Would like input on the differences between 19" wheels versus 20" wheels.

Thank you.

 

Cheaper tires,better ride,longer life.

 

The above points are all true but; the XK/R on 19's just doesn't have the same look as it does on the right 20's...night and day imho. At the dealership saw my car with the 20 Nevis's side by side vs another new XKR with the stock XKR 19's only affirmed my choice. The ride quality is pretty decent too. The nice thing for 2012 was the Nevis rims and other 20's were now a $3500 option vs $5000

 

Also, less chance of rim damage from hitting pavement joints and pot holes. You get an extra 0.5" of sidewall rubber to protect your rim and give you a better ride.

The only upside of 20" would be if you prefer that looks.

Albert

 

18's and 17's are even better choices than 19's (read the link below)... but looks count in my book, big part of the reason why I/we bought a looker like the XK. I never thought I'd ever buy a car with 20's but again, the current XK is one big cat.

Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver

 

They really should have tested the same width tires in each wheel sizes. That way even the skidpad numbers would have been much closer between the 15" and the 19" sizes. They used 235-wide tires for the 19" while only 195-wide for the 15" rims.

I'd be quite happy with 17" or 18" for my XK. I actually prefer to see and feel some rubber around the rim, instead of the look where the rim almost appears to be touching the pavement.

Albert

 

I don't know if a 235 would be right on a 15 especially for the test, as they increased tire width to the appropriate rim size. I agree with and appreciate the extra comfort of more sidewall but I think 17's, 18's are far too small for cars as large as the current XK.

 

It would definitely depend on whether you're putting them on an XK or an XKR, and an '07-09 or '10+. These 4 groups have different spring and shock valve damping, only newer ones have limited slip diffs, and they probably all have different roll bars as well. That makes the C&D test invalid for us, and where they used a range of 4 diameter wheels on the VW, with the suspension not tuned for the larger than OEM 19's, the newer XKR is only made for the 19's and 20's...not 18's or 22's.

I can only speak for the factory 20's on my XKR, and over the last two days I marvelled at what great ride quality they provide. Someone whose very critical of low profile tires has made me particularly conscious of ride, noise and performance on the factory 20's, and over those two days I drove for hours on a mix of county roads, secondary highway, major interstates, and on big city downtown roads that were in pretty poor shape. There was no road surface or speed that upset the 20's, or made them anything but comfortable to drive on. I love them, but the 20's are the popular wheel for the '10+ XKR, and the car is no-doubt tuned well for them. They are also impressive on the road course with the factory tires, but that won't be a consideration for most.

I have heard that the '07-09 XKR suspension favors the use of 19's, likely due to their different shock valving, and I don't know about the XK's. I did notice when researching my XK/XKR purchase that every car I found listed on Auto Trader across Canada had the optional 20's, and a dealer told me that's the only way they order them. I guess that $5000 option reflects consumer demand...and great profit for the dealer!

Bruce

 

Not too many years ago even the Lamborghini Countach was equipped with 15" wheels and really wide rear tires. If I remember correctly it was 345x35-15 on 12" wide rear rims. Plenty of sidewall rubber at that ratio.

 

A 345/35 whether 15, 16, 17, 18, 19 or 20+ I don't believe should not change the size of the sidewall, as the aspect ratio stays the same, right?

The last Countach was produced some 22 years ago so I'm not so sure about the " not too long ago" comment; that was a looong time ago; ahh those were the days...lol

I had quite a bit of seat time in the 5000QV in the late eighties, and was asked to drive one in a television commercial for Philips Lamp. Most of the supercars of the day including my beloved 930 turbo's rode on much smaller diameter rims comp'd to modern day versions and were designed to do so; the much wider rear tires/rims had mostly to do with the drivetrain layouts and cars weight distribution than anything else especially for those with rear/mid engines. C&D knew what they were doing for their test as they simply wanted to see if there would be any benefit increasing the size of the rim over what the car was designed for and if so by how much.

Bruce

Even though our cars are designed to handle 20's I doubt there's any performance benefit other than maybe a larger contact patch which could also be achieved with a 19, although the 20's sure look a heck of a lot better. I too am amazed how compliant the 20's are.

