Bruce

You appear to point at me with the above comment so, let me list some of my qualifications on suspension design and solutions:

I raced for decades from autocrossing to road-racing in some of the most popular US racing franchises. I won autocross championship (all handling) and won (3) GT-2/3 Regional Championships as well as (1) West Coast Road Racing Championship. I also finished second in the open wheeled Formula Super-unlimited yearly road racing championship and won countless other races and top-3 finishes over those decades.

I did all my chassis, suspension, body and engine work, so I must have understood something about suspensions.

Having said that, my chief problem is NOT that you, or anyone else buys or likes big wheels BUT, the fact that when I go to purchase a car the smaller wheel/higher sidewall options are non existent.

Besides the preferred looks (by some, not me) those extreme large wheels and low profile sidewalls provide hardly any advantages while they stick you with many disadvantages (unsprung weight, road-damage, cost, ride comfort, etc). Next time at the race track, please note that some of those low powered street/modified race cars on street legal R compound tires using small rims and tall tires tend to turn far faster lap times than any of the supercars with big wheels and super low profile tires. I used to laugh when we had street-car days and the guys with their super-duper street Porsches, Ferraris, etc, thundered around the track about 10-20 sec/lap slower than the 132 hp Mazda RX-7 modified stock race cars. I heard one Porsche owner angrily yelling that the stop-watches used to measure their lap times against the RX-7 had to be off and cheating.

The truth is that, like you said, there are many variables to top handling. The underpowered cars beat the high powered street cars because they had a much lowered center of gravity, much stiffer springs and much tighter shock rebound controls. They go around the turns far faster with greatly reduced weight transfer and body roll. When they need braking, the braking distances are far shorter than those of the 4000 lbs street cars. The extra engine power can not possibly make up the difference in the short straights between turns. The apparent advantage of a 20" tire, the fact that it sits so squarely on the pavement, can be its disadvantage when the body rolls over it, the suspension compresses and the camber and toe-setting naturally shift during extreme cornering loads. It can also be a disadvantage during shock rebound action over elevation changes when a stiff sidewalled, very low profile tire can actually leave the ground, while a higher profile tire simply expands from compression, still maintaining partial ground contract.

You are correct in saying that suspension science effecting ride harshness has progressed significantly over the decades. That, mostly due to the computer controlled damper actions that adjust the damping rates thousands times a second. That advance is clearly seen on my '08 XK which actually rides better on its 19" tires than my '05 did on its 18". Yet, the same progress, if transferred to a 16" or 17" tire would make those ride even better, as well.

Would you say that it is possible for a 20" wheel to provide the same ride quality as a, say, 17" would, using the same suspension components? Like I mentioned above, I was not happy with how the 20" rode on the Supercharged XJL over bad pavement, of which we have too much. From a sports cars, such as the XK or XKR, one usually expect a harsher ride but, most people buy a luxury sedan expecting a silky smooth, quiet ride with still decent handling. These days it is very difficult to find a luxury car that matches the ride comforts and tire noise absorbation of an earlier model of the same brand. On my longer drives I actually will take my SUV exactly because with its high profile sidewalls it gives me a superior ride over bad pavement than my street cars with the low profile tires.

I keep thinking, going back nearly 3 decades when I used big 16" street legal tires on my Mustang to win the autocross championship against the top modified high powered cars, including Porsches, Corvettes and even a Jag E-type. If anyone wants more cornering speeds and handling than what that car and those tires provided, that person should voluntarily check himself into a jail, for what my local Sheriff friend told me would be a criminal traffic violation :-)

Albert

 

Newbeee here following this thread. Daily driver...100 mi/day. Keee-rist my 20s look sweet and I am thrilled with the ride on Bridgestone Potenzas.

I do appreciate the viewpoints but are we approaching analysis paralysis?

BTW, thanks Bruce H. Us "un jaguar educated folks" can sometimes feel intimitated here.

Best to all,

 

axr6,

I think Both Bruce and RJC are directing comments to me not you, and it was never my intent to cause this kind of confrontation.

Physics already dictate the flaws of low profile tires, so to me the only valid question on the table is "is it noticeable to the average driver".

That is a question only the car owner can ultimately answer.

My whole involvement with the post was intended to address the OP question of pros/cons to wheel size. My response being "There are a few pros and several cons". Seems I didn't do so well in my overall wording.

As long as the OP understands the pros/cons, and buys accordingly, then he/she has made an informed decision regardless of the direction chosen. It's those that don't ask, and don't research that I often see follow up posts asking "Why the ride got harsh", or curse "I just bend another rim!" I feel bad because someone never took the time to tell them it would happen.

In the end it is always their car, and their choice.

