Up Travel vs. Down Travel and Limiting for 37" Tires (1 Viewer)

[kbahus]

I have been paying close attention to all of the 37" tire threads and have confused myself. Hopefully it is just my poor logic and lack of thorough solid axle suspension knowledge that needs straightened out.

It seems that a 50/50 up/down travel suspension works best such as the FOR kit, however I am fairly sure that Nay runs a 2" bump stop spacer. I know this has to reduce the up-travel 2" but does this also reduce the down travel the same amount? So a 3.5" lift without the spacers has a lot of articulation, but doesn't spacing the bump stops limit the travel down to the same as say a 2" lift at 8" of travel vs. the previous 10"?

So now if I take say a 2" lift and throw 37" tires on the truck, space the bump stops down 2", will my total travel be limited to 6"? Wouldn't the best compromise be to utilize as much articulation as possible without the use of bump stops or do larger tires make up for the lack of suspension travel? It just seems like a catch 22 to me and this is why I am confused. Why would I want to go from being able to fully flex out my 285's without rubbing to big tires and less articulation?

 

[js93cruiser]

up travel=bad
down traved=good
it should be a 90/10 ratio, if you look at any serious off road rig, they have maybe 2-3inches of up travel,if you have all up travel you get very tipsey on rocks

 

[kidglove13]

I run about 40-60 +/- up/down It does just fine off road.
I have run into plenty of situations were that up travel was needed every bit of it when put into awkward flexed out situations on the trails.
There is no real magic number of up vs down.
You have to remember that the 80 is not considered a hard core off road rig like others.
I do not think 10/90 up/down is really a good set up for an 80 personally
Say you have a 12 inch travel shock that would be like only 2 inches of up travel and 10 inches of down travel.
First off you would be dropping your springs out all the time, ask me how I know this.
The 80 needs to be alittle more balanced than 10/90
Just my 2 cents

 

[Ozdunc]

I run 12" travel shocks with 2" bumpstops. You need this to stop the shock over compressing cause of its greater length over stock.
This gives me 4" up/8" down travel.
I can run fully laden over 4" corrugations at 60mph and the truck feels well balanced and controllable, but still has enough down travel when wheeling through more technical stuff.

If you want to run 35s or bigger you'll need the bumpstops to prevent rubbing. If you want to keep your current shocks you can just space the shock mounts down 2" as well. This will give you full travel but proportionally more downtravel.
Say you had 8" travel shocks with 4"up and 4" down. Adding a 2" bumpstop would give you 2" up and 4" down, losing 2" of up travel.
Space the shock down 2" gives you 2" up travel to the bumpstop but 6" down utilising the full travel available in the shock.

HTH

 

[kbahus]

Thanks for the information guys, I just assumed that up travel was just as important as down travel. With regards to spacing my current shocks down 2", how do I accomplish this? Will I need more lift in addition or can I just play with shock spacing? My real goal here is to run a set of military 37's for summer wheeling but be able to rotate back to my 285's for winter time driving or extended trips (gearing aside). I already have a 2" lift and would like to keep it low if possible.

 

[Nay]

There is plenty of theory on "best" travel. If you want to race baja, you'd better not have mostly down travel. If you want to clear very large tires, you don't want a ton of up travel into the body.

Having said this, these are not independent variables. The 80 is very heavy for a quad coil rig. As you add lift, quite a bit of extra spring rate is typically introduced, which means the coils are not getting substantially longer. Tune your travel to mostly down, and a lot of it will be outside of the range of the motion of the springs. Tune it up, and you may be picking up tires and causing sudden "loading" shifts in relatively moderate terrain.

If you start limiting travel in an unbalanced way, then you will start forcing the vehicle to move rather than the axle - this is not a good thing in general, and particularly not for a such a (top) heavy rig. If I have a 10" travel shock with 50/50 balance, my suspension can articulate equally in 5" of shock travel in either direction. If you have a 12" travel shock that is 4" up travel and 8" down, your suspension can only articulate 4" before one side is forced to do all the work while the other side is now rigid against the body (bumpstop).

If you are looking for maximum suspension balance and greatest predictability of body motion, I would choose the former setup over the latter.

Remember that bumpstops should only perform one function: to keep the shock from over compressing. A longer shock or an eye to eye style conversion will always lead to a longer actual or effective compressed length, meaning you have less up travel available. Bumpstop extensions are needed to protect the shock from bottoming out, but you have to design the shock travel you want first.

This is the main reason I am generally critical of OME suspensions. They use the same shock on the stock height suspension as the medium/heavy, which means you are adding 2.5" of up travel on the taller lifts (and even more if you don't have enough weight to compress the "heavy" coils by 1"). This is fine if you are planning overland travel with a lot of weight, but it is horrible for technical wheeling.

The point is to buy a suspension that is designed for your usage, and make sure that you don't have a component such as an improper shock in the mix.

 

[yOHda]

i had 2" of uptravel of my pickup when i first built it...i was constantly bottom out crawling, let alone hitting anything with any speed. 4" uptravel at least is a much better setup.

