Jaguar XKR 4.2 with 18” wheels
 

Has anyone “downgraded” wheels to 18” size looking for reducing as much unsprung weight as possible? Stock wheels seem heavy and I have no idea if this route will have noticeable benefits

Thanks

Previously asked and answered:

https://www.jaguarforums.com/forum/x...eel-xk-190076/

thanks, I had read that thread but If I’m not wrong it’s an XK who had 18” wheels stock. I’m asking if any XKR owner has experience this downsizing intentionally and can tell us advantages and disadvantages

Many aftermarket wheels are much lighter due to less mass and forged wheels like HRE can be even lighter. I had 20" Sentas and they were nearly 40 pounds apiece. I went with aftermarket 20" wheels at almost half the weight. Reduced un-sprung weight does make a big difference in handling, if you need it otherwise it's entirely unnecessary. The main thing you have to confirm is wheels barrel clearance for the calipers. I have the Alcons fitted and there are barely any 19" wheels that will fit and highly unlikely ANY 18" wheels available.

I use jaguar 18" wheels for my winter tires.
For reasons not conflicting with this line of reasoning: https://www.tirerack.com/winter/tech...jsp?techid=126

It seems 2007 Jaguar XKR uses 18” wheels: 18x11”:

Jaguar XKR GT3

Most real race cars use 18 inch wheels, perfect balance of sidewall and race brake clearance. It keep in mind that race cars including the one you referenced are just shells of the street version. The Apex car you reference has true race car brakes, not the OEM brakes, race suspension, drivetrain and chassis modifications.

It also doesn't hurt that real race cars have carbon/carbon brakes, so smaller disks do more stopping.

Made by Alcon, but different than the ones you put on your car.

Yes, Alcon and AP Racing with smaller, usually 385mm rotors, are 2 of the biggest names in pro racing however CeeJay, carbon ceramics are NOT used in professional racing - much too costly and much too easy to damage.

The Verizon Indy Car Series is using carbon-carbon brakes from PFC.

Sorry I should have specified I’ve spent a number of years in the pits at IMSA, PWC, WEC, GT and Cup cars competitions. I have specifically spoken with Patrick Long’s chief mechanic and others such Rebellion, Flying Lizard, etc on this subject and was told cheap virtually indestructible (on the track) metal discs would not be replaced by fragile expensive carbon.

Please advise what are these wonder 20" wheels that.come in at around 20lbs?

I noticed a distinct difference after my wortec discs went on which reduced overall unsprung by 45lb in total, if I could save another 80lbs that would be amazing! :)

I’ve floating 400mmx36mm 2-piece AP Racing rotors with alloy hats which save a great deal straight away as well as lighter fixed 6-pot alloy calipers.

As for the wheels, they are 9 inches in the front and 10.5 in the rear, Verde Axis very simple Y-spoke design with very little alloy material in the design which helps contribute to their lower mass.

EDIT: I think actually mine weight in at around 22-23 pounds apiece and recall a friend had a set of HRE forged alloys that were about 18 pounds apiece. BBS have some lightweight wheels as well.

Jah, you seem to have underestimate the weight of your new wheels, as the below link shows the front @ 9" are 33lbs and the rears at 10.5" are 36lbs

https://verdewheels.com/wheel/v99-axis/4929/1902/

So best case scenario you are carrying a minimum 42lbs more than you thought.

Can't find a weight saving on the AP site, but based on the above, you may well be carrying more weight than you thought. Before I fitted my wortec I made an effort to actually weigh them in comparison to show my weight saving, and that was new discs vs old 4yr worn ones and it was 45lbs and is documented on a thread somewhere.

Before my Vulcan's (with TPMS fitted) went on I weighed them with TPMS fitted on Saturday, they were (IIRC) 32lbs fronts on 9's and 38 on rears at 10.5", so a mere 2lbs difference (if my math is right) from your non-standard wheels...so you may want to amend the 'light rims' from your signature. :D

Your years in race pits should have taught you this no?

Sure, larger diameter wheels weigh more, but also larger diameter tires (numerically)weigh less. I don't know any figures, so don't rag on me.

With less profile, a stiffer structure is needed to maintain the same weight loading.
When I shopped for wheels and tires in order to go lighter, I found:
18" tires availible were lighter than either of the tire options for 19" and 20".
19" and 20" tires are about the same weight.

Likely the 18" size for the J has a softer structure, but the 19" and 20" both have similar structure to eachother, and thus similar weight.

When it comes to weight remember that material profiles that allow for enough stiffness will add up in weight.
This also means that a forged wheel is not likely to be designed to be lighter than a cast wheel when it comes to cars in the X150's weight bracket.
The forged material has more flex before breaking, so it is tougher than cast.
However, forging does not make any significant increase in stiffness.
Stiffness of wheel is an important handling factor and both cast and forged wheels of equal design profile and stiffness will end up with roughly equal weight.
The difference is when you smash it up on the curb lap after lap, etc...

My weight statement was based on weighing the wheels with a calibrated scale.... As for what is stated on what you linked I have no idea what that number represents. And again, I weighed the Sentas as well at around 40 pounds apiece.

Tyres tend to vary greatly in weight based on model even if the same spec, I know because when I was picking track tyres I found some were a little as 26 pounds while others the same size were over 30 pounds.

But that doesn't detract from what is on actual manufacturers website , so unless you actually took pics of your 'calibrated weighing' then that's just pfft!