jf1sf5's forester

I bought my '97 Foz in 2002, second hand with 90'000 km.

The first year, I changed the OEM springs for Dobinsons, the wheels and tires, 1 inch lift blocks and a 8 mm thick aluminum sump guard after a big dent in the sump but no hole !

The rear Dobinsons were too hard, changed them for SF springs on SG self leveling struts.

In 2006, I wanted to go further with the mods and prepared the Foz for a saharian trip to Morocco, fitted some BFG AT's, Quaife front diff, rear SG LSD diff, SG disc brakes and larger SG rear track.

In october 2007, ready for the trip, drove about 1'500 km on very sandy/rocky trails and corrugations that blew the rubber of the rear top hats but drove back home with pieces of truck tires (no Subarus in Morocco !)

https://www.forum4x4.org/attachment.php?attachmentid=55663&d=1364158577
https://www.forum4x4.org/attachment.php?attachmentid=55664&d=1364158647

2010, bought some second hand Proflex evo2 coil overs that were made for the Forester engaged by Bruno Picard for the 2008 Dakar rally...cancelled.

2012, changed the BFG AT for General Grabber AT, as good or better off road with less noise on road, with Compomotive 16x7 ET30 wheels.

And discovered "www.offroadsubarus.com" that helps me modify my Foz !

2013, 1,59:1 low range, DCCD and rear Quaife diff because after some readings, I think the helical diffs suit my needs better (rain, snow)

Pics to come but I'm no good with computers !
 
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jf1sf5 said:
I think that I should make a write-up of my HotBits coil overs for everyone to understand how I calculated the lengths of the coil overs, of the strokes, of the springs, etc…I'll try to do that in an understandable english…soon !
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Would LOVE to know more about the exact bits used from HotBits :)
It looks like we have a HotBits importer here in Canada, I'd be interested in getting a quote from them on a setup like yours.
 
Ok, so here it is !

I opted for the HotBits DT2 coil overs for several reasons, the first one is that they are the unique company that was ok to make them custom at my specs with no extra charge. I have 3 years of experience in rebuilding the Proflex coil overs I now have in a box…

My specs :

Maximum stroke to keep the wheels on the ground as long as possible

Comfort as its my DD

Possibility of height adjustment and tune of the compression and rebound

Price…

Ok, so for comparison, the OEM SG struts have 19cm stroke front and 20cm stroke rear.

The OEM hydraulic setup is comfortable oriented but you can not make it stiffer (or softer). Therefor, most people put harder springs to make the car feel firmer for better handling but thats not good when going off road because you need wheel travel (stroke) and also not good on road because it gives a harsher ride. So the best is to have some OEM (approximatively) spring rates and tune the stiffness with the hydraulics. On the HotBits DT2, you can tune the compression and rebound very easily with the knobs that open or close the oil passage.

The OEM spring rates are approx. 30N/mm front and 27N/mm rear. For the coil overs, it is nearly impossible to find 500mm long springs so it is easier to put 2 springs on top of each other but therefor, they have to be twice as hard for the same result because each spring compresses for itself. That gives the spring rates for the front 2 springs 250mm x 60N/mm which is the same as 1 spring 500mm x 30N/mm….ok ?!

Very long springs are needed to allow full compression, thus why the spring seats are very low on the housing and also to have a minima of preload.

With the rear coil overs, I have 26cm of stroke and I wanted them fully closed on compression (like when diagonal spin occurs) so lets say I have 700kg on the rear right coil over (car on a horizontal surface weighs 1'450kg, approx. 750kg front and 700kg rear). The rear springs are rated 27N/mm which is about the same as 27kg/cm. For every 27kg, the springs will compress 1cm. (700kg weigh : 26cm stroke = 27kg/cm)

Now there is the ride height. The best is to have none or as little preload on the springs when on full droop because it will "eat" some compression. With 54 kg (to make it easy) of preload, it looses 2cm of compression or you have to add 54 kg of load in the boot to compensate !

