What's the rule of thumb for buying a used car?

There's no rule of thumb and it's rubbish to only get cars newer than 4 years because then you could fall into the trap of thinking a 4 year old car will always be in better shape than a 10 year old car. Somebody could destroy a car in 2 years if they didn't look after it whereas a car could last well over 20 years if it's maintained properly.

Also, don't worry too much about a mechanic. You would be very lucky if you knew a mechanic personally who would come look at a car for you so that's definitely not an option to consider unless it's available.

I've bought a few used cars (both dealer and private) and here's my advice:

-Find a car you like first (don't just go to a dealer with no idea what you want). Narrow it down to make and models and year of production (or 'mark', which refers to each particular model and the length of time that model was produced during). Then you can search for (e.g.) 'Mark 5 Golf buyers’ guide'. This will show you some common faults and things to look out for with the specific model.

 This is especially useful if you are looking to buy a performance car (like a hot hatch) because there are often owners clubs that provide very detailed information about specific parts that are critical and need maintenance.

 - Check the car hasn't been written off and repaired (it will be labelled as Cat C or Cat D if it is an insurance repair job).

- Check the car has full service history paperwork so you can look through to make sure it has had oil changes, brake & engine maintenance each year. Some cars have longer service intervals but even so, it's best to keep an eye out for proof that maintenance has taken place.

- Check if there are any 'advisories' on the latest MOT certificate. These are problems that have been found with the car that aren't required to be repair for the MOT to pass. They may not be legal requirements but could become worse and be a fail in the next MOT.

- Mileage is a big factor. Although many cars can get to 200,000+ miles with no problem, you should perhaps avoid smaller cars (like Minis, Fiestas) etc. that have more than 10,000 miles for each year the car has existed. Also if a 5 year old car has a low 3,000 miles on the clock find out why (often it's genuine where it's been stored in a garage by an old person and only used once a week etc) but you should always question it. 

- Check the cam belt change interval for the car. This is an essential service that can lead to a ruined engine if it fails. If a car's cam belt change interval is 20,000 miles and the car has 21,000 miles on the clock then make sure the cam belt has been changed and also be aware if the interval is approaching and it hasn't yet been done as it is very important to do so.

- Check for rust around the body work & brakes and even if you aren't car savvy, check under the bonnet for obvious leaks and excessive dirt (which could point to an oil leak). You don't have to be an expert to spot the obvious.

- Check AutoTrader for the exact specifics of the car (make, model, mileage, engine size etc) to find a realistic price to bargain with. Use a close tax or MOT expiration date, windscreen chips and other maintenance requirements that will cost £50+ each to rectify to try to get a lower price if the asking price is close to the value. For example if a car is worth £2000 and the asking price is £2000 but the tax & MOT are due and there is a chip in the windscreen then that may all cost £250+ to rectify so bargain with that plus a bit extra to get a tank of fuel ;)

Finally, take it for a test drive. It's not easy to hear small creaks when you're concentrating on driving an unfamiliar car but if the steering, clutch, brakes, gears or steering don't feel right to you or there are loud knocks from the suspension then avoid.

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How does tire recycling work?

Tires are recycled typically in several ways. After tires are delivered to the recycler, they have the bead removed. This is a tough wire along the inside surface next to where the tire is mounted on the rim. It's mechanically cut or pulled out. The tire is then fed into a device that cuts it into large chips. 

The steel belts are removed (though not easily recycled due to the amount of rubber stuck to them) followed by removal of the nylon cords that are also part of the construction of the tire. The remaining rubber is then ground into smaller pieces.

 Where the two methods differ is that in one method, this is done at room temperature while in the second method, the tires are cooled in liquid nitrogen and cryogenically ground into various sizes from several millimeters in diameter down to a size similar to talcum powder.

 Larger sizes are often used as-is for ground cover (mulch) or subsurface fill. In the latter case, a layer of tire crumb beneath the topsoil and grass of a park allows the water to percolate quickly from the surface and reduce puddling after rain. 

