Here's an idea for FSAE TTC Round 4...

[exFSAE]

I think most can agree that low temp / startup grip is pretty crucial in FSAE. It has been a while since I've looked at the data but I don't think the warmup period captures this at +/- 2deg slip.

What if we were to add the following test...

<LI>Start with new, sticker tire.
<LI>With tire unloaded (in air, LR control set at some fixed number), start the belt up to test speed.. 45 or 60 mph whatever ti is.
<LI>Change control set point to some nominal condition, say 250lb, 0 camber, 12psi
<LI>Immediately start an aggressive slip angle sweep.. say +/- 6 or +/- 9 deg at a fairly high sweep rate.
<LI>Continue for 15, 30, 45 seconds... whatever it takes to really get the bulk tread temp up pretty high


If 250lb isn't generating enough heat at such low speeds, maybe try 350.

Idea is to emulate a worst case scenario of getting in and having to drive aggressively on cold, sticker tires.

Might be some interesting stuff to see how cornering stiffness and peak grip evolve as that tread comes up to temp.

I also think the same test with some water spray and wet tires would be pretty eye opening.

[BillCobb]

If you test a cold, unheated, tire in the condition of first use, run it on test, then warm it up unworn by putting a few degrees of slip on it at a very heavy load and cycle it at low speed while using talc to eliminate the crumbs, then test it, and finally test the fully heated, worn-in tire, you will have something to study. All the Pacejka coefficients for the fit will evolve and you can make them time or temperature, or distance dependent in your model. This means defining the parametric changes in all the the coefficients and running the play. While stiffness change won't be large, max grip level changes will be. You'll also have in front of you the few coefficients that really matter to your vehicle's performance.

Then all you need to do is figure out a way to heat them and start the tire chemistry before your event begins. (Torpedoe heater in a 'tent' is my favorite, a boiling hot water tub is next...).

[exFSAE]

Allright Cobb, I'll bite.

So you're saying...

<UL TYPE=SQUARE>
<LI>Sweep 1 - Cold, sticker tire. No warmup or breakin.
<LI>Sweep 2 - "Warm" sticker (?) tire, warmed up with high load roughly linear range
<LI>Sweep 3 - Hot tire after it has gone through full limit sweeps
[/list]?

[J.R.]

I don't know if thats worth it for the bulk of us. Most of us will scrub our tyres in first since we don't have a ton of extras, so won't this "qualifying" style tyre test only benefit teams with budgets large enough to do the testing themselves...? Or were you talking about starting with a cold but scrubbed in tyre, and testing it, such as the first run of autocross? That would be cool to see!

Also, if memory serves me correctly, the tests are run at 25 mph, but the machine can spin up to 200... Now that would be a test I'd love to see, 10in tyres at 200 mph! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[BillCobb]

I thought I read the OP's desire was to have a decent manifest of tire performance from cold sticker to end-of-run grease, nicht var?

From what I've seen at the autocross, my plan would help you through all phases of this trek. That presumes you have a ride and a driver who can use the capability of the tire as it warms up. Given a sim model, you can modify the tire data on-the fly to alter tire heating effects while running the play. Toyota has a paper out on this ...

Modification of Pacejka coefficients for pressure effects is old news. You only need to do a few to convince yourself that this works pretty well for heat, too.

[exFSAE]

Originally posted by J.R.:
I don't know if thats worth it for the bulk of us. Most of us will scrub our tyres in first since we don't have a ton of extras, so won't this "qualifying" style tyre test only benefit teams with budgets large enough to do the testing themselves...? Or were you talking about starting with a cold but scrubbed in tyre, and testing it, such as the first run of autocross? That would be cool to see!

Also, if memory serves me correctly, the tests are run at 25 mph, but the machine can spin up to 200... Now that would be a test I'd love to see, 10in tyres at 200 mph! http://fsae.com/groupee_common/emoticons/icon_wink.gif

The idea is more to emulate the first run of an autocross. Which tire (or compound really) is going to give the best instant grip off the line and for that first minute?

Might also be worth doing that whole test.. then letting the tire sit for a while and completely cool down.. and do it again. Identify which tires / compounds are consistent run after run or session after session, which turn to rags.

I use sticker tires just as a worst case scenario.

[exFSAE]

Aw man, no other takers?

If I was doing FSAE again this would be the #1 thing I'd be looking at in tire data, compound characterization.

[Yellow Ranger]

We're thinking about trying a couple different autox setups and watching how quickly the tires heat up with each settings. The problem is the lack of money for testing fresh tires multiple times. We'd like to try it with the two Goodyears and Hoosiers, but we'll see what we can afford and have time to test.

I believe that the raw data has the warm up cycles from the tires in it- maybe some conclusions could be made on how quickly each tire starts to perform at a 'normal' level- I'm not sure though, we'd have to look at it. Wonder if they're willing to do that involved of a test for us rather than the standard sweeps at a given speed...

Has anyone had any luck with autox setups whether it just be lots of camber, higher ICs, pressures, etc?

[ben]

I can see the desire to characterise compounds in the TTC because it's expensive for teams to do it themselves.

Personally though I don't think it will tell you anything really objective due to the belt surface.

For me I'd be suspicious of any team telling me they'd selected a tyre based on its grip level from the TTC data. The only argument you can really make objectivelly is based on the construction characteristics.

Ben

[exFSAE]

Sure. Peak grip levels from a FT are obviously going to be far from reality.

But you would think you could more or less objectively rank how quickly the tires build temp, and at least the shape of a grip vs temp curve, even if the absolute magnitude is off.

Just some ideas. Compound seems like it dominates so much in this series and would be tough and expensive for teams to test otherwise.

[BillCobb]

Peak grip levels from a FT don't have to be far from reality, even with Calspan's air bearing, it's just they CAN be if the test environment is poorly maintained or the tire interface not conditioned. Maybe Dave G. can/will fill in the details. I've gotten some 2.56 and 1.4 max values from left & right side Cup tires when you set up the experimant correctly. These are the right answers. They know what to do...

[ben]

Originally posted by BillCobb:
Peak grip levels from a FT don't have to be far from reality, even with Calspan's air bearing, it's just they CAN be if the test environment is poorly maintained or the tire interface not conditioned. Maybe Dave G. can/will fill in the details. I've gotten some 2.56 and 1.4 max values from left & right side Cup tires when you set up the experimant correctly. These are the right answers. They know what to do...

Dave G = Dave Gentz? He's doing some work for me in January. I'll be trying to get some reasonable mu estimates from the race track to compare with the FT.

Ben

[exFSAE]

Cup tires are a slightly different animal... it is hard to knock down the grip level of these tires on that surface.

[BillCobb]

That's the correct Dave G. Give him my regards. XF: There's always a way. Suggest you look at the glass as repairable instead of cracked up.

[exFSAE]

Sure. I was under the impression though that in Round 3 they had gone through some different surfacing options in an attempt to knock the grip levels down to an appropriate level?

[ben]

Originally posted by BillCobb:
That's the correct Dave G. Give him my regards. XF: There's always a way. Suggest you look at the glass as repairable instead of cracked up.

Will do. I'm definitely a "the glass is 100% over-engineered" than a "glass is half empty person" :-)

Ben