I am considering putting 20' wheels on my XF 2011 before delivery vs the standard 18'

how much will the ride quality deteriorate

Regards Louis

 

Reports vary, probably because ride impressions are very subjective.

I find the ride on my base XF quite hard with 18 inch wheels. Some report hard ride with larger diameter wheels, some do not.

Without the computer adaptive suspension the ride will be harder the lower the tire sidewall. That is objectively measurable.

Also, large rims are a cosmetic matter. Additional performance is not necessarily going to result from larger rims.

Rim damage is exceptionally easy to achieve with 20 inch rims.

 

I downsized to 18" on my X350 from Speang 20", as the ride was really harsh, completely unacceptable in fact.

It is your choice, but I would not do it if it was me, I'd spend the money on something else nice.

 

I find the ride marshmallow soft, but as Jagular said it's subjective. What irks me is the added unsprung weight that 20" wheels force you to carry that affect the handling.

 

Even allowing for a subjective viewpoint there is no way the XF ride can be described as "marshmallow" soft.

Compared to any reasonably suspended road car the XF is firm or even hard.

The current fashion for large wheels and ultra low profile tires has nothing to do with handling. Tire companies, wheel manufacturers and car manufacturers are all happy to cater to this bizarre and very expensive fashion statement.

Road & Track did an interesting handling comparison a few years back fitting a BMW M5 (I think it was) with plus 1 and plus 2 wheels and tires. The best handling was at plus 1 from stock but the best ride/handling combination was the stock sizing. The worst was the plus 2 which I think then was a 19 inch wheel.

Most bizarre of all are those who say they do not like the way smaller wheels do not "fill" the wheel wells as if that ever had anything to do with driving. The various appropriate wheel and tire combinations will all fill the wheel wells to exactly the same extent, or the gearing, speedo, ABS and traction control will all be unhappy.

 

My 05 XJR came with 19" wheels and high perf. tires and I loved the car. But I loved it a hell of a lot less after 8 hours on the road. When the time came I installed All Season tires on the same wheels and that helped somewhat.

My ideal car would be XJ8 short with 18" wheels, All Season tires and comfort suspension. But, and this is a big but, I could never, never-ever give up my SuperCharger.

 

Even the 18" diameter wheels are somewhat iffy for those who like more sidewall. And it is not really realistic to gain any sidewall height by going to higher aspect ratios because with the overall diameter fixed, a higher aspect ratio just means a narrower section width to maintain the same overall diameter.

The Jaguar manual typically gives two pressure ranges. A lower one for "comfort" and a higher one for "normal". Normal implying the capacity to run at higher speeds common in Europe.

The question is, does anyone have a viewpoint on whether lower or higher tire inflation pressures are likely to be best to provide protection against rim damage?

 

[QUOTE=jagular;340821]Even allowing for a subjective viewpoint there is no way the XF ride can be described as "marshmallow" soft.

Compared to any reasonably suspended road car the XF is firm or even hard.

I drive in "Dynamic" all the time and that feels too soft. I never use the standard setting as it makes me feel seasick. I don't think you could describe either setting as "firm".

 

When you go from 18" to 20" wheels, and assuming you match tire sizes and profiles so that you maintain the same overall diameter, you often get more unsprung, rotating weight (but that depends on the materials used; there are instances where light 20" wheels can weigh the same or less than 18"s), which degrades acceleration, handling and ride, and generally you get crisper turn in. You may or may not get more overall grip. Even if they weigh the same as your 18"s, you most likely will suffer some ride degradation. How much is dependent on too many factors. For instance, different tire brands and models have different characteristics. Some maker's tires may have softer sidewalls compared to another's, and thus could help make up for the shorter sidewalls you would run with 20"s. For most passenger cars, the ideal wheel size is 18" or 19". Usually 20"s require too many adjustments or compromises. The XFR was developed to run with 20"s, but if your car was not, and performance, ride and handling are important to you (more so than looks), then stick with 18"s or 19"s. If I had a choice, I might have spec'd my car for 19"s. Also, tires for the 18" and 19" wheel sizes tend to be more readily available and less expensive. Finally, not all tire shops can mount 20" wheels with low profile tires without damaging or marring the wheels. When it comes to wheels/tires, weight is the enemy. That is not to say you should compromise safety in order to get light weight, however (e.g. certain wheels made for track use can be very light but could break/bend easily - people are surprised by that, but think about how tracks are smoother than public roads and have no pot holes, grates, expansion strips, etc. and it makes sense).

