Wheel size Vs Handling

OK, i know that many of you will think that this has been done to death so far and say that bigger wheels = poorer handling, but i have NEVER seen anything that convinces me yet (scientifically speaking, but lots of experience says otherwise), and even if its true no one has ever come up with a logical explaination for why this is the case.

Here we go

As wheel size increases, tyre wall size decreases such that rolling radius stays (roughly) the same. Therefore 17s with a higher tyre wall should be roughly the same rolling radius as 19s with a lower tyre wall.

With me so far ?

My very basic understanding of tyres etc, is that flat road (not bumpy) handling is better with lower profile tyres (ive never seen lambos, ferraris or Porches with massive high profile tyres, and they are designed to handle well)

Therefore, if the rolling radius is similar, and the tyre wall is smaller for 19s vs 18s or 17s, then why is the handling worse ? Surely it should be better.

Im off to play 5 a side now, so wont get chance to read the answers until tonight/tommorrow

DISCUSS

C a n o f w o r m s - s t a n d b a c k ! ! ! !

I think its more weight of the rim and offset than diameter. Have you ever tried to find aftermarket rims in the correct offset, they're bloody expensive as you have to go with the top quality manufacturers like bbs, volk, etc and some off them are nearly £3k a set.

It definitely HAS been done to the death but here goes again.

Its all about the footprint of the tyre. When you are cornering there is a lot of force put onto the tyre. This causes the following to happen..

/__/ /__/ when turning left

\__\ \__\ When turning right

The / and \'s represent the tyrewall. The smaller the tyrewall is the less flex you will have allowing the tyre to tilt. This then causes the tyre to lift off of the road.

Arggh, can't do that... ok..... Paint time....

It takes less force for the lower profile tyres to lift off of the tarmac. This means they will lose grip earlier than those with a larger profile. To combat this its better to have softer tyres on larger alloys (probably what ferrari etc do).

the side wall flex also takes some of the bumps out of the road. No road can be made completely smooth, look at F1 and how the cars skip about on 'road' tracks. I believe most of their ability to deal with bumps is due to the tyre flex and not the shocks and springs.

to get to 19" or 20" wheels the sidewall has to be of such a low profile that there is no flex left in it.

You could put 19s on stock suspension and it would be okay (mine was), but if you lower and stiffen the suspension then the ability to cope with bumps will lessen and the handling will go off accordingly.

I had TRD springs on my UK spec, car handled great on the smoother roads, but it skipped like a kangaroo on the majority of roads, so much so that I had to ease off a number of times to avoid throwing it off the road.

To add to the good info from the above posts, remember that the OEM equipment & setups (i.e. wheel size, spring rates and to a lessor extent tyre choice) are the result of the R&D paid for from massive budgets, and aimed to give a certain type of ride (e.g. compliant, comfy, 'sporty') over the typical expected road surface (UK Supra's springs are different to the Jap Supra's springs in this respect).

As Branners says, the tyre itself is PART of the wider suspension system and is thus calculated into the equation of how much 'squidge' for example will occur over a bump at speed. If you go larger rim size and smaller tyre wall to keep a constant rolling radius, you've also made the suspension [i.e. the wider suspension system as I called it earlier] stiffer and more harsh as as result. It'll skip more over bumps as a result, and be uncomfortable.

Ideally, if you HAVE to go big rims , you should also fit softer suspension to compensate, but most people blindly fit harder springs instead, making the end result doubly bad! Of course, if you do go softer suspension, you have to start worrying about things like tyres rubbing against wheel arches during turns/compressions, the need for bump stops and the compromise that brings, - and worse still if its lowered, ground clearance during the same. Suddenly the car is hugely compromised and it would cost serious time & money investment to put right properly so I suspect most people either pretend it's all good or they wish they'd just left it stock all along.

Several points to be taken up here...

Top brand sportscars that run 19" or even 20's are also down to cosmetics. You cannot impress a customer with a ferrari running on 17" wheels today. The difference is that they are building the car and suspension to work with this size wheel where as a 15 year old supra with some kind of after marked suspension probably isn't the perfect match to whatever wheel size it might be running.

