How much suspension travel to design in

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

Not sure how much upwards suspension travel to design into my trials buggy that I'm building.

Now before everyone starts telling me to design in a cool 12" of up travel, remember that more upwards suspension means the engine needs to move up, centre of gravity moves, the bonnet comes up higher, prop angles increase, and suspension links get steep which messes the suspension geometry.

So I'm really looking for ideas on what is a balanced number to go for.

At the moment I'm not yet concerned with droop (ie downwards suspenion movement). I'm trying to fix my drivetrain and suspension layout and that's mostly affected by upwards suspension travel, ie how much the suspension can move up upwards from ride height.

A bit of reading on the American forums says to start at half my full suspension travel and work from there. So if I go for 12" travel then I should set upwards travel to 6". For trials where speed is much less then I'm guessing I can reduce this quite a bit. Maybe 4" ?

That would leave me 8" droop for flexing.

Whatever the ideal travel for trials, I'd like to increase it a bit so that I can take part in occasional comp safari just so that I have somewhere to open up the throttle a bit just for kicks.

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

I should add that this is a fairly lightweight build using Suzuki SJ drivetrain and light Vitara engine, built into spaceframe. Wheelbase 88".

Xpajun · Posted: Sat Jan 02, 2016 10:57 am Post subject:

From my experience of trialling I wouldn't say that suspension travel is that important. Suspension travel is more for obstacles like rock trails etc. (possibly why it's very American).

For trials you are looking at good breakover angles, along with approach and departure angles, plus, of course, good traction (tyres) and low gearing and lightness, the latter you already have with a Vit.

RichardD · Posted: Sat Jan 02, 2016 4:53 pm Post subject:

Another vote for reasonably modest suspension travel on a light vehicle

IME for trials, traction is everything and if you build in too much travel you end up with not enough weight on the wheels dropping down and therefore losing traction.

Also, I feel that droop is everything (careful Laughing

). You can spend £££ and have serious brain ache moving the drivetrain around and end up without any real benefit.

At the risk of teaching you to suck eggs .... major articulation will also attract axle tramp and spring warp (on coils or leafs) which leads to yet more compromises. Not to mention that weight transfer front to rear will also be affected .......

Good luck Wink

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

Thanks. Though I need some suggestions for what travel to actually go for! Or examples of what other trucks have. I've already got a number in mind but would like to know other's ideas before I say.

RichardD, I don't know what axle tramp and spring warp is but I'll look it up.

I'm currently designing for my roll axis (how much suspension travel makes wheels turn) and anti-squat/anti-dive (how much the suspension lifts the car under acceleration). The anti-squat I can design for but the roll axis I don't know what to do with it. I know in an ideal world it would be zero but I don't know if zero can be achieved and if not what's an acceptable number. I know Rockwatt did some nifty suspension geometry to get zero roll axis but that's out of my league.

RichardD · Posted: Sat Jan 02, 2016 7:28 pm Post subject:

Axle tramp is when the side to side movement of a live axle under drive pressure. It will have a tendency to bounce and can lead to breakage.

Spring warp: live axles cause the wheels to rise and fall in an arc so the springs, especially leaf, will get bent and twisted.

The greater the articulation the more movement.

mike328 · Posted: Sat Jan 02, 2016 8:47 pm Post subject:

I take it you're plugging numbers into the 3/4 link calculator? If so then the other information you read (from America, I guess Pirate) is pretty accurate. Don't shoot for more than 60deg between axles and if you do decide on long travel put limit straps in the middle to stop both wheels drooping together and giving your props a hard time.

In my opinion though, diff locks will get you further than big travel.

Don't plan for a specific length just see what will work with your chassis/body/tyre/shock/prop/steering combination...everything is a compromise... then head for a 50/50 up/down split if you want an all-rounder Smile

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

With my suspension travel I am *guessing* that 3" - 4" upwards travel is plenty plenty for trials. I'm going for 4" to 5" to get a bit more so that the buggy will be more versatile and can do some high speed fun as well. 5" is seems too much, so maybe 4".

Mike, yes I've got the Pirate4x4 suspension calculator. It's ten years old so I'm guessing it's accurate or someone would have noticed by now!

Mika, what do you mean by 60 degrees between axles?

Ah is that what the limit straps are for! I always wondered why someone wouldn't just design the suspension limit into the shocks, but I get that now, if the strap is in the middle then it allows an individual wheel to droop further, but not both at once. Nice.

Ok spring warp I get now. The photo below sums it up nicely!

Spring warp only happens on three link suspension if there's a panhard bar. I'm going for four link, but that in turn means I need hydraulic steering which I think will stop me entering some events, but not yet sure how many.

mike328 · Posted: Sun Jan 03, 2016 8:24 pm Post subject:

Sounds alright to me Smile

60deg between axles; when front axle is parallel to ground the rear will be at 60deg to it, body will be hovering around somewhere about 30deg.

