EP3 Suspension -> Inverted tie rod question.

[Chi]

2.5-3" is quite a fair bit.

I would highly recommend the inverted tie rod ends while adding some decent camber especially if you are wanting to track later on.

But be warned, DC5 and EP3 tie rod ends are different, so be careful when you order a set and specify which ones you need.

[BRU51N]

If you lower it by more then 2" you may as well need roll center adjustment ....

what is the purpose of the roll center adjuster? besides the bump steer and steering correction.. are there any other negative effects without it?

its mainly a daily car so i dont intend to worry about things for track.

[tinkerbell]

i undeleted your post as i would like to know the answer to your important question too!

[nippon]

do dc5/ep3 steering arms have a slight angle stock?

[m0nty]

what is the purpose of the roll center adjuster? besides the bump steer and steering correction.. are there any other negative effects without it?

its mainly a daily car so i dont intend to worry about things for track.

A RCA is fitted to the bottom of the hub assembly. If you excessively lower a car the LCAs will be in a similar angle to the tie rods. Having RCA will increase the travel of the LCA like the pictures below. The concept is similar to the te rods. It also helps reduce body roll as the suspension strut is under more consistant and even load.


Standard Height


Lowered without RCA fitted


Lowered with RCA fitted


As you can see in the pic the tie rods will still have an incline. Adding the inverted tie rods removes bump steer effect.

[ChargeR]

A RCA is fitted to the bottom of the hub assembly. If you excessively lower a car the LCAs will be in a similar angle to the tie rods. Having RCA will increase the travel of the LCA like the pictures below.


Standard Height
http://www.jsracing.co.jp/js3/img/ro...eradj/FIG1.jpg

Lowered without RCA fitted
http://www.jsracing.co.jp/js3/img/ro...eradj/FIG2.jpg

Lowered with RCA fitted
http://www.jsracing.co.jp/js3/img/ro...eradj/FIG3.jpg

As you can see in the pic the tie rods will still have an incline. Adding the inverted tie rods removes bump steer effect.

Nice pictures guy. Allow me to elaborate.

As you lower your car the roll centre, or the point at which the suspension at a given corner of the car will roll around as the whole chassis rolls relative to the ground, migrates toward the ground as shown in m0nty's pictures above. This movement is particularly extreme in a macpherson strut car such as an EP3 or DC5.

As the roll centre migrates away from the centre of gravity the centre of gravity has a larger moment arm to act on the suspension, because the roll centre and the centre of gravity get further apart, which results in larger roll moments and higher overall chassis roll, which when excessive is undesirable. Particularly on DC5 and EP3 because our camber gain with compression is negligible at the front so excessive roll motion corresponds to a significant loss in camber relative to the road and hence less cornering traction.

In addition to this roll centre adjusters when used on DC5s and EP3s return the lower control arm to a much closer angle to stock relative to the ground. This will significantly improve the amount of camber gain with suspension compression which is nice because as your car rolls you want to gain camber to keep the tyre from rolling over with positive camber.

Roll centres are important for a heap of other reasons including interesting transient behaviour but these are the most significant for an amateur tuner I think. Suffice to say if we can get the bumpsteer and roll centre geometry closer to stock on a lowered car we are making improvements.

Overall, adjusting tie rod outer pick up points, inner tie rod pivot points, and lower control arm attachment locations all change bump steer characteristics, which makes me wary of the one size fits all approach of most of the components available to correct these things on the market.

Adding the inverted tie rods removes bump steer effect.

This is incorrect. Changing the location where the tie rod meets the steering arm on the strut changes bump steer behaviour however it is a big call to claim that it corrrects it in all situations .

[m0nty]

Nice pictures guy. Allow me to elaborate.

As you lower your car the roll centre, or the point at which the suspension at a given corner of the car will roll around as the whole chassis rolls relative to the ground, migrates toward the ground as shown in m0nty's pictures above. This movement is particularly extreme in a macpherson strut car such as an EP3 or DC5.

As the roll centre migrates away from the centre of gravity the centre of gravity has a larger moment arm to act on the suspension, because the roll centre and the centre of gravity get further apart, which results in larger roll moments and higher overall chassis roll, which when excessive is undesirable. Particularly on DC5 and EP3 because our camber gain with compression is negligible at the front so excessive roll motion corresponds to a significant loss in camber relative to the road and hence less cornering traction.

In addition to this roll centre adjusters when used on DC5s and EP3s return the lower control arm to a much closer angle to stock relative to the ground. This will significantly improve the amount of camber gain with suspension compression which is nice because as your car rolls you want to gain camber to keep the tyre from rolling over with positive camber.

Roll centres are important for a heap of other reasons including interesting transient behaviour but these are the most significant for an amateur tuner I think. Suffice to say if we can get the bumpsteer and roll centre geometry closer to stock on a lowered car we are making improvements.

Overall, adjusting tie rod outer pick up points, inner tie rod pivot points, and lower control arm attachment locations all change bump steer characteristics, which makes me wary of the one size fits all approach of most of the components available to correct these things on the market.

Spot on. Cred to you for typing that out. Too hard for me to lock myself away on a Monday at work.

[ChargeR]

Spot on. Cred to you for typing that out. Too hard for me to lock myself away on a Monday at work.

Thanks for the pics . I was going to draw my own but I could not be bothered.

Also it should be noted that m0ntys pics show a double wishbone suspension. The effects with a macpherson strut are even more extreme!

[Chi]

You cannot completely remove bumpsteer, you can only reduce it.

There is too many things that contribute to bumpsteer, from bushings, to suspension geometry to hubs etc.

[TODA AU]

The RCA is added to bring the roll centre closer to the Centre of gravity.
Without the RCA, though the COG is lowered, the roll centre is further lowered.
The RCA lifts the roll centre closer to the new COG.

Per Sam's picture...
A = Centre of gravity
B = Centre of roll

Hope that helps

Edit... I type too slow, ChargeR sumed it up quite well

[tinkerbell]

very glad i undeleted BRU5IN's post now...

great work on the additional info guys

[Elwood]

Chi and Sam..

The T1R ends were recommended by several people who have used them. But i guess its like anything, some people don't like them.

[m0nty]

This is incorrect. Changing the location where the tie rod meets the steering arm on the strut changes bump steer behaviour however it is a big call to claim that it corrrects it in all situations .

Blanket statement. I like closure. Saying Chi can be a little ghey at times is the same. Just say he's ghey and be done with it.

That said, yes I was a little too simplistic in approach.

[Senator]

hi guys, i just got BC RSD installed today and the steer rake angled up, machanics said it'll cause steering to be loose and wont spin back when turning. Will inverted tie rod fix this... still noob