Irs (Independent Rear Suspension) In 205

[foreigner 0]

Thats not right:

 

http://howmanyleft.co.uk/combined/peugeot_405

 

http://howmanyleft.co.uk/combined/peugeot_205

 

 

that's awesome site.

[foreigner 0]

Yep 100% agree, spring rates must have to be insane!

 

yep, but aren't they chepaer and easier to change than bars??

[Henry 1.9GTi 36]

having always suffered from understeer unless being very agressive with the wheel and trail braking I would be more inclined to put money and thought into the front setup. Sort out the roll centre and bump steer issues get some good camber compensation and remove the horrible horrible bending loads associated with a coilover. Honestly the contact patch load variation of my car was awful when compared to the rear. All front grip lost so no matter how stiff I made the rear the car didn't respond. This is in dry conditions with low speed being more neutral than highspeed which tended towards understeer.

 

edit: anyone read the "toe out for turn in" article in racecar engineering? Something to consider as well if you don't like your turn in.

Edited August 14, 2011 by Henry 1.9GTi

[maxirallye 2]

The turreted rear suspension on mine, ran it for 30 minutes prior to engine failure at LLandow, Colin was timing me driving my and my mates car with 25BHP more, my car was .5 seconds a lap faster.

[Cameron 16]

having always suffered from understeer unless being very agressive with the wheel and trail braking I would be more inclined to put money and thought into the front setup. Sort out the roll centre and bump steer issues get some good camber compensation and remove the horrible horrible bending loads associated with a coilover. Honestly the contact patch load variation of my car was awful when compared to the rear. All front grip lost so no matter how stiff I made the rear the car didn't respond. This is in dry conditions with low speed being more neutral than highspeed which tended towards understeer.

 

edit: anyone read the "toe out for turn in" article in racecar engineering? Something to consider as well if you don't like your turn in.

 

Not much you can do to the front without some serious work though.. I'm trying to make mine fit with as little cutting and welding on the body as possible but to get any kind of decent geometry the upper wishbone pick-ups will have to be welded to the chassis leg. No chance of keeping the standard track width either, I'll most likely be moving to 1500mm.

 

I haven't read my copy yet, it came through the door last week.. toe-out is something I've been banging on about for a while!

[Anthony 1,003]

toe-out is something I've been banging on about for a while!

Depends what the application is though - it's not very pleasant on a road car having any notable amount of toe-out (IMO)

 

I've got a set of tracking gauges so I can easily play around now, but certainly I've always gone for either zero toe or a tiny smidge of toe-in, which seems to be the best trade off between turn in response and the car not wanting to pull around on rutted and broken tarmac. For a track based car that mainly gets used on nice smooth tarmac, I'm sure more toe-out would work quite well.

[stu8v 68 1 Cars]

Whats everyones "take"on modifying the front subframe?

 

Instead of using 309 arms, move the pickups further outwards to compensate?? just an idea

[jackherer 543]

You'd get all sorts of bump steer issues, the arc the wishbone follows is closely tied to the arc the steering arm follows. Spacing the inner track rods from the steering rack might help compensate it out but I don't know how feasible that is.

[Cameron 16]

You'd get all sorts of bump steer issues, the arc the wishbone follows is closely tied to the arc the steering arm follows. Spacing the inner track rods from the steering rack might help compensate it out but I don't know how feasible that is.

 

As above, unfortunately it's never as simple as just moving pickup points about. If you don't know exactly what you're doing (and you're not going to without doing a lot of homework or having tonnes of experience) then you risk ending up with all sorts of handling nasties.

[engine killer 6]

As above, unfortunately it's never as simple as just moving pickup points about. If you don't know exactly what you're doing (and you're not going to without doing a lot of homework or having tonnes of experience) then you risk ending up with all sorts of handling nasties.

Forgive my asking, from my understanding, the length of arm should be as close to the length of the track rod so that they are running about the same arc to minimise bump steer. By using 309's arm and track rod which are slightly longer than 205's, the difference between arm and rod should be same but the ratio is less, will this be any benefit on reducing bump steer?

 

I have a spacer between the hub carrier and the rod (using rose joint instead), it is about an inch and it eliminates a lot bump steer.

[Sandy 191]

The pivot on the steering track rods are in the same place on both, so the track rods need to be extended to match the 309 wishbones, either by using the correct rod or by winding out the rod end; tomato tomato it does the same thing, just the amount of thread left in the arm different.

