Throttle Steer

[THR]

I did a sprint on monday at colerne. my first one.
so, i now know that my car has a serious handling problem, in that it has big throttle steer from the rear. (causing me to spin flat in 3rd at about 85mph)
u can feel it when u get off the throttle, and if the car is in roll when u let off it slides.
the balance throu the corners isnt too bad. springs are a bit stiff, probs done by the previous owner to reduce the throttle steer effect.

so the question is, what can cause this? how can i fix it?

the car is a clan crusader, with mac strut at the rear. 40:60 weight dis.

[enzo]

OK - since no one else is answering, I'll give it a stab.

First off, I'm not familiar with your car (wrong side of the pond), so I've got to pose a couple of basic questions first.

1- Is it FWD or RWD ? (as I said - basic !)

2 - Does it throttle steer when letting off while straight ?

3- When you say "it slides", are you referring to the whole car, or just the rear end?

4- How are the rear Mac Struts located ? Links & rubber bushes ? Links & nylon bushes. Links & rod ends ?

5 Are these links set up to produce a lot of anti-lift ?

Get back with whatever info you can.

[THR]

the car is rear engined rwd, 60% rear weight.

the car throttle steers every where, but yes on the straight too, altho u dont notice it too much then cos u can compensate for it with out thinking, its in the corners it catched u out

the read end only sildes due to the throttle really, when u let off, the springs are a bit stiff i think that previous owner has increased to reduce this effect.

mac struts are located in the chassis by rotating bushes at the top of the shock.
and the wishbones are located by a bearing on the bottom of the shock/hub. and rubber bushes onto the subframe.
the steering arm of the hub is now screcured to the car by a rose joint.

the suspension is set up to do wot ever peugoet decided, i have no idea! its a front wheel drive car, put in the back of a car.

hope this casts some light on the prob!
thanks

[enzo]

OK. Maybe we can make some progress here.

I think your problem is mainly tat of flexing of the rubber bushes tht locate the lower a-arm. The fact that the problem exists while going straight eliinates a host of other potentials.

Most modern manufacturers lay out mac strut setups so that the kingpin line intersects the ground outboard of the center of the tire contact patch. (The distance is called the "Scrub Radius") This is so that, when you get a flat, that intersection point moves to the tire center, thereby reducing or totally eliminating the severe pull to that side that accompanies a flat tire. The scrub radius also helps make the steering lighter when turning the wheels while sitting still - it is not needed for rear drive wheels that don't steer.

As you get on & off the throttle, the tire tries to drive around that intersection point. If the lower arm can move (flex at the rubber bushes), the tire will rotate slightly & point to a new direction.

If both driveshafts are the same length, much of the problem is eliminated (unequal length shafts produce unequal 'tugging' on the strut). This is why manufacturers try, as much as is possible, to produce layouts that equalise shaft lengths.

If you can, replace those rubbr bushes with either alu bushes, or nylon, to stabilise the a-arm.

Also, if the rules allow, as well as your pocket book, check to see where the kingpin ground intersection point lies, & offset the wheels outboard to compensate. Of course, it is quite possible that Peugeot has that point somewhere else, maybe even inboard of the contact patch center. If so, you are stuck with leaving the offset as is.

You might also want to check to make sure that the 2 rear wheels have the same offset - differing offsets will definetely screw things up !

Double check the caster also - even small differences side to side will give problems.

Don't worry too much about the stiffness of the springs - spring rates have no bearing on mechanical grip. Lack of grip is usually traceable to too much swaybar, too-stiff shocks (especially in the extreme low velocities), and frictions in the suspension system (including shocks).

Of course, it's possible that I'm 100% wrong in my analysis ! If that ends up being the case, you are on your own !

Good luck !

[redback]

I have no experience with a clan crusader either but have worked on open wheelers for years. Enzo seems to be pointing you in the right direction. The two things I see most that cause this sort of thing with new drivers is;

1)the basic wheel alignment is way out
2)the driver being over aggressive into the corner

I suggest a copy of Carroll Smith's - Tune to Win, a decent alignment (not from a tire shop) and consider your driving technique. Hope this helps.

[THR]

so bushes it is then!

to try and reduce the steer i did replace the bushes in one side of the suspension, cos the bolts had worn giving play, this improved the handling as u can imagine.

and perhaps u are right about the fact that the steer in a straight line is caused by this. hadnt thought about that.
with 180 odd bhp in a car this could very well happen i figure.

however i was looking at the setup earlier on, and the way the hubs are teathered to the subframe, (rather than the steering rack) looks a bit iffy, cos they must be located a lot lower than the orginal rack.
this may give it bump steer a bit.

the aliment of the suspension isnt too bad, we set it up only a few weeks ago which improved the handling a lot, esp braking.

the driver was being over aggresive into the corner, lifting and turning at the same time isnt recommended, but the rear steering didnt exactly help matters a lot!


thanks

[THR]

one thing
is nylon 66 really suitable for bushes??

i got loads of this as i can "borrow" it from work.

[enzo]

It's been years since I last used nylon for anything, so I can't advise there. I WILL advise that you make plenty of spares & check & replace frequently at the first sign of any wear, or the problem will be back to haunt you again !

[enzo]

Any update yet ?

[THR]

after looking into it a lot.

ive found it probaly isnt bumpsteering, cos the tie rods are about where they should be. (got a look at a real 205)

how ever i took the wishbone off the car to look into the bushes and they weigh a TON!

so i think the answer is to make some tube wishbones, opposed to the huge cast things at the moment.

and then use rod ends to take away all the twist.
this should save about 3kg i reckon.

i can then also design into the wishbones a rollbar attachment.

this is a slightly more expensive thing to do tho than replace the bushes! but will last longer and be better overall i think.

soz about the delay, ive been to uni, doing a spot of drinking...hehe

[enzo]

Good luck - I hope it all works !