IFS as IRS?
 

I was thinking this morning (it rarely happens) and a thought came to me with which I thought I would torment Lat-G. What about utilizing the front suspension, say off an AWD S-10, or an FWD car like a 70's Toronado, as an IRS? Gives good adjustment, yes? What might the downside be? I know the Fiero used a Citation FWD suspension in the back.

Thoughts?

Merry Christmas!
Bill

Funny enough, I was JUST talking to a former student about this very subject. IMO, the S10 a-arm suspension is a great starting point for a custom IRS. The drive components might be a little light-duty for a heavy (3000+) car with serious horsepower, but other than that I don't see any downside to using it. I would definitely correct the camber curve geometry to match the tire being used.

agreed, you will want the rear to not be as aggressive as the front, and be more predictable for when on the edge.

It appears I subscribe to a different philosophy on IRS design...

First, take a look at sucessful short/long arm IRS systems. You'll notice the caster is at zero, caster gain is reversed and steep, camber gain is slightly more aggressive, and anti-properties are reversed. Not to mention bushing design needs to be looked at due likely issues with shudder when powering out of a corner. And this is just a start!

I'm trying to think about how you could make a IFS work without too much trouble, and I'm not seeing it. I guess it could be done, but not something I'd be happy with.

How were such difficulties solved in the Fiero design? Did they perhaps swap the spindles from side to side?

Merry Christmas!
Bill

when running, large rear tires, as most of us do, there is more grip when the full tread width is in contact with the track surface, if designing in alot of camber gain, or alot of initial camber with a 335 rear tire, you are defeating the purpose of having that much rubber on the back end, this is true both on stick axle rear and irs. of course this is coming from a more competition/track view.
most alms gt cars, rolex gt cars etc with 11 and 12 inch wide rims, tune there chassis for around 1 inch of bump, both to keep mechanical grip levels high and to keep from having huge amounts of weight transfer.

Jake, what you mention is balancing the line of forward traction and lateral grip. Most radial tires will have more lateral grip with a small amount of negtive camber. The rear tires like some negative camber just like the fronts do.

Solid axles will benefit from negative camber also - I've done this myself with very impressive results, to the point I either need to raise the static RC by 1" or increase the rear roll rate by about 5000 lb-ft/rad.

yes i agree, they like some neg camber, but not to the point of wanting .75 to 1.0 neg camber gain per inch like a front susp may have.
I as well tune with the rear rc height, depending on track configuration, speeds, etc. its always a balance of getting the car to rotate, but still have good forward bite coming out of the turn. Thats when adjustable rc, double adjustable shocks etc come into play when fine tuning on the thresh hold.

Respectfully, my opinion differs. Because of packaging and the desire to reduce angular misalignment with CV axles, the overall bump/rebound travel in performance-oriented IRS systems is often reduced. To make up for the reduced travel, the camber gain is increased. Obviously this isn't a set-in-stone rule, but appears to be a modern trend.

I agree to disagree.:)
We are talking about different platforms and uses, which is why we have different thoughts on the subject.
keep it going, discussions always help everyone out.
thanks