Making front coilovers, cutting out MORE than 40mm from the strut casing?

[teh luckinator]

I asked this question on club4ag but I never really got a solid response.

Has anyone done this?

I'll be in the process of making coilovers, Ground Control sleeves and springs, AGX's, etc. I've always seen people cut out 40mm from the original strut casing, AND THEN put a 20mm spacer at the BOTTOM, so that it sits flush with the top of the strut.

So I'm wondering, instead of having a 20mm spacer at the bottom, why not just cut out that extra 20mm from the strut casing and have NO spacer? I'm by no means a suspension expert, I can barely put shit together, but thinking about it...

Spacer at the bottom means shock is raised 20mm
Efficient shock travel will be raised 20mm

So if the spacer is eliminated, that means it'll sit lower, and the optimal shock travel will be lower. This would mean that the car would have to sit lower in order to be in that range, correct?

I'm looking for someone who's actually done this, but please people, chime in if you can.

For reference, this is how my car sits currently:

http://everythingisbeast.files.wordpress.com/2010/04/img_14221.jpg?w=600&h=400

http://laurante.files.wordpress.com/2010/04/img_4180.jpg?w=497&h=372

Stock non-cut strut casings in the front, NO springs, so it's just sitting on the shock haha. I'm trying to achieve this height and still have decent shock travel... if that's possible.

Cheers!

[fantapants]

pm slydar, or wait for his response here but im you wont be able to get the suspension into a useable stroke range with the casing cut that short....

[ke70dave]

bloody hell thats low.

problem might be that when you cut that much off, you are gonna need a monster RCA to get the LCA to sit where it should, otherwise you are gonna have some epic bumpsteer.

im almost finished my ae86 coilovers, i bought them already cut/welded, and they fit ae92 shocks (~330mm) in without any spacer....so i dunno if they are gonna be alright or not. i got some 40mm RCA's, only cause they were cheap...

this is my first experience with ae86 gear, but it cant be as low as the s13 stuff that is in there.

[Sam-Q]

ok so the new dampner has a 60mm shorter body correct? by memory I worked out that for every incriment the car is lowered the dampner body length should be shortened 2/3 the amount to keep the valves in the middle. Your car at a guess looks 150mm lower, lower than unsagged stock that is. So you need a dampner body thats 100mm lower but I could be getting mixed up here. Either way I can't see 40mm out of ideal in either direction being much of an issue. Afterall if you look at off the shelf big name suspension packages they use the standard casing and shaft length with springs that are about 50mm lower, although this could be a cost cutting thing. If I could be bothered and you want me to I will work it out again to make sure I am giving the right figures.

ke70dave: I am sure you already know this but I will explain for the others reading; I have found long RCA's are either not available in decent thicknesses or they just don't fit. As a guess I would say they are Tarago front wheels, not sprinter so 14". This would mean with a blocked off grease nipple the max thickness is about 40mm or so, I am a bit unsure as it's been many years since I was playing with that stuff under my car. One other thing no change in height causes bump steer in our type of cars, well unless you have stuffed it all up with S13 gear that is. That's because bump steer is caused by different arc's of axis between the lower control arm and the steering arm's. What you are talking about though is the effect of the front sideways roll center being pushed massively downwards, that's some kind of bad Voodoo stuff that I don't get.

[Jonny Rochester]

I once did what you surgest and cut 60mm from the strut rather than just 40mm + a 20mm spacer. The negative effect this has is that you have reduced droop. When I jacked the front of the car up, the front wheels would hardly droop at all from normal position. On the bumpy roads in the country, the front wheels may leave the ground for a moment over a crest or bump, which is not good for grip. And if you lower the car so much that you do have some droop, then you have other issues with the car being so low. Legal ride height in Australia is 100mm off the ground. Also bump steer is effected by the angle of the lower control arm...

[Sam-Q]

Also bump steer is effected by the angle of the lower control arm...

how? I don't think it is

[wntdae86]

ackerman principal google this one boys ... bump steer will take over on this for sure

[Sam-Q]

the offet acherman arms are from factory offset by the steering rack being shorter than the lower control pivots by the same proportial degree. I think your wrong.

