I posted a similar thread on the fabia forums but I can't quite catch the amount audience for the type of subject matter im looking for. (thanks simonk24 for the input in the other thread).

So I've been trawling through the internets for more information about handling characteristics for different sized wheels. Came up with a few answers but didn't really have enough for a good understanding.

In my application I have some lightweight 16s and some normal 17s. - 16s are much more agile and moves quicker, response is much better on in most speeds, however once you get into the light high speed cornering the response is a little delayed, uneven surfaces upsets the car a little compared to the 17s. Its still planted but perhaps you'll feel the rubber or sidewalls? Im not sure. Ultimately I'd like to find a cost effective solution for my situation, but Im inclined to understand more about different sized wheels.

I appreciate that tyre compound will play a large factor in this so assuming one can get the same specs for both wheels -

Why Touring cars run a certain size and Formula cars are completely different?

Why 'hot hatches' nowadays run 19-20inch wheels? Purely for show?

Is there a relationship between size of car and wheel size? or is it more of power to wheel size ratio? or weight to wheel size ratio?

You mention Tyre Compound,

but Aspect Ratio/Profile.plays a very important part to the wheel tyre combination and weights or regulations for certain types of motorsports and for road use. Then Speed/load rating, compounds, tread types.

(sidewall height, percentage to tyre width and actual tread width)

Total diameter, rolling radius/circumference, etc etc

Then so much more to size or width than just weight or strength, brake clearance, cooling etc.

http://www.torquecar...lloy-wheels.php

http://www.kouki.co....size-calculator

http://www.tesco-tyres.com/help/speed-rating

george

Is there a relationship between size of car and wheel size? or is it more of power to wheel size ratio? or weight to wheel size ratio?

Not really an answer but IIRC the original Audi Quattro was fitted with 14" wheels.

I'm not really qualified to answer the question, but my experience of comparing 16's to 17's (years ago on the Scooby ) was that the 17's seemed to offer better levels of grip but at the sacrifice of ride comfort. I'd always put this down to the amount of sidewall available, although I can't remember if the tyres were similar load rating which may be a factor. I'd also guess the stiffness of the sidewall plays an role in the "responsiveness" of the tyre. Saying all that, my driving style has changed a bit since then and so you should probably take my findings with a pinch of salt

Not strictly relevant, but I highly recommend having a look at some of these videos if you haven't seen them already, particularly the one about tyres and feedback:

http://www.donpalmer.co.uk/videos.html

Chris

You're also going to get into issues like construction, particularly if you start swapping tyre makes or models when you swap rim sizes.

If we hold tread width, compound and tyre construction constant, so the only variables are wheel size and sidewall height.

The 16"s will have a lower unsprung weight, which is better for acceleration, braking, and suspension bump response (hence ride comfort and ability to stay in contact with the ground through holes and off ridges).

The 17"s will distort less as you turn the steering, and as g-loading comes on and off them, so the car will turn (and stop turning) faster. This is nothing to do with over and understeer; it's all about reaction speed.

Not really an answer but IIRC the original Audi Quattro was fitted with 14" wheels.

In the same timescale, most "normal cars" had 13s, hot hatches had 14s, and the supercars of the day had 15s.

http://www.mrtyremotorsport.co.uk

Thanks for the links and input guys, lots of good reading/watching there.

Perhaps let me steer it in a more focused direction,

Cars nowadays have big wheels however it still feels quite composed when handling uneven surfaces/bumps etc. Which I guess is compensated by suspension set up (assuming tyre profile/compound is constant receptively).

Since the difference between bigger and smaller wheels predominantly is 'reaction time' or bump response, all one has to do is to change that characteristic to make it mimic the different sized wheel?

eg. 19 inch wheels with low profile tyres are harsh compared to 18 or 17s. To decrease the harsh ride car designers or tuners lowers the rebound of the suspension? or 'soften' the suspension in some way?

Follow on question - So I guess motorsport limit the specific tyre/wheel size so competitors need to work round this issue. Does this mean that in that particular motorsport (eg touring cars) the wheel size is optimal for that type of race or is it simply an educated guess and go from there?

Also look at what tyre (and profile) you can get in 16 vs 17.

I have two sets of Pro Race 1.2's (well in fact three but who is counting!)