Also, comparing track/race cars to street cars are not really working i my mind. Skipping across a surface is an entirely different matter than skipping in a road car. You might be able to get a car running fine on extremely low profile on track but not on the road which, again in my mind, is down to the suspension setup.

Go ask a race car engineer; i would think that they do a lot of thinking between which wheels go with which suspension for what purpose.

90% of a road car (especially if you go 19"

But still.. No real science has come up, which was actually what was the question

I'm understanding the thought of Scott M but I'm not convinced. Isn't what ever tyre low or high profile created so that it can make use of the sidewall while turning? Is it really lifting on the inside? My thoughts is that main issues with ultra low profile would be difficulty putting down reasonable power as well as sacrificing comfort but possibly gaining a bit more sharpness in the steering.

I have at some past time, made a post explaining just WHY I have such a bee in my bonnet about ultra low profile tyres on most old cars. It's down to camber change, and bush compliance, do a search, if you like.

...Is it really lifting on the inside?

If I understand what you're asking, then the answer is yes. Chalk mark the edges of the tyre and part way down the sidewall and go & cane the car round a few corners (somehwre safe of course!). How much (roll-off I blieve it is called) will depend on whether you're running positive/negative/neutral camber and how aggresive that amount is (look at some race cars from immediatle in frontbehind and the tyres are almost 'falling' into the bodywork). The wider the tyres, the more impact roll-off will have on the amount of grip you have during cornering, as the tyre will go from placing a big, wide, flat area on the road to its equivalent of standing on tip-toes.

I have at some past time, made a post explaining just WHY I have such a bee in my bonnet about ultra low profile tyres on most old cars. It's down to camber change, and bush compliance, do a search, if you like.

And I recall you saying something like "When designing a a racecar chassis, the first thing they do is pick a wheels size, and build the rest around that". Very telling.

You can get stock settings on 18" wheels though

C a n o f w o r m s - s t a n d b a c k ! ! ! !

Well im back (and we won our 5 a side match 5 - 2 - yippee)

It was a can of worms wasnt it and there are certainly more scientific and sensible reasons given than in previous threads ive seen,

Thanks everyone.

I feel i now able to summarise all that has been said so far

1) Basically, it seems like its all part of the balance of the car. Change one thing, and ideally you need to change another thing.

2) The stock car setup is a compromise between handling and performance.

3) You can get better handling by changing something, but you will more than likley reduce comfort.

4) increaseing wheel size and decreasing tyre wall size accordingly (i.e. 19s) will give poorer road handling (due to being less able to cope with bumps), BUT might give better track handling due to less bumps ?

This last point (No 4) im not so sure about, as peoples experience seems to say otherwise, but from the explainations above SHOULD be the case. Im not sure at all !!!

4) increaseing wheel size and decreasing tyre wall size accordingly (i.e. 19s) will give poorer road handling (due to being less able to cope with bumps), BUT might give better track handling due to less bumps ?

No, read my post.

The only way to get better handling (with the wheels) is to increase the footprint of the tyre while keeping the tyrewall thickness the same.

No, read my post.

 

The only way to get better handling (with the wheels) is to increase the footprint of the tyre while keeping the tyrewall thickness the same.

Others in this thread seem to disagree and say its more to do with camber settings.

Im not in a position to varify either viewpoint, but both seem logical to me.

To get the handling to its optimum its a combination of everything. The reason i put "with the wheels" in brackets was to single out that the only way to increase the handling.... with the wheels..... was by increasing the footprint while keeping the tyrewall thickness the same.

You asked about "Wheel size vs Handling", that i can answer.... camber settings etc etc i don't know anything about.

Edit: People weren't disagreeing in this thread. The way i read it is that everyone agrees with the previous comments and then added in additional information that contributes to the handling.

I haven't disagreed with anyone in this thread, I wouldn't dare for one, there are some big-hitters regarding knowledge & experience in this thread.

