Weight question

[XJoachim]

I'm in the process of calculating my suspension setup and need the sprung weight front and rear o the XJ. Stock weight is OK, if anybody has some numbers with bumper and winch that's welcome too. Thanks.

 

[XJoachim]

btt, nobody ?

 

[Wiley Coyote]

I’m running a pretty stock rig, just a 2” lift and 31” tires. No brush guards, wenches or armor plating. Mine weighs 3850 with me, full tank of gas and all of my crap in it. At least according to the scales at the local garbage dump.

 

[Matt]

I’m running a pretty stock rig, just a 2” lift and 31” tires. No brush guards, wenches or armor plating. Mine weighs 3850 with me, full tank of gas and all of my crap in it. At least according to the scales at the local garbage dump.

He wants the sprung weight - so unless you know the weight of your axles, rims and tires you cannot know the sprung weight from the gross weight...

XJoachim ; the easies way for the front is to take your springs to a spring shop and have them determine the spring rate (they put it in a press with a gauge on it and measure the force to compress the spring a few inches...) The once you know the spring rate - measure the free length of the spring - reinstall and measure the loaded height - the number of inches x the spring rate will give your the sprung corner weight...

For the rear there is a similar way to measure the rate of the leaf springs but it is more of a pain to pull them out...

If I had to guess I would say your are fitting coilovers - you can also make an educated guess - figure a D30 weight 250lbs and rims are 30-50lbs depending on type, tires? who know what you have - then just take the front tire patch weight and subtract the estimated unsprung weight - then when you get your springs calculate the rate of the coilover (primary and secondary springs - plus a tender if needed) and then measue the loaded height and compare to free length for you sprung value (you may need to order more springs if your guess was not very good but they are only 50 to 70$ each...

HTH

Matt

 

[MaXJohnson]

I think my '90 4dr, 4.0 was around 3200 lbs when new. They've gone up a few hundred pounds through the years since then. The weight distribution is roughly 55% front/45% rear, so for total weight that would be

front - rear
1760 - 1440

for unsprung weight, take the full weight of the axles (equipped) at 225 for the D-30 and 175 for the D-35 plus about 45lbs per tire or 180lbs. Also add half the weight of the springs, shocks, suspension links, track bar, drag link and drive shafts. I estimate 65lbs front and 45lbs rear for these. That's a total of 690lbs with 380lbs being on the front and 310 on the rear.

subtract these weights from the total front/rear for an estimated sprung weight of:

front - rear
1380 - 1130

This is an estimate for a stock 1990 4dr

 

[XJoachim]

Matt, you're right, i'm estimating to fit coilovers but i don't want to throw out too much money for coils because i have to keep them. Sending them back would be more than the coils cost. Therefore a coil also has about double the price for me than for you because of freight.

MaXJohnson, thanks, thats what i wanted to hear. I made my own estimation and our numbers are really close so i think that are numbers to work with.

With that numbers in mind i think i will go with a 250/350 combo front and a 200/250 combo rear for a 14" travel shock. I added 200 lbs. for a winch bumper and a winch, what do you think about that

 

[MaXJohnson]

With that numbers in mind i think i will go with a 250/350 combo front and a 200/250 combo rear for a 14" travel shock. I added 200 lbs. for a winch bumper and a winch, what do you think about that

According to my slide rule you'll end up with spring rates of 145.8lbs/in front and 111.1lbs/in rear. I've never run coil-overs, but the rear rate seems a little soft. You could use 200/300 for 120lbs/in.

The forumula, if you don't have it is:

1/K total = 1/k1 + 1/k2

cheers

 

[Ed A. Stevens]

Matt, you're right, i'm estimating to fit coilovers but i don't want to throw out too much money for coils because i have to keep them. Sending them back would be more than the coils cost. Therefore a coil also has about double the price for me than for you because of freight.

MaXJohnson, thanks, thats what i wanted to hear. I made my own estimation and our numbers are really close so i think that are numbers to work with.

With that numbers in mind i think i will go with a 250/350 combo front and a 200/250 combo rear for a 14" travel shock. I added 200 lbs. for a winch bumper and a winch, what do you think about that

Measure the deflection of the existing front coils to make a good guess of the current front sprung weight. This allows you to calculate the true sprung weight by measuring the coil deflection at each front corner. Someone on posted the typical XJ coil rates (and they can probably get you close).

