Solid axle or IRS?

[RV8a/Stalker]

So here is the age old question that my brother and I debate regularly.

Which handles better on a smooth race track, a properly prepared car with a straight axle or a car EXACTLY THE SAME but with IRS.

Please back up your theories with details.

This should be good!

[JohnCh]

I don’t think there is such a thing as a smooth racetrack ;) So if you are just asking if there is a performance advantage on track for IRS or solid axle, then I think the easy answer is to look at race series for purpose built race cars ( i.e. not converted street cars). Do any of the top cars in any of these series use a solid axle when it isn’t required by the rules? Race car designers rarely pick the slower option unless budget or rules dictate otherwise.

-John

[slomove]

I would not suggest that a live or solid axle has a performance advantage (it may be a little lighter than a DeDion or IRS, though). But on the racetrack in a Sevenesque car it appears to have no disadvantage, either. There have been wins in race series with live axle cars (e.g. Team Birkinsport in the California NASA Enduro a few years back and Walt Zettner in a Texas NASA series) against some serious semi-professional competition. I guess the overall setup and performance of the car and the driver skill are far more important than the axle configuration.

On the road the IRS is obviously supposed to have a smoothness of ride advantage. On the other hand I can not complain about ride comfort in my life axle car at all (given good shocks and proper suspension setup). I do a fair bit of long-distance touring and should have noticed.

Gert

[JBH]

So if you are just asking if there is a performance advantage on track for IRS or solid axle, then I think the easy answer is to look at race series for purpose built race cars ( i.e. not converted street cars). -John

Well...that's true, but Mustangs (race converted street cars) in the Grand Am and Koni Challenge series are quite competitive with the live rear axle. I don't understand Ford's rationale, but it's hard to argue with the results.

I think the advantages to IRS are lower unsprung weight and the flexibility in setup for different tracks, conditions and drivers.

[JohnCh]

Don’t get me wrong, I’m not saying a solid axle can’t be faster/handle better than an IRS setup. Heck, the Westfield has IRS and by all reports a Caterham handles better (don’t tell anyone I admitted to that). I’m assuming the question posed concerned designing from a clean sheet of paper and tenths of a second matter. Perhaps RV8a/Stalker can clarify?

-John

[Elv15]

Running on a track the only issue I am aware of that could highlight a difference between IRS and a solid axle is riding the kerbs. With a bumpy kerb, you could lose traction easier with a solid axle.

The only other think I can think of would be that setting the the roll center would differ between a IRS and a solid axle car. Though, I'm not sure there is a large enough delta for this to make a noticeable difference.

[RV8a/Stalker]

Don’t get me wrong, I’m not saying a solid axle can’t be faster/handle better than an IRS setup. Heck, the Westfield has IRS and by all reports a Caterham handles better (don’t tell anyone I admitted to that). I’m assuming the question posed concerned designing from a clean sheet of paper and tenths of a second matter. Perhaps RV8a/Stalker can clarify?

-John

I am talking about 2 identical cars except for the rear suspension. Hmmmm designed from a clean sheet of paper have not thought about that. I guess to make this much simpler it is more of a general question.

Race tracks are not smooth???? If memory serves they are MUCH smoother than most roads in San Diego!

[JohnCh]

Race tracks are not smooth???? If memory serves they are MUCH smoother than most roads in San Diego!

I live in the PNW. Our tracks are only smooth immediately following a resurface ;)