Hello,
Im new to this site and would like to ask advice on what size wheels should be on my jag.
I have a 2004 x type 2.0d se estate which has got 225/40 R18 tyres on it but I find the ride bumpy
Can I put smaller rims on with bigger tyres to make it more comfortable
Ive seen some BMW 17" alloy wheels with Pirelli p6000 tyre 225/45 R17 so would these fit and would it make the ride any different ?
Any help or advice would be great.
Thanks in advance
Pete

 

pete69, first off, welcome to the site. You will find lots of useful information here. So, sit back, do some looking around, learn a litlte bit and enjoy a cup of joe as you do. As you will find out, we are a friendly bunch and as a result, we like to get to know one another (we like to be a different kind of car group). As a result, we ask that you stop by the "New Member" section and introduce yourself. There you will find out who the people are that make this place what it is.

As for your tire question. There are a few things that you can do to make your ride a little smoother. You can try lowering your tire pressure from 35 PSI (240 KPa) down to say 32 PSI (220KPa). You will be surprised as to what that can do for the ride. The down side to this method is that you open up the 18" rims to more possible damage from potholes and whatnot.

As for switching over to the 17" BMW wheels, the bolt pattern is the same, I would just check on the offset to make sure that it matches up to what you currently have. The BMW tires will be about the same diameter overall, but you will have a 1/2" (13MM) more rubber between the road and the rim. This will allow you to run your tires at a lower (but safe) tire pressure and still not damage the rims. But, the lower the tire pressure is, the more likely you are to damage the rims. Just a fact of how things work.

Just to give you an idea of what I run, I have 235/40R17 wheels (yes, these are non-stock size tires) with a max pressure rating of 44 psi. I run 35 psi (240 KPa) in the front and 32 psi (220 KPa) in the rear. The front end of our cars carry a bit more weight when there is only a driver in the car than the rear does, therefore requires a slightly higher pressure. If you tend to drive with 4 people in the car or a fair amount of stuff (say 100 Kg of stuff or more) in the car, then I would say to run 35 psi (240 KPa) all the way around. A trick that you can do to see if you are running the correct pressure is to get your hands on some white paper and some colored chalk (or colored paper and white chalk) and rub the chalk over the tire say half way around the tire. Do this on all 4 corners if possible, if not, atleast the front and rear of the same side. Now, lay the paper down on the ground so the chalky portion of the tire will run over the paper as you roll the car forward on a flat surface. After you have rolled the car over the paper, look at how the chalk go transferred to the paper. You should see an exact copy of your tire tread on the paper. If the center is really easy to see but the outside edges of the tire are hard to see, you are running too much pressure. Kinda like if you can barely make out the center of the tread but the edges of the tread are very obvious, then you need to run more pressure (not to exceed the tire rating). From there, you are playing a balancing game of comfort driving over tire wear/life.

Hope this helps and if you have any questions, let me know.

 

Hello Thermo,
Thanks for the reply and info.
I will take your advice and go on the "New member" section.
I think as the wheels for the Bmw are ending soon will leave them untill I get a bit more advice from people on here but will tomorrow try changing the tyre pressure as you said.
Are 18" standard or are they an after market and if so why would someone change to bigger tryes if it feels more of the road on these cars ?
Cheers
Pete

 

Pete, 18's were an option with the X-Types. They were standard on the Sport editions unless it was optioned down to the 17's.

As for upgrading to bigger rims, it is a matter of what you want the car to look like. Some people are willing to accept a harsher ride to have a certain look. Why do people lift trucks, why do people beef up their engines to go really fast (when they can't drive fast 99% of the time)? If it is aftermarket, it is because someone before you wanted the look.

 

Hi Pete69,
Tire choice can make a huge difference. I also have 225/40r18.

My first set in that size were Toyo Proxes4 which is a high performance directional summer tire. Very stiff ride, but handled like on rails. Poor treadwear, they're a soft compound.

Currently I have Continental Extreme Contact DWS which is a performance all-season with asymmetrical tread. Much smoother and quieter, but lacks the cornering grip of the Toyos. No appreciable wear yet at about 7500 miles.

All tires are a compromise - shop around, read customer reviews, and choose what fits your needs.

 

Hello,
Thanks for the freindly advice.
I have a work college which owns a S type and he has bought a set of tyres on wheels for his which are 17" and I think he said they were 55 instead of 40 which I have and I could try them so would they fit ?
I bought an estate for the reason's of carrying fishing and camping gear all of which don't weight alot and am a lorry driver so am not a fast driver and belive if you need to get somewere quick you leave early so I dont need tyres to be "stick to the road for racing"
I also own A motorbike which is sat in my garage but feel tyres were so important on that but in a car feel I just need legal,comfortable's tyres.