Is my explanation clear enough ?

The adjustable top mounts are for camber adjustment and are really needed, especially for the rear because on full droop, the coil over is very close to the chassis and the tire. To fix this on my SF, I installed SG 41,5cm vs SF 40cm lateral links... and it gives a better look !

A suivre...
 
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Very good explanation of the HotBits calculations....I understood that. I have been really interested in a real coilover aspect to my lift like this as opposed to spacers only. I will have to take your experience and hopefully acquire some of these myself someday. I really like the idea of longer stroke with softer springs and damping control. Hmmmmm....
 
I look forward to hearing about your experiences offroad with the new suspension!
 
updates from your recent holiday?

or are those posted elsewhere? ;)

<<EDIT>> found the trip report!! reading it now :cool:
 
Will make a small mod next week…

Change the HotBits pivot top mounts for oem because these little pieces of rubber make the drive much smoother on the highway. The very small irregularities can't be damped by the shocks at high frequencies so you feel them in the back and it ends to be quite uncomfortable on long drives.
 
Very good and clear write up about your custom HotBits suspension jf1sf5. Sounds like you've got it all worked out and I'm definitely looking forward to seeing it in action!

I contacted the Australian HotBits distributor about a month ago regarding suspension for the SH. No reply as yet and I'm not holding my breath waiting for one either. Not very good customer service from the Aussie distributor.
 
Really interested in your suspension setup, but none of the pics are working and of course the youtube videos aren't either. Arrggg.
 
Sorry to hear that…they work here :shrug:
 
Switching out the SF rear lateral links to SG lateral links is that plug and play and alignment or there a little more to it than that?
 
Its plug and play ! If you want a sway bar, you'll need to swap it too.
 
I refuse to run sway bars, haha

Looks like this might be my next project in the next cpl weeks!
 
I was able to get everything to work on my phone.... Now I'm even more curious about your suspension set up. Do you have any side profile pics of your car on a flat surface?

Such a sweet ride. Need more pics!!
 
No recent ones…most are taken on the tracks when diagonal spin occurs…!

I'll take a few for you on a flat surface and on ramps to see the coil overs stroke next time I go to my friend/mechanic to do the top mounts swap.
 
Swap is finished but was not plug and play. Did the swap using SG top mounts front and rear

Front : Had to make some 13mm spacers between upper spring perch and top mounts to allow enough flex.

Rear : Did some 25mm spacers to gain the loss of stroke due to the silent-blocks (rubber bushings) and welded upper spring perch to fit 60 mm inner diameter springs.

Pics to come !
 
Losing the factory strut top mounts has stopped me from buying a set of hotbits, so I would like to see some pictures of how you made them work. Any benefits to a 60mm spring, or is that just to work with the factory top mounts? Importantly for me, would you change the specifications of the coil overs if you were ordering them to suit the factory strut tops? I was thinking of getting the RSI with the external canisters so they can be mounted out of the way.

How often are you servicing them?
 
60mm ID springs is what HotBits uses for their coil overs so I just adapted the rear SG top mounts with home made upper spring perches to be able to re-use them. The guy that machined the spacers and the rear upper spring perches took some pics…I'll ask him to send me a copy.

If I had to order them today, I would buy them "nude". I mean without the pivot top mounts nor the springs as their springs are not long enough for the stroke. I bought them with "subaru" hydraulic specs and that suits my needs (comfort). The front stroke can't be any longer (24cm) but the rear can be a bit longer (29cm oem top mounts vs 26cm with the HotBits pivot top mounts).

I don't know how the HotBits RSI (inverted) coil-over works but they have the same design as my Proflex and what I didn't like is the stick slip effect due to bad lubrication between the shock body and the strut housing. I didn't find a way to make them work smoothly on tarmac.

If I hadn't have the 2 leaks (o-rings on compression knob), I wouldn't have serviced them yet, they work great and have a basic design making them easy to work on.

Hope it answers your questions !
 
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