 

[Walking Eagle]

up travel=bad
down traved=good
it should be a 90/10 ratio, if you look at any serious off road rig, they have maybe 2-3inches of up travel,if you have all up travel you get very tipsey on rocks

Spoken like someone who knows nothing about it. Nor about math for that matter. 10% uptravel and 2-3 " of up travel. Humm.... so that would be 18-27" of down travel? Those are some pretty massive shocks for an 80 series. Extended length has to be about 5 ft?

 

[Walking Eagle]

Remember that bumpstops should only perform one function: to keep the shock from over compressing. A longer shock or an eye to eye style conversion will always lead to a longer actual or effective compressed length, meaning you have less up travel available. Bumpstop extensions are needed to protect the shock from bottoming out, but you have to design the shock travel you want first.

Yep, bumpstops should only perform one function - keep the tires out of the body. Adjust your shock mounts accordingly.

Seriously though, to answer your questions more directly -

Yes, Nay has a 2" bumpstop spacer - that is included in the FOR kit. It doesn't technically reduce the uptravel. 3" of lift would give 3" more uptravel if everything else is left the same (as Nay says is one of his issues with OME).

If you have 3" of lift, and a 2" bumpstop spacer - you've gained 1" of uptravel.

If you leave the shocks the same, and put a 2" bumbstop spacer (with or without lift springs) you've lost 2" of travel.

With stock springs if you put a 2" bumpstop on and relocate your shocks 2" you've gained 2" extension - lost 2" compression.

With 2" lift springs on, 2" bumpstops, and relocate your shocks 2", you've not changed your uptravel or down travel one bit.

Once you start replacing shocks (which you should doo if you're lifting a truck 2-3" - heavier springs rates will make stock shocks ride like crap). with longer shocks it's no longer a 1 for 1.

Say you put 2" lift springs, 2" bumpstops, and 2" longer shocks on. Uptravel stays the same, but you likely gain some down travel cause the longer shock will have a greater amount of travel. It's not a 1 for 2 deal, but it's not real far off. (1" travel gained for 2" longer shock).

For normal use on a lifted 80, as in one you're doing to daily drive and then wheel on the weekend, I think the guys saying 50/50 w/ 10" total, or 50/50 40/60 w/ 12" total are in the happy medium.

Me, I'm not very medium, but I am very happy. I'm closer to 5" up travel - which gives me as much up travel for normal driving and higher speed dirt as a 50/50 on 10" bilstiens or 11" OME L's, or the like. But then I have 9" of down travel. There are maybe a dozen guys on the board running 14" travel shocks, some on 4" lift, some on 6". It's almost needed on 6" lift just to get a shock long enough to give any down travel w/o redoing shock mounts. It just means I get a little more flex than the guy with 50/50 10" shocks. Only one big draw back. I can't fit 37's as easily. I end up putting my axle at such an angle when articulated that with 3" bumpstops, 4-5" supsension lift (J-springs in rear are 4-5 depending on weight of truck), 1" body lift, and an inch or so fender trimming , I"m boarderline rubbing, vs. the guys with less bumpstop, no-body lift, and no triming.

 

[PKP80]

up travel=bad
down traved=good
it should be a 90/10 ratio, if you look at any serious off road rig, they have maybe 2-3inches of up travel,if you have all up travel you get very tipsey on rocks

In line w/ Eagle, and totally disagreeing w/ you JS! I've seen a rig that runs 2" up and about 12-14" down, looks cool, but that's about it. The rig is useless unless it is in the rocks. Up travel doesn't get the credit that it deserves. 40/60 or 50/50 like the pre-runner guys works really well, key is you have to either have the lift to accommodate (which can get tall if you want to run 14-16" shocks), or start cutting stuff (fenders/wheel wells), I like to cut stuff)

 

[Walking Eagle]

key is you have to either have the lift to accommodate (which can get tall if you want to run 14-16" shocks), or start cutting stuff (fenders/wheel wells), I like to cut stuff)

Throwing a 1" body lift on helps with clearance - I'm runn'n 14" XL's which are 36" extended -monsters - real big body to get in the way of everything. Gets you some clearance above the stock rear mounts and some clearance at the brake booster in the front. I've found cutting wheel wells leads to fires, which leads to visits from the fire department, which leads to redoing a whole interior, which leads to truck being down for 4-5d months!

 

[js93cruiser]

Spoken like someone who knows nothing about it. Nor about math for that matter. 10% uptravel and 2-3 " of up travel. Humm.... so that would be 18-27" of down travel? Those are some pretty massive shocks for an 80 series. Extended length has to be about 5 ft?

i keep forgetting you guyes dont like rocks

 

[js93cruiser]

In line w/ Eagle, and totally disagreeing w/ you JS! I've seen a rig that runs 2" up and about 12-14" down, looks cool, but that's about it. The rig is useless unless it is in the rocks. Up travel doesn't get the credit that it deserves. 40/60 or 50/50 like the pre-runner guys works really well, key is you have to either have the lift to accommodate (which can get tall if you want to run 14-16" shocks), or start cutting stuff (fenders/wheel wells), I like to cut stuff)

i am talking about serious crawling, not like the 6 inch rocks most on here play on, up travel sucks, look at alot of buggys, they all have between 2-5 inches of up and all down, it keeps you stable.

