JohnInKansas
JohnInKansas SuperDork
8/28/19 12:21 p.m.

Hoping someone can help me get a feel for the effect polar moment changes have on vehicle handling.

I get the concept, so no need for weights on yardsticks, I'm hoping for more like these identical cars with different PMOI handle differently, and this is how much differently they feel with weight in different places.

I guess an "easy" answer would be put four bags of cement in the passenger seat and do a couple laps as a baseline, then put the cement in the trunk and (on the front bumper?) and repeat to feel the difference.

ProDarwin
ProDarwin UltimaDork
8/28/19 12:24 p.m.

Your experiment isn't isolating Polar MOI though... you are screwing with weight distribution and CG as well.

 

A better experiment would be put 4 bags at the firewall/trunk wall front and rear (over the axles), then move the 4 bags to F/R bumpers (assuming same distance from axle centerlines).

JohnInKansas
JohnInKansas SuperDork
8/28/19 12:26 p.m.

In reply to ProDarwin :

Yeah, it would have to be two in front and two in back, and equidistant from the "baseline" location to be accurate.

morello159
morello159 Reader
8/28/19 1:26 p.m.

Find someone with a NA Miata and a w10 mr2?

Streetwiseguy
Streetwiseguy MegaDork
8/28/19 3:42 p.m.

Back when dinosaurs ruled the earth, I did a lot of autocross in my 82 Z28.  A good friend had built a Corvair with the mid engine 350 swap.  Similar power delivery (me less power), similar weights (Me more weight), similar tires, dramatically different weight distribution.

The feel from the drivers seat was very, very different. 

nderwater
nderwater UltimaDork
8/28/19 5:08 p.m.

Interesting ideas. I'm still chasing the on-the-limit rotation feel of the Ferrari 360 I once got to autocross.  No car I've ever driven since quite captures that.

Carbon
Carbon UltraDork
8/28/19 5:12 p.m.
morello159 said:

Find someone with a NA Miata and a w10 mr2?

Or an nb miata and a zzw30 mr2, very similar concepts, incredibly different results. Especially when you add copious amounts of  power. 

Knurled.
Knurled. MegaDork
8/28/19 7:17 p.m.
Carbon said:
morello159 said:

Find someone with a NA Miata and a w10 mr2?

Or an nb miata and a zzw30 mr2, very similar concepts, incredibly different results. Especially when you add copious amounts of  power. 

Or a 4000 Quattro and a 1.8l AWD Impreza.

 

Similar weight/weight distribution but the Audi is decidedly more slow in its responses.

JohnInKansas
JohnInKansas SuperDork
8/29/19 7:59 a.m.

Barring platform comparisons due to lack of friends with available vehicles and suitable venue to push them to their limits, I'm thinking weights on the go kart on smooth, wet pavement to reduce traction. Not sure where I'll find smooth, wet pavement...

I have some (really rough) numbers comparing a hypothetical chassis with different driveline configurations. Looking to decide on the compromise, low polar moment or extra grip/acceleration. 

Driven5
Driven5 UltraDork
8/29/19 9:42 a.m.
JohnInKansas said:

Looking to decide on the compromise, low polar moment or extra grip/acceleration. 

Are you certain that it's an either/or proposition?

JohnInKansas
JohnInKansas SuperDork
8/29/19 10:37 a.m.

Not at all. Nor will my kart test get at all the issues, as I'd only be changing the ballast points to simulate the PMOI and ignoring additional drive wheels. But it *should* give me a ballpark idea how willing to rotate each of the setups would be. I think.

Tyler H
Tyler H UberDork
8/29/19 2:58 p.m.
Carbon said:
morello159 said:

Find someone with a NA Miata and a w10 mr2?

Or an nb miata and a zzw30 mr2, very similar concepts, incredibly different results. Especially when you add copious amounts of  power. 

MR2 and Miata are a great example of cars with inherently similar feel with different PMOI.  

NOHOME
NOHOME MegaDork
8/29/19 3:12 p.m.

How about a mechanism that responds to the steering wheel inputs, so that when you turn the wheel, the mechanism reels in a couple of heavy weights from the extremities of the car towards the middle? Variable Moment of Inertia

 

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