Well been plain sailing for a few months since swapping the battery for a new one, until one morning I notice tyre is a bit down on passenger side front, check with gauge and its at 19psi (nearly half what it should be!), other front is slightly down at 30psi, rears ok. Pumped it up, pressure didnt drop overnight. Drove 200 miles the day after, all good. Then come the morning tyre is down again. So I get it in to my garage for what I assume is a puncture, and the tyre tech tells me ive got a crack and a flat spot in my alloy.

Getting it welded and refurbed for now (Im aware people are split on this) as there arent any 2nd hand nevis fronts available at the moment. I must admit, people saying these alloys are like butter doesn't fill me with confidence this will be the first and last alloy I crack with this car. So to solutions:

Drop to 19" oem alloys, more sidewall (I like the tamaras)
Swap to aftermarket 20" alloys (better quality?) there are some tasteful BBS ones around for less than new oem
increase tyre profile all round by 5mm, cheaper than buying 19s and new tyres, but will it cause issues besides slight speedo inaccuracy? 5mm isnt alot, but adding it to a 30mm or 35mm profile tyre is a 15%+ increase is sidewall, so must make some difference?

Id like your thoughts, and your stories if this is a prolific issue for other XKR owners riding on the oem 20's.

 

If you decide to go different, I may want your rear wheels.

 

are they really that rare, or just rare in US? They all need a light refurb anyway.

 

How would you increase profile by 5mm?

I've accepted the fact that these rims will crack at some point. Comes with the 20" territory. OEM vs Aftermarket, I don't think it makes a difference.

Happy that my new set hasn't yet, but I do keep 2 of the 'good' ones from the old set around just incase.

I guess that's my solution to this... keep a spare front and spare rear laying around while the cracked ones are sent out for repair.

 

Well when it comes time to replace tyres I'd go for 40 profile at the front, 35 at the rear, instead of the usual 35 & 30 that it runs on.

I knew there was a likelyhood, but I'm not sure I can deal with the inconvenience of cracked alloys multiple times a year

 

Oh you're saying the aspect ratio on the tire size. Gotcha.

 

Alster, can I ask where in the UK you are to have such bad roads?

I've only done a mere 10k miles in mine in the last 30 months, (lockdown and having two other cars) but no issues in Somerset.

I've a set of Vortex for Summer with MPS4S's and Vulcan's for winter an with M&S rubber & no damage to report thus far.

If I were to g aftermarket I'd probs go with Oz racing wheels, but because mine are 10.5" rear and 9 front the cost would be circa £2.8k

 

I ended up with 19's from a XJ with the taller XJ spec tires and love them since mine is a commuter car and the interstate has been under widening construction for six years. I think the softer sidewalls also hook up better.

 

I feel that the stock tyre pressures (2008 model) are too low at 30 PSI on 20"inch rims, should be a minimum of 35psi or higher.

 

Which would make the ride harder and is more likely to lead to a buckled/damaged wheel if you hit a pothole or curb too hard surely?

Also in heat (that you have in Oz) wouldn't a 35psi soon raise to something like 37 in high temps? Here in the UK my pressures rarely increase from season to season, but notice (on the rare occasions if goes above 80f) that the cold psi increases by 1 or 2. Albeit when driven in hot environmental conditions the tyres will be softer

 

The Cumbria roads are pretty awful, sometimes theres no avoiding the potholes as they cover the width of the road. As mines a daily driver I wish I had a cheap 2nd runabout sometimes.

I think either way I need bigger sidewalls, ive always thought that 45 should be the minimum profile on UK roads, but that would look a tad silly on an xkr. Whether the xkr can accomodate 20s with a larger tire profile is something I need to find out.

If i remember, our UK jags recommend 2.5Bar (36psi) front and rear for the 20" wheels

Ride yes, but more likely alloy damage I dont think so, the tyres there to prevent the shock directly hitting the alloy, but I can follow your logic.

 

The higher the pressure the more likely that the tyre gets damaged. Lower pressure lets the impact through to the wheel.

My handbook has 2.5 Bar cold all round (36 PSI).

Remember that the cold pressure is set so that at running temps the pressure is correct. There is also a fudge factor that for higher speeds, you need more pressure to reduce overheating but that might mean some overpressure and central tyre wear too. It is all a compromise but the manufacturer knows best.

 

I've had the opportunity to compare and contrast wheel and tyre options on the two door models. In recent years I've had:

2001 XK8 - 18 inch Impeller
2005 XK8 - 20 inch Sepang
2007 XK - 19 inch Carelia
2014 XK - 20 inch Kalimnos

For resilience on our pothole strewn roads combined with comfort, 18 inch is the best but doesn't look as good as a larger diameter wheel. The two cars on 20 inch have both given harsh ride quality.

I had a front 20 inch Kalimnos bent on my current XK. It was straightened and refinished by the local branch of The Wheel Specialist but annoyingly lost around 2 PSI per month whilst the other three maintained constant pressure. It took many months to find a new Kalimnos at a sensible price (list is 711 UKP from Jaguar) and I had it fitted on Wednesday.

Undoubtedly 20 inch wheels look the best by today's standards but I won't be having a vehicle with them again. Too prone to damage and give a harsh ride quality. I like to feel the road through the steering - not the base of my spine. For me, 19 inch is the best compromise for appearance, resilience and comfort.

Graham

 

I was originally going to swap to 19s, before I bought the car as I thought the ride would be too harsh. I was pleasantly surprised that even though it runs on 20s, the ride is excellent, firm but comfortable id say. Im still thinking which is better, grab larger tyres for the 20s or downsize to the 19s.

 

The placard sticker at the door is 2.0 bar (29psi) front and 2.3 bar (33psi) rear which I thought was too low of a pressure for 20" low profile tyres where the local roads are pitted with potholes. The low recommended pressure could be use to our low 110km/h max speed limit on the highways.

I'm running 36psi all round ATM. BTW Tesla model S 21" rims / tyre combo runs 40PSI all round.

 

It's a big expense to change the wheel/tyre set for 19 inch although you could subsequently recover a proportion from sale of the 20 inch wheels. It really only makes sense if you plan on keeping the car for several years. If not, the larger tyre option is less painful. When I was disatisfied with the 20 inch on my XK8, I just changed the car.

Graham

 

The placard should also state the tire size.
My car came equipped with 19” wheels, and IIRC the placard says 30/33 (front/rear) for the 19’s. Someone with 20’s equipped had a placard that said 33/36. Which explains why I thought the 20’s I put on my car rode too soft. Increasing psi 3-4 helped remove that squishy feeling.

 

Well im thinking 7 years of ownership at least, so there may be sense to make the change, but other things coming up like gearbox oil change, SC service, tyres etc. On another note, alloy came back today. Im no paint or welding but im pretty happy with the welding and refurb, though not the cheapest, it looks good. Good to see they did the repair far further down than the crack to make sure they got it all, it could've only been 1cm or so.