 

This is a often over debated topic.
It really boils down to two sides.... Looks vs Traction (ie big rims vs small rims.)

I'm sorry to burst bubbles here but for those that have any belief that big rims give you better traction, then you really need to get yourself back to the library or your local track and start reading/talking to those that understand the dynamics of a suspension and how all the pieces work. I might recommend Fred Puhm's "How to make your car handle", where suspension theory is covered in extreme mathematical detail. Although an older publication, it covers all current suspension designs in detail.
It really is simple physics, with three key players... mass, inertia, and footprint.

This is a sliding scale that you the owner get to select where you want to be... If you favor big LOOKS then the price is traction. If you favor TRACTION then the the price is looks. As we each drive cars for a different reason, its up to you to decide which side to tip the scale. You don't get both.

Our cars big rims came out of the marketing department, not the engineering department. When the stock holders ask "Which will sell more cars this year" . The marketing department answer is "Everybody is buying BIG rims". So the engineers are told "Make it work as best you can, because above all things, we need to sell more cars."

Looks sell....


Vince

 

Entirely correct.

I used to be racing SCCA GT-2 and GT-3 on 13" rims with slicks using tall sidewalls and a cold pressure of only 14 psi. No 20" street tire/rim combo could match that performance. Also, do not forget about the significant weight penalty for using large rims. They weigh a ton not only because they are BIG but, because they have very little tire sidewall cushioning and must be made stronger and heavier than a smaller wheel with more sidewall.

Vince is right, it is a marketing issue. For me, I think that big wheels are the worst auto-related trend in decades.

Albert

 

Look at F1, I think it is a 14 or 15" wheel. Honda believed in more tire, less rim in their S2000 and NSX; both iconic cars that were noted for handling. They've fallen prey to the marketers now. Too bad.

I agree and like to have a little more rubber to the road. Another consideration in deciding 19" or 20" is the selection of tires. Look on any tire vendor site and there's much more available i 19's. A better tire compound will do a lot more than the diameter. Heck, Bridgestone S03's are available in 19's for XK! Talk about performance!

 

I have tried for years to suppress what I consider blind belief in the "big rim equals performance" mentality.

Sadly over this time I have found that although you can prove that bigger rims offer less traction (hence less safety) less comfort, and higher vehicle maintenance costs (on an astonishing factor), some owners simply do not care about any of those factors over "looks".
Seems odd to me especially when looking at the safety side of the house, but then, we have been forced to put our families in harms way over much worse car mods (like hopping cars, slammed suspensions, and blinding headlights) so in the big picture, big rims do set pretty low on the "bad move" scale.
As an avid car nut and autocross/track guy, I have never chosen a mod that makes my car perform worse. Every mod I do is to improve performance, safety and handling. (And yes, I plan on going to 18" rims as soon as I can get my finances together.)

Vince

 

The Jaguar RSR XKR GT2 uses 18's, not 15, 16 or even 17 inch rims.

Jaguar XKR vs. XKR GT - Find Out Which Jaguar is Quicker at RoadandTrack.com

So does the new 2012 Porsche gt3 cup car
http://www.topspeed.com/cars/porsche...-ar113406.html

These road racing and lemans type cars have had their rims increase in size over the years; there's also been much talk of why NASCAR doesn't use low profile tires with larger wheels but the safety bladder would not fit and also interfere when they need to cut away pieces of the car to allow for clearance after a crash.T

Bottom line is the XK is a STREET car and VERY few of the total produced are used on the track and if so they should have a seperate set(s) of wheels and tires for that.

The current XK is a large two door 2 seater and looks weird with stock suspension height for any rim size less than 19 and looks best with 20's but not larger.

 

Exactly,
Which is probably the smallest you can fit over the calipers.


Vince

 

So what about the F1 15" wheels previously mentioned, I'd imagine F1 calipers are very robust and I'm sure if 15's would be better they'd use that arrangement.

If your car's calipers permitted, would you put 15's, 16's or even 17's on it? Luv to see how that would look.

