Outer Limits 4x4 Board

Ok guys....
what's more advantageous - up or down travel in a high flex, low speed application? Include ratios in your answer.

MMmmm BUMP and DROOP!

linited up travel - say 3-4" is good.
Then 10-15" down, whatever your shocks will handle

But balanced front to rear and with an amount of anti-squat that suits the terrain you are driving on mostly.

Hard to quote ratios, but I prefer more droop to bump. I like the compression to be controlled (ie know when I'll bottom on the bump stops) but I wouldn't go to the ends of the earth to build a droop/ramp queen. I'd rather spend time behind the wheel learning about lines, balance and speed control.

I had traditionally thought that more droop was better with little comp. This is the way my front is setup. But I was reading on POR about how if your vehicle is setup this way, then you are effectively raising the centre of gravity in certain situations. This is why I had chosen the lower stance to start with.

What they were saying is that if you climb a rock on one side (say front right) then your bumpstops quickly come into play and limit the travel on the right side. As you drive further up the rock, the whole front of the vehicle climbs vertically whilst the left keeps drooping.

Where as if you had more compression ability, then the right side would compress further before the front of the vehicle starts to lift.

The question is, does this benefit outweigh the benefits of having the vehicle sitting lower at other times?

What they are saying can possibly only happen in a set situation. As we all know there are a lot more factors involved as to how a vehicle travels over terrain. CG, weight transfer, momentum and personal driving style will all play a part in handling. It is too hard to set the rig up for every situation, height adjustable susp may help there, ballast transfer, even gyroscopes can help stability.

IMO everything is a compromise!

Area54 wrote:What they are saying can possibly only happen in a set situation. As we all know there are a lot more factors involved as to how a vehicle travels over terrain. CG, weight transfer, momentum and personal driving style will all play a part in handling. It is too hard to set the rig up for every situation, height adjustable susp may help there, ballast transfer, even gyroscopes can help stability.

IMO everything is a compromise!

That's not the point that I'm getting at

Everything is always a compromise.

The reason that I started this thread was to get some opinions on what is good and what isn't. For my front suspension, I expect to use all of the travel on my rancho 99012 shocks but the ratio of comp to ext is affected by where I place my shock hoops.

Just looking for some feedback before I setup my new shock towers.

What size tyres do you plan to run? this is prob the first consideration. set to full comp with zero tyre scrub, droop will be what it will be.

Area54 wrote:What size tyres do you plan to run? this is prob the first consideration. set to full comp with zero tyre scrub, droop will be what it will be.

Good point Troy. I'd forgotten the rational side of this debate. Unfortunately I'm not in a position to ascess the size needed for the tyres I wish to run (haven't got any tyres at the moment).

I suppose the best way is to set the shocks up where at full compression, I think the tyres will scrub (or just clear) and let the rest sort itself out.

Hopefully, I'll still be able to get some more uptravel then I currently have. Maybe I'll have to borrow someone's tyres to do some critical measurements

beebee wrote:... But I was reading on POR about how if your vehicle is setup this way, then you are effectively raising the centre of gravity in certain situations. This is why I had chosen the lower stance to start with.

What they were saying is that if you climb a rock on one side (say front right) then your bumpstops quickly come into play and limit the travel on the right side. As you drive further up the rock, the whole front of the vehicle climbs vertically whilst the left keeps drooping. ...

I would assume then that the ideal ratio in this respect is 50/50, with balanced articulation front to rear. This in many respects would virtually dictate your spring rates and free lengths to make it work "ideally" with a given shock.

G'day all,

I agree a 50/50 ratio is probably the best for flex, but if you were to do this your cg would be too high (for big flex vehicles)

But remember different suspension systems flex in different ways, like a 5 link flexes different to a 3 or 4 link setup.

I personally think that if one wheel is droping (droop) then you want the opposite wheel to be compressing by force of the link setup (eg a 3 link setup)

Remember guys, with limited "bump" compression, you will increase your Centre of Gravity with axle compression (when on the bumpstop)

Ive got so little up-travel on my new rig that at 50/50, id only need standard shocks. with like 4" total travel.

BJ then you could increase the ride height to increase the bump clearance.

I guess when we talk of compromise in this respect it is then between the ability to cross up on ramps and through ruts etc with a taller ride height and it's ability to deal with side slopes.

But, I think the talk on POR may also be more relevant if the rig is not balanced from front to rear. If there is only 2" of bump travel and 10" of droop then that I would have thought would be fine as long as the front and rear do the same. It may hurt in the rough stuff though every time the suspension bottoms out.

beebee wrote:Ok guys....
what's more advantageous - up or down travel in a high flex, low speed application? Include ratios in your answer.

About 35% up and 65% down is the best ratio to start with.

Pal wrote:About 35% up and 65% down is the best ratio to start with.

It's the best ratio based on what??????? If that's your personal opinion, then fair enough. If you think think that your suggested ratios are the "best" across the board for all rockcrawlers then please elaborate.

I agree that everything is a compromise. Like Beebee suggested, having more uptravel can lower your COG when flexing but you have to compromise based on how much diff-chassis and tyre-body clearance you have.