Again, I did want to apologize to those I offended, and especially the OP for destroying his/her post by provoking unnecessary tempers.

peace
Vince

 

Albert,

We're on the same page, and the shrinking selection of higher profile tires indicates how both automotive design and consumer demand has changed. The light-weight "momentum" track cars are slowly disappearing as their aging donor street cars are decaying. My 3400 lb Supra TT street/track car that used to be heavy is slowly becoming a light-weight compared to all but the factory purpose built race cars that are thinly-veiled as street legals. Meeting modern safety requirements adds a lot of weight.

When I built it for track use I also designed it's suspension, and had custom damper valving to match my choice of spring rates. I selected staggered profile tires front to rear to optimize turn-in, rear grip on corner exit, and for brake fitment, and chose the light 3 pc wheels to fit those tires. They're 30 and 35 series like the Jag, but 30 mm wider. I can balance the car on the head of a needle and it rides better than when on stock suspension...owing to the superior spring and damper valving. I was reminded of that when I temporarily swapped in the stock suspension to have the race dampers refreshed and my wife asked why the car was riding so poorly! The XKR exhibits that same combination of superior handling and ride quality on its 20's, albeit on street rubber vs R-compounds.

The story I like to recall is the day I was lapping Mosport while a Fort Lauderdale team was there sorting out their 997 in preparation for Daytona the following week. I had known one of the team owner/drivers for a few years and at the end of the day I asked him what times they were lapping. They were a little off their goal and a bit disappointed. I didn't have the heart to tell him I was lapping a fraction of a second quicker. A year later they asked me to drive in the ALMS with them!

Bruce

 

Glad I took one more look here as I already moved on.

It's all good Vince and thanks for the completely unnecessary apology. There's a lot of passion when it comes to our cars and sometimes it really shows. I am very happy this sleepy forum is picking up some nice momentum and we should all be proud to be a part of each others experiences. I've even gone as far as sharing a very personal, very painful medical issue so I can help prevent any of you from potentially getting harmed. Again, no apology needed on my end and you're a real gentleman for doing so.

 

Vince,

You merely encouraged me to broaden the discussion with first-hand experience for hopefully the benefit of all...and for that I thank you. I am curious though about your desire to lay out a bunch of money when finances permit to buy 18" wheels and tires for your XK. It just seems like an awfully poor use of funds. Do you think they will provide a marked improvement in performance that is currently lacking?

Bruce

 

Yes, most definitely. By far the most beneficial thing I gain is ride comfort with the extra sidewall (I am gettin' old after all). But the comfort can also come from reducing unsprung weight.
With the right rim and tire choice, it should be possible to drop an easy 10lbs of unsprung weight off each corner (you have to admit 65lbs for a tire/rim combined weight is astonishingly high, which is what my 19" dial in at). Team Dynamics Rims or OZ Racing come close to 20lbs for an 18x8.5 so it may even be possible to get into the high 40lb range tires and all!
Although deep pockets can find light weight 20" rims, I can go down to 18's AND buy some of the best high end tires for less than those rims would cost (and still have money left over).

So for my driving style, 18's are where I'm headed... better ride quality, improved response to road imperfections, and lower annual maintenance/tire costs all spell "Win" for me.

Vince

 

A variety of softer side-walled tires would accomplish all 3 and retain the car's stock appearance. Wouldn't reduce unsprung weight, but would save you the cost of buying a set of wheels! Be sure to let us know your impressions when you make the change.

Aahmichael,

When I checked to see what model these wheels would be going on I found it was for a 2013 XK you have on order. With your preference for a less aggressive look I wonder if the 18's might be a good choice for you also.
Bruce

 

Bruce

I bet if felt good to be lapping faster than that Porsche :-).

I remember the Supra TT and the fact that it was considered "too heavy". That was the time when I got my first TT RX-7 that was about 5 - 600 lbs lighter. The 16x8" wheels on that car weighted something like 13 lbs each. It was just about unbeatable as a stock car on the track. I remember making the hard decision to switch to 17x9.5 wheels at 17 lbs each. Gaining 16 lbs were like pulling teeth.

Way back in the 70s I had a 2+2 Lamborghini Jarama. The press complained about it being too heavy. It weighted 3450 lbs and had the 4 liter V12. Indeed it was heavy for its time. As a member of the board of Directors of the Lamborghini club, I went to the factory campaigning for them to differentiate themselves by making their cars super light weight, using carbon composites. I said that for the price they were charging that technology should be included. I actually showed the model by making a carbon fiber hood for my Jarama in my own garage that weighted 7 lbs, compared to the 51 lbs steel hood of the car. By the time I got done with my mods on the Lambo, it blew the doors off of the Countashes, Miuras and various Ferraris, including the Daytona.

