WHY do bigger alloys mean worse handling?

[anna]

going by ive now had volk 16s, sotck 15s for a months, and my new lightweight 17 now.
by far the better option is the 16s and 17s.

in the 15s, my car felt suicidal, more in a straight line as it happens.
16s, great
17s, feel better than the 16s.

my new current 17inch setup

7.5j fronts, 215/40 et45
8.5j rears, 245/35 (believe to be as close to the stock RR as you can get), et35.

if the sotck 15s offset and width were imporved, i recon they could be awsome as well, however, at the moment in my car (toms rear and front struts, toms antiroll bar, lowered on adjustable suspension), i would have the 17s any day for the handling.

hmmm, interesting. So have you increased or decreased the offset of the midpoint of the tyre relative to the hub? I would suggest that your straight line stability on 15's would have been improved with some camber and toe-in (all geometry settings which may well be 'wrong' now you have different sus?)... It could also be the tyres you had on - they can make a huge difference even with exactly the same make/size/type - variation can still be huge

[anna]

Anna, i was so hoping to get in before you on that one, i even grabbed my car suspension theory book to make sure i was waffling off the right sheet but alas, you beat me again.

nice try

(next time, I promise!)

[jimGTS]

i would have the 17s any day for the handling.

Jim be careful not to confuse roadholding (ie mechanical grip) with handling which is what the car does once you exceed the limit of grip.

oh right, ok .
everyone refers to it as "handling" tho.
"it handles great in the corners", stuff like that. there obviosuly not talking about the back end slidding out, but the way it sticks the road.
(anywoo, different thread entirely )

[anna]

i would have the 17s any day for the handling.

Jim be careful not to confuse roadholding (ie mechanical grip) with handling which is what the car does once you exceed the limit of grip.

oh right, ok .
everyone refers to it as "handling" tho.
"it handles great in the corners", stuff like that. there obviosuly not talking about the back end slidding out, but the way it sticks the road.
(anywoo, different thread entirely )

It's sort of a combination to be fair. I don't know if you know of the terms understeer, neutral steer and oversteer, but handling can be described in how the vehicle behaves in these terms in the corner, pre and post limit. The point about more grippy tyres is that they tend to 'snap' quite a lot at limit, which could cause an understeer behaviour to turn into sudden oversteer. This is obviously bad handling. Even if a vehicle is great in the everyday ranges, it could still be described a badly handling vehicle if it does not provide enough cues to the driver at the limit.

[jimGTS]

Jim be careful not to confuse roadholding (ie mechanical grip) with handling which is what the car does once you exceed the limit of grip.

oh right, ok .
everyone refers to it as "handling" tho.
"it handles great in the corners", stuff like that. there obviosuly not talking about the back end slidding out, but the way it sticks the road.
(anywoo, different thread entirely )

It's sort of a combination to be fair. I don't know if you know of the terms understeer, neutral steer and oversteer, but handling can be described in how the vehicle behaves in these terms in the corner, pre and post limit. The point about more grippy tyres is that they tend to 'snap' quite a lot at limit, which could cause an understeer behaviour to turn into sudden oversteer. This is obviously bad handling. Even if a vehicle is great in the everyday ranges, it could still be described a badly handling vehicle if it does not provide enough cues to the driver at the limit.

surely tho the best track tyres, are the tyres that grip the most??? i understand the OS and US aspects, now confused why its not a good idea to have a good grippy tyre, especially on the track where it doesnt matter to much that you may spin (obviously it does on a public road).

[Lauren]

oh right, ok .
everyone refers to it as "handling" tho.
"it handles great in the corners", stuff like that. there obviosuly not talking about the back end slidding out, but the way it sticks the road.
(anywoo, different thread entirely )

surely tho the best track tyres, are the tyres that grip the most??? i understand the OS and US aspects, now confused why its not a good idea to have a good grippy tyre, especially on the track where it doesnt matter to much that you may spin (obviously it does on a public road).

