18s won't fit over my brake. The 20s barely fit and they probably ARE 20s because 19s also won't fit. Maybe they would, I've never checked.

What I DO know is that going from 20s to 19s would only add 12mm between the road and the wheel, and that's IF the tire size is increased to match the diameter of the tires on the 20s.

THEREFORE, if you want the 20-inch look but want the supposed "19-inch ride", simply get slightly larger tires. They fit EASILY. Besides, slightly larger tires would look a bit better inside the wheel wells AND get the actual vehicle speed closer to what's displayed on the Speedometer.

 

A stiff 19" will ride harder than a soft 20".

There are many aspects of the system.

I found with my Porsche 944 that the tire designs for 17" wheels differed greatly from those for 15" and 16".

I could achieve similar results with 15" or 16", but as soon as the move to 17" was made the tire construction changed dramatically.

It is my belief(without testing) that the tire structure of 19" and 20" for our cars would yield similar results. Change of brand and tire model; or tire pressure would result in a greater difference than keeping all other factors the same and making the change from 20" to 19".

The larger outer tire diameter would make a difference.

When it comes to ride, one of the more important aspects is the seating surface. Think of the two chassis Lotus F1 car. You could have rocks for wheels and suspension, but with the right seating arrangement still be comfy.

 

KJ07, I'm a fan of the Bridgestone brand, and also the Conti DWS. My concern from your comment is that you have not said what 'Model' Bridgestone you came from. The DWS is very capable and accurate to the task they were designed for. If you were expecting Summer tire performance from an all-season formula and tread design, then you have clearly seen that it is not possible. I am sorry to hear the DWS do not work well on our cars thou... I cant think of another all season I would rather run (including those from Bridgestone).


I take it you have the Alcon package (15.75 inch rotors)? Base XK rotors (12.83 inches) fit within Jags 18" rim. The first gen Alcons may indeed not fit a 19" rim. I do know the 15" rotors on my base 2010 XKR do fit 19"rims.

It is interesting to note that folks today are swayed by marketing to believing that larger rims 'must mean better performance'. That simply is not the case. Of any measurable performance aspect of a tire, the only category a larger rim wins in is called 'turn-in'. The 20" will however break loose sooner (both spinning and cornering), ride harsher, damage rims quicker, and cost significantly more. That's common knowledge in the race industry, and pretty self explanatory if you study how a tire interacts with the road (think 'contact patch' and lower pressure conformity to the road surface. Slip angle and cornering force are key role players as well).

Vince

 

I also have the 15" rotors, and there is less than one inch between the caliper and the wheel. Therefore 18s will not fit. Of course, I'm sure some wheels are shaped differently than other wheels and that some may provide clearance.
I'm sure the 19s will as they were offered OEM.

 

 

So, those Contis were Bridgestones! That reminded me of this old joke.

A World War II pilot is reminiscing before school children about his days in the Royal Air Force. (Joke best delivered with a good thick British accent)

"In 1942," he says, "the situation was really tough. The German Luftwaffe was a very strong air force. I remember, " he continues, "one day I was protecting our bombers and suddenly, out of the clouds, these fokkers appeared.

(At this point, several of the children giggle.)

I looked up, and right above me was one of them. I aimed at him and shot him down. They were swarming. I immediately realized that there was another fokker behind me."

At this instant the girls in the auditorium start to giggle and boys start to laugh. The teacher stands up and says, "I think I should point out that 'Fokker' was the name of the German-Dutch aircraft company"

"That's true," says the pilot, "but those fokkers were Messerschmitts!"

 

 

Until now, I thought my wife was wrong ...

 

Plasti Dip: Put 3-4 layers on and if you don't like it or want to change it just peel it off. I love the stuff.

 

Yep that has been suggested before...Easiest way and cheapest to see if you get the right look

 

New tires will always feel squirrelly. so it may go away with a few more miles. Also larger rim sizes tend to run at higher pressures. The door Plaque listing is really kinda a joke once you leave the OEM tire. I guess I should say it is a 'rough estimation' at best.

All tires will require tuning to get the most out of them. Back in my track days, I use to even have different pressures right to left side depending on where the cars center of gravity was.

V

 

I have been running the Conti's (on 20's) at a higher pressure, so they 'feel better'. Time will tell if added miles helps (didn't get a chance to put on many last year).

 

Fair nuff...
Question for you 20 inch rim owners (that came as stock OEM): What pressure does your door plaque say?

Just curious...

Thx

 

Mine say 33 front and 35 rears. I run my Conti DWS 06 at that pressure and the ride is pretty comfortable. I have about 14K miles on the rears and 6K on the fronts. All have a lot of life left in them. The ride is much better then the OEM Dunlops.

 

I have the 20" wheels and conti dws 06s on my X150 XKR and I think it rides as good or better than my X100 XKR with 18" wheels rode with Pirelli OEMs, Bridgestone Potenza RE760 Sports or it's current Firestone Firehawk Indy 500s; and that car has had most of the suspension rebuilt. Not shockingly, the platform is tighter and I think that helps a lot, since the tramlining and jarring at uneven pavement upset the chassis more on the older car.

Next spring, since the rears are near replacement, I am thinking replacing with Michelins or Bridgestones; always been impressed with every tire I've had from either brand.

 

Ok, that may explain it. IIRC, the door placard pressures for my 19" equipped car is 30 front and 33 rear (can anyone verify that? I'm at work). So my running +4 all around, isn't much more than the OEM 20" recommendation.

 

Tire pressures??? Why are you all worrying so much about tire pressure? God, we started at 14 on the track and it blew to 34 when they heated. We put bleeders on to keep the pressure at 33, then we just did nitrogen. That is over 110 mph average...hello. We are not driving 110 in our street car. Put it at 32 and go drive the danged thing lol.

 

Mine are the factory finish... I think its an understated elegance.

 

Traction, safety and performance can be important to some people.

Starting at 14psi tells me you are into drag events. Drag tires barely touch the same physics required of a performance automotive tire.
Anyone with track experience knows 2 or 3 psi can make a lot of difference (overssteer, understeer, sidewall roll over, footprint size, tread life, etc...), and yes you should be running Nitrogen whenever possible.

Both my XK and XKR have run up near the limiters because I actually love to drive them (hence also making sure they are Y rated). At those speeds, or even less, like slicing through a twisty canyon, traction and safety are paramount to me.

Admittedly, I'm **** about getting the most performance out of my cars, but that is also part of the fun. The 'set it and forget it' mentality is foreign to me.

Vince

 

Clever name unsure what your current suspension is like but one of the immediate first modifications I did on mine were the spring upgrades .

Unfortunately the standard xk and xkr aren't really designed to be pushed close to the limit

Would highly recommend going spires springs the handling is literally night and day