[Jezza86]

goes pretty quiet in that first vid, might have stalled. whats the abs do when the car stalls (i dont know im non abs). tires hold shape pretty well when its tipping, might have benefited from airing down.
he was already sliding backward with wheels to the left which caused the rotation, and in the 1st half a second of the vid you can see theres a ledge that the drivers tyre drops off, bytes the shale/rock and thats what starts the roll.

[hooki]

macguyverjimny wrote:

Thank you

Saw this vid and i got the shakes,

Seems his front wheels slipped on the slopes and the front wheels was turned a bit sideways, while reversing.

See link

http://www.youtube.com/watch?v=r0SjQKF_34A

haha he ends up in the passenger seat

[jdk81]

macguyverjimny wrote:

Went the weekend to a guy who is reallly good with vehicle dynamics and have been into alot of extrem 4x4 challenges to discuss the manufacturing of custom radius arms for a 3 inch lift.

Well we all know lift raises the CoG of a vehicle.
Heres the catch.... anyone who is good with vehicle dynamics works or has worked in the industry.
Im not sure how the engineers for modded vehicles do their tests, but accredited dynamic vehicle handling testing places, test the vehicle in its current state.
Everything is based off its current in-use, as to be loaded form.
The maximum lateral acceleration is based on this new higher CoG.
This applies to speeds and rates of change etc during all the dynamic testing.
ISO or american standards.

The biggest issues for dynamic vehicle handling is tyres and suspension.... These all have a combination spring and dampening rate.
If your shocks are underdamped.. (this can occur if your springs are uprated with normal shocks, or under rated shocks go with your normal springs) you car will be really scary. It will roll and sway around, and get out of control with the correct inputs.
If your car is overdamped, it will suck ass too.. on a rough ride, it will be horrible and dangerous too. Offroad when bouncing etc itll understeer lots.
This whole combination is whats essentially getting tested.
Dont need thousands of dollars testing to know that a higher CoG means you will roll easier...

What this all means in an onroad application... well, learn the vehicle and drive appropriately.
technically, with the correct overall suspension system, a silly skyscraper sierra can pass the test.
Think how loaded trucks pass the tests etc..

Offroad, well a little lift is accepted, but it raises your CoG
This limits the type of extreme stuff you can drive.
For most users, you wouldn't notice it.
You would shit your pants before getting anywhere near it, or think its a bad idea and not try it.

A body lift, will raise the CoG much less than a suspension lift.

Tyres will also raise the CoG

The biggest factor in offroad accidents is driver error.
Error in judgement (about attempting it), poor line, poor throttle control, etc etc

[shep]

Buy a WRX

[31zook]

They both flipped due to Bad driving. If any car was in that situation they would of done the same thing.

And Monley do you really want a 12" belly? That seems way to low for me...

[monley]

31zook wrote:

They both flipped due to Bad driving. If any car was in that situation they would of done the same thing.

And Monley do you really want a 12" belly? That seems way to low for me...

Should be fine for nt conditions

[Gwagensteve]

As has been discussed many times, suspension lift doesn't fit a larger tyre. The only ways to fit a larger tyre are guard trimming, body lift, or bumpstop spacing.

So, all three methods of gaining tyre clearance can be employed irrespective of suspension lift to fit a given tyre.

Adding suspension lift to improve clearance is pretty silly, because it will reduce stability, and in any case, it doesn't improve clearance in the only place that matters- under the axles.

Changing springs might be necessary to improve load carrying, or to restore compression travel once the bumpstops have been spaced down, but beyond the absolute minimum necessary more lift just creates more compromises.

I don't believe in the idea that a certain belly height is too low. A range of practical considerations will dictate the minimum belly height. Once they are dealt with then basically, the lower belly height the better.

So if you are concerned your jimny will be unstable at 3" of lift, ask yourself whether 3" of lift is required for the tyre size you want to run- that is, do you need so much bumpstop spacing that you need 3" of spring lift to retain acceptable compression travel. If you don't, then I can't see the reason for that much lift.

PS I haven't checked both videos, but in the first one, the roll was due to a poorly set up car (gearing, lockers) and driver error. A stock height jimny would have rolled in the same spot driven the same way.

Steve.

[joel]

^^
to gwagen,
agree mostly, yes i went up 40mm as that was the only way to get a HD spring,
but the only benefit i see with the 3'' lift is the better aftermarket castor corrected radius arms available.

[Ausuki]

jimmy91 wrote:

Ausuki wrote:

Why would you run 215/75 tyres under a 3 inch lift?

maybe because he fucking wants to

Touche,

Yes he can do what ever he fucking wants to his own car.
But if he wants advice on how a mod will effect his vehicle then finding out why he wants to do it and what he wants it to do, will help
people give him better advice.

[atari4x4]

there has been no mention of adding to the wheel track to counter act the increase in ride height?