 

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OK. Shorter post next time.

I will also use paragraph breaks.

I noticed also that no matter how many spaces I put between words, they come out automatically formatted to be compressed.

 

The smaller the wheel the taller the sidewall, regardless of aspect ratio, if the rolling diameter is to remain constant. Indeed, if the rolling circumference is to remain unchanged the aspect ratio and tread width of all variations that fit a particular car are fixed by the dimensions of the stock wheel and tire.

All other things being equal, ride will be more comfortable the taller the sidewall.

Also, often overlooked, the total volume of air inside the tire is less as aspect ratio gets more extreme on larger rims. Ride comfort is affected by the spring rate of the tire itself. The smaller the internal captured volume of air inside the tire the higher the spring rate for that tire. Often you will note that lower profile tires require higher static tire pressures. This is to reduce the deflection of the sidewall under varying loads, i.e. higher spring rate in the tire.

With the adjustable suspension the XFR on 20 inch rims is supposed to have an acceptable ride. If you do not have that adjustable suspension then likely the ride will be much worse on 20 inch rims. The standard springs and shocks are suitable for the 19 inch rims which come standard on the premium luxury level. The "Portfolio" trim with 20 inch wheels can be a bit too firm for most people's expectations.

 

No filling the wheel well doesn't have to do with driving, it has to do with appearance. Appearance btw, is why most people upsize their wheels.

Have you actually ever upsized or are you just repeating what you've read/heard? A reasonable increase in overall diameter of a wheel and tire combo does not inhibit any of those systems from carrying out their intended function. In fact, cars are engineered to handle reasonable variations in overall diameter. Yes, the speedo is slightly off but the rest of those systems are smarter than you give them credit for.

 

OP, since ride quality is so subjective, your best bet is to go to your dealer and drive an XF equipped with 20s. The ride will be less compliant for sure, so you'll have to decide whether the look of 20s outweighs the reduced ride comfort.

 

Thanks you for the informative advice. I am going to run the 18' wheels and when I need to replace Tyres I may replace them with 19' Caravela but only for the" Look" - I will never drive fast enough to put a 13' wheel to the test.

Kind Regards Louis from Newport in Sydney Aus.

 

I just took delivery of an XF with the 20's. I drive on good roads most of the time, so when I do hit a few bumps I don't mind it. But I love the way the 20's look on this car. I don't regret the 20's at all. Good luck.

 

Actually, Jagular is right for most conditions.

 

I respectfully disagree. An exact or almost exact match is not needed to keep your electronics in tact. The industry standard calls for overall diameter (OD) within 3% of stock and that's a conservative standard. On our cars that's more than 3/4". As I mentioned, cars are engineered to function normally even with a modest change in OD. Just think about tire wear alone. You can wear through 1/4" of tread before needing to change tires. THat's a change of 1/2" in OD. Certainly, the engineers account for this.

 

From Tire Rack:

"The other size consideration is overall tire diameter. Since many of the functions of today's vehicles are highly computerized, maintaining accurate speed data going into the computer assures accurate instructions coming out. And an important part of the speed equation is your tire's overall tire diameter.

For cars and vans, staying within a 3% diameter change is desirable. Pick-ups and sport utility vehicles (SUVs) are usually engineered to handle up to a 15% oversize tire. Most tire dimensions can be calculated. For more information review the Tire Tech article, "Calculating Tire Dimensions." While at first a 3% diameter increase or reduction in tire diameter may sound very limiting, in most cases it allows approximately a 3/4" diameter change."

15% for pickups and SUVs! That's 5" or so depending on the truck. I've personally run tire/wheel combos with ODs of .80% over stock on a car and 4.6% over on a truck. The point is, there's leeway built in.

 

Keep on trolling, I'm busy elsewhere.