Which spoiler looks better? Discuss...

 

I think the S spoiler is too big and a tad boy racer; I like the one that came stock on my 12R it's of perfect proportion

 

I'm gonna get the aerodynamic package and the bigger spoiler at some point. The spoiler on the XKR-S does look a little "rice-ish" to me (along with the front end).

 

Let's see some good pictures of each. I like the spoiler Mina sells, but want to see more picture before I would go ahead and purchase.

 

In case anyone didn't know, the spoiler on the 2008 XKRS, black pack, speed pack, XKR75, and XKR175 are all the same. The Mina RS spoiler is the same as those I just listed but a replica of the OEM. I believe they call it the "RS" because it's the replica of the 2008 XK"R-S" styling kit.

 

I saw on Top Gear that they claimed the XK car got light in the front at about 130 MPH or so and driving anywhere near its top speed of 155 was suicide. Wouldn't this larger rear spoiler make that effect worse?

Vector

 

Gonna have to check the "light in the front end" claim out. Given how close to the ground the front end is on my XKR that's kind of hard to believe.

The Mina RS spoiler ($250) is about $300 less than the Jag upgrade spoiler ($564). If the quality is good that is a good buy.

Ghostrider - I'm assuming you have the Mina spoiler? Is the quality and fit good?

 

Episode here:
028 Top Gear - Jaguar XK Convertible - YouTube

Go to 5:00. It's all about the golf clubs.
Vector

 

My favorite episode... Alas the reasoning was a bit lame, and I suspect more a comedic view rather than reality.

As a certified aircraft mechanic and aviation buff, I can offer pretty good assurance that the spoiler has little to do with the front end lift.
First is the design.... This is a "spoiler", not a "wing". As the name implies, it is designed to break up the airflow at the rear of the car, not present any significant amount of down-force. (You would use a wing for that.) The spoiler just disrupts the airflow to avoid "lift" at the back end.
The car shape in general is a wing, with a curved top surface and flat undercarriage. The arc of the hood and roof-line itself is most likely the cause of the 130mph front end lift.

Sadly the "spoiler" itself is a trade off of looks over function. Rather than letting the airflow smoothly exit the rear of the car, it creates a rather large vortex (or area of low pressure turbulence) behind it. We normally call this "drag" on aircraft, and it not only attempts to hold back the car and rob mpg, but can add significantly to noise thanks to the buffeting air.

If you were to view the spoiler as a downward force, the distance from the mounting point to the rear axle would be the distance of leverage. compared to the distance and weight of everything forward of the real axle, I'd humorously guess it to be a ratio of maybe 5,000:1.

Vince

 

The rear spoiler should indeed provide some amount of downforce, especially as the resistance to air increases.

As for lifting the front end, this would be more of a function of the aerodynamics of the front end. For the spoiler to provide lift of the front end, the dynamics would need to be such that there would be a torque or rotational force around some point (near the middle, center of weight) of the car. The rear spoiler is not creating a rotational force, but simply a down force (vector component down) on the rear of the car, not a rotational or torque force.

If you push down on the rear of a car you don't simultaneously lift the front end. If the car were on a see-saw or fulcrum point then I could see that happening.

 

Loving the aero discussion. I wouldn't worry too much about Jeremy's XK impressions above 130 mph as they might not even apply to the newer XKR's front end and suspension changes. Please post your comments if you find it a problem in your daily commute!

Btw, wouldn't a more pronounced spoiler provide a little more rear downforce in the same way a Gurney Flap does? And if a different spoiler actually improved the merging of the airflow above the car with the air under the car would that not speed flow and reduce drag under the car, and reduce lift?

 

You can't believe 50% of what comes out of Jeremy Clarkson's mouth!!!

He has zero journalistic integrity. He is for entertainment purposes only!

 

I would think so.

Faster flow under the car, especially given the much smaller area will create a low pressure area under the car and suck the car down more. The air flow over the top of the car, given the higher volume will be *somewhat* slower, and definitely have more resistance due to volume of air, which will create a difference in downward pressure as well.

 

I had a 2011 XKR at about 145 mph at Homestead Raceway during the Advanced R Performance Academy. I didn't notice any lightness in the front end. And I certainly didn't feel suicidal at that speed.

 

rscultho: I actually bought the oem larger spoiler 2 years ago and the rest of the kit from Mina (rear diffusor, side skirts and front splitter) last year. I would think you can't go wrong with the Mina spoiler if it's good quality especially when it just sits on top of the trunk using double sided tape. OEM also uses double sided tape. It's the Mina side skirt and rear diffusor that you need to be more careful as it uses epoxy to stay on. The shop took a tough time to have those installed because the pieces would warp on the edges. Maybe someone who actually bought the Mina rear spoiler can chime in better.

Here was the OEM spoiler before I had it painted and installed: https://www.jaguarforums.com/forum/x...spoiler-36866/

 

Thanks Ghost. The price of the Mina spoiler is so much cheaper than the OEM...

The OEM front splitter is $expensive$ - a little over $900 from Jag. Mina's is considerably cheaper.

The OEM side skirts are $348 each from Jag, and any of this from Nalley would be 15% off plus I could go pick it up in Roswell. There's a guy near me (within a couple miles) that could paint the parts. I have not asked how the OEM side skirts are held on.

The rear OEM valance is ~$580, with 15% discount puts it cheaper than Mina's.

So if I get Mina's Spoiler and front splitter, that's about $500 plus shipping. OEM rear valance and side skirts would be $520 + (756 x.85 = $642).

That's a total of $1742 for the parts, maybe another $300 to $400 to paint and install.

 

Just so you know, if you buy several pieces from Chris at Mina, he's great at cutting you a deal. You should definitely call him for a quote before you do anything. Awesome customer service.