Hi All,
I'm looking to reduce to moment of inertia or rotational mass of these over size 18 rim/tire arrangement that 56 pounds each. There has to be some serious horsepower and gas milage losses with these rims that look like they belong to an inner city high school drop-out. Does anyone know what the smallest rim size that will clear the front brakes on the 2001 base model XKR? 17's are still pretty large. Would like to find some light weight tires to match.
Thanks,
Mike

 

For the x100 series xkr 18's are the smallest you can put on a xkr. For the x150 series 07 and up, 19's are the smallest. They need the big wheels for the big brakes. What wheels are on your current car?

 

What brand wheels do you have on the car now? You don't need to go smaller to save weight, you can just buy high quality forged wheels and good tires.

 

If it has non-Brembo brakes then 17's will fit. Possibly 16's that are forged.

 

Can't really help ya too much, but I have looked at this for my XK, trying to get down to 18", and only a few otioins exist. One is heavy factory "Venus" rims, another is custom made, and a third is to adapt off our silly 5x108 pattern into something more universal (5x114)
Hard to think of an XKR on somethingas small as 17", but only the R owners would know....
I think 19" was the smallest ever sold on the XKR, while 18" were offered for the XK for several years.

Here is some helpful rotor info all may appreciate:
From 2007 to 2012, Jag has put 3 rotors on the FRONT
2007-2009
XK used 12.83"
XKR used 13.98"
Alcon Option bumped to 15.75"

2010-2012
XK used 13.98"
XKR &S used 15"

Jag has put 3 rotors on the REAR.
2007-2009
XK &R used 12.83"
Alcon option bumped to 13.87"

2010-2012
XK used 12.83
XKR &S used 14.8"

This was collected from various rotor vending sites, so accuracy is only as good as what they could tell me...

Vince

 

Looking at the space between the caliper and the inside of the 18 inch rim, it looks as if 16 inch rims might fit. Just wondered if anyone has tried it. All things being equal, (no matter what the quality of the rim or tire manufacturer) the smaller rim diameter has a smaller the moment of inertia and a lower the rotating mass and associated horsepower loss. There is also another reason why formula-one cars don't run the ultra low aspect ratios, short sidewalls do not conform to real world road surface irregularities.

 

No doubt...
But your "preaching to the choir" in my case, as I have defended that thought for years....
That said, few here buy a Jag to race, and as a highway cruzer, the base design does quite well. You will find most here feel looks trump practicality... I just bow, and admit "to each their own"... We all love our cars for various personal reasons.

Good luck in your persuit, and keep us posted. As I said, your directions are limited, and even those require a good amount of expendable cashflow. (Something I am limited on).

Vince

 

Cast 16" (such as OEM Jag) will not clear the front brakes unless you fit the smaller XK8/XJ8 brakes. Forged 16" might clear since they're thinner and have more room on the inside.

F1 cars have a bunch of rules regarding car construction including the size of the wheels which have nothing to do with ideal performance. They're always coming up with new rules to slow the cars down.

 

Thank you for the replies folks,
I'll let you know if i come across some light weight wheel-tire combinations and maybe an easy way to evaulate the associated differences in horse power requirements.
ToronadoMike

 

You must REALLY hate the look of 20"s then.