 

Hello,
Me again.
The wheels that my work college have look exactly like mine on his S class but are 17" with 235/50 17 tyres on Would theese work on my X type ?
Cheers
Pete

 

Pete, those tires are going to rub. I have 235/40R17's on my car and I get very minor rubbing at a specific point when I turn. The tires are just barely touching the wheel well liner. Going with a slightly larger diameter tire is going to mean you will more likely have more rubbing. Doing a day run or something like that is not going to be harmful to the car. But I can not say to run this for ever and ever.

 

Hello,
Now im probably going to sound really dumb but I thought if it went from 18" wheels to 17 " one it could have a lot more rubber and less alloy ?
So what sort of size wheel/tyre should I be looking for for a more comfy ride?
Cheers
Pete

 

Pete, you have a few things you need to consider when trying to fit a different size tire to the car. The easiest to understand is tire height. Really the size rim has very little to do with whether the tire is going to rub or not, there are more factors with the tires that you need to worry about. Sure, a 20" rim is going to be more likely to rub than say a 16" rim. But, at the same time, I can make a 10" rim rub too based on the rubber I put on it.

With all this being said, I would recommend making your life easy and checking out Tire size calculator. This has a nice calculator on it that you can compare what you have and what you want to install and even tell you the difference between the two tires. Put in your current size tire and then what you are looking for is a tire that will have the rim, width, and aspect (more on this in a moment) that is within 1/2" of what your current tires are.

Ok, aspect, that is a ratio of the sidewall height to tread width. This is normally expressed as a number (say 40), which is really meaning that the sidewall height is 40% of the tread width. So, if you go with a wider tire, but you keep the same aspect, you end up with a taller tire because your sidewall is getting larger. IN your case, because you are dropping down in rim height, you can maintain the same tread width and go with a larger (higher number) aspect. This is where the calculator is going to make life easy unless you like punching numbers on a calculator (I can teach you how to do it long hand if you want).

In your case, if you go with different rims, your best bet would be going with a 225/45R17 tire as that will be the closest you can get (off by 0.5%, or 0.3 MPH error at 60 mph-speedo would indicate 60.3 mph when actually doing 60.0 MPH).

When looking at rims, this is where things can make you start scratching your head. There are 2 numbers that are vitally important to your car and both essentially refer to the same measurement. These are offset and backspacing. Backspacing is the easiest to understand. In short, if you lay a straight edge across the back side of the rim and then measure from the edge of the straight edge touching the rim to the area where the hub touches the rim, this is backspacing. Ultimately, your new rim should have about the same backspacing. If you go with a slightly wider rim, your backspacing may need to increase just slightly. But, this is where understanding how the wheel is sitting inside the wheel well helps out a lot.

Offset is a bit more complicated to understand, but you have to imagine a line running through the center of the rim top to bottom (as if the rim was mounted on the car) that would be in line with how the tire rolls. Now, measuring from this line, you are measuring to the back side of the hub (where the rim bolts to the car). Sometimes the hub is towards the outside of the car from this imaginary line (like it is on our cars) and this is referred to as positive offset (our cars require a +40mm offset for the 17x7" stock rims). This is a better number to use because what you are doing is by keeping the same offset (regardless of rim width), you are keeping the center of the tire in line with the center of the wheel bearing. By doing this, you are keeping the torsional stresses (those stresses trying to rip the tire sideways off of the car like you would get when going into a high speed turn) to a minimum because the weight of the car is pushing straight down on the bearing. You get the center of the rim and bearing off of each other, you start putting more stresses on the bearing as the difference gets larger. Getting back to how the offset is measured, as you change the rim width, it changes where the center of the rim is, and therefore if you had 2 different width rims, but with the same backspacing, they would have different offsets.

I know I am probably getting into this a lot deeper than you are wanting, but when looking at rims, this can make the difference between a car that will be problem free and one that can be nothing but troubles. A tire shop will sell you anything you are willing to pay for. A good one will tend to refuse to sell you something that will put things too far out of kilter. But a knowledgeable purchaser is a wise person and they can make their own decisions.

So, based on your current tire size, look at the 225/45R17, but you can also look at the 235/45R17's too to widen how many tires you can look at. With the rims, look for a 7" wide rim with the +40mm (+/-5mm) offset. From there, you will have most of the basics taken care of.

 

WOW THERMO !!!!!
Thanks for that.I will have to read it a few times to try to understand most of it but will also have a look at tyre calculator aswell.
Thanks for taking the time to help.
Cheers
Pete