Dallas J

iTrader: (1)

Sounds like this weekend was just as good as last weekend. Wish I could have done both for sure.

Listening to the launch is an interesting reminder how stock the engine is for STU compared to SM. Feels like playing old Gran Tourismo when you do a few mods in how fast it neutral revs.(edit, skip to 19sec for launch start)


What do you guys see for accel G's?

Jim3142

iTrader: (2)

Not sure. I don't calibrate SoloStorm for G loads, but I've done the spreadsheet thing for theoretical use and at the car's current power, I'm around .65-.70 G's. I haven't tuned for 93 and I still have some power mods to add this summer (planning to stay on 91 for convenience).

4wd4me

Nice to catch up with you again as well! and super fun racing as usual.

You've inspired us to rethink our setup a bit and raise the ride height. Our car simply refuses to take a set on bumpy concrete and plant itself properly in transitions or sweepers, so much oscillation it's crazy. I'll have to post up some video and compare our in-car to yours... hop induced understeer sucks ;-)

Dallas J

iTrader: (1)

Im going to be doing some testing to see if its possible that big swaybars might be a culprit on my car for the on throttle hop. Not sure what you guys run for bars, but in my case Im starting to wonder if it could be a cause. Will be trying some crazy rates and tiny bars as a test in the near future.

4wd4me

We currently have the stock front, drilled stiffer, and a hotchkis rear on soft, and higher spring rates; we've tried the opposite as well (Whiteline bars, 150lb softer springs)...

I'm (mostly) convinced now it's because we've had the front of our car too low from day one, with the front roll center in the dirt.... but I don't have any math to back that up. We've got our spring wheel rate numbers, bar rates, roll stiffness front and rear, NF front and rear, etc... but is there a handy formula\modifier for the effects of ride height, specific to our chassis? Something like, if your roll center is is ideal it's a value of 1, and then depending on ride height that value changes and modifies the roll stiffness calculation, somehow?

Our original setup guy was always about keeping the CG low, with the bumpy Packwood, and Crows, and Lincoln to an extent, I'm not certain it's doing us any favors though.

I was also wondering if NF played into it, or the delta between the front and rear NFs... but, over the years we've moved that delta around a lot as well, from 0 (same NF f/r), to similar to stock and then up to 0.5 stiffer rear, and in talking to Jimmy it seems he's running an even bigger delta front to rear, and yet his car looks pretty good over them bumps

:-?

Dallas J

iTrader: (1)

If we think about the root cause of hopping, something is causing an un-dampened reaction. For a while I thought it could be caused by the tires itself but I'm not sure I feel that way anymore. Seems some experts expect the tires to be adequately dampened and pretty stiff. If the rear is a primary source for it (in my case, with high front RC, I think this is correct) then the rear tires really probably aren't the culprit.

So that leaves Swaybars and geometry conditions. Swaybars are an easy test, disconnect, does it still do it? I should have thought of this in crows where we got hopping on power. The effect could be additive also and caused by multiple things, but at least I would have seen one of the variables.

The next option would be geometry conditions. There I think 2 things could be causing it. One would be RC is so low that the outside is being driven down (anti-jacking effect) due to geometric conditions. That would probably be more seen up front where RC drops about 3:1 with ride height. Rear RC when dropped at my ride height may only have the lower control arm angled up 1/4" (just barely). That shouldnt cause that much effect though. RC should be roughly ground level, though will be working on rear geometry here really soon.

I also suspected squat geometry but the rear trailing arm, even lowered, has a lot of anti squat built in. So much so, at stock right heights that angle must be pretty steep. Is that a rally thing maybe? Go look at the angle of yours, its pointed up pretty good. So thats not really an issue.

Circling back to all the options, I would guess Shocks just not adequate for your rates, Front roll center, and rear swaybar. We do know going softer springs and higher ride height seems to fix things, but thats not a reason to not keep trying to solve it with stiff springs and low ride heights.

MrAWD

I would also think that not enough dampening would cause this...

Dallas J

iTrader: (1)

Wasnt that the first things I put down

Though, there does seem to be something else really going on. Not everyone with hop is going to be equally excessively under damped. In crows, I did try to crank my shocks up close to max with starting around the middle, hop barely changed.

Another though, I use to get corner entry hop and that is now completely gone with my uprights fixing RC. The hop I see now is fully felt in the rear outside bucking down on heavy accel loads in corner exit. Unfortunately I dont know if I'll be able to root-cause the issue because I dont have enough accel traction on our normal Asphalt compared to the ultra high grip of crows. But I bet if I raised the rear the hop would reduce.

MrAWD

You really expect me to copy first part and paste it, than do it again with the last one?? Man...

MrAWD

On a more serious note, there are two parts of the shock movement that could cause this. One is that we've mention above for not having enough rebound and allowing wheel to drop down faster than it should. The other side is when wheel is going up over the bump - too much of low speed compression (and/or too high level for high speed compression adjustment, depending of the shaft speed) would raise the car and create another body movement that you don't want to have there either.

LetsGetThisDone

iTrader: (1)

I'm sure the car loses anti-squat as it is lowered though. I think that because raising rise height seems to fix it, that definitely points to a geometry issue.

Jim3142

iTrader: (2)

I'm using the stock FSB but have my Cusco swaybar brackets set to soft (so something like 85% of the stock bar's stiffness), and a Whiteline 26mm RSB on full stiff, springs are 600f/900r. In October of last year, I went to full stiff on the rear bar with 700f/1000r spring rates and it was very willing to rotate (would oversteer easily with a small lift and a slight pitch into a corner), but handled bumps badly and corner exits would have the inside rear pogo up and down as it you applied throttle. Mack Tsang hopped in my car for an event when the car was setup this way, here's the video (note how badly the car was hopping):
We swapped back to Bridgestones to start this year (with the softer rates) and still had the hopping over bumps and on corner exit, but not as bad as before - really the big change was going back to Nexens, so I suspect the stiffness of the tire also plays a big part in all of this (assuming that the Nexens are a softer tire, in terms of tire stiffness). Though the hopping isn't completely gone, the car does handle bumps a ton better and doesn't have trouble getting the inside rear down on power.

My friend Ric got pictures of run groups 1 and 4 from the Crows Tour: /

4wd4me

some in-car from the pro, I had to over correct on the first turn-in as grip had improved exponentially. Watch my head bobbling around, that shows the hop and general ungoodnesss of it all...

Dallas J

iTrader: (1)

So much steering wheel shuffle!

Definitely looks like hop on entry vs my hop in crows only on exit. Would lead me to believe RC is certainly contributing.

Ayoustin

iTrader: (2)

Was at the track this weekend and noticed that on my RC1 tires I'm getting hop on corner exit in some corners. I'm still on factory diff and mustache bar bushings which I'm wondering if they're playing much of a part in the hop.