It took close to 30 years for Lamborghini to finally make a carbon chassied and bodied car that weighted around 2200 lbs. I no longer follow them, not even sure if it is in production. But, for the prices exotics charge that should be the differentiating factor against your garden variety of low priced, high performance cars, such as the Mustangs that may just nip them these days on the racetrack (Boss 302).

Yes, I consider 64 lbs for a 19" wheel a "crime against automotive technology". It hurts my performance senses. Will I change mine, like Vince is thinking? Maybe, if I can solve my droning issue first, which will allow me to keep the car longer term to make the investment worthwhile. I just called a muffler shop asking them to install a crossover pipe near the cat converters, hoping that it will even out those "pah...pah....pah...pah..." exhaust pulsations in the exhaust that give me a headache. The shop was not too thrilled about doing it so, I will have to search for an other muffler shop. That is about the extent I am willing to go, if it still drones after that I may have to trade the car. Hate to do it as I otherwise love the car.

Albert

 

The 19s are standard, and that's fine with me. When the dealer asked me if I wanted to "upgrade to 20s" I honestly didn't know what the difference was, or why people spent so much money to get the bigger wheels. I've learned a lot in this thread, and thanks to everyone for contributing to my education.

 

Glad you were able to make a decision. Too bad you have to wait months to get the car. I had to wait 5 days and I could hardly stand it. I guess it's ok to go a little off-topic now....

I simply never get tired of passing Porsches. It's probably some kind of a flaw, but I simply can't help it.

I seriously looked at buying the RX-7 TT as well. Such a beautiful and high performance car in every respect. I became concerned about durability on the track though and ended up buying a '93 MR2 T instead. I did suspension and power mods and continue to track it. I chose forged NSX rims (15/17lbs) to get the tire combination on the car that I wanted. Only thing to fail has been the stock turbo from running higher boost lap after lap, but the Garrett's been a champ since 2003!

The story I like to recall in that car is the day I wore down a friend's new GT3 until he finally let me by at a lapping day. I was all over the back of it around every corner at Mosport, and most of the bits in-between...but I just didn't have the grunt to make a pass on the up-hill straight where he could get about 4 lengths on me that vanished in the brake zone. Eventually he started getting a little tired and loose from seeing nothing but MR2 in his mirrors and reluctantly let me by. In the paddock we chat and he pulls out a 350 whp dynograph of his engine, and guesses the MR2 is closer to 400 whp. At first I didn't have the heart to tell him...but then with great humility I said... 286! He was experienced, but with a lot more seat time in his Viper GT and ACR. None-the-less it was a Porsche... and I just never get tired of passing them!

Bruce

 

I agree for the most part but when I get an XKR, I'll follow the lead of the Jaguar tuners Arden and Startech. They use 21's on the XK model. It's good enough for them and good enough for me. SHould provide lots of eye catching action too.

 

You made a good decision for reliability. That was one thing the Mazda rotaries lacked. They were fine when running stock boost but, when running higher boosts the engine was basically a grenade. One bad tank of gas and the engine would be gone. No warning; if you hear a rotary ping, it is too late, might as well start pulling the engine. Stock boost was 10 psi. My present ported street RX-7 is set on 19 psi boost to get close to 500 engine hp on 103 octane VIP race gas (it gets expensive for gas). I changed one engine in this car when right after an exhaust change the engine pinged near redline and that was it. Turned out that the fuel pump was weak, could not deliver enough fuel at redline, thus leaning out the fuel mixture and burning up the apex seal. Of course the broken seal vented into the twin turbos, destroying both... yeah the pleasure of turbos...

In SCCA no turbos were allowed so, we bridge-ported the engines. We got about 245 rwhp in GT-3 and about 285 in GT-2 specs. I think the min. weights were around 2000 lbs for GT-3 and less for GT-2. My engines were good for about 1 season (15 races) and when they blew, it was almost always the carbon apex seal that would let go. Once I lost 3 engines (3 seals) in 3 consecutive race weekends. But, they were cheap to rebuilt, less than $1000 for the apex seal change, doing the work myself. They also ran fine on regular gas vs. high octane race gas for 3 times the price for piston race engines. Rotaries were terrific race engines but, I would not recommend them for street use when over boosted.

Your friends GT-3; what race sanctioning body was he running with? That hp figure sounds very high for a GT-3 engine, if it was under SCCA.

I do share you pleasure of blowing off Porsches, particularly the rear engined 911 variations. Can't believe that people hold those cars in such high esteem. Stock 911s never made good race cars.

Pictures:
1) First lap action coming off Corkscrew at Laguna Seca. GT-1 Vette leads, I'm second in the teal Mazda, right behind is the barely visible wing of a Superunlimited Porsche and a factory Ferrari World-series race car. Behind are couple of quick Baby Grands and a 911. That was also pretty much the the usual finishing order.