FWIW, most XJ's with minor weight additions run ~700# spring weight per corner up front (~1400 total). The rear weight varies more because spare tire placement can really alter the distribution, but it's usually ~80-90% of the front spring weight (the weight balance of a loaded XJ is not as bad as most expect).

If you are under a budget I would only order the primary rate coils, the coil with the spring rate you want when close to the full compression travel of the shocks, until you can identify the true sprung weight. You can order in advance, and swap (if the vendor is willing to trade springs) later to the final combination, but you will need to pay the postage (and I read you understand it may not be worth the cost).

Lately the trend as been to a higher front spring rate on the wildmen rigs, compared to a few years back, more along the lines of the RE ZJV8 220#/in rate and the old Rancho 240#/in spring rate. This is because the more rigid rate provides more responsive handling on the road and still allows good articulation. The normal aftermarket XJ coil only provides ~10 inches of total deflection (why we see so many unseated XJ coils at full extension) so your 14-inch travel coilovers can be tuned better than the typical XJ coil, and still have a fairly rigid primary spring rate (something like the 250#/in you mention). The 250/350 coil stack provides a reasonable jump in rate, from 146#/in to 250, so (IMO) it's not too bad of a choice. A stock XJ coil is somewhere between 145 and 160#/in so the combined coil 146#/in rate should work as a starting point. A 250/450 coil combination makes the rate ~161#/in, slightly more rigid, but not enough to get excited about until you test the ride.

The rear spring rate is more of a guess, as the XJ leaf pack is progressive rate, although fairly low compared to the front rates (maybe someone can post some published numbers). I am making an educated guess (SWAG) that 200#/in will result in a fairly rigid primary rate, with a large rate jump from the combined 111#/in rate from the 200/250 coil stack. It will likely ride harsh, and kick up some on the rear at speed when you hit the spring rate transition (unless you really tighten the dampening, and make it harsh all the time). Maybe we can do better for the rear spring combination? A 150/350 combination nets a similar 105#/in combined rate with a 150#/in primary. Some published numbers for the rear spring rates available for other lifts, with subjective feedback on how they ride, will help.

You will probably need to run keeper or lightweight tender springs to lower the ride height to where you want it to be. We can get more in detail later.

 

[MaXJohnson]

I think the XJ rear leafs are at least 200lbs/in from the factory. I've seen wheel rates(the amount of spring rate applied at the tire contact patch) published at least once at 120lbs/in front and 165lbs/in rear. Your ratio of spring rate vs wheel rate may change depending on how you mount the coil-overs. For a decent street ride, the rear rate is typically stiffer to avoid body pitching in harmony with expansion joints, dips, etc.

As mentioned in my previous post, your rear spring rates seem too soft.

You may want less difference between primary and secondary coil rates if street ride quality and slow speed crawling/climbing are your primary objectives. Just the opposite for high speed running on uneven terrain where you'll be using most of your available travel.

 

[XJoachim]

I have just nothing in my rear cargo area, no spare tire, no tools, nothing. So i think the rear is just about right. Not too soft to give a stable ride but soft enough for off roading. We don't do high speed races here, just slow wheelin'.

I calculated the rear with a total sprung weight of 1200 lbs and the front 1600 lbs (winch + bumper). The attaching points of the coils will be almost exactly the same as the attaching point for the long arm.

Rear will be 600 lbs per corner which will be a wheel rate of 107 lbs. in. with an angle correction factor of 0.985 will result in a 109 lbs. in. spring rate. This results in a dual rate of 193/250 or 150/400. As this is a daily driver too i opted for a bit stiffer tender spring at 200/250.

Front (800 lbs. per corner, 0.985 angle correction) gives a spring rate of 145 lbs. in. which will be a 250/350 combo. I may be talked into a 250/400 combo for a 154 lbs. in. rate.

Are my calcs somewhat reasonable? This will be 14" travel

 

[vintagespeed]

You're calcs are on the money if you're working with a 50/50 split between the springs (both same length) and the springs are mounted exactly vertical. When you're angling your coilovers you'll have to stiffen the spring rates to account for it. You can find calculators on the swayaway site.

The rear is tricky because you have to find a balance with the front, if you increase the front rate the rear will do all the work & vice versa. I would do one end first (front) get the details worked out & then do the rear.

 

[XJoachim]

They will be equal length coils. Thanks for helping everybody, now i just have to raise the funds for this project.