V1 Stretch’s ext. track goblin #386 SS/TC

[Stretch2126]

Are your lower control arms and tie rods level with the cars loaded with normal weight, looks like they are angled up. This may be some variation of bump steer. If they are angled up to start with that will increase bump steer even more as you load the front end under braking.

Unless I have ridiculous caster the steering rod end will always have a little height over the rack. The lower control arm is level but the video angle might give the idea that it’s raised. Keep in might this video I have the shocks stiff since the vibration comes on quicker, same stiffness I race with.

 

[Stretch2126]

As for DS I can’t tell if it’s opposite or parallel hop when driving. Can’t see that fast in real time and I’m really only looking at one wheel.
This is only when tires are sticky and brakes are balanced. Too little valve, fronts usually just lock. Too much and rears will lock. This is what happens when it’s at the right threshold to really get stopping force applied. Also why its amplified on Hoosier slicks.

 

[Gtstorey]

Is this running some sort of race tire?

 

[TravMac]

I've got the same issue - so curious what you find more. I thought it was a loose jam nut or shot control arm heim joint, but I fixed what I could find and still no improvement. I got the solid billet rod end mount kit to see if that helps stiffen the corner too, but haven't tested it yet.

 

[Stretch2126]

I've got the same issue - so curious what you find more. I thought it was a loose jam nut or shot control arm heim joint, but I fixed what I could find and still no improvement. I got the solid billet rod end mount kit to see if that helps stiffen the corner too, but haven't tested it yet.

Let me know if that helps cause I’m grasping at straws here too.

 

[Stretch2126]

Is this running some sort of race tire?

It will do it on any tire really, but I can stop harder on a slick and it comes on faster. My street tire is a falken rt660.

 

[Ross]

Finding a good wheel alignment mechanic is essential to a good handling goblin.

Check that the suspension & steering parts aren't worn out, take your time to get the suspension level, with weights on the seats.
Then get a laser wheel alignment, with a mechanic who is willing to take his time, and get it right.
I like to bring weights to put on the seats, as this helps get the alignment right... but some shops have their own weights.

 

[Stretch2126]

Big update:
I think I have solved my wheel shake. After a lot of research and multiple runs with the car I thought of strengthening the lower control arms. I added a cross brace about an inch or so down from the inner heims since I can flex the arms by hand. Also info from an FSAE right up and friends in the racing industry recommended stiffening the lowers due to the force they take in high braking/traction moments. Also dropping the tire pressure in the front helped mitigate the front from having its spring hop moments. Also it happened when the shocks were stiff, leaving the lowers to take the brunt of the change in geometry. If I really try I can get a very minor wiggle, but it locks up a split second after and that wiggle isn’t trying to rip the front apart. It also happens maybe 1 out of 10 tries instead of every time.


Anyways, went racing in Orlando on A7s and had no hop issue. New setup is 300/400 front to back on springs, and made it very tail happy on lift off, but the loose setup makes it fast. One tenth behind 1st overall (b mod car). Glad to be back in the seat.

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[comegetjoe]

Big update:
I think I have solved my wheel shake. After a lot of research and multiple runs with the car I thought of strengthening the lower control arms. I added a cross brace about an inch or so down from the inner heims since I can flex the arms by hand. Also info from an FSAE right up and friends in the racing industry recommended stiffening the lowers due to the force they take in high braking/traction moments. Also dropping the tire pressure in the front helped mitigate the front from having its spring hop moments. Also it happened when the shocks were stiff, leaving the lowers to take the brunt of the change in geometry. If I really try I can get a very minor wiggle, but it locks up a split second after and that wiggle isn’t trying to rip the front apart. It also happens maybe 1 out of 10 tries instead of every time.
View attachment 53255

Anyways, went racing in Orlando on A7s and had no hop issue. New setup is 300/400 front to back on springs, and made it very tail happy on lift off, but the loose setup makes it fast. One tenth behind 1st overall (b mod car). Glad to be back in the seat.

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It appears to be quite a handful.

 

[Stretch2126]

It appears to be quite a handful.

It was. Also for reference tire temps were definitely over 140 and surface was hot gravel essentially. Running at 2pm in Orlando was warm. I did 180 on one run, but it wasn’t uncommon to slide on that later corner for a lot of people. If anything it’ll make me a better driver but I might try it for a little longer.

 

[Rttoys]

. If anything it’ll make me a better driver but I might try it for a little longer.

this it will do. At least you will know what the car is capable of, that’s for sure.

glad the cross brace worked. I was out of ideas.

 

[Stretch2126]

It’s definitely a relief I didn’t have many ideas after that. Just for open info I used 1” DOM at .083 wall tube.
The good news is I can race again. Bad news is the splitter with 15 inch wheels doesn’t agree on ground clearance on hard brake/turn moments but for the street it looks sweet lol. I made a little scoop for the cutout and I usually have a 7 degree difference between iat1 and iat2 cruising.

 

[Stretch2126]

Ran that the FIRM for the first time today. 300f/400r springs were a little more predictable now but had some trouble getting initial heat in the front. Probably could’ve been a little more aggressive in some spots but the new course got me.

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[Rttoys]

Good run.

 

[Rauq]

I looked back through your thread and didn't see anything on this, most folks run the stiffer spring at the front because it's got a smaller motion ratio than the rear (1" wheel travel in the front is 0.5" spring compression, 1" rear travel in the rear is 0.9" spring compression, or something like that). Do you have the softer ones in the front on purpose?

 

[Stretch2126]

I may have wrote it on a different thread. I switched them just to try it. After doing research on different control arms since I was tackling that for a while I also saw what spring rates cars like lotus and Porsche were using and I figured it wouldn’t hurt to try. It makes the car much more tail happy, but I found that as long as the fronts have temp it doesn’t seem to understeer on throttle as bad. Also on the street I run everything full soft and it’s not as hard on you hitting bumps.
My run this weekend wasn’t as fast as I’d liked but I was struggling with front tire temp. I didn’t corner balance it after swapping so that probably didn’t help either.

 

[Desert Sasqwatch]

Pick up a pair of 350lb springs and try them with the combination you have now. Do a 300lb front and 350 rear (should make less oversteer - less tail happy) then do a 350lb front and 400 rear (same thing, only stiffer in the front). Sounds like you are close to the combination you like best and a little more tweaking of the spring rates could get you to the sweet spot.

 

[Stretch2126]

Pick up a pair of 350lb springs and try them with the combination you have now. Do a 300lb front and 350 rear (should make less oversteer - less tail happy) then do a 350lb front and 400 rear (same thing, only stiffer in the front). Sounds like you are close to the combination you like best and a little more tweaking of the spring rates could get you to the sweet spot.

I’ll have to see if they make some in that range. Would be worth a shot.