Hoosier 20 x 7.5/ 13

[BillCobb]

By ignoring kinematic and compliance (steer & camber), you are not doing car engineering, you are playing in a sandbox with an evaluation process that is too simplified. The question for you would be how will you determine what the K&C parameter values are ? I'd advise you to get some structural analysis going and a measurement system (a machine or a mechanism) to systematically obtain the influence coefficients that modify (attenuate) the tire forces and moments at each axle).

Only then can you run the play for useful tire evaluations. Do you really think/believe that its possible to have all of your tires running up to the peak SA ? Yeah I know some will claim they have been successful with their primitive models, but it was not because of the reasoning they followed. Luck is not a continuous process.

BTW: Correlation between CS and Relaxation is generally not a very good one. Relaxation and rim width is MUCH better. There should be some relaxation measurement attempts in the next round of TTC data. And just how will/would you factor relaxation effects into your tire selection process ?

[MotorCity1]

By ignoring kinematic and compliance (steer & camber), you are not doing car engineering, you are playing in a sandbox with an evaluation process that is too simplified. The question for you would be how will you determine what the K&C parameter values are ? I'd advise you to get some structural analysis going and a measurement system (a machine or a mechanism) to systematically obtain the influence coefficients that modify (attenuate) the tire forces and moments at each axle).

I definitely agree that this evaluation process is simplified. Modeling the raw TTC data (scaled down to account for different coefficient of friction based on operating surface) is what I felt was a logical first step in understanding the general behavior of each tire. I'm aware that compliances exist everywhere and until they are accounted for, any conclusions I make will not be indicative of reality.

Do you really think/believe that its possible to have all of your tires running up to the peak SA ?

Nope, anything as small as a crack on the track surface would attenuate the tire forces. Compliances that aren't accounted for such as Wheel rim deflection, upright deflection, etc. would have the same effect..too much heat cycling, conicity, improper care of tires, ...I think that's the idea you were trying to get at, and if so, I agree that under extremely rare circumstances, if any circumstances at all, will the tires approach their peak SA, Fy, Mz...

BTW: Correlation between CS and Relaxation is generally not a very good one. Relaxation and rim width is MUCH better. There should be some relaxation measurement attempts in the next round of TTC data. And just how will/would you factor relaxation effects into your tire selection process ?

I'll investigate those effects some more. Relaxation effects would affect transient response..so I'd say a transient vehicle model of some sort would be necessary to properly account for these effects.

Thanks for the feedback!

[BillCobb]

MC-1: I would expect, seeing that you are Wayne State and in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world and with a VERY large number of Wayne State graduates working the industry, that you could be successful in getting 'company' support for testing a FSAE car on a K&C rig somewhere without much begging. Yes, the short wheelbase usually alllows on 1 end of the car to be tested at a ime. But the folks in A2 (you know, a city full of people who think otherwise), have gotten this done on weekends with volunteer alumni support.

Since MTS also has a large Engineering and Product Support in the Detroit area, I would venture a guess that you could also get an invite to Eden Prairie and get on a machine out on the Test Floor ready to be shipped out to wherever in the World.

If you can get a simulation running, steps to open you eyes would involve 1) a car with only mass and nonlinear tires with only FY. Then add MZ. Then add some steer and camber compliances to each axle, and finally the MX. An overlay plot of nonlinear responses (understeer/oversteer, max lat, and response times) for each condition will surprize not only yourself, but quite a few judges as well.

Compliance management is the professional approach to designing a great car, including all 'race car's. You can make a great career out of this, as I did.

I always am amused when I hear 'expurts' state that MZ has little effect on the car, when I know there are no MZ steer or camber compliance parameters or mechanisms to install them in their models. Don't be one of 'them'. Why do you think worn tires tighen up a car and kill it's sidebite ??

[DougMilliken]

... in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world...

[disclaimer -- we are N. American reps for ABD]
Everything Bill said, and a mention that MTS isn't the only supplier of K&C rigs -- there is an ABD SPMM at the FCA (former Chrysler) Proving Grounds in Chelsea MI, as well as Goodyear in Akron. I know that the Goodyear SPMM has been used with FSAE cars and suspect that Chelsea has also.

[Tim.Wright]

Cue the MTS vs ABD discussion.

[Zac C]

Cue the MTS vs ABD discussion.

As far as I know there's only one person that's had extensive experience with both the MTS and ABD machines. His take is that both machines are more or less equivalent in terms of capabilities. The ABD machine is WAY better to work with in terms of required maintenance schedules though. Unless you're planning on owning and operating your own rig that's probably less of a concern.

The Goodyear machine is still an option for paid testing if you want to go that route. Sponsored testing probably isn't going to happen there.