 

Lowering with standard 205 or 309 arms spoils the roll centre and induces bump steer. The most preferable way to deal with the roll centre is to move the outer joint down (limited by wheel size) and bump steer by doing the same with the rod ends our moving the rack, but it's all impossible stuff to get right without really knowing where you are going with it. Example being bump steer, which draws an "S" shape over the travel, so you need to drop it on the right part of the curve, rather than going more or less one way, so to speak.

[engine killer 6]

I have been searching and studying about bump steer for a while, although it is not that simple but somehow I guess I understand the theory a bit. Also, the height from the rod pick-up point to arm pick-up point on the sub-frame side and hub carrier are different, this make a lowered car bump steer badly, correctly me if I am wrong.

 

After roughly measuring the length of rod and arm and heights between them and drawing a few arc to model the case, I concluded I have to lower the rod pivot point on the hub carrier side. No I did not calculate the amount I have to lower but just by wild guess and luckily I got it close and it eliminated bump steer. The car no longer nervous at about 100mph.

 

I am still working on the roll centre kit, for sure I have to rework on the bump steer kit once the geometry is changed.

 

this helped a lot http://www.longacreracing.com/articles/art.asp?ARTID=13

Edited August 18, 2011 by engine killer

[feb 47]

Depends what the application is though - it's not very pleasant on a road car having any notable amount of toe-out (IMO)

 

I've got a set of tracking gauges so I can easily play around now, but certainly I've always gone for either zero toe or a tiny smidge of toe-in, which seems to be the best trade off between turn in response and the car not wanting to pull around on rutted and broken tarmac. For a track based car that mainly gets used on nice smooth tarmac, I'm sure more toe-out would work quite well.

 

My (limited) experience from wheel alignments is the same.

When I bought the Forester the car didn't give me any confidence at all on anything but smooth tarmac; after having the wheel alignment checked it turned out that there was (a lot?) of toe out which would probably explain this.

 

After the alignment (settings below) the car was totally transformed, I could tell what it was doing at last and had a lot more confidence in it. It still wasn't perfect for my liking though until I got rid of the coilovers.

As I understand the Saved values were before the alignment and the Actual after but I might be wrong.

If anyone can shed some light it would be good.

Edited August 18, 2011 by feb

[Cameron 16]

I have been searching and studying about bump steer for a while, although it is not that simple but somehow I guess I understand the theory a bit. Also, the height from the rod pick-up point to arm pick-up point on the sub-frame side and hub carrier are different, this make a lowered car bump steer badly, correctly me if I am wrong.

 

The article you linked to is for double wishbone suspension, for MacPherson struts it's a bit more tricky since the upright moves in an ellipse rather than an arc. This is due to the strut compressing axially and the BBJ moving in an arc, and since your outer track rod balljoint moves in an arc the two never match up and you'll always end up with some degree of bump steer. You can never eliminate it with struts, only minimise it!

[engine killer 6]

The article you linked to is for double wishbone suspension, for MacPherson struts it's a bit more tricky since the upright moves in an ellipse rather than an arc. This is due to the strut compressing axially and the BBJ moving in an arc, and since your outer track rod balljoint moves in an arc the two never match up and you'll always end up with some degree of bump steer. You can never eliminate it with struts, only minimise it!

 

Thanks for your explanation.

 

Hmmm may I assume if we neglect the strut (MacPherson), if the pivot points for rod and arm are on the same horizontal level (or may be same height) on both subframe side and hub-carrier side and they are also in same length, the bump steer can be eliminated.

 

My friend (mechanic) showed a bimmer e36's front geometry once and he told me that bimmer's bump steer seems like NONE. I found out it's arm and rod are about the same length. So this make me think of a smaller ratio between rod and arm should improve the bump steer issue, am I on the right path?

[Cameron 16]

Yeah I would think that if the wishbone and track rod were the same length, absolutely parallell and on the same plane (i.e. same height from the ground) then you wouldn't get bump or roll steer. It's going to be very difficult to get the steering rack down there though, as it would have to go through the subframe.

[Rippthrough 98]

You might just get a narrow rack in front of the subframe but getting the steering column there would be hell. And it'd have to be a hell of a compact rack to stop it hitting the floor.