Jim,


the best track tyres are those that provide the most progressiveness in feel when you are within the tyres slip angle. A higher profile tyre will have a larger slip angle, ie it lets go of its grip more slowly, so its easier to handle the car when it starts to go beyond the limit of grip. When people talk about cars "handling like its on rails" they are not going fast enough and they are talking solely about the amount of mechanical grip. as Anna points out the contact patch has an important part to play in all of this, lower profile tyres will have a stiffer sidewall as wel as a shorter longitudinal contact patch with the road surface. For example on a MK1 you lose progressivenes by fitting 195/50/15s when compared with 185/60/14s regardless of the make/spec of the tyre. Though of course the waters are muddied somewhat further by how different the same size tyres with different compounds feel.

I run A539s on my MK1 NA solely because they provide a medium level of grip (F1s are grippier for example). The important thing is for me that the A539s are nicely progressive and allow me to balance the car pretty well once i have gone beyond the limit of grip whereby the car starts to handle. I could put really sticky tyres on the car, but then it would be boring as all i would be experiencing for the most part would be the mechanical grip rather than the cars handling.

[jimGTS]

oh right, ok .
everyone refers to it as "handling" tho.
"it handles great in the corners", stuff like that. there obviosuly not talking about the back end slidding out, but the way it sticks the road.
(anywoo, different thread entirely )

surely tho the best track tyres, are the tyres that grip the most??? i understand the OS and US aspects, now confused why its not a good idea to have a good grippy tyre, especially on the track where it doesnt matter to much that you may spin (obviously it does on a public road).

Jim,


the best track tyres are those that provide the most progressiveness in feel when you are within the tyres slip angle. A higher profile tyre will have a larger slip angle, ie it lets go of its grip more slowly, so its easier to handle the car when it starts to go beyond the limit of grip. When people talk about cars "handling like its on rails" they are not going fast enough and they are talking solely about the amount of mechanical grip. as Anna points out the contact patch has an important part to play in all of this, lower profile tyres will have a stiffer sidewall as wel as a shorter longitudinal contact patch with the road surface. For example on a MK1 you lose progressivenes by fitting 195/50/15s when compared with 185/60/14s regardless of the make/spec of the tyre. Though of course the waters are muddied somewhat further by how different the same size tyres with different compounds feel.

I run A539s on my MK1 NA solely because they provide a medium level of grip (F1s are grippier for example). The important thing is for me that the A539s are nicely progressive and allow me to balance the car pretty well once i have gone beyond the limit of grip whereby the car starts to handle. I could put really sticky tyres on the car, but then it would be boring as all i would be experiencing for the most part would be the mechanical grip rather than the cars handling.

right, so having a bigger profile creates more thread becuase of tyre roll or tyre flexing or what ever its called. the tyre stretches more in the corner, hense giving more grip.
and a lower profile, doesnt flex as much mid bend, hense its more likely to let go.

am i along the right lines??

[-o< [-o<

[Fred]

Smaller rim, larger profile vs larger rim, smaller profile:
In maintaining the overall size of the wheel/tyre combo, you could choose a smaller rim with a larger profile tyre, or a larger rim with a smaller profile tyre. The larger rim selection would mean that the contact patch would be shorter than a wheel with a larger profile (but they would be of the same width).

(My head hurts )

The way I understand it :

To maintain 'Handling' and improve 'Grip' , we must choose a wheel and tyre that has the same aspect-ratio (profile) , BUT has a larger Rolling-Radius (Circumference) forcing a wider tyre width , than the Standard setup (provided everything else is constant).

