Rear-end is kicking up on truggy, fix?

[Finnster]

So I have been running my Hyper and CRT.5 quite a bit on a local track for practice. I have been noticing quite a bit of kickup of the rear end on my CRT.5 after a hard landing, or an uneven landing where the rear wheels land 1st. Basically the truck then bounces up in the rear and usually loses control. If I land flat its fine.

I'm not quite sure what adjustments to make. The shock oils seem pretty well matched to the shocks, but might I need heavier oil in the rear? If I were to change springs, what direction to go, softer or heavier? (I can make a case in my head for either o_0 )

[rawfuls]

Sounds like the rear end is a bit too stiff (), and so, when you land on the back wheels first, sounds like it can't even compress, so it bounces right up..

Try softening it up, if not, try making it more heavy, since it COULD be compressing all the way down, and rebounding right away..

[BL_RV0]

Sounds like you need softer springs, heavier oil or both.

[rawfuls]

With Softer springs, then heavier oil, doesn't that make the same thing? No adjustment?

[BL_RV0]

Softer springs and lighter oil would be the same or vice versa.

[rawfuls]

Umm... what?

So, if you have Heavy, with Heavy oil, and you swtich to Medium and HeavIER oil, doesn't that even it out, to the same as Heavy and Heavy?

[Snipin_Willy]

Heavier oil is going to increase dampening, but you don't want it to be over dampening. with the same springs you'll see a slower rebound.

Same oil lighter spring will lessen your rebound, but will not affect your dampeneing.

What shocks and springs are you running in the rear?

[rawfuls]

Ohhhh, okay, I always thought it was just heavy + heavy = REALLY Heavy, and that was all to it, thanks!

And sorry for the hijack...

[MetalMan]

How about lighter oil in the rear? If the rear is too stiff that can also cause it to bounce.

[Finnster]

I have the LX1 buggy shocks. Stock LX1 shocks IIRC... maybe slightly heavier. Some coils were cutoff as per the BB shock mod. Set it up a long time ago really. :) 30 or 35 wt IIRC. Maybe I wrote it down in that thread... I should go look for it.

Its not insanely stiff, the (rear) chassis bottoms out from a 18" drop or so.

I don't think I want to go w/ too much a stiffer spring, but not sure if it kicks up due to too much springiness (lt oil) or too stiff a spring. Maybe some other reason...
I'm thinking lighter oil might be the key. It seems a bit slow on the rebound if you push it down. Tuning can be such a bitch...

[Finnster]

Ok Cool, found my setup:

Originally Posted by Finnster

I have the rear LXOne shocks installed in the back, but have not cut any coils. 30wt oil. Still waiting for the F springs to come in to finish it.

Ran it a bit in some rough sandy areas, and the back seems pretty good so far. It does sit a bit high, and I noticed it tended to roll on asphalt were it would hold or slide before. Its def got to come down a bit.

Otherwise I was looking at getting some lighter springs as well. My .5 has the OFNA Ex chassis and small 3S 2500 batts, and @ ~2000g+, may be lighter than some RCM ext chassis conv. Anyway...

I couldn't find a rate for the std yellow LX1 springs. So I tested it and came up with a value of 76 gF/mm (or 4.26lb/in, 0.75 N/mm (trx style).)


Spring rate converter FTW

I also found an HPI Spring that fits well. Now the package rates that as 71 gF/mm (3.96lb/in, 0.70N/mm) but I tested that as well and came up with 59 gF/mm (3.3lb/in, 0.58 N/mm.) IDK why I came up with such lower values than HPI did. My method was slightly crude, but was very reproducible.

Shouldn't matter too much, as I just wanted to get a relative rating to the other springs in that series for the Hellfire. The blue spring I used was softest, while the OFNA yellow spring seems closest to the HPI silver (soft) spring FWIW. The springs are long @ 80mm vs ~72mm for the OFNA's, but both need to be cut down anyway.

GO-Ride: How do you determine what length to cut the springs too? Why wouldn't you cut them short enough to use the stock shock mounting holes? LMK, as I don't want to trim any springs until I am sure on what I am doing. Thanks

Then later I tweaked it:

Originally Posted by Finnster

I took the .5 to the track and was happy with the mods. I used pink jato springs in front, and cut down blue HPI springs listed above. 30wt oil all around.

RCM Mike also took a look at the mod and was impressed by it. Good job on the thumbs up from RCM!

After some discussions w/ Mike, it was decided the oil could go down slightly in the F and up in the rear. I'm going to go for 27.5wt in F, and 35 in the R and go from there. I'll have to take a 2nd look at the yellow springs as well. Race weight is 1950g for my .5.
...

So looks like I have quite soft springs in the back, and I did go to 35 in the rear. Huh...

ok.. So now I'm thinking maybe keep the 35wt or so, and go up slightly on the spring. I want to lose a bit of R traction as its a bit too planted and could slide a bit more in the turns. Chassis does slap a bit much in the back imo. Sound reasonable? The F I have down just perfect, but the rear is not quite there yet.

Thanks for the interweb again. I know I wrote this down on a setup sheet last year, but who knows where that went to...

[BL_RV0]

Sounds like a good fix. Let us know how it does.

[brushlessboy16]

Ian and rawfuls you guys argue like an old married couple.


There could be one of two things finnster
A. the suspension springs too hard and the suspension is rebounding because of the oil being too light

B. the rear suspesnion is too soft all the way around (oil and springs) and is getting seat bounce. (rear chassis slap) and that is kicking up the rear... had the same problem with my revo.

First try upping the preload on your rear shocks, if that doesnt work try stiffer springs and oil.

[rawfuls]

He wishes..