I know it seems reather elementary but the theory of why front wheel drive cars under steer given they have stiff front and less stiff rear, just hit me. Here's something I posted on another message board.

Yes it is. I really don't know why, but the theory is that you want the rear end to drift out a bit. So you stiffen up the rear, and add more pressure to the rear tyres. Now that I think about with all the power and weight in the front you don't want a stiff front end. Reason. Think about when you go into a turn. You want the most grip on the outside tyre. Well if that side is really stiff then the tyre is just going to slide out on you, b/c you're not allowing it to have much range of motion i.e. dampening and rebound which it needs to handle the added weight or Gs that are being put on the tyre.

Its kind of like if you have a stiff front end and if you go into a turn weight (Gs) transfers to the outside tyre, well if that side is stiff then the tyre is going to lose traction b/c the shock/springs can't absorb that energy or weight transfer.

Am I right do I get a cookie?

 

Yes you are right That why the factory Hondas in Firehawk and Escort Challenge ran very very light or disconnected front sway bars.

 

no cookie for you!

well, almost. you get some crumbs. you're on the right track, but still haven't arrived at the answer. search is your friend. if you search, you will find! i'll give you a hint though. there is a lot more to a front drive car understeering then you think.

nate

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x &raquo;</TD></TR><TR><TD CLASS="quote">no cookie for you!

well, almost. you get some crumbs. you're on the right track, but still haven't arrived at the answer. search is your friend. if you search, you will find! i'll give you a hint though. there is a lot more to a front drive car understeering then you think.


nate</TD></TR></TABLE>
I guessing the oversteer issue if you stiffen up the rear? Or am I still missing something on understeer....... oh wait better search. We shall see.

 

You have a lot to learn weedhopper :-)

Basically you are right - softer front and stiffer rear do make the car understeer less (or oversteer more - its the same thing really).

But there is the law of diminishing returns for a stock type car. Here's why - as you soften up the front the body rolls more and more for a given lateral load. There is nothing wrong with body roll as long as the tire stays flat on the ground. If you have double wishbones or another suspension type that can add negative camber as it compresses than the tire will stay flat. But if you have MacPherson struts or another suspension type that does not add neg camber as it compresses than the tire patch is no longer flat on the ground and you lose grip as the car rolls.

Also if you go too soft and you get enough roll to hit the bump stops then you can have disasterous consequences. When you hit the bumpstop then your spring rate goes instantly form ~200 lbs/inch to infinity. And the car can very quickly transition form understeer to severe oversteer or from neutral to severe understeer because of the instant weight transfer.

So, the answer is - it depends. If your front end can handle softer spring rates without losing contact patch or bottoming out then you might go softer. But some cars (like torsion bar CRXs) actually get less understeer with a bigger front bar. Go figure :-)

I recommend going with what others have done with the same car and who use it for the same purpose as you want. Also pick the person you model your car after carefully. There are a lot of wrong-headed people out there. Use moderation and only make one change at a time.

Finally, recognize that suspension changes can make your car unstable. So test gently, gradually come up to the limits and DO NOT DO IT ON THE STREET. I read a story by a Miata owner who installed a bigger rear sway bar with adjustable end links and then promptly went out to his favorite twisty road and proceeded to "test" the new setup at the limit. The result was the car totalled on a flat bed. If he had not had a roll bar the 3 rollovers the car did would have killed him. It turns out that he had installed the bar incorrectly and it totally bound the rear suspension once it compressed a little.

Regards,
Alan

 

Thanks for that info.