I think thats the most complicated sentance I've ever formed ,

[SimonPearse]

dont see why rim size /tyre width affects contact area, it's dictated by tyre pressure and reaction.

well, sorry, but it does

Ok, so my explanations above are taking the tyre to be quite simplistic thing, which it obviously isn't. Tyres really are the true 'black art'. You are quite right that tyre pressures will affect the contact patch, as will the 'reaction' (or load). But, fundamentally, if everything were to remain the same, then the larger rim/smaller profile tyre will have a much shorter, and possibly wider contact patch. simply put the side walls will be unable to deform as much longitudinally, so making the patch smaller.

There is no question that it affects the contact patch shape, put in real cases it has a negligable effect on the total contact area. (yes I have measured it!, and it was not easy to do. My measurements were made with a selection of goodyear F1's in a range of (non mr2) sizes. I put shoe pollish on the tyres, put one on the corner of my kit car and lowered them onto a sheet of paper on top of some bathroom scales, then measured the size of the resulting footprint. It took all weekend to do 4 tyres, each at 3 loads, 3 pressures, but it proved the point.

[Speedy]

while not in motion?

[anna]

Smaller rim, larger profile vs larger rim, smaller profile:
In maintaining the overall size of the wheel/tyre combo, you could choose a smaller rim with a larger profile tyre, or a larger rim with a smaller profile tyre. The larger rim selection would mean that the contact patch would be shorter than a wheel with a larger profile (but they would be of the same width).

(My head hurts )

The way I understand it :

To maintain 'Handling' and improve 'Grip' , we must choose a wheel and tyre that has the same aspect-ratio (profile) , BUT has a larger Rolling-Radius (Circumference) forcing a wider tyre width , than the Standard setup (provided everything else is constant).

I think thats the most complicated sentance I've ever formed ,

The best tyre for going round track (i.e. the ones that will give you the quickest lap time) will really be driver dependent.
*Usually* what happens with tyre design is that additional grip (which to me means less sideslip angle generation for a given lateral force) will be compromised with the amount of slip that will be generated at the limit. This means that technically, the quickest way round the track would be to operate at the top of the lateral force curve for a really grippy tyre - however, you would soon bin it several times from a road disturbance, or perhaps even a gust of wind - Unless ofcourse you will be quick enough to pick up on the slip of the tyre going, and be able to bring it back from the brink. I doubt if you will be able to drive a tyre like this at more than 80% of it's capacity, and falling off the track sure ain't the fastest way around it.
Compare that with a more progressive tyre, but one that ultimately you are within you capability to take over the limit slightly but be able to control, then you will be able to drive the car around the track at, say 95% of it's capacity - any disturbances will slow you down, but should be recoverable - so even if the ultimate grip level of the tyre is less, it may be the better option in terms of lap times...

but hey, it might not...

In terms of tyre size, wider tyres should really require different geometry settings to make sure the steering feedback is as good.... Same with diameter - technically you should go through the 'tuning' process again....

[anna]

dont see why rim size /tyre width affects contact area, it's dictated by tyre pressure and reaction.

well, sorry, but it does

Ok, so my explanations above are taking the tyre to be quite simplistic thing, which it obviously isn't. Tyres really are the true 'black art'. You are quite right that tyre pressures will affect the contact patch, as will the 'reaction' (or load). But, fundamentally, if everything were to remain the same, then the larger rim/smaller profile tyre will have a much shorter, and possibly wider contact patch. simply put the side walls will be unable to deform as much longitudinally, so making the patch smaller.

There is no question that it affects the contact patch shape, put in real cases it has a negligable effect on the total contact area. (yes I have measured it!, and it was not easy to do. My measurements were made with a selection of goodyear F1's in a range of (non mr2) sizes. I put shoe pollish on the tyres, put one on the corner of my kit car and lowered them onto a sheet of paper on top of some bathroom scales, then measured the size of the resulting footprint. It took all weekend to do 4 tyres, each at 3 loads, 3 pressures, but it proved the point.

Were the larger rim size tyres wider?
What was the resultant contact patch size between each tyre at the same load and same pressure?