2) Partial Formula grid at Thunderhill. My car is #69. I chose that number since it looks the same when upright and when upside down :-). You do get upside down occasionally in hard racing :-).

3) Victory lap at Laguna Seca at the Corkscrew turn-in, with my crew chief squatting on the passenger side, holding the flag.

Albert

 

Great photos! Racing certainly provided you the opportunity to hone your driving and wrenching skills!

His 911 GT3 was bone stock, and we were doing regular open lapping days.

Bruce

 

My '07 XK came with 19" wheels and all season tires. I've had the car a bit over three months and have found the handling and ride quality to be top notch. I have a 20 mile round trip commute over a variety of roads, and the speeds are from 20 mph to 55. Road quality, well, it is mid west, spring, which means potholes. I have no complaints, and find this car lets me miss more potholes than I hit.
I think the 19 's look plenty large for a car this size, and would drop to 18 's if money was no object. I guess for a more "classic" look, I never even considered going up to 20 inch wheels.

 

Your car looks beautiful.

 

Apparently Ian Callum wanted 21 inch wheels on the new Jag's but Jaguar made him settle on the 20 option.

Ian Callum article and Jaguar feature
Jaguar, the quintessential British luxury nameplate has been enjoying a rebirth for some time. Ford Motor Company took over Jaguar in 1989, improving quality and reliability and ushering in a new modern design language with the 2007 introduction of the new XK coupe. Though Jaguar was sold to India’s Tata Motors in 2008, Ford left Jaguar in great hands with technologies already developed and product planning firmly in place along with a brilliant design chief at the helm, Ian Callum. Taking a glance at the new XJ sedan tells enough of the new passion and craftsmanship infused into Sir William Lyons’ legendary company. “I always felt Jaguar really needed to be a modern car company….We have [had] a lot of retro stuff in the past, a lot of heritage and now it’s time to move on,” Ian told me as we perused over his work on the XF sedan. Affable and down to earth, Ian has his thumb on the pulse of the next generation of luxury car buyers. “I want young people to like this car...because that’s the future customer,” he remarked. His design ideas reflect modern philosophy that has resonated in the marketplace, “If I had my way I’d have 21-inch wheels.…I’m sure some of your friends would pick 21-inch wheels….The bigger the better.” Though management made him settle for the 20-inch wheel option, he was able to get other ideas through. “The grille [has] got a lot of sparkle to it,” he told me in regard to the chrome wire mesh that adorns the nose of the XF along with a new Jaguar symbol. Most notable, however, is his work on the interior, especially the innovative gear shifting knob and the motorized vents. “I wanted something that will be fun when you get into the car….It really feels like a theatrical event when [you] get into the car….Is it necessary? No. Is it fun? (Yes.) And that is what it’s all about,” Callum expressed. The new energy and approach is evident in Jaguar’s breathtaking products. “I think it’s (XF) the best proportioned car in its class…a full five-seater,” Callum commented. The final iteration of the XF surprisingly retained a lot of the concept C-XF that debuted in Detroit two years ago. My query of this fact prompted Ian to reveal a secret,“[It is an] actual fact. When we did the C-FX concept, this car was done….The concept is derived from this car.” In theory, concept cars provide the template to create the design language for products to come. “The thing about concept cars is that designers want to express themselves….It gets us to the next level of creating,” opined Ian. Before Ford sold Jaguar, the XJ was already in the works and a previous conversation with Ford Global Design Chief, J. Mays, reiterated the process. This is captured by the XJ’s stunning looks which are based on the “maturing” of the XF’s design language in which a stretching of its lines produced a brilliant ultra luxury sedan. With an extended-range version of the XJ planned and a new E-Type coupe rumored, Ian and his design team are sure to amaze the public for years to come, bringing a profitable renaissance to Jaguar. Jaguar International - Market selector page

 

So, Callum thought the XF dahs vents were fun. Interestingly it was a HUGE turn-off for me but, then, I am older and not his target population. When I first opened the door of an XF and looked at that plain, all aluminum dash with, what appeared to be, blanks, it reminded me to a cheap 1960's vintage American car with most options missing, replaced by blank panels. Only after I found out that those cheap looking "blanks" were motorized vent openings. Still, I shut the door quickly saying to the dealer that the interior of the XF did absolutely nothing for me.

Then, I moved on to the new 2011 XJ and was impressed with its interior as well as with the exterior. I still think that it will be my next Jag as long as I can get the car with a tire/wheel combo to deliver that silky ride and handling that my old XJ used to.

Albert

 

Just look at how nice it looks with 21's.
They fill up the arches and provide huge grip.
With the proper tire selection, the ride will still be nice.

 

Sorry, not buying the huge grip part.

Vince