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  #61  
Old 29th September 2017, 12:57 AM
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The front weight is about 790Kg and rear about 610Kg under what I am taking as the lightest driving situation. I'm guessing my rear would be close to yours but the front is a fair bit heavier. A little over 10Kg would be bullbar and extra lights hanging so far forward over the front axle and the rest would be EJ253 and extra chassis strengthening in the SG.

Under full articulation I figure I'm going from 395Kg to 790Kg of weight on the compression front corner, with 35N/mm springs this gives me (790-395)*9.81/35=110.7mm of up-travel. I will reach bump stops before this happens. But let me know if I'm doing anything wrong, I've already had a lot to learn.
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  #62  
Old 29th September 2017, 09:07 AM
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I did a calculation for Jeremiah22 two years ago, here it is :



Weight front : 845 kg - 100 kg (unsprung weight) = 745 kg - 40 kg (strut spring force at ride height, 20 kg per side) = 705 kg

Spring rates : 1x 254 mm x 50 N/mm + 1x 254 mm x 40 N/mm = 1x 508 mm x 22,2 N/mm ((50 x 40) : (50 + 40) = 22,2)

705 kg : 22,2 N/mm = 31,7 cm (amount of compression of the springs at full load like when diagonal spin occurs)

Spring length at ride height : 508 mm - (317 : 2 = 158) = 350 mm (divided because the weight is on both front wheels)

Ride height : 350 mm - 165 mm (thread height) = 185 mm (rod length)


Weight rear : 710 kg - 100 kg = 610 kg - 40 kg = 570 kg

Spring rates : 2x 280 mm x 40N/mm = 1x 560 mm x 20 N/mm

570 kg : 20 N/mm = 28,5 cm

Spring length at ride height : 560 mm - (285 : 2 = 142) = 418 mm

Ride height : 418 - 165 = 253 mm

I did this calculation if you want to have maximum stroke (what I did to mine).

Your hydraulic settings are quite hard I think but its easier to change the oil than the settings. HotBits uses ATF Dexron III (viscosity 34 cst@40°C). I changed for Motorex Fork Oil 7.5W because it works much smoother (no stick-slip) but has the same viscosity because my settings are like oem Subaru struts and I can harden the compression with the knobs (DT2)

Et voilą ! Hope it helps you !
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Last edited by jf1sf5; 29th September 2017 at 04:17 PM.
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  #63  
Old 29th September 2017, 04:19 PM
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Quote:
Originally Posted by Red XS View Post
The front weight is about 790Kg and rear about 610Kg under what I am taking as the lightest driving situation. I'm guessing my rear would be close to yours but the front is a fair bit heavier. A little over 10Kg would be bullbar and extra lights hanging so far forward over the front axle and the rest would be EJ253 and extra chassis strengthening in the SG.

Under full articulation I figure I'm going from 395Kg to 790Kg of weight on the compression front corner, with 35N/mm springs this gives me (790-395)*9.81/35=110.7mm of up-travel. I will reach bump stops before this happens. But let me know if I'm doing anything wrong, I've already had a lot to learn.
What does the *9.81 refer to ?
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  #64  
Old 29th September 2017, 11:56 PM
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* is what I use for multiplication, / for divide and 9.81 being Kg to N conversion. It looks like you did Kg divided by N/mm gives an answer in cm, which is easier.

I not 100% sure I'm following all of your calculations, is the Springs rates row calculating an existing spring rate with 254mm long springs?

Currently on level ground my 250mm long 45N/mm springs are compressed to a length of 160mm. This suggests there is (250-157) x 45 = 4185N of force through each front corner. Or 4185 x 2 / 10 = 837 Kg on the front. I think this figure is slightly on the high end, but there's a few sources of error in this method, spring sag, over rated springs, a couple of mm of measurement error ect.

Under articulation, full compression corner, the spring compresses to 75mm and this is with the coils hard packed against each other. This limits me to 82mm of up travel. Force on the compressed corner should be at least (250-75) x 45 = 7875N or 787.5Kg

So I'm estimating the front springs to be supporting a mass of about 790Kg

My plan was to use 35cm long 35N/mm springs which on level ground under an estimated 790/2=395Kg will compress to 35cm-395/35=23.7cm

And under articulation, under an estimated 790Kg will compress to 35cm-790/35=12.4cm

So these springs will allow 23.7-12.4 = 11.3cm of up travel, however I only have about 10cm before I reach bump stops.
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  #65  
Old 30th September 2017, 02:15 PM
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Yes, 254mm are 10" springs.

This calculation was made with 2 springs on top of each other, worked well but had some rubbing on the strut housings, and spring perch were very low on the strut threads. Jeremiahs solution with barrel type springs is better, they have more usable length for a given length. I would suggest you going this route.

http://eibach.com/america/en/eibach-...-barrel-spring

http://swiftsprings.com/products/uni...prings-25.html

Swift springs have a 4" OD on 16" springs, Eibach stay with 3" OD for all the lengths thus I installed Eibach springs.

If the springs are too short, you will have coil block on full compression before using the total amount of the shaft...no good !

How far from the top of the strut housings are the lower spring perch actually, front and rear ? Is it the ride height you want or do you want to go higher/lower ?
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Last edited by jf1sf5; 30th September 2017 at 04:51 PM.
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  #66  
Old 1st October 2017, 11:02 AM
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Yeah I've got spring block all around and left rear is rubbing on the strut housing with the 250mm springs.

The Boynes springs I'm getting are 75mm ID wound down to 60mm ID on the end for mounting. These were a bit cheaper then barrel springs and should clear everything. So I'll see how these go first. But if I have any issues those eibach ones look perfect!

On other news today was the first time taking the hotbits offroad. I'm still missing out on some uptravel due to the spring block, however I did get through sections with out wheel lift that I previously would have lifted wheels. So it's already looking really good! Will post video tomorrow.
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  #67  
Old 2nd October 2017, 03:58 AM
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Yesterdays trip to Mundaring Powerlines. Previously I did lift wheels right in the air through this section. The only other vehicle on the day which did this section as easily was an XJ Jeep. Landcruisers and Patrols all had big wheel lift, I think another factor for this was the difference in wheel base.
https://www.youtube.com/watch?v=oSQr...ature=youtu.be
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  #68  
Old 2nd October 2017, 08:46 AM
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Easy
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Old 2nd October 2017, 04:49 PM
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How did you modify the rear top hats ? How much shaft length did you loose in the rear top hats, 25mm ? You still have 275mm stroke, right ?

Short and long springs are the same price but for our application, springs are never long enough. Ask at Boynes the usable length of their springs and compare with the Eibach or Swift because they may fabricate springs with the same specs but with 2 or 3 more coils meaning you will block earlier.
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  #70  
Old 2nd October 2017, 11:49 PM
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At the moment I just stacked the hotbits supplied upper spring perch on the unmodified top hat so am losing closer to 50mm.

I will modify the top hats at the same time I fit the next springs so will probably only lose about 25mm at the best. Plus the 60mm bumpstops can compress to 30mm. So should be 245mm of usable stroke.

Boynes have 260mm usable travel on the data sheet. They say it will be slightly more than this due to having the ends wound down, but lets just call it 260mm. So 15mm to spare. To get the right ride height I will have 5mm of compression at full extension. So really there's only 10mm to spare...

Eibach and Swift both have more usable travel despite being a shorter spring.
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