[wntdae86]

when the car is low down like that everything will change a few degrees ...
low control arm will go up a bit there for makin bump steer off the chain

[wntdae86]

Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii. It was invented by the German Carriage Builder "Lankensperger" in 1817, then patented by his agent in England Rudolph Ackermann (1764–1834) in 1818 for horse drawn carriages. Erasmus Darwin may have a prior claim as the inventor dating from 1758. [1]

A simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. The steering pivot points are joined by a rigid bar called the tie rod which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult to arrange in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles

[wntdae86]

Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed manoeuvres. Some race cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low speed maneuvers.[2]

[Jonny Rochester]

how? I don't think it is

The reason you have RCAs (roll centre adjusters) is probably more to do with bump steer than roll centre.

With front end geometry, it's complicated, everything effects everything. You can't make one adjustment that does not effect everything else in at least a small way.

To make it more complicated, the standard car does not come with zero bump steer. And it does not come with perfect theoritical ackermann steering. Camber and caster and toe also change slightly when the wheel moves up and down.

On a standard KE70/AE86, when the lower control arm moves from its normal angle towards horizontal (when under load) it also causes the wheel to toe out. I call this "negative bump steer" because I havn't found the propper term. It causes slight understeer and makes it safe. When we talk about bump steer in a bad way, its because the vehicle roll causes oversteer.

If you lower the car so the lower control arm is horizontal, and goes past that angle when loaded, then you may get some bump steer (the bad kind). Your messing the factory geometry in any case.

[teh luckinator]

i always thought lower meant more bumpsteer. and i thought rcas were to correct that D=

less droop is fine, roads aren't bad here anyway. jonny, besides that, any other comments as to cutting 60mm? was it beneficial at all?

btw i want to post this car here for the sole reason of the fact that i freaking love it:

http://laurante.files.wordpress.com/2010/04/chicago-914.jpg?w=497&h=372

WEEEE!

[Frak]

I have been running 60mm cut on my struts for probably 10 years(maybe more), I have set the ride height up so that I have 2/3rds of the piston travel for compression and 1/3rd for rebound(I am running 48511-AE031), it is more important for me that I DO NOT runout of compression travel, if I run out of rebound, the wheel will become lightly loaded or even leave the road(I generally only have this on tight corners, such as round abouts) If I were to run out of compression travel the spring rate will instantly go to infinity which could have DIRE consequences in handling(snap oversteer/snap understeer). If I am cornering hard at the track and the inside front wheel leaves the road, it's lightly loaded anyway and isn't doing much. I run 45/50mm(can't remember) RCA's.

[teh luckinator]

thanks frak!

just convinced me to do it haha. where the hell am i supposed to get 50mm rcas @_@ i have... 35mm (?) ncrcas from t3, stock lca so i'd like to keep them to get that extra track and negative camber.

[ke_70]

I have been running 60mm cut on my struts for probably 10 years(maybe more), I have set the ride height up so that I have 2/3rds of the piston travel for compression and 1/3rd for rebound(I am running 48511-AE031), it is more important for me that I DO NOT runout of compression travel, if I run out of rebound, the wheel will become lightly loaded or even leave the road(I generally only have this on tight corners, such as round abouts) If I were to run out of compression travel the spring rate will instantly go to infinity which could have DIRE consequences in handling(snap oversteer/snap understeer). If I am cornering hard at the track and the inside front wheel leaves the road, it's lightly loaded anyway and isn't doing much. I run 45/50mm(can't remember) RCA's.

would of you gone 60mm or 40mm=20mm if you could do things again?

[Frak]

would of you gone 60mm or 40mm=20mm if you could do things again?


Personally I'd go the 60mm cut each time, to be honest I have never felt a negative, even when driving on Adelaide's crap third world roads, sometimes I can feel it lift a wheel but it has never felt dangerous. I'm running AE831's in the rear which have a little more droop, I have had it lift rear wheels as well and again when it has it has never felt dangerous. I can understand fully why some guys want more droop(suspension!) and understand why manufacturers put so much on factory cars to aid stability etc I do like my cars low tho ;)

[AJPS]

Personally I'd go the 60mm cut each time, to be honest I have never felt a negative, even when driving on Adelaide's crap third world roads, sometimes I can feel it lift a wheel but it has never felt dangerous. I'm running AE831's in the rear which have a little more droop, I have had it lift rear wheels as well and again when it has it has never felt dangerous. I can understand fully why some guys want more droop(suspension!) and understand why manufacturers put so much on factory cars to aid stability etc I do like my cars low tho ;)

I went with 60mm too.

