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Old 04-15-2016, 06:50 PM   #1
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Default Cut the bump stop or not



Here is a good picture of the car sitting on the bump stop in a high-c compression turn. Considering cutting the bump stops in half to get a little more usable travel. Has 550# springs on the front, might need a bit more rate it seems. Will have to re-evaluate that depending on what it does with smaller bump stops. Car is 1900#


A: Cut the bump stop and leave spring rate alone and reevaluate afterwards

B: Leave the bump stop long and add spring rate

C: Cut the bump stop and add spring rate



Car generally sets FTD unless there's a kart, or is within a tenth or two. It's pretty sorted for the small course, as is. Just not sure if I'm leaving Gs on the table with the long bump stops. Appreciate any input. It's a lot stiffer and much lower CG then a miata but the geometry is pretty much the same.
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Old 04-15-2016, 07:23 PM   #2
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What suspension is it on? Its front heavy right? something non bp in there?

Missing too much info.
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Old 04-15-2016, 10:14 PM   #3
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50/50 on the scales with me in it. 460whp lsx. FM vmaxx extreme track
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Old 04-15-2016, 10:49 PM   #4
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You're giving up lateral Gs by not having good shocks in it
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Old 04-15-2016, 11:15 PM   #5
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Yup, put something decent in there that can dampen a higher spring rate properly.

If you put this thing on a road course with a bumpy long sweeper, you'd feel it bouncing off those bump stops. More travel won't help, it'll just lean the car more before it hits them or binds the springs.
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Old 04-15-2016, 11:29 PM   #6
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Damping isn't an issue on the autox course, it isn't bouncy in the least. Everyone loves to knock these shocks, but they work. These springs can't bind with the travel available, fortunately, and more travel does help, because you need more force to continue to compress the spring. I do understand that on a maximum effort corner, it's still going to (and should) sit on the stops, but it's the quick transitions that I'm looking to keep it off the stops on.

The road course is indeed going to be a different animal and will tackle that in a few weeks when the first semi local NASA event starts this year.

I cut them back to 26MM from 50mm (-3 donuts). The goal is more fluid short transitions. We'll see how it goes tomorrow, if I don't like it I have an extra set of stops that I might do -1 or -2 donuts on.


Wheel rate is lower then expected because of the negative offset of the wheel/tire, plus it doesnt lean nearly as much as a miata, a combination of the far lower CG and the wide track/negative offset. It barely has 2 degrees of camber in it now to keep the pyrometer happy, I had started at 3.8 and have dialed it back 3 times now. It's certainly a learning experience, because it doesn't behave like a miata, but it feels like one.

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Old 04-15-2016, 11:34 PM   #7
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Better shocks, custom 15x11 wheels, and light brakes are on the winter build agenda. Right now I just need seat time and to save money.
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Old 04-16-2016, 12:04 AM   #8
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I'm out
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Old 04-16-2016, 04:17 PM   #9
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Just remove the bump stops, you don't need them. Maybe softer springs too? 550 seems a bit high.
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Old 04-17-2016, 01:37 PM   #10
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Uh, no.

Second place this weekend behind my friend's FM dwarf sprinter, which is ok. Wasn't a very fast course. Bump stops were definitely a positive change, am going to take 1/3 off the rear stops to match.

It needs more spring in the front, not less. Maybe 700#.
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Old 04-17-2016, 04:12 PM   #11
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Sorry, I wasn't being helpful. I was joking, since I run 750/550 on my street car, and I feel I need a bit more spring.

Your car is awesome, I should have just complimented you. That must be such a blast to drive!
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Old 04-18-2016, 10:57 AM   #12
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cut them. not going to put a wheel into the fender on that car.
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Old 04-18-2016, 11:02 AM   #13
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Another reason to go Exocet.. no need for damper position sensors
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Old 04-18-2016, 12:09 PM   #14
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Quote:
Originally Posted by thumpetto007 View Post
Sorry, I wasn't being helpful. I was joking, since I run 750/550 on my street car, and I feel I need a bit more spring.

Your car is awesome, I should have just complimented you. That must be such a blast to drive!
It's just the MO around here when asking for suggestions to or not to do, that people suggest spending $2k on shocks/springs like it's the only reasonable course of action. Well, duh, if that was in the budget, it would have been an option

Miata springs (and alignments) dont really translate well to the exocet because the CG, wheel offset, and shock positions are all way off - but I do think it needs more spring in the front, perhaps all around.
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Old 04-18-2016, 03:47 PM   #15
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Quote:
Originally Posted by Dietcoke View Post
It's just the MO around here when asking for suggestions to or not to do, that people suggest spending $2k on shocks/springs like it's the only reasonable course of action. Well, duh, if that was in the budget, it would have been an option
If you have an LSx-powered Exocet, attempting to convince the general population here that a $1700 set of shocks is "out of the budget" is going to go over like a lead balloon.

The only real answer to your question is "it depends". I know very, very experienced autocrossers that rely heavily on bumpstop tuning in applications similar to your own. I know others that tune purely on spring rate and only use the bumpstop to prevent shock damage. Both theories can work depending on the exact application, but you're going to have to forge your own path. Should you cut your bumpstops? Maybe. Will it increase grip? Maybe, maybe not. Will it make the car better in transitions? Maybe, maybe not.
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Old 04-18-2016, 07:18 PM   #16
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The change was good, oddly it was hitting the rear bumps before the front which felt funny in the car, which is why i'm trimming those some to match.

All things are relative when you talk about budgets. There isn't anything particularly expensive on the car. Lots of china, junkyard, used, etc. It works well for what it is, and its bonkers in a straight line. Eventually it can very easily become $1000 more, $1500 more, $700 more, $1700 more, etc etc etc. Seat time is what I need right now, because it's hard to quantify the usefulness of a change until you've figured out what you've got - and I'm not there yet.
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Old 04-18-2016, 11:05 PM   #17
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If the rear bumpstops engage before the front you should get some oversteer. I'd try trimming the rear and letting the front slightly longer. This is essentially reducing rear springrate until the bumpstop engages.
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Old 04-18-2016, 11:09 PM   #18
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Add about 300 pounds to your spring rates and you'll be happy.
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Old 04-19-2016, 09:32 AM   #19
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Quote:
Originally Posted by wannafbody View Post
If the rear bumpstops engage before the front you should get some oversteer. I'd try trimming the rear and letting the front slightly longer. This is essentially reducing rear springrate until the bumpstop engages.
When the bumps hit, it gets instantly loose. You can feel it progress into the oversteer. The first time it did it, I was took by surprise and ended up in the grass. Hence the need to match the rears to the front.

Leafy I think that may be a viable option, if only to test for a weekend. Maybe 850/500 or so (Already have some 500s laying around), see how it likes that, or if the shocks will handle those rates reasonably. I dont know if anyone has really put a proper race spring on one of the top tier vmaxxes before.
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Old 04-19-2016, 12:02 PM   #20
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Quote:
Originally Posted by Dietcoke View Post
When the bumps hit, it gets instantly loose. You can feel it progress into the oversteer. The first time it did it, I was took by surprise and ended up in the grass. Hence the need to match the rears to the front.

Leafy I think that may be a viable option, if only to test for a weekend. Maybe 850/500 or so (Already have some 500s laying around), see how it likes that, or if the shocks will handle those rates reasonably. I dont know if anyone has really put a proper race spring on one of the top tier vmaxxes before.
Around MT.net we usually put proper race springs on proper race shocks. YMMV.

In for science. That car looks beast-mode. I'm curious what you can eek out of the Vmaxxxxxxxxes.
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