I'm not sure about how a vehicle's handling on a bump-free track would differ if it is:

- initially fitted with (for example) 17" wheels and tyres to suit

- then fitted with (for example) 19" wheels and tyres with the same width, rolling radius, contact footprint and makeup

I think it'd be worse at cornering in the latter scenario, but I can't remember why.

(edit to say - handling would certainly be compromised in the real world where there are bumps, of course)

Agree.

But "handlling" as a term is also relative as well as "footprint" can be. You might be able to get the best footprint in one situation with one setup that will be very different in results in another situation (ie high speed cornering comparede to straight line launch).

Handling on roads are very different to handling on track.

And handling could include steering response, which I'm guessing will be different with large wheel sizes compared to stock wheel sizes (which again might be reverse propotional with grip and other handling aspects)

It would make a difference on a track due to a lack of bumps but the problem with the footprint would still be there.

Picture it this way, if you have a set of 17's with stock tyres on the tyre is going to sit like this (__). Obviously its exagerated but its just for quickness. If you then shorten the sidewall of the tyre its not going to have the same amount of flex and give to allow it to contact the road the same. You could lower the pressure to get a similar footprint but that wouldn't be the best idea for obvious reasons.

Also, as has been mentioned in the previous comments, the footprint would change when corning due to the lack of flexibility in the side wall. The crappy drawing i made describes this although its exagerated. The tyre could be wider but it won't make any difference as there isn't enough flex in the sidewall to allow the pressure to be evenly distributed across the width when cornering hard.

IMO though this is all in extreme situations when driving the car HARD. Other than the comfort aspect i really don't see any issue with bigger wheels and smaller tyres, just don't expect to go round a corner as fast/hard as you can with stock wheels. I doubt i would corner as fast/hard as my car could anyway, i like a spirited run but "on the edge" isn't the best idea when its my pride and joy.

Lots of good input there.

I doubt i would corner as fast/hard as my car could anyway, i like a spirited run but "on the edge" isn't the best idea when its my pride and joy.

It can be relatively risk-free on some corners of some tracks. I drive like a granny on the public roads!

It can be relatively risk-free on some corners of some tracks. I drive like a granny on the public roads!

- but you don't at The Ring...Remember spotting you a couple of years ago through Hatzenbach

My 2p's worth

Ive got large 19's on my car and its lowered on Eibach pro springs.

You will suffer a harsher ride on poor rds as your reducing the side wall of the tyre so less give in the tyre, a benefit with a smaller sidewall is less tyre roll so sharper steering but less forgiving if you get it wrong.

Yes the car will tramline on crap rds but not that badly. I dont use mine as a daily driver so its not on crap rds very much so doesnt massively concern me, if your cars a daily and you commute on crap rds as youve no choice then not ideal.

The car round Silverstone and Donington is fantastic in the dry but suffers a little in the wet as ive also got much stiffer TRD anti roll bars which combined with the wheels and springs is too stiff for the wet and really needs adjustable roll bars and or a softer spring rate.

I drive within the parameters ive inflicted on myself but with the geo done correctly to allow for my set up im as happy as pig in ***t with how my car handles.

It has also had the big wheels fitted for quite some time

(over 40k) and its still on its original wheel bearings and it flew through the mot yesterday.

I stood with the guy who tested it and made him double check each wheel, he said nope there spot on so its not eating wheel bearings because of the extra load.

I dont doubt its not an ideal set up as Toyota intended but the way my car still drives and looks then im v happy.

You definetly need to get your car set up properly if you fit bigger wheels and lower it and also to make sure nothings siezed on the suspension and no loose joints or worn bushes, you cant just slap them on and expect the car to be any good.

Speak to Chris at Center Gravity, he set my car up and test drove it quite quickly round the private test track in Atherstone and he thought it was pretty good.

Prepares to be:flame:d by the pureists

- but you don't at The Ring...Remember spotting you a couple of years ago through Hatzenbach

I do quite like the Nuburgring, especially that bit.