Can't bottom out blue/gray rocket ?

[RacerX10]

Is it conceivable that there isn't enough travel on a blue/gray rocket RF to hit the ground with anything under these conditions :

Raised cross member upgrade NOT DONE
Drop spindles installed
RF standard 7" Integra IDA shock w/ Eibach 550# bump spring installed, NO spring installed on coilover.

When I put this on the car yesterday, and jacked up the LR, and the car was fully sitting on that RF bump spring, nothing under the car (cross member, etc) was within 3-4" (estimate) of hitting the ground.

Is this normal ? That bump spring is around 2.25" tall I think .. is that enough to keep it out of the ground ?

My starting C-C measurement was 17.750 inches.
When the car is sitting on the bump spring, the C-C is 15" .. so I'm never going to get to a 3" number, let alone a 4" number.


Just looking for thoughts on this. It may be just fine as is .. it's jut not what I was expecting from reading on this forum and looking at the smash number suggestions I got from rocket.

I put it all on the smasher last night and at the 15" C-C with the standard spring and the bump spring installed, it was at 2500# at that 15".

I wonder how much farther the travel would go after it's hit that bump spring ? Didn't look to me like it had much travel left in it before coil binding.

[TheJet-09]

Starting with the disclaimer that I know nothing about Rockets and have never used a bump spring:

1) If I correctly picture what you did to check clearances (bottoming out), you most likely had little to no tire deflection/squish...in all reality, hard to duplicate a dynamic state while the car sits statically in your garage.
2) That RF C-C statically seems low (17.75"). My car (a Lazer) is 18.5"
3) You don't mention what the standard RF spring rate is, or the preload, but to get 2500# in 2.75" of travel, they would have to be pretty high/heavy.

[RacerX10]

Starting with the disclaimer that I know nothing about Rockets and have never used a bump spring:

1) If I correctly picture what you did to check clearances (bottoming out), you most likely had little to no tire deflection/squish...in all reality, hard to duplicate a dynamic state while the car sits statically in your garage.
2) That RF C-C statically seems low (17.75"). My car (a Lazer) is 18.5"
3) You don't mention what the standard RF spring rate is, or the preload, but to get 2500# in 2.75" of travel, they would have to be pretty high/heavy.

Thanks Jet

Zero tire deflection, I don't have an engine in the car right now so there's almost no weight up there. I hadn't thought of tire deflection at all !

It's the number I got from Rocket on the C-C. The XR1 Rockets are 18.250, but apparently the Blue/Grays are 17.750 <shrug>

I smashed with a 250# spring over the 550# bump spring. They suggested #200 spring, but I'm going to be switching to a steel block motor, and I was worried about burying the front so I thought I'd try that #250 first, then reduce that if it's not getting over like it should.

[TheJet-09]

What's the RF load at 17.75"?

[RacerX10]

What's the RF load at 17.75"?

650 pounds

[billetbirdcage]

650 pounds

Your numbers are off. From what I see your hitting you bumpspring way sooner then the 15" you said.

With the numbers you gave, at ride height you should have 5" of exposed shaft (which I doubt is correct)

17.75 - 15.00 = 2.75" of gap to bumpspring
2.75 gap + 2.25 height of bumpspring = 5" of shaft exposed on a the shock with nothing on it

No way are you getting 2500# at 15" with a load of 650 @ 17.75 with a 250# spring unless the bumpspring is being compressed a ton at 15"

To get that 2500 you would have to be compressing the bumpspring 2+".
650# + 687.5# (250 x 2.75) = 1337.5#

You either don't have 250# spring and is way stiffer or you are hitting bumpspring way earlier then 15", something doesn't add up at all.

With a 17.75 ride height pin to pin, you usually run a 6" shock or least a 6" body to get an extra .5" of travel before shock bottoms out or to get more gap to bumpstop.

[billetbirdcage]

You also said seems close to coil bind? you need to use a 12" spring and an extended travel one at that (coils spaced farther apart not like an old yellow spring)

[RacerX10]

Here's what I'm working with :



I confirmed the 17.750" C-C measurement at ride height.

It's a 12" spring. There's just a bit under 4.5" of travel to the top of the bump spring.

Apologies on my number from earlier, you are correct that it was wrong.

The correct # at 15" is 1819#. I was looking at the wrong info earlier .. went back and checked my "notes" (pictures on my phone)

[billetbirdcage]

It's a 12" spring. There's just a bit under 4.5" of travel to the top of the bump spring.

That's with the spring not on the car so once on the car its likely gonna compress least 2" or so, so that gap is gonna close down to less then 2 to 3" so it's hitting the bump spring before you get to the 15".

At this point not sure what your asking? You probably don't have enough exposed shaft to get more gap to the bump spring so your likely to not bottom the car out as I doubt you can get more then 4" total travel out of the RF with a bump spring in there

[RacerX10]

I guess my question is if all of this looks normal .. this is my first time working with a spring smasher instead of just scales and ride heights

[TheJet-09]

Does Rocket recommend the 200# spring with a bump stop (rubber) or bump spring? Just curious. I'm not sure the steel block warrants going up to a 250#, but I have nothing to base that on. My concern would be the extra rate from the beginning of travel (as you eluded to). By comparison, I run a two stage on the RF, and my effective spring rate until locked out is only 126#...but with an aluminum block. There's only one way to find out though.

