UKC

What are the advantages and disadvantages of -

smaller alloy wheel and thicker tyre
larger alloy wheel and thinner tyre

(obviously the overall diameter has to stay the same)

In reply to ow arm:

Bigger wheels and smaller tires means less tire deformation as you accelerate, brake, and corner. It gives better handing and control.

It also means less deformation as you go over potholes and bumps. A slightly rougher ride and greatly increased chance of punctures and/or cracked alloys.

Super skinny tires can also be more expensive, especially when going to 17" or above.

In reply to Jack B:

Good answers.

I prefer steel wheels.

Don't get stolen.

Stay inflated. I hardly need to re inflate tyres between buying replacements. Alloys have to pump up every week.

Bend rather than crack on a big pothole. Can repair with a hammer.

With the cart tracks we call roads nowadays use at least 65 profile tyres.

In reply to ow arm:

+cheap, compliant ride, potentially lighter
-calliper/hub clearance, appearance, flexible sidewall impedes precision, potentially heavier, lower performance tyre choices

+stiff sidewall enhances precision, potentially lighter, performance tyre choices, bigger brake options
-Crashy ride, potentially heavier, expensive

No it doesn't, changing the gearing without touching the diff is one good reason to change wheels and tyres.

jk

In reply to Jack B:


Well, in controlled condition of the kind that exist on race tracks, and do not exist on public highways, they might.


Many of the good things that you get from a tyre when driving on public roads, and especially unseen roads, come from the sidewall. Less sidewall, more problems.

Narrower tyres with larger sidewalls provide the following.
- Ride quality
- Resilient steering feedback less affected by lack of compliance
- Compliance (with the road surface in uneven conditions and ice or snow)
- Shorter water clearance path
- Protection from rim damage
- Probably lower cost (which can be substantial for popular sizes)
- Less susceptibility to tyre wear problesm through misalignment

The principal disadvantages of this approach are the rim diameter limiting the size of the brake disc you can fit and heat dissipation.

Limited brake disc size is especially problematic if you use normal aftermarket brake pads that are fit for nothing. High quality brake pads are £100 so it can be difficult to understand why people spend £1000 on bigger rims and fragile tyres. Heat dissipation is rarely a problem in the UK but in warmer climates you have to be careful about how well the tyre-rim combination dissipates heat. Having your tyres melt can be a bit of a problem on the basis of both safety and cost.

The choice of rim width is crucial. Traditionally, a rim width of 80% of tyre section width was seen as being a good choice from a handling point of view. BMW will be higher and many will be lower.

For the last 40 years I have been using modified road cars with narrower tyres as part of the plan. The rim/tyre ratio is always over 80% and is currently over 90%.

The UK has a particular reputation for car specifications with large rims and wide low profile tyres. The main reason for it is sell more expensive tyre to dim susceptible people who are willing to buy into racetrack chic.

Unfortunately, insurance companies understand as much about this as police officers. Nothing.

In reply to Rick Graham:

Cracking post.

Steel is superb.

In reply to ow arm:

great replies as always.
a sub question - avoiding sidewall damage, which would be best? i drive on narrow roads and often have to pull right in to the hedge to allow tractors and lorries past

In reply to ow arm:

The more sidewall, the more give.

For verge-ploughing, there is not question. Avoid the modern big wheel thin tyre approach.

In reply to ow arm:

Low profile tyres tend to get nipped against the wheel when you plunge them into the hedge. That said, if that's all you're concerned about I'd just run what your car came with and see how you get on. That sort of rural driving describes most of my motoring over the years and I've never damaged a tyre (big or small, tall or low profile) by running into the verge when not in competition.

jk

In reply to ow arm:

I am afraid life is not so simple as to say big wheel and small tyre means better handling/control, it all depends upon how your car is set up.

Normally big alloy small tyre wall means a heavier combination which in turn means a greater unsprung mass which tends to be a bad thing as far as suspension goes and hence handling on corners at speed.

Also the flex of the tyre wall tends to give more progressive "give" when approach limits of grip.

You really need to know something of how your car suspension and geometry is set up to be able to predict which would best suit your requirements. About the only thing you can say with confidence is that British roads are not really that suitable for low profile tyres due to the number of pot holes.