I run bilsteins with softer (7kg) springs. I run helpers too.

So its pretty low, has stroke both ways and doesnt pick up wheels.

[ke_70]

what the positive then frak?

they way i understand is it just lets you go lower is it all it does?

[Frak]

The positive for me was, at the ride height I am running I have a lot of compression travel, due to reasons stated above with regards bottoming out and increases in spring rates.

I run 6.7 springs with no helper and the spring is captive.

[marvis]

Sounds like a winner.

AJPS do 40mm RCA's..

[takai]

I run a 50mm cut out of mine, with Tokicos. I found a 60mm cut simply meant that i didnt have enough spring height to maintain the 100mm IPRA height limit. At the time i had 2 options, 1 to cut less out the next time around, or 2 to buy longer free height springs in the same rate.
My hand was forced by bending the AE86 stub axle, so i moved on to XT130 struts and cut less out.

[Jdm-Mcc]

I love when all the bull shit gets dropped when the fellas in the know step up :) frak is pro.

[Frak]

Different set ups for different people/applications, what I run suits me, it may not suit someone else's driving style or application, so don't just take what I say as gospel, the best is for everyone on this forum to add their own point of view then as a group work out the best way.

[Sam-Q]

thanks frak!

just convinced me to do it haha. where the hell am i supposed to get 50mm rcas @_@ i have... 35mm (?) ncrcas from t3, stock lca so i'd like to keep them to get that extra track and negative camber.

I suggest you get rid of the NRCAs unless you have a specific reason for keeping them like Takai

[AJPS]

I suggest you get rid of the NRCAs unless you have a specific reason for keeping them like Takai

What sam said

[marvis]

What Dave said.

[takai]

I suggest you get rid of the NRCAs unless you have a specific reason for keeping them like Takai

Yeah, if you arnt forced to keep the stock LCAs then ditch them for longer ones and use standard RCAs. Also depending on how hard your suspension is you dont need to make up the entire suspension drop in RCA height either.

But hey, if you are asking about these sort of questions then calculating effective wheel rates and change in ackermann is probably a touch beyond where you are at now.

[blair]

The positive for me was, at the ride height I am running I have a lot of compression travel, due to reasons stated above with regards bottoming out and increases in spring rates.

I run 6.7 springs with no helper and the spring is captive.

200mm springs?

Would you have more stroke if you could, or less? or is what youve got just right?

Trying to figure out the neg's and pos's of the amount of stroke a shock has, and where it sits in that stroke range accordingly! :)

[Clinton]

http://everythingisbeast.files.wordpress.com/2010/04/img_14221.jpg?w=600&h=400

cool pic lol

[boost+k]

i have 60mm cut out of mine.... IMO its too much, but that will depend on tyre size and how much lock you run etc

i have to run quite big bump stops to stop the tyre contacting the inner guards at full lock under compression, also have also moved the brake lines and mount to clear the tyres

[Low Style]

AJPS do a 50mm/40mm RCa as well (Dont know if it helps)

[Sam-Q]

i have 60mm cut out of mine.... IMO its too much, but that will depend on tyre size and how much lock you run etc

i have to run quite big bump stops to stop the tyre contacting the inner guards at full lock under compression, also have also moved the brake lines and mount to clear the tyres

I read this as being so wrong. Firstly what has the length of the strut have to do with bottoming out? Did you use a bump stop with a linear compression rate?

[assassin10000]

I'm reading 'bump stops' as steering stops... given the description.

Andrew

[Sam-Q]

now that I re-read it yes it sounds right, pretty obvious actually

[blair]

They are still all things related to how low he is running and the amount of lock he has. neither of which are affected by 60 vs 40 mm cut!!??

[Sam-Q]

m point exactly

[boost+k]

im talking about bumpstops for the shocks

the issue is clearance in the inner guards... the more lock you run the worse this contact becomes, when you cut 60mm out and do the dry test to set the bumpstops ie, no springs, no bumpstops, car on ground to test it all clears while turning and set the ulitmate lowest compressed bumpstop height you will find that you need quite big bumpstops...
(if the strut casing was longer the bumpstop would be smaller and you would still get decent droop) so 40mm is about a good middle ground IMO

you could try and overcome this with neg offset wheels and flares or small tyres but then theres ground clearance issues