Independent suspension?

Submitted: Thursday, Jun 03, 2004 at 19:04
ThreadID: 13427 Views:1976 Replies:4 FollowUps:7
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I am curious about the pros/cons of having independent springs in regard to entry/exit angles for serious off road.
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Reply By: Member - Roachie- Thursday, Jun 03, 2004 at 20:51

Thursday, Jun 03, 2004 at 20:51
I'm no engineer, but the way I see it the problem with IFS (which I guess is what you're referring to?) is that the fulcrum from where they pivot is relatively close to the hub and as such it severely limit the amount of travel (ie: up and down) that the wheel can arc through. As such, in extreme off road conditions it is far easier to find yourself with a wheel cocked-up in the air while an otherwise similar vehicle with a beam axle (which has far more articulation available across it's whole length) would simply (?) walk over/through the obstacle.
Hope this helps is just my opinion/understanding.
AnswerID: 61572

Reply By: Member - Captain (WA) - Thursday, Jun 03, 2004 at 21:49

Thursday, Jun 03, 2004 at 21:49
Another problem with IFS is that diff ground clearance changes depending on where the wheel is in travel in relation to the diff.

Imagine driving along a track with a centre ridge of say 100mm (typical bush track scenario). Diff clearance is say 200mm, but as the track has a 100mm ridge, diff clearance is actually 100mm. Now one of the wheels drops into a pot hole of only 50mm (2").

Due to the weight transfer, lets assume the wheel travels up 25mm (VERY conservative). So now, your wheel has dropped into a 50mm hole, the suspension has risen 25mm, for a total change of 75mm. This means your diff has only 25mm clearance. Hope there isn't a 25mm rock sitting on the track ridge. If it had of been a rigid axle, diff clearance stays at 50mm.

May not be the best explanation, but I hope you get my drift about how the diff can easily bottom out.


AnswerID: 61576

Follow Up By: rolande- Friday, Jun 04, 2004 at 01:19

Friday, Jun 04, 2004 at 01:19
This is off subject but I was wondering about your snorkel, looks to be the airtech / nissan design. I am looking at putting one on the GU, have been priced $240 by Nissan and up to $380 for an airtech. They look the same and I believe are made by airtech. Which do you have and do you find it O.K. Would you fit same again next time? Any thoughts appreciated
FollowupID: 323088

Follow Up By: GaryW - Friday, Jun 04, 2004 at 08:15

Friday, Jun 04, 2004 at 08:15
Captian, theres no doubt IFS has problems to do with travel but I don't get your point regarding center ground clearance. Center ground clearance on my LC100 IFS is far better than a live axle because the axles do not come out from the diff horizontally rather they come at a slight angle down from the diff. Diff is higher off the ground (Even without a lift)

Neither do I think your maths is right above. If body drop 75mm on one side then center will only have dropped about half that (say 37.5mm) in your example a live axle would have dropped 25mm in the center a difference of 12.5mm. There would be an argument that the weight transfer you talk about would also slightly raise the opposite side of the vehicle raising the center. Net difference would be negligable.

The other disadvantage with IFS is that the "arms" that hold all the IFS gear at each wheel significantly lower ground clearance at the wheel causing problems in deep ruts.

FollowupID: 323098

Follow Up By: Member - Captain (WA) - Friday, Jun 04, 2004 at 09:56

Friday, Jun 04, 2004 at 09:56
Hi GaryW,

I didn't explain myself very well so I will try again (would be a dam sight easier if I could do a diagram!). Imagine you could lift both wheels up on your vehicle at the same time. On a live axle, the diff moves up with the wheels. On an IFS, the diff is fixed and only the wheels move up. So, in relation to the ground, the IFS diff is now closer to the ground.

Lets assume bothe IFS and live axle vehicle have 200mm ground clearance under the diff. The Live axle is always fixed at 200mm, but the IFS only has a MAXIMUM of 200mm and gets progressively worse as the wheels compress into the guards. I hope this makes sense because it is a real issue with IFS vehicle.

And Rolande, I believe the airtech and the Nissan are the same, but their is nothing in the box to indicate its an airtech (I looked). I paid $265 (thought I got a good deal) and fitted it myself (if fitting yourself, need an air ratchet due to the Nissan inner snorkel behind the guard). The Nissan one comes complete with all parts, including rust preventative, template S/S screws etc, and is of a very high quality.

The only problem with the Nissan snorkel is that donaldson pre filters need a special adaptor (never seen one commercially) as the Nissan snorkel is not vertical where the ram clips on. But the Nissan one looks HEAPS better than the Safari IMHO (and prefer the Nissan badge than the air tech). I have also previously fitted a safari snorkel to my 80 series and that kit was of the same very high quality.


FollowupID: 323116

Follow Up By: GaryW - Friday, Jun 04, 2004 at 10:30

Friday, Jun 04, 2004 at 10:30
Hmmm. I think you are right that trying to explain without diagrams is difficult.

FollowupID: 323120

Follow Up By: Member - Jeff M (WA) - Friday, Jun 04, 2004 at 14:55

Friday, Jun 04, 2004 at 14:55
I see what your saying Captain, but all three of my IFS 4bies have the Diff so high up that you would have to take your sump out before you took the diif out, and they are normally covered up by a heavy duty bash plate. Your live axel Diff does not have a bash plate over it and I dare say it would hang down a lot lower.
So from what your saying a worst case scenario for me with IFS is I will bottom out and scrape my bash plate... Who cares, that's what it's there for, smashed my Feroza plate so many times I lost count, never stopped me going anywhere, never damaged anything (other than the plate).
FollowupID: 323157

Follow Up By: rolande- Friday, Jun 04, 2004 at 22:52

Friday, Jun 04, 2004 at 22:52
Thanks for the info, will go with the Nissan unit.
FollowupID: 323217

Reply By: Member - Nobby - Friday, Jun 04, 2004 at 07:50

Friday, Jun 04, 2004 at 07:50
Thanks guys. The query was actually for my son so I will pass the answer on. I'm content just to cruise along on the beach etc with the stock Jack.
AnswerID: 61611

Reply By: Moose - Friday, Jun 04, 2004 at 13:10

Friday, Jun 04, 2004 at 13:10
Nobby - no-one mentioned any positives which you asked for. Better ride on the road is one.
AnswerID: 61662

Follow Up By: Member - Jeff M (WA) - Friday, Jun 04, 2004 at 14:56

Friday, Jun 04, 2004 at 14:56
Yeah spot on Moose, better ride, safer handling and better protection for the Diff just to name a couple.
FollowupID: 323158

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