Board logo

Sierra IRS
ProjectX - 10/2/06 at 09:11 PM

Hi guys! I'm new here and just starting a Locost build.

I've decided to go the Sierra IRS route. Any suggestions or comments would gladly be welcomed.

[Edited on 10/2/06 by ProjectX]

ed_crouch - 10/2/06 at 09:19 PM

Welcome to the forum.

I take it you have heard of the McSorley plans??
If not, you need to do a websearch on Jim McSorley. On this website, there are complete plans for the wider (+4) Locost.

You may, however, consider goingfor a DeDion setup on this car, as I do not beleive there are any plans about for IRS.

Designing your own IRS is fine as long as you understand about roll centre height, and are happy to design the rear suspension mounts with this in mind.

DeDion is halfway between IRS and live axle, and many say it gets you the best of both worlds.

HTH.

Ed.

ed_crouch - 10/2/06 at 09:24 PM

I should say that some think IRS is better than DeDion is some circumstances (provocative remark number 1!), but only if you get the geometry right!! A badly designed IRS could make the car handle worse then the QE2!

Ed.
P.S. If you are interested in DeDion, could go to www.gtstuning.com. Darren sells a DeDion kit.

dnmalc - 10/2/06 at 10:02 PM

Try looking at Rorties IRS This is a set of fully detailed plans but these are not for a +4 so you may need to modify some of the dimensions

ProjectX - 10/2/06 at 10:30 PM

Thanks Guys.

Yes I have the Mc Sorley plans and will be building from them. I have looked at De Dion setup but not sure if it will be as good as the IRS.

Planning on using a Sierra LSD to aid traction etc etc.

The plans I have drawn up lead to a roll centre about 1 inch from ground?

Will obviously have longer lower arms to correct and provide slight negative camber on sus travel/bumps.

Also planning to mount wheel centres about 1 inch behind diff drive position and mount coil overs angled toward rear bulkhead to help with dive on acceleration.

My biggest concern is what type of hub carrier/plate to use with the shafts. Dont yet own any to look at.

Thanks
J

t.j. - 10/2/06 at 11:17 PM

quote:
Originally posted by ProjectX
Thanks Guys.

Yes I have the Mc Sorley plans and will be building from them. I have looked at De Dion setup but not sure if it will be as good as the IRS.

Planning on using a Sierra LSD to aid traction etc etc.

The plans I have drawn up lead to a roll centre about 1 inch from ground?

Will obviously have longer lower arms to correct and provide slight negative camber on sus travel/bumps.

Also planning to mount wheel centres about 1 inch behind diff drive position and mount coil overs angled toward rear bulkhead to help with dive on acceleration.

My biggest concern is what type of hub carrier/plate to use with the shafts. Dont yet own any to look at.

Thanks
J


Hey,

I'm using the tiger avon IRS must say that i redraw the rear because of the roll-centre en de instant centre is on the "wrong" side of the wheel.

Buy the books "how to build your own sportscar" and the tiger avon book.
And don't trust the measurements!!

Grtz

ed_crouch - 11/2/06 at 01:35 AM

ProjectX,

"Roll centre 1 inch from ground."

I may be wrong here, but a roll centre 1 inch from the ground may be a smidge low??

As I understand it, to prevent body roll in cornering, the CoG of the car wants to coincide with the roll centre axis, i.e. lie along it at some point, and you will *STRUGGLE* to get the CG that low!!

Feel free to correct me, cos I am not the expert!!

Ed.

t.j. - 11/2/06 at 08:41 AM

quote:
Originally posted by ed_crouch
ProjectX,

"Roll centre 1 inch from ground."

I may be wrong here, but a roll centre 1 inch from the ground may be a smidge low??

As I understand it, to prevent body roll in cornering, the CoG of the car wants to coincide with the roll centre axis, i.e. lie along it at some point, and you will *STRUGGLE* to get the CG that low!!

Feel free to correct me, cos I am not the expert!!

Ed.


I'm also not the expert.

Only by the advice I collected here i'm planning to have a roll-centre at 50 mm at front and 100 mm at the rear.

To low roll-centres gives a sensitive steering and is ment for race-cars. See also: http://www.locostbuilders.co.uk/viewthread.php?tid=38565

grtz

907 - 11/2/06 at 08:41 AM

So how do I calculate my rear roll centre?

Anyone got a diagram, website info, etc?

Paul G

britishtrident - 11/2/06 at 12:08 PM

De Dion has better geometry than IRS.
It has none of the tramp or torque reaction problems encountered putting power down with live axle.

The unprung weight is very close to double wishbone irs.

It feeds loads into the main chassis Structure in a better location that double wishbone IRS.

Only real down side is loss of independant movement in single wheel bump situation and that is a bit of a red herring.

britishtrident - 11/2/06 at 12:28 PM

quote:
Originally posted by ed_crouch
ProjectX,

"Roll centre 1 inch from ground."

I may be wrong here, but a roll centre 1 inch from the ground may be a smidge low??

As I understand it, to prevent body roll in cornering, the CoG of the car wants to coincide with the roll centre axis, i.e. lie along it at some point, and you will *STRUGGLE* to get the CG that low!!

Feel free to correct me, cos I am not the expert!!

Ed.





CG height should always be a above RC height if the RC height and CG height conincide you get zero roll and a car that would feel pretty odd to drive and be unpredictable.

Sports cars have low roll centres and depend on spring or anti-roll bars stiffness to control the roll.
Normally on a Locost type car the front roll centre is lower than the rear, giving a roll axis that slopes down toward the front of the car.

1" (25mm) is well within the normal range of front roll centre heights for Locost style car, rear roll centres tend to be higher ranging from 50 to 250 mm depending on the suspension design used.

The suspensension layout Avon use is valid just not a good choice for the a sports car.

darrensdad - 11/2/06 at 12:40 PM

my MK has de dion set up and in the dry i have never had the back wheels spinning ,but as my son darrenw says i am not trying hard enough!!!
must get out more!!!

t.j. - 11/2/06 at 07:24 PM

quote:
Originally posted by 907
So how do I calculate my rear roll centre?

Anyone got a diagram, website info, etc?

Paul G


look at this site gives information: http://www.7builder.com/

jon_boy - 12/2/06 at 02:32 PM

907 if that doesnt help what kind of suspension do you have and i should be able to help..

907 - 13/2/06 at 04:42 PM

quote:
Originally posted by t.j.
quote:
Originally posted by 907
So how do I calculate my rear roll centre?

Anyone got a diagram, website info, etc?

Paul G


look at this site gives information: http://www.7builder.com/





Read this, read that, clicked here, clicked there,

I couldn't find it.

Give us a clue.

Paul G


p.s. It's Sierra IRS Jon

[Edited on 13/2/06 by 907]

t.j. - 13/2/06 at 06:02 PM

quote:
Originally posted by 907
quote:
Originally posted by t.j.
quote:
Originally posted by 907
So how do I calculate my rear roll centre?

Anyone got a diagram, website info, etc?

Paul G



look at this site gives information: http://www.7builder.com/





Read this, read that, clicked here, clicked there,

I couldn't find it.

Give us a clue.

Paul G


p.s. It's Sierra IRS Jon

[Edited on 13/2/06 by 907]


Hi Paul,

Cheer up

look at: http://www.7builder.com/SuspensionGeometry/SuspensionDynamics.doc

Helped me a lot!

Grtz

907 - 13/2/06 at 06:11 PM

That's the little bu**er

Thanks mate

Paul G

Bob C - 13/2/06 at 08:02 PM

That site is a goldmine of hard- won information - well done, & thanks Mike (if he still reads this forum!)
Bob C