1 x 16's

1 x 17's

So which should I use on my track car? I will be going for some RB5's of similar, so I think looking at profiles 17's have better "race" tyres. Whilst 16's dont (or are silly expensive)

But my only worry is the performance difference as I want more not less  

The other limiting factor with wheel size is the size of the brakes, touring cars have monster 4 or 6 pot calipers on huge discs, I should imagine this is the first thing they consider when choosing wheel sizes, the other consideration is unsprung mass and inertia, they are both trade offs against each other, the effects of unsprung mass would affect a race car more than a road car for sure... Another factor in choosing wheels may be purely down to sponsorship, if for example a company like compomotive or oz were supplying the wheels then the teams just get what they are given and use them.

T.Spark - Major head scratching! Would be interesting to hear your thoughts/outcomes on the matter though. Maybe try one race 16 another 17s? lol I suppose you'll have to set up the car slightly differently which will be a pain..

Common size will be easier to source cheaper replacements though.

The other limiting factor with wheel size is the size of the brakes, touring cars have monster 4 or 6 pot calipers on huge discs, I should imagine this is the first thing they consider when choosing wheel sizes, the other consideration is unsprung mass and inertia, they are both trade offs against each other, the effects of unsprung mass would affect a race car more than a road car for sure... Another factor in choosing wheels may be purely down to sponsorship, if for example a company like compomotive or oz were supplying the wheels then the teams just get what they are given and use them.

Why are they trade off against each other? smaller wheels have lower unsprung mass and lower inertia? isn't lower inertia good?

Having more inertia Is better when coming out of corners because it consumes less energy accelerating the car because the heavier wheels act as a flywheel, but the affects of this are marginal.

http://www.btcc.net/...regulations.php

I have ran standard 16's and standard 17's and the 17's were alot slower down the 1/4. But had different tyres on, so I cannot put it down simply to size of wheel. IIRC my terminal speeds however were also down (1mph or so) which tyres wouldnt really effect so imho 17s made the car slower (due to weight perhaps?)

However the difference between light weight pro race 1.2's in both sizes are no doubt even less than the above, so wouldnt effect it in such a way, then add the fact the tyres you can source will be better in application of 17's and again the chance of bigger 4pot/6pot brakes behind the 17's means...

The ibiza will be running 17's this summer  

Having more inertia Is better when coming out of corners because it consumes less energy accelerating the car because the heavier wheels act as a flywheel, but the affects of this are marginal.

NO! Having more unsprung inertia at steady speed means that you have to increase inertia still further when you accelerate, so you accelerate more slowly.

Lol I'm going to end up liking everyone's post at this rate.

I thought inertia means the force required to change the Moment. High inertia requires higher force to change a direction?

But I only know v basic mech theory..

Sent from my GT-N7105 using Tapatalk 2

Lol I'm going to end up liking everyone's post at this rate.

I thought inertia means the force required to change the Moment. High inertia requires higher force to change a direction?

But I only know v basic mech theory..

Sent from my GT-N7105 using Tapatalk 2

Inertia is the ability of a body to resist acceleration. This means that higher wheel inertia reduces the rate at which you can accelerate and brake.

An article just a few months ago in either EVO, Top Gear or CAR described and discussed how car designers draw cars with wheels and tyres that suit the design, and then engineers try to get that over large and almost no black tyres to work on a vehicle.

Cars drawn just like they have been getting done for decades now.

There is a compromise on performance and limiting availability of tyres for some Supercars & then unsutable large wheels fitted to Junior hot hatches in 19" etc,

style and looks over function, performance or real world use basically.

Audi is one manufacturer with lots of UK Dealershipsir or just the salespeople that try to get you not to take the smaller wheels and non sports suspension (no cost option) when buying a car,

talking lower residuals because of being less desirable when being sold,

and less involved handling, when actually it can just be rubbish and jiggly handling on Uk roads, potholes and wheels easily kerbed or damaged..

For almost everyone the 'Non Sporty super dooper hard fast willy wagging' set up will be just fine.

Then Audi give in, let you tick the boxes for the 'Less Sporty vehicle'. only later to tell you this is not available or there will be a delay on your build.

(funnily the Demo model available will often be on the taller rubber, boring/old fart not fast like an Audi driver suspension and they are happy to sell you that car after its done its rounds of showing off the comfort of the ride.)

george

Found this Article when looking for the one i wanted to find.

Why Touring cars run a certain size and Formula cars are completely different?

Different rules controlling max wheel size. many F1 designers would love to run bigger wheels as then they can use bigger brakes and cool them better.

Why 'hot hatches' nowadays run 19-20inch wheels? Purely for show?

Pretty much, yes. Big wheels are fashionable. Especially in the UK it seems. A supermini hot hatch does not need 20" wheels, even 17" is towards the "too big" end of the scale IMO.