It is one good use for a limit strap that most people haven't picked up on, but most use them to stop shocks from topping out and then bump stops to stop bottoming out (its not that healthy to ram shocks open or closed repeatedly).

In your pic of spring warp, it looks like panhard rod or steering link has broken and that's a 'get me off the trail' repair! Wink

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

60 is quite a bit of flex! I haven't got as far as seeing what flex I'll be able to get, that will come later when I put the shocks into my design. But why the 60 degree limit?

I just spoke with AWDC and with hydro steering I'll only be able to take part in low speed events. I want this buggy for trials but I'd hoped I could do a comp safari event every so often just for kicks.

To get rid of the hydro steering I need to switch to 3 link suspension and I'm not a fan of that.

mike328 · Posted: Sun Jan 03, 2016 8:50 pm Post subject:

Xpajun · Posted: Sun Jan 03, 2016 9:45 pm Post subject:

You need independent suspension if you ar going for high degrees of flex and keep the tyres flat

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

I looked at independent.

The problem I found with independent is basically cost. If you want big suspension travel you need the diff in the middle of the car so that you get long suspension arms. But every mass production car has the diff to the side to clear the engine and to keep the prop shafts straight.

So you either have to buy racing diffs which cost almost as much as my entire buggy budget (for one diff!!), or build your own diff housing which I plan to do in phase two.

Even then you end up with compound prop angles (where the prop angle goes sideways to get to the diff as well as downwards) and I don't know how you get around that. I think some pro builders move the engine to one side, others live with the compound angle.

Solid axles are so much easier and cheaper and for low speed off road apparently they're better.

Xpajun · Posted: Mon Jan 04, 2016 1:30 pm Post subject:

RichMayo · Posted: Mon Jan 04, 2016 1:44 pm Post subject:

Xpajun · Posted: Mon Jan 04, 2016 5:08 pm Post subject:

You could also raise the engine and gearbox providing it's a buggy build

There would be many ways around the problem - there is quite a few spider designs around now

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

What are the spider designs? I've seen lots of talk about them but don't get what they are? I looked up the "Yellow Spider" that lots of people mentioned but still can't tell what it's all about?

Xpajun · Posted: Mon Jan 04, 2016 6:39 pm Post subject:

mike328 · Posted: Mon Jan 04, 2016 9:38 pm Post subject:

That buggy is Cool

I thought spider chassis were somehow tied into the eurotrial proto class??????
All I could find out in this link, just gotta learn Scandinavian so I can read it Laughing

http://pirate4x4.no/forum/forumdisplay.php?114-West-Coast-Spiders

Theres a couple of that type car and some other cool chit here;

http://forum.difflock.com/viewtopic.php?t=28065...662925a06ba34e92d

Undiplomatic · Just got MTs Joined: 10 May 2010 Odometer: 483

What physically makes a buggy a spider and not just another buggy?

mike328 · Posted: Mon Jan 04, 2016 10:44 pm Post subject:

I just thought it was the same sort of thing as Crawler/Bouncer/U4...etc.. all technically just buggies with a minor change in spec and what people do with them....???

Someone who knows please step in and educate me Smile

Xpajun · Posted: Mon Jan 04, 2016 10:55 pm Post subject:

mike328 · Posted: Mon Jan 04, 2016 11:59 pm Post subject:

RichMayo · Posted: Tue Jan 05, 2016 10:13 am Post subject:

I think you'll find that's a insect buggy. (smug emote)

mike328 · Posted: Tue Jan 05, 2016 6:18 pm Post subject:

baloo · Posted: Sun Feb 14, 2016 6:59 pm Post subject:

cynic-al · Posted: Mon Feb 15, 2016 12:45 pm Post subject:

I had 11" shocks on my RRC with slighlty more down than up although I was aiming for 50/50 and I never felt I needed any more travel than that. OK others looked cooler and I guess you could argue were more stable but with front and rear lockers they didn't get any further. I had maybe 3" of very soft spring lift and no body lift. I fitted wider axles and hacked the body to fit the 36" tyres.

I did consider putting a bump stop in the middle for when your bouncing up and down but as I didn't do anything that fast I didn't find I had a problem with the axle hitting the sump etc so never got around to it. I did have outer bump stops to save the shocks getting bottomed out but never got around to straps to stop them being over extended but never had a problem with breakage, I guess it's not as hard on shocks as bumping down on them.

I tried trialling and despite all that I lost by a mile to a guy in an almost standard Ford Maverick... think they must have been cheating Confused