[MasterSbilt_Racer]

I guess my question is if all of this looks normal .. this is my first time working with a spring smasher instead of just scales and ride heights

Your 1800# is way too early in travel. (Less than 3"). You can thank Rocket for the short pin to pin measurement at ride. Ideally, you'd be at 3.5" or so with that load. Depends on what the car can travel before you bottom out. I'd guess the car could handle around 4" with drop spindles. So, I'd look for 2400# at 4", 2100 at 3.75" and 1300# at 2.75", for rough numbers. As billet suggested, probably need a short body rf shock.

[RacerX10]

Sounds like I maybe better take another pass at that RF w/ the 200# spring instead of the 250#, and see if it gets the numbers down lower where they should be ..

[billetbirdcage]

Sounds like I maybe better take another pass at that RF w/ the 200# spring instead of the 250#, and see if it gets the numbers down lower where they should be ..

You're bump spring is too tall, I don't think your going to help anything going to the 200# spring. At 15" to have that load your already on the bump spring a fair amount and it's gonna coil bind shortly. I doubt you can even get to 4" without it being coil bound and locked up.

You need a short body shock or something besides a 2.25 tall bump

[RacerX10]

You're bump spring is too tall, I don't think your going to help anything going to the 200# spring. At 15" to have that load your already on the bump spring a fair amount and it's gonna coil bind shortly. I doubt you can even get to 4" without it being coil bound and locked up.

You need a short body shock or something besides a 2.25 tall bump

New shocks aren't an option at this point so I gotta figure out a way to get this set up with what I have

I got two different (actually 4) setups from rocket. The one that is technically for the blue/gray didn't have a bump spring / bumper rubber at all, it's just a straight up #275 and nothing else. My objective with the bump spring was to get over on the RF.

The XR1 setup has the 200# w/ bump spring, but when I ordered the parts to do that I didn't realize that the XR1 has 1/2" more C-C measurement than the blue/gray (not sure that's enough to matter, though?)

[RacerX10]

got the shock up here on my desk, did some measuring

it's 20.250" C-C full extended, and has 7" of stroke available

rocket says 17.750" C-C @ ride height. that means we're using up 2.500" of our 7" to get down to ride height

7" stroke shock - 2.500" to get to ride height leaves 4.500" of stroke available for travel

4.500" of stroke available - 2.500" tall bump spring leaves you 2" of travel before you start getting in to the bump spring

looking at Rocket's 3" and 4" numbers, it absolutely *has to* get into the bump to get the figures they're saying I'm looking for

so I'm starting to think some significant portion of my problem is that #250 spring I put on there instead of the #200 they told me to, and the remainder is my targeting the ride height load instead of the 3" / 4" loads

[billetbirdcage]

got the shock up here on my desk, did some measuring

it's 20.250" C-C full extended, and has 7" of stroke available

rocket says 17.750" C-C @ ride height. that means we're using up 2.500" of our 7" to get down to ride height

7" stroke shock - 2.500" to get to ride height leaves 4.500" of stroke available for travel

4.500" of stroke available - 2.500" tall bump spring leaves you 2" of travel before you start getting in to the bump spring

looking at Rocket's 3" and 4" numbers, it absolutely *has to* get into the bump to get the figures they're saying I'm looking for

so I'm starting to think some significant portion of my problem is that #250 spring I put on there instead of the #200 they told me to, and the remainder is my targeting the ride height load instead of the 3" / 4" loads

BUMP SPRING
Free Length = 2.25"
ID = 1.34" / 34mm
Rate = 550 lbs/in
Travel = 1.19" <===== 2" to bump spring + 1.19 travel of bump = 3.19" total travel of RF and it's solid <--- That's my point

[billetbirdcage]

Put it in the smasher and run it down to about 14.75" and slowly run smasher down like .050 at a time until you see the poundage go up at an extreme rate. Because that's when its solid around 14.56"

Think your gonna find you around 1900# at 14.75" and once you coil bind it's gonna sky rocket and can't travel any more then around 3.25" to 14.5 centers. Changing to the 200 spring will just make the 14.75 @ 1750 but still gonna coil bind at 14.50ish

[TheJet-09]

Looking at your first pic, I'd get rid of the rubber travel indicator (it serves no purpose with that set-up and will probably "remove itself" once under race conditions). It's probably only 1/8" but it sounds like you need all the space you can get right now. And once again, I've never used a bump spring, but does it need the spacer on top like that? Is there anything underneath as well, between the bump spring and the cup? Just wondering if you can't get a little more travel out of what you have.

[RacerX10]

so all of that was premised on beginning at ride height and I think I've read in rocket's notes that they're not that concerned with ride height over there so picking it up to wherever it needs to be to hit the 3 in number might be what needs to happen?

when ppl are smashing springs for the RF are they targeting the ride height number or the 3 in number?