[macguyverjimny]

Atari,

Are you refering to that i need to wide the wheel track by using offset rims or wheel spacers?

You are right i had no plan on doing that, might be stupid to ignore that. Thanx for the help.

[jdk81]

For every Inch you raise it through tyre lift (realistically you would want to increase the track width between 2"-4").
To try and somewhat maintain the increase in COG and trackwidth to a relationship between 45 and 30 degrees.

Body lift requires less track width increase (as you only raise a portion (id guess 1/3) of the vehicles mass)
Tyre lift requires the most track width increase, as it raises everything.
Suspension lift will have pretty similar effects as tyre lift (probably 4/5 of mass raised)

Thinking this way helps you keep your eye on the CoG values.
Once you get carried away with lift (Tyre lift, suspension lift, and body lift) its starts to need huge track width increase to maintain stock roll over angle.

Can be done with wider tyres, offset rims, wider diffs, last resort is wheel spacers etc.

[3cyl]

The first video is just what happens when people in relatively short vehicles get out of shape on a step on a hill. A more experienced driver would have saved that. Guess from now on he'll know the early signs and stop and reverse before it comes to that. Looks like he had a fair bit of momentum up his sleeve too.
I guess the biggest problem with Jimnys is they're too new still and you can't just get a cheap shitter to study the laws of physics and how they apply to your car. Once you've been to the edge a few times you'll taunt those bossy laws of physics. Also you'll apreciate a low COG and know why experienced guys say low as possible to do the job. The second video just looked normal, just that the guy didn't know his car's limits.

[shep]

monley wrote:

31zook wrote:

They both flipped due to Bad driving. If any car was in that situation they would of done the same thing.

And Monley do you really want a 12" belly? That seems way to low for me...

Should be fine for nt conditions

Haha you are in for a surprise unless you just drive where all the plebs drive

[joel]

^^ was going to go at his comment... but i figured i can let him find out the hard way lol
your getting generous in your old age

[alien]

jdk81 wrote:

.... trackwidth....

also take into account the weight of the larger rims and tyres. you add a fair amount of unsprung weight down as low as it'll go when you go bigger rubber... also keep in mind that going from a 15x5.5-0 offset rim to a 15x7-13 (the most common size) is straight away a 2.5" track increase, and you havent even added the wider tyres onto that yet.

adding width to the track is also difficult in some cases - jimnys for instance require a lot of guard chopping to go much wider than a 15x7-13.

[royce]

jimmy91 wrote:

Ausuki wrote:

Why would you run 215/75 tyres under a 3 inch lift?

maybe because he fucking wants to

Pull your head in, posts like that get you watched and watched people usually end up banned next time somebody is in a bad mood

[PORL]

Lol^^ I like unnamed 3rd person

[Mike57]

Gwagensteve wrote:

As has been discussed many times, suspension lift doesn't fit a larger tyre. The only ways to fit a larger tyre are guard trimming, body lift, or bumpstop spacing.

So, all three methods of gaining tyre clearance can be employed irrespective of suspension lift to fit a given tyre.

Adding suspension lift to improve clearance is pretty silly, because it will reduce stability, and in any case, it doesn't improve clearance in the only place that matters- under the axles.

Changing springs might be necessary to improve load carrying, or to restore compression travel once the bumpstops have been spaced down, but beyond the absolute minimum necessary more lift just creates more compromises.

I don't believe in the idea that a certain belly height is too low. A range of practical considerations will dictate the minimum belly height. Once they are dealt with then basically, the lower belly height the better.

So if you are concerned your jimny will be unstable at 3" of lift, ask yourself whether 3" of lift is required for the tyre size you want to run- that is, do you need so much bumpstop spacing that you need 3" of spring lift to retain acceptable compression travel. If you don't, then I can't see the reason for that much lift.

PS I haven't checked both videos, but in the first one, the roll was due to a poorly set up car (gearing, lockers) and driver error. A stock height jimny would have rolled in the same spot driven the same way.

Steve.

I agree with Steve here. I have a 40mm lift and 215 tyres and if anything I would have larger diameter wheels before any more lift. I scrape the diffs when I get into deep rutted sections whether in sand or mud. I don't recall ever hitting the underside of the vehicle yet. I have some slight scraping with the 215 tyres on the front and more lift will not stop that, I need to extend the bump stops by a small amount to solve that issue. My next upgrade (if I ever felt that I needed it) would be gearing, guard chop, bigger tyres and upgraded CV's and front axle. More spring lift would not be on my agenda.

[jdk81]

alien wrote:

also keep in mind that going from a 15x5.5-0 offset rim to a 15x7-13 (the most common size) is straight away a 2.5" track increase, and you havent even added the wider tyres onto that yet.

Example
Sorry for being about sierras.. but its the info I found/have
I would imagine jimny static stability factor would be very similar.