Outdoor amphitheaters often use this material. Other sizes can be blended with fresh rubber (non-vulcanized) and fashioned into new products. Things like door mats, floor covering, and inexpensive rubber goods can be made in this way and the tire is merely a compatible filler. 

Several years ago, a trio of companies (ATR, Praxair and Sti-K in Canada) explored methods of re-vulcanizing recycled tire material. There were some Russian and Malaysian patents on this topic. By careful blending of raw isoprene with finely ground tire crumb along with some other ingredients, and subjecting it to severe shear forces, the rubber from the tires and the fresh isoprene can be combined in a manner that allows it to be re-vulcanized into more sophisticated rubber goods.

To my knowledge, this process has not been commercialized in a large scale but holds the prospect of being able to convert large amounts of tire material into useful products. One use of cryogenically ground tire has been banned in some locations - the use of the material as road or highway fill. Because small amounts of metal may remain in the tire crumb, it is prone to catch fire if compressed in large quantities and in contact with moisture and oxygen. 

One spectacular case of road-bed fire was reported in the western US several years ago. The only other use of tire material in large quantities is energy recovery where tire material is burned to produce electricity in much the same way coal is burned.

Because of sulfur content, this is not a clean process and special care must be taken to prevent excessive air pollution when using tire material in this manner. Another product developed in the late 1990's was a high-impact composite of recycled tire crumb and resin to produce a tough, chemical and fire resistant - essentially bullet-proof plastic. 

This formula has been placed into the public domain by NIRIS, Inc. to promote the recycling of tire material into useful products. (It free to use without payment of licensing fees as long as NIRIS is credited with the discovery of the formulation.)

Tread rubber is 'crumbed' and made into soft surfaces for playgrounds, horse exercise yards etc.
The rubber crumb is now being used in tarmac to resurface roads. 

Whole tires are sometimes used to 'engineer' groundwork but it is illegal to landfill whole or part tires.
Whole tires are strung together and sunk of the coast to form artificial reefs for fish breeding.

The most environmentally friendly disposal method is to use the tires cut up into 2" squares and then used as a fuel in cement kilns. The volcanic temperature attained ensures the tire and any residue actually disappears! It also provides a readily available cheap fuel for the kiln. 

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Proper tire pressure for bigger, aftermarket tires

There are 2 schools of thought.

1) match the load carrying capacity

2)  If there is the same of more load carrying capacity, match the inflation pressures.

Let's do #1:

On every vehicle sold in the US, there is a vehicle tire placard which lists the original tire size and the proper pressure for that size.  Since 2008, the placard is supposed to be on the driver's door frame, but prior to that it could also be in the glove box, on the fuel filler door or on the trunk lid.  For as long as I can remember, Ford has been putting the placard on their trucks on the driver's door frame.  Go look and see if what follows is correct.

According to Tire Guides, the vehicle tire placard for a 2003 Ford F-150 Crew Cab with LT265/70R17's would say the inflation pressure is supposed to be ........  Well none of the versions I see came with T265/70R17's.  There is quite a few variations here:  4X2, 4X4's, Lariat's XLT's, etc.  And none of them list an LT265/70R17.

But there is a version that has P265/70R17 (and 32 psi front and rear) and I am going to assume that is what your vehicle says.  Please check, because everything I quote from this point forward will depend on that inflation being correct.

So the load carrying capacity of a P265/70R17 at 32 psi is 2205#.  In order to carry the same load, an LT315/75R16 needs to use ...... well, the charts don't go below 35 psi - and I think that means those kind of tires should be used below that pressure - even if it means unusual wear.

So even though the load carrying capacity is adequate, I don't think you can do #2.

Also, inflation pressure isn't the biggest factor in even wear.  Wheel position (as in drive vs steer) had more effect.  Drive tires tend to wear in the center and steer tires tend to wear in the shoulders and regular rotation will even the wear out - and that is more important than inflation pressure.

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