 

[Ozdunc]

If you start limiting travel in an unbalanced way, then you will start forcing the vehicle to move rather than the axle - this is not a good thing in general, and particularly not for a such a (top) heavy rig. If I have a 10" travel shock with 50/50 balance, my suspension can articulate equally in 5" of shock travel in either direction. If you have a 12" travel shock that is 4" up travel and 8" down, your suspension can only articulate 4" before one side is forced to do all the work while the other side is now rigid against the body (bumpstop).

If you are looking for maximum suspension balance and greatest predictability of body motion, I would choose the former setup over the latter.

Whilst agree totally with what you said, you could argue that from completely the opposite way.
Your 5" travel shock can only droop 5" into an 8" hole before one side is forced to do all the work whilst the other side is hanging uselessly in the air.

kbahus, you need to look at spring ratings and the load you are going to carry as well as the shock lengths, and of course what you want to do with the truck. I don't rock crawl like Nay does, but my rig will go anywhere I point it fully laden over technical terrain and thousands of miles of corrugations in the outback.
4" up/ 8" down works well for this. To much up makes a fully laden truck too tippy.
I don't strictly need 8" down, but its nice when you go for a play

 

[dafun1]

One thing to point out is that 2" of lift with 2" bumpstop and 2" of either longer shock or spaced shock does put you back to an original shock travel amount, but it spaces that "original amount" downward 2", thus the potential need for brakeline extensions. I agree that 10 up and 90 down is completely impractical for such a heavy rig that doubles as a family ride for most. Very few folks on this site have an 80 that is a dedicated trail rig that they tow to the trail. They are amazing vehicles, but I would go with something lighter or fab a buggy if I was just going to tow it to run rock.

 

[Ozdunc]

Good point about the brake lines, with a spaced down shock mount that 2" lift becomes a 4" equivalent for the lines on full droop.
Check the handbrake (ebrake) cable as well.

 

[dafun1]

And I see you haven't flipped your 2nd vehicle yet Js93. The three link must be holding up this time around. And does the 93 stand for your birth year buddy, because you sure act your age. "the 6 inch rocks most on here play on"... who says junk like that? Ahh an 18 year old . We were all young once . Keep up the arrogant and overconfident banter and see where that takes you though bud !

 

[Mark W]

We have had a couple guys join us for the Alaska Cruiser Trek who thought that setting their rig up with minimal up travel was a smart thing to do. Keeping the entire group moving at less than 5 mph as we headed 35 miles down a river to the nights camp was... infuriating at best. Any faster and the "rock crawling" suspensions bottomed out constantly. The guys who run this route with me routinely can average about 17 mph and hit speeds of 30 in a couple of places.

You have to decide how you are going to use your rig before you decide how to set up just about any part of your suspension. And if you set it up for very narrowly found conditions, don't interpolate that to a wider use scenario.




Mark...

 

[Walking Eagle]

i keep forgetting you guyes dont like rocks

i am talking about serious crawling, not like the 6 inch rocks most on here play on, up travel sucks, look at alot of buggys, they all have between 2-5 inches of up and all down, it keeps you stable.

Now we're 2-5" up rather than 2-3? So at 10/90 that's 45" downtravel?

Check out a KOH rig once. Tell me how much up travel they have. If it was 2" as Mark W says, the race would take for ever cause no one could go over 5mph. I'd listen to him before I listen to me.

Back to the OP. Got side tracked answering the question you asked rather than giving the answer you need.

If you want to run 37's and not get into a bunch of custom stuff, get a lift w/ shocks tuned to match, then you don't have to worry about thinking if you have lost up or down travel, it just works. At the risk of bursting into flames - Just copy what Nay has and you'll likely be happy. It'll still ride and drive fine on the 285's, though they'll look tiny in comparison.

 

[CreeperSleeper]

i am talking about serious crawling, not like the 6 inch rocks most on here play on, up travel sucks, look at alot of buggys, they all have between 2-5 inches of up and all down, it keeps you stable.

I can see where you are coming from. If you are dropping a tire into a hole (or between rocks), you want there to be enough droop to keep the body level. Also, too much up travel will "lower" your belly and may make issues when climbing.

However, you are mistaken in your math. Too little up travel and you will get tippy when climbing. This is a posser shot, but it shows what I'm talking about:

I am on my bumpstop on the drivers front and the pass rear. If I would have had more up travel, the body would be more level than it is.

The point I'm trying to make is the "optimal" suspension depends on how you drive and where you drive. Personally, I would like to get as close to 50/50 as I can for the wheeling I do. However, there are more important things than up and down travel!

Oh and there are quite a few of us that play on rocks... It may just be that you don't know as much as you think you do. I have learned that there is always something to learn!