[SimonPearse]

well, sorry, but it does

Ok, so my explanations above are taking the tyre to be quite simplistic thing, which it obviously isn't. Tyres really are the true 'black art'. You are quite right that tyre pressures will affect the contact patch, as will the 'reaction' (or load). But, fundamentally, if everything were to remain the same, then the larger rim/smaller profile tyre will have a much shorter, and possibly wider contact patch. simply put the side walls will be unable to deform as much longitudinally, so making the patch smaller.

There is no question that it affects the contact patch shape, put in real cases it has a negligable effect on the total contact area. (yes I have measured it!, and it was not easy to do. My measurements were made with a selection of goodyear F1's in a range of (non mr2) sizes. I put shoe pollish on the tyres, put one on the corner of my kit car and lowered them onto a sheet of paper on top of some bathroom scales, then measured the size of the resulting footprint. It took all weekend to do 4 tyres, each at 3 loads, 3 pressures, but it proved the point.

Were the larger rim size tyres wider?
What was the resultant contact patch size between each tyre at the same load and same pressure?

rims were 13*4.5, 13*5.5 , 13*7 and 15*6, Dont have a note of what the tyre sizes were, but they were a selection of apropriate (for the rims) widths and profiles ranging from 100% (that one was not a goodyear) to 70% (basicaly what I could rummage up from my cars + 1 from a scrappie). All measurements taken at the same load and pressure

[anna]

Were the larger rim size tyres wider?
What was the resultant contact patch size between each tyre at the same load and same pressure?

rims were 13*4.5, 13*5.5 , 13*7 and 15*6, Dont have a note of what the tyre sizes were, but they were a selection of apropriate (for the rims) widths and profiles ranging from 100% (that one was not a goodyear) to 70% (basicaly what I could rummage up from my cars + 1 from a scrappie). All measurements taken at the same load and pressure

well..... the suspense is killing me
Go on, you know you want to scan those prints in and post them up with all the info

[SimonPearse]

binned em a couple of months ago (you have to use loads of shoe pollish to get a decent print and it makes a mess!) For anyone who wants to repeat the test make sure that you put planks under the other 3 wheels to raise them to the same height as the bathroom scales, and put a sheet of formica on top of the scales to allow the paper to slide as the load comes on (as the suspension moves it tears the paper if you are not carefull). If you use brown pollish you can see where you have put it on the tyre a bit better. I used graph pape and counted the squares. I'll chack the tyre sizes later on and post them up.

[Speedy]

Here is a good definition of 'handling', given by somebody who knows considerably more on the subject than most people on IMOC

"Handling is the undefinable quality which encourages the driver to make use of all of the available grip"

He went on to use an original mini and a 80's 911 as examples. In the mini, we all cane it around, even pulling the handbrake etc etc. In the 80's 911, you don't go anywhere near the limit of friction because it'll probably kill you when you fly past it without noticing. So even though the 911 would be a faster car in the hands of an expert, and it's got more grip available (on it's uber tyres), it doesn't actually 'handle' as well as a mini.

Other points which might be of interest - understeering / oversteer is not a very good definition of how the car actually behaves once you have large slip angles, and also that (and here is something for you) - a rolling tyre has no lateral resistance.

[SimonPearse]

- a rolling tyre has no lateral resistance.

OK I'll bite....
care to enlarge on this implausible-sounding claim?

[DotNetter]

- a rolling tyre has no lateral resistance.

OK I'll bite....
care to enlarge on this implausible-sounding claim?

this isn't to do with how giroscopes work is it!

cheers


Wayne

[jonb-]

- a rolling tyre has no lateral resistance.

OK I'll bite....
care to enlarge on this implausible-sounding claim?

Unless it has a yaw angle.

I /think/ he means a rolling tyre generates no lateral resistance until put through a slip angle. Then it gets confusing.

I think.

[SimonPearse]

that would be a lateral force not a lateral resistance, and either way that is not seemd to be claimed.