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GRM-live episode with an aerodynamicist


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1 minute ago, JDChristianson said:

Sort of like running wider ties they are just heavy and add rolling resistance...who would want that?  

I kinda agree with that one.

 

There is such a thing as too wide for the power and weight of the car.

 

I guess that is similar to aero.  There could be too much drag for a light low hp car...

 

Hmmmmm...  That IS a good analogy.

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6 minutes ago, wvumtnbkr said:

I kinda agree with that one.

 

There is such a thing as too wide for the power and weight of the car.

 

I guess that is similar to aero.  There could be too much drag for a light low hp car...

 

Hmmmmm...  That IS a good analogy.

Is a 275 Hoosier to big for a miata?  

 You can get too big of a tire for autocross where you need heat to build in the first turn of a 60 second run.   I think it be harder to get too big for road racing 

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1 minute ago, JDChristianson said:

Is a 275 Hoosier to big for a miata?  

 You can get too big of a tire for autocross where you need heat to build in the first turn of a 60 second run.   I think it be harder to get too big for road racing 

Sure.  I just know that there is diminishing returns on how much extra grip you get for each increase in width.  Compare that to the increasing penalty from weight and aero of wider tires and there is absolutely a place that wider is worse.

 

That being said, wider tires "typically" last longer than narrower tires.

 

I wonder where the crossover point is between wider and slower?  I imagine weight, hp, longevity, heat, and aero all factor in to it.  Would be difficult to get good repeatable numbers.

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1 hour ago, Crank Yankers Racing said:

Why worry about aero? Doesn't work at our speeds and only adds drag. 

 

I'm the first person to admit when I'm wrong, but I still think that's a pretty valid statement when discussing homemade wood spoilers and splitters on 150hp crapcan cars.  I mean, if you watch the video he even says that the flat plank on the back of the car to stop the air probably costs 15ish HP at 100mph.  But, since we're now allowed proper rear aerofoils designed for maximum DF/min HP loss on 200+hp cars for measly 10pts, well now, that's a completely different story.

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  • 2 weeks later...
On 7/27/2018 at 12:40 PM, wvumtnbkr said:

I kinda agree with that one.

 

There is such a thing as too wide for the power and weight of the car.

 

I guess that is similar to aero.  There could be too much drag for a light low hp car...

 

Hmmmmm...  That IS a good analogy.

 

We tested this on an admittedly outlier car for Champ (close to 10lb/hp), and found that on two very different courses we got similar results when comparing 225/50/16 on 8j vs 255/40/17 on 9.5j - the 255's are significantly (roughly ~1.5 to 2s per lap) faster. On a really bumpy track with somewhat rough braking zones in a couple of spots, we expected the much lighter 16 inch setup to be closer or faster, but it wasn't. The lighter smaller 16 inch wheels felt smoother and tracked better on the bumpy track, but lap times were still worse as the 17 inch setup provided more lateral grip in all the turns, acceleration should have been better on the 16's but it is very very subtle to the point of not being able to see it easily in the accelerometer data..

 

Given the ability to fit and afford 12j wheels it would be fascinating to test 305/335 to see if the lap times and wear improved further, but packaging and budget aren't going to allow that (at least for us). The larger 17" wheels/tires grip better, and last much longer, our testing has pointed to the larger setup in every quantitative measure, subjectively, some things are better on 16s, but for racing, there is no question for our application. Interestingly because of the wear rate of the 225s, the larger tires are cheaper to run in 16/24 hour events because we can get a full event from them, where we can't expect same from 16's.

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