I have a hard time picturing what something will look like so that was a help.

No offense to those who love 'em, but the classic Benroy door shape would also solve the problem but they just don't look right to me...
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