Front beam spring weight...

[gilmarlin]

I have a tube chassis four seat buggy with a beam front end, I'm changing out the old Doetsch 2.2 coil overs to Fox 2.0 coil overs and was wondering what weight springs people are using. The old shocks used a 225lb and a 175lb spring combo and worked okay, but I had to adjust the springs down more than I wanted to get the ride height I wanted. Any feedback is appreciated...

[dustymojave]

The shocks don't hold the car up. The springs do that.

Different shocks that same length should use the same springs. If the old setup was difficult to get the ride height you want, then maybe the ride height isn't right for the car. If you have no droop, the ride will be harsh and skittery. It's also possible that the springs were the right spring rate, but too short. Lots of potential issues to deal with. Some think that coilovers are the simple final answer, but not so simple as it seems.
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Richard
Offroading VW based cars since 1965
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Retired from building Bajas, Fiberglass Buggies and Rails in the Mojave Desert. Also Sprints & Midgets, Dry Lakes, Road Race cars. All types New and Vintage
SoCalBajas Member
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[gilmarlin]

I understand how coil overs work, my question was what weight springs are people running on this type of car with good results. I'm just trying to get a reference point for the spring weights. It could be that the old springs were worn out and sagging more than a new set of the same weight.

[JWHracing]

On my baja with 1-3/4 front arms I run 200 over 300. I wouldn't run more than a 200 upper spring. you probably need at least a 250-275 lower spring.

Your current combo is only 98.5 lbs when the springs are working together at ride height. Keeping the 175 upper and going to a 250 would be 103 lbs, 175/275 would be 107 lbs. 175/300 would be 110.5 lbs.

Sometimes it's just going to involve trying a bunch of different springs. I have 2 milk crates full of extra springs I have tried on my car. Once I get a set I like, it always seems like I change something on the car and need more or less spring.
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65 Baja - Class 5 Unlimited Race Car

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2017 SADR 1300 Class Champion
2016 AZOP Limited Buggy Champion

Currently "retired" from racing

[gilmarlin]

Thank you, I appreciate your input...

[TVander]

Here is my rail with 4” longer arms and 12” fox shocks. My top spring is 10” long and is 100lbs, the bottom is 12” in length and is 150lbs. I do a lot of driving on dirt roads through the woods and they work very well. I am also building a Baja and will be needing shocks for it, I may very slightly on the heavier side for it.

[PhillipM]

I run 100lb/inch at the wheel, which is a straight 165lb spring on mine with an small 80lb tender just for the last inch or two of droop - otherwise the ride height would be too high or the spring would come unseated.

[gilmarlin]

I have been trying to use the calculations in this tutorial to determine the corner weight on my car. https://www.youtube.com/watch?v=NLhqHPILqn0 My shocks are 2.0 and have 10" of travel, the springs are both 10" tall. I had my springs tested at a local suspension rebuilder and they said that they were 225# and 175#. Using those springs and making sure the stop nuts for the sliders are not touching, my springs compress to 18.5" when I take the car off the jack and after jumping on the front bumper and letting the car settle, the springs settle to 17"or 3" less than the uncompressed height of 20". At this point I'm confused as to what this means. 225 + 175 = 400 divided by 3 = 133.33 pounds corner weight??? At this height I have 7" of shaft exposed and the car is sitting a couple of inches lower than I would like.

[DHale_510]

Dual spring rates are calculated by the product divided by the sum.
You have [225x175] / [225+175]= 98.4 #/".
So a 3" compression shows 295# of load. This seems to be on each side. Seems wrong.
This means you have uncalculated leverage on the springs. The lower shock mount is not at the center of the trailing arm, it's more or less at the halfway point. This control arm ratio is a square function, if is indeed at the halfway point then your 100 #/" is an effective 25#/" [per side, 50#/" for the front suspension, 50x3=150#, seems a bit low].
Stock VW front beams work out to about 75#/" and compress about 2.5" at rest. There is no leverage issue, well there is at the beam, but the 75# number is measured after that, not the leaf spring itself.

Maybe you really just want to see how much the front drops with a known load, like your 200# girlfriend, and dive the numbers for #/", then see what that 3" means .

Dennis

[gilmarlin]

Okay, assuming that my un sprung corner weight is @295lbs, I tried using this calculator. https://www.crawlpedia.com/spring_rate_calculator.htm#comments For (A) I used 10 (B) 0 (C) 8 (D) 6 (E) 30 (F) 295 That calculates to a 174 spring rate X 2 or 348 lbs of spring necessary. Right now the combined spring weight I have is 400, so if I have figured this right, I have a little more spring than I need right now???

[gilmarlin]

[gilmarlin]

Well, after getting the Fox 2.0 shocks rebuilt at Fox, I discovered a couple of things. First on a 10" 2.0 you're supposed to have a 12" bottom spring and a 10" top spring, instead of (2) 10" springs like both pairs of shocks I was dealing with had. Second, after removing the springs from the old 2.0 Doetch shocks I discovered that not only was one leaking, the other was binding and not returning by itself. My ride height problems have disappeared now that I have shocks that aren't binding and I'm pretty sure that I still have too heavy a spring even though I changed the lower springs to 200 and left the 175's on top. I think I'm going to borrow a pair of 125# top springs and see how the car feels...

[Mike E.]

[gilmarlin]

There are a bunch of good videos on youtube in regard to spring rates and theory by https://www.crawlpedia.com/spring_rate_calculator.htm I found their info to be helpful as I was putting together my front end.[/quote]

That's what I used to calculate everything...