Again our cars are street cars and not track cars and there are plenty of items on them the marketing dept created that have increased the allure of these cars; ascetically larger wheel's up to a point look better and as I stated very early on offer no additional benefit...nuff said.

 

I dunno, that F1 wheel/tire combo looks kind of good to me...

Ok, arguing over "looks" is a waste of time. We tend to have different tastes in most everything, which is great.

On the other hand I am not sure I understand your issue with smaller wheels/taller sidewalls combo for the XKs. After all the tire diameter for the smaller rims would be exactly the same so the XK would not look under-tired. Since I had 18" on my '05 XK and now 19" on my '08 XK I would probably prefer both the looks and the street performance of a set of 17".

What is unfortunate that they got us to the point where we have to openly celebrate a luxury car that actually has a decent ride these days; something that was taken for granted years ago with taller tire sidewalls. I test drove a Supercharged XJL and I would not be happy with its ride over broken pavement. It was riding on 20". The XJLs were always known for their silky ride; so much for that with the big wheels. I told the dealer that the XJL would be my next car purchase but, I'd pay extra to switch to smaller rims on it.

Albert

 

If you think "looks are a waste of time", a) you bought the wrong car and b) I'd hate to see your taste in women lol j/k
F1 15's on an XK yuck.
This topic is more than 'well done'...moving on...

 

I get a little annoyed with these criticisms of 19" and 20" wheels and tires because they lack the understanding and/or recognition that the tire is just one component of a suspension system that is thoroughly designed to take advantage of the benefits of the low profile, with the goal being to maximize the tire's contact patch and grip. They achieve that goal, but there are definitely trade-offs to consider, and I'll share some thoughts.

The buyer of particularly an XKR consciously accepts a variety of trade-offs, as do buyers of every other brands highest performing models who not-so-coincidentally mostly also use 20" wheels with the same 30 and 35 low profile tires. Those cars all top the performance charts, and you can be sure their suspension engineers used every high tech advance to optimize that performance while minimizing the trade-offs. Formula 1 designers do the same, and it should come as no surprise that the tires aren't the same as on your Jag. We're not talking about owners of 1990's sporty cars and luxury sedans swapping out their 15" 50 series all-season's for 20's.

Having done auto-crosses and track events does not make you any kind of an expert on suspension design or low profile tires. It does however allow you to learn the handling balance and limits of your particular car, and develop the driving skill to extract the most from that particular set-up. Experiencing numerous cars on the track and exploring those handling limits gives you the ability to offer comparative and useful comments about their performance, and this is why you'll often see professional race car drivers reviewing high performance vehicles on race tracks where those limits can be safely explored, monitored, data-logged and compared. Performance of these cars has improved over the years, with suspension and tire technology advances leading the way, and I've personally never heard any of them say large wheels and low profile tires are no good.

When I bought my XKR I immediately took it out on the race track to test its handling limits in a way not possible on public roads, and ultimately at the safest place to do that. I was very impressed with how well the car performed, and any concerns about the 20" wheels, tires, suspension, brakes, overall handling balance, weight, etc were laid to rest. I'm looking forward to more seat time at my home track (Mosport), and compare it to a variety of cars, including a very powerful and well-sorted track car I've run at many tracks across the eastern and central US and Canada.

Now I've been specifically talking about the 2010 XKR which I chose for its higher performance suspension and driveline upgrades that were introduced that year, and I did want the 20" wheels and slightly lower profile tires. A quick test drive proved the tires to be compliant enough for our street use, and a day on the race track confirmed it had the performance I wanted. I suspect that the 19" might be a good match for the softer suspension of the older XK and XKR's, and newer XK's, where their buyers may have different performance or comfort goals, or willing to make different trade-offs.

My best advice to buyers would be to try different factory wheel sizes if you think the pros and cons of lower tire profile could be an issue for you, or just go with the smaller ones if you're not concerned about any performance improvements that the lower profile tire might offer, and would prefer to avoid the extra costs associated with the 1" larger wheel and tire. If on the other hand you just like the look of the larger wheels and find the ride quality acceptable then don't fall victim to biased views of others. Do your own research. I found a good article with a google search that outlines the pros and cons in a rather factual manner that I'll post if I can find it again.

Bruce