There are also ABD setups at Morse Measurements in NC (open for private testing) and Honda in OH (probably have to know someone).

I should probably also mention that even though a somewhat large number of teams have tested on various K&C rigs I have yet to see a very strong student effort in using the data. That list of teams includes some of the international powerhouses. Maybe that's changed in the last couple years though.

[Tim.Wright]

I've used the data from both - and for basic tests my impression is that both rigs are capable of more or less the same things.

The thing with the ABD rig (for basic tests) is that I don't like the way it carries out the wheel centre longitudinal force tests. They strap the wheel to the wheel pads and apply the longitudinal force but the problem (in my opinion, correct me if I'm wrong Doug) is that the wheel pads cannot rotate about the lat and longitudinal axes so it can't control the Mx and My propery.

So in the end you don't get a pure wheel centre force - there is always a bit of a "parasitic" Mx and My there as well. The MTS wheel pads on the other hand have 6 degrees of freedom so they are able to control all 6 force/moment components perfectly.

For more detailed stuff there are a few differences:
ABD rig cannot do single wheel lift/warp inputs
ABD rig can (with a software upgrade) measure the full inertia matrix of the vehicle as well as finding the CG location in 3 dimensions.

[MotorCity1]

MC-1: I would expect, seeing that you are Wayne State and in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world and with a VERY large number of Wayne State graduates working the industry, that you could be successful in getting 'company' support for testing a FSAE car on a K&C rig somewhere without much begging....

During the design/manufacture/assembly of this past year's car, we just aimed to limit compliance as much as possible from start to finish..but never considered using a SPMM as an option, because our focus was more on completing every event at competition (which we did, for the first time in school history and had the best finish in school history in the process).

Now, this seems like something worth pursuing. Thank you all for the information.

[BillCobb]

Like many other car designers, builders and users, the transition from a paper design to a working car has to pass through reality. This means making the parts exactly as drawn, installing them in exactly the design position, and contemplation of the attachment point flexures. (Even a 'perfectly' built car can have hidden flaws in a K&C validation because the method of clamping the body/frame to the reference ground can install an artificial constraint if the frame is weak or the attachment locations are coincident with modal vibration points).

But what we see so often is careless positioning and installation of parts (i.e. your ride-steer is to be held at +- 1% at 5% understeer - symmetric by design, but as built it's -19% (oversteer) on the left front and +7% (understeer) on the right front wheel. Because of fastener stretch (as in undersized), the hysteresis in your roll camber curves puts the plots off the graphic window. Oh, and your rear roll stiffness is very nonlinear (unexpected, of course). Because of your steering input shaft design, the car has more front compliance steer than a ?? And as for wheel bearings ? I'm sure they are expensive, but did anyone check their runout after you tightened that castle nut with an air wrench ?

Seen it all. Enough for a lifetime....

[Zac C]

I've used the data from both - and for basic tests my impression is that both rigs are capable of more or less the same things.

The thing with the ABD rig (for basic tests) is that I don't like the way it carries out the wheel centre longitudinal force tests. They strap the wheel to the wheel pads and apply the longitudinal force but the problem (in my opinion, correct me if I'm wrong Doug) is that the wheel pads cannot rotate about the lat and longitudinal axes so it can't control the Mx and My propery.

So in the end you don't get a pure wheel centre force - there is always a bit of a "parasitic" Mx and My there as well. The MTS wheel pads on the other hand have 6 degrees of freedom so they are able to control all 6 force/moment components perfectly.

For more detailed stuff there are a few differences:
ABD rig cannot do single wheel lift/warp inputs
ABD rig can (with a software upgrade) measure the full inertia matrix of the vehicle as well as finding the CG location in 3 dimensions.

Yeah, I've used data from both types of machines, as well as some one offs that various OEMs made before K&C rigs were available as a turnkey solution. I'd agree with your assessment. In terms of general operation MTS machines are a pain, not just for K&C rigs, but for everything. The hydraulic systems they like to default to for almost everything require a lot of upkeep. The electric systems ABD runs require almost zero.

I'm slightly less concerned about the residual MX and MY though. The wheel pads don't rotate about the x and y axis, but you've got the 6 forces and moments measured at the footprint and the displacement coordinates for your wheel center and your contact patch. It gives you enough information to post-process out any residuals, especially if you run the test at a couple offsets or use the Y-axis to minimize the overturning moment.. There's always the option of using the rigid wheel substitutes too (this will severely limit your test throughput).

The inertia stuff is more than just a software upgrade btw. You need a special set of body clamps that have 6 axis load cells built into them and some other expensive bits. It's a pretty small subset of rigs that have this capability.