When using a full body, I would rather pick my ride height first, then use as much uptravel as I can get based on how much of my body I want to cut, then ensure that my suspension geometry maximises the potential droop as well.

In terms of what works the best if you don't have any constraints, I would say it's more personal opinion than fact. It depends on your driving style and preference. For example, I prefer reasonably balanced flex front to rear but remember that FJ-40 in the states that was SPUA in the front with virtually zero front travel but mega rear travel. That guy apparently liked it. Also consider the raging debate about antisquat, some like heaps of anitsquat with a limiting strap and others like a bit of squat.

Personally, if I were making a tube buggy, I would aim for around 50/50 between up/down and front/rear but if compromises were to be made I'd prefer a little more down travel and more flex in the rear.

Regards,
Matt.

Zookymatt wrote:
Personally, if I were making a tube buggy, I would aim for around 50/50 between up/down and front/rear but if compromises were to be made I'd prefer a little more down travel and more flex in the rear.

Regards,
Matt.

That's how mine will be....hopefully sooner than later

Interesting to see peoples views

I think that just picking your ride height to determine your uptravel is the only option in most cases and then the rest of the travel is downwards. How you control the down travel is more important IMO than juat how much you got.

Most of the US comp buggys run the winch on the front axle and a limiting strap on the back. These straps normally dont have much slack in them at ride height so this fairly well forces them to have 50/50 up and down cause the centre of the axle carnt droop.

The other extreme example is Pete Antunac rig. He uses very stiff springs and has only about an inch or so uptravel in most cases (from what I saw a tuff truck and a few videos) He hs a lot more down travel than up but his compromise is how low his ride height is.

Sam

I think a balance as zookymatt said is probably going to work the best in most situations. It will give you a more controlled feeling when you are driving as it will be a bit more predictable than a flex monster that relies on huge amounts of flex from just one end. Also I think having lockers at both ends will overcome any "lack" of wheel travel. i have seen super flexy rock rigs with lockers that put down so little contact pressure with all 4 wheels on the ground just spinning tyres whilst a more traditional stiffer sprung vehicle with lockers just walk thru the obstacle.

So balance I think is the key for most vehicles.

I'm not going to quote a percentage becuase I don't think it's that precise - but I'd prefer more droop than bump anyday.
ou wanna keep the COG as low as possible, but maximum wheel travel - as for tyre clearance - grinder
But remember you want the droop ideally still to be sprung to get ground pressure.....None of this coils rattling about in the buckets

I see someone mentioned the 40 in the US that was sprung under front with hydrualics rear can't remember the guys first name but surname is Jordan, in a couple of events last year both the first and second placed vehicles where setup thi way and Chris Durham has been killing it for years with sprung under leafs against all the best US rock buggies. Look at Kermit down here how many big flex large tyred monsters has he beat in the last 2 years. The current trend is to go for low weight 2500lb very low CG and of course high power to weight ratio not extreme articulation as exteme articulation can be a real problem with any kind of off camber situation.

all4fun wrote:Look at Kermit down here how many big flex large tyred monsters has he beat in the last 2 years.

Best "wincher" I've ever seen

Shorty40 wrote:

all4fun wrote:Look at Kermit down here how many big flex large tyred monsters has he beat in the last 2 years.

Best "wincher" I've ever seen

Given that the bump stop is in the same position ,There hypothesis of a vehicle having a better spring rate at a higher ride height has a lower cog=
Aboriginals have a simaler name for there religion.

all4fun wrote:I see someone mentioned the 40 in the US that was sprung under front with hydrualics rear can't remember the guys first name but surname is Jordan, in a couple of events last year both the first and second placed vehicles where setup thi way and Chris Durham has been killing it for years with sprung under leafs against all the best US rock buggies. Look at Kermit down here how many big flex large tyred monsters has he beat in the last 2 years. The current trend is to go for low weight 2500lb very low CG and of course high power to weight ratio not extreme articulation as exteme articulation can be a real problem with any kind of off camber situation.

Todd these outlandish statements are incorrect, inconclusive and prove nothing.

The names of these two competitors are:
Don Robbins and Tracy Jordan. There vehicles are vastly different now, so what you said no longer applies they are no longer front runners in those vehicle, but in thier current vehicle Don is spotting for Tracy and the rig has no hydraulics but a cool rear steer axle. It has been placing consitently in the top 5 this year.

I know Chris Durham is spring over axle and running Superlift springs. I may be wrong, but it is pretty rare, in fact, yeah I am right, I will stake money on it.

Also have a look at where Chris Durham is running these days!!!

POS wrote:Also have a look at where Chris Durham is running these days!!!

2nd at EROCC behind ken blume?

But EROCC is a little different in that some big names were not present and the courses are DIFFERENT due to the terrain to the other rock comps.

Personally I like the idea of plenty of uptravel. One thing i've wanted to try (victim would be an LJ or Sierra) is keeping the COG super low by having standard ride height but getting more uptravel by notching the chassis. You'd need to make sure you have enough room in your wheel arches for the tyres obviously but for something like this it really wouldnt be much of an issue. Give it some clearance by running big tyres and keep the belly nice & flat with nothing hanging out to grab at rocks etc.