15x5.5-0
stock size is 205? so 102.5 beyond wheel mounting surface to outer edge of tyre?

15x7-13 Using 10.5" wide tyres = (10.5*25.4)/2 + 13 = 146.35mm beyond WMS per side (total is double this).
To get the increase, 146.35-102.5 = 43.85mm increase in track-width per side (1.72")
87.7mm (3.45") overall track-width increase (combined sides)

Try 15x8-25 (31x105)
10.5*25.4)/2 + 25 = 158.35mm beyond WMS per side (2.2" increase per side) or 4.4" overall

Static stability factor of a stock sierra
between 1.08 and 1.13
http://www.waltersforensic.com/articles/accident_reconstruction/vol1-no12.htm
Static stability factor is
http://www.nhtsa.gov/cars/rules/rulings/rollover/Chapt05.html
1/2 track width, divided by height of CoG
track width = 1310mm
==> CoG = 1310/1.1 = 1190mm high.

=degrees(atan(1310/1190)) = 42.25 degrees.
So a sierra can go 90-42.25 degrees = 47.75 degrees to where it rolls over, based on their testing... apparently.

This is intuition, as I CBF calculating it
I'd suspect every 1" of body lift, will raise the CoG of empty vehicle 1/3"
For every 1" of suspension lift, will raise the CoG 4/5"
For every 1" of tyre lift, will raise the cog 4/5". Taking into account tyre and rim weight etc.

Using the static stability factor, to attain the stock relationship, if the CoG raises 1" we multiply it by the stability factor of 1.1 to find the desired track width increase per side.
So 2" of body lift means you raised the CoG 2/3", applying stability factor, means you need 0.73" increase in trackwidth per side.
So 2" of suspension lift = 2*4/5 * 1.1 = 1.75"
so 2.5" tyre lift = 2.5*4/5 * 1.1 = 2.2"
So we need 0.73+1.75+2.2 = 4.7" of trackwidth increase per side, to maintain stock static stability factor.

We are now chasing our tails, as 9" total trackwidth increase is huge....
When viewed in this light, its easy to see why the 2" BL, 2" suspension lift and tyres is getting a bit on the nose.
SPOA would be horrendous.

Even 31x10.5 on -25 offset rims are still worse than factory stability factor, without any other lift.
2.2" increase per side, whilst raising it 2.5"

[alien]

My SPOA sierra is 150mm taller than stock (including tyres) - its actaully lower than a 2" spring, 2" bodylifted sierra on 31s, which would be 165mm taller.

I run 15x7-38mm rims and 31x10.5" tyres - this means my sierra is 188mm total wider track width than factory.

Add to that the extra unsprung weight of the larger tyres and its very stable indeed.

[jdk81]

Highlights the biggest difference between theory and actual (and even different tyres).
Most 31x10.5s seem to be under 31" and a fair bit wider than 10.5".
But the km2 33*10.5" width is much narrower than a bighorn 31*10.5".

I presume you measured the car?
Do the tyres measure close to 12.5" wide when resting?
Imo the offset is a little extreme, the track width is nice.
So your total overal lift is 1" lower (to the sill).

anyone know how much a sierra tub/body weighs etc?
Be interesting to know how much BL affects cog

Ill dig up the tyre weight thread when i get home and do some calcs to see the change in height of cog between stock and 31*10.5 muds on a sierra.
(would be similar on a jimny too).

[sideways]

I can attest to how stable Aliens Sierra is. It doesn't feel like the stereo typical SPOA car is meant to at all. I think the long springs help a lot though, it's super predicable.

[alien]

from what i recall of sierra body weight, theyre effin' heavy!!!

[SierraDan]

Just drive it..

[atari4x4]

SierraDan wrote:

Just drive it..

slant angle?

[SierraDan]

atari4x4 wrote:

SierraDan wrote:

Just drive it..

slant angle?

Sounds like it.

[Red89]

alien wrote:

Add to that the extra unsprung weight of the larger tyres and its very stable indeed.

Just to illustrate the advantages of a bit of extra unsprung weight



But as Dan said, no amount of science and theory is going to make up for driver error which from what I have seen is one of the biggest causes of rollovers. So put in the smallest lift you can get away with for the tyre and then just drive it, you will learn to fell when it starts to get sketchy.

[atari4x4]

OMFG that slant angle

[royce]

Red89 wrote:

alien wrote:

Add to that the extra unsprung weight of the larger tyres and its very stable indeed.

Just to illustrate the advantages of a bit of extra unsprung weight



But as Dan said, no amount of science and theory is going to make up for driver error which from what I have seen is one of the biggest causes of rollovers. So put in the smallest lift you can get away with for the tyre and then just drive it, you will learn to fell when it starts to get sketchy.

Nah its got nothing to do with the tyre weight, its cause you used a blue tarp, if it was a silver tarp it would of flopped there for sure