Handling - low or high profile tyres??

[TheJimi]

Kawasicki said:

Some people are very aggressive in direction changes, with sharp steering inputs. Lower profile works better here.

Low profile tyres exacerbate aggressive steering inputs, imo - thus, they don't work "better" for that style of driving.

[lostkiwi]

Kawasicki said:

There is no simple answer. This is what I think…
Higher profile tyres are generally slower through transient manouvres, as they generally have a lower yaw eigenfrequency and less yaw damping.
Higher profile tyres give more warning to the driver that ultimate grip is approaching, but the actual breakaway of grip doesn’t seem any less benign than low profile tyres, especially in transient manouvres, where it is usually much worse.
Regards vertical behavior, I think the importance of unsprung mass is a little overstated. It is much better to have a wheel and tyre assembly that is properly damped, by offering a fairly direct connection between the road and the damper, than a wheel and tyre assembly that is a kilo or two lighter. The tyre should be stiff enough vertically to actually deflect the wheel over bumps, to activate the damper. Using a tyre as a damper is pretty rubbish.

Some people drive very smoothly, with smooth turn in and considered steering. Higher profiles work well for this steering type.
Some people are very aggressive in direction changes, with sharp steering inputs. Lower profile works better here.

From an interview with Juan Pablo Montoya by Maurice Hamilton:

http://bbs.hupu.com/10990274.html said:

One of the biggest lessons I had in life was Jackie Stewart driving ?us at Oulton Park. He changed my career.
MH: Really? Was that in a touring car?
JPM: Yeah, a Ford Escort Cosworth. He took six of us - people like Allan McNish, Ralph Firman, Jonny Kane - and we drove the cars around Oulton Park. Jackie went out and was seven tenths quicker than anybody. It was impressive.
So, it's my turn to get in the car with him. After a few laps he says: "OK, let me show you." It feels like he's driving at five miles an hour, then we come into the pits. My dad is there and he says: "That was the fastest lap!" I'm like: "What the f*** are you talking about? He was doing five miles an hour!" It was unbelievable.

I'll stick with higher profile and learn to drive properly....

[Kawasicki]

TheJimi said:

Low profile tyres exacerbate aggressive steering inputs, imo - thus, they don't work "better" for that style of driving.

What do you mean by exacerbate?

I want to turn in to a corner aggressively, so I need to steer aggressively. Low profile tyres respond faster to aggressive steering.

[TheJimi]

Kawasicki said:

TheJimi said:

Low profile tyres exacerbate aggressive steering inputs, imo - thus, they don't work "better" for that style of driving.

What do you mean by exacerbate?

I want to turn in to a corner aggressively, so I need to steer aggressively. Low profile tyres respond faster to aggressive steering.

Most of the time, aggressive inputs aren't needed, so if you've got a driver who's driving style is aggressive and binary, low profile tyres will exacerbate those inputs.

So you've got a car that's constantly overreacting.

[Kawasicki]

TheJimi said:

Most of the time, aggressive inputs aren't needed, so if you've got a driver who's driving style is aggressive and binary, low profile tyres will exacerbate those inputs.

So you've got a car that's constantly overreacting.

Some times aggressive inputs are required. Aggressive driving isn't necessarily binary, it can be very smooth.

[lostkiwi]

Kawasicki said:

TheJimi said:

Most of the time, aggressive inputs aren't needed, so if you've got a driver who's driving style is aggressive and binary, low profile tyres will exacerbate those inputs.

So you've got a car that's constantly overreacting.

Some times aggressive inputs are required. Aggressive driving isn't necessarily binary, it can be very smooth.

I don't quite get how aggressive can be smooth. The fastest way to drive a car on tarmac is not to unsettle it. Any sudden input is likely to provoke a loss of grip.
This is exactly what my quote from JPM illustrates.

[TheJimi]

"aggressive" is probably the wrong word to use to describe the kind of inputs Kawasaki is trying to describe.

Edit: just realised it's Kawasicki

Edited by TheJimi on Thursday 10th September 11:19

[mwstewart]

Yes, fast but smooth - unavoidable in certain sections. I got what he meant.

[Kawasicki]

lostkiwi said:

I don't quite get how aggressive can be smooth. The fastest way to drive a car on tarmac is not to unsettle it. Any sudden input is likely to provoke a loss of grip.
This is exactly what my quote from JPM illustrates.

Aggressive driving doesn't have to unsettle the car, though sometimes an unsettled car is faster. If a driver has to thread a car quickly through a very tight, twisty course, then aggression is required. Look at onboard footage of rally drivers on twisty tarmac, the steering inputs are not smooth....the car motion is fairly controlled - but the steering inputs are not.

[TheJimi]

Kawasicki said:

lostkiwi said:

I don't quite get how aggressive can be smooth. The fastest way to drive a car on tarmac is not to unsettle it. Any sudden input is likely to provoke a loss of grip.
This is exactly what my quote from JPM illustrates.

Aggressive driving doesn't have to unsettle the car, though sometimes an unsettled car is faster. If a driver has to thread a car quickly through a very tight, twisty course, then aggression is required. Look at onboard footage of rally drivers on twisty tarmac, the steering inputs are not smooth....the car motion is fairly controlled - but the steering inputs are not.

We're at crossed purposes. Re-read my posts please.

I'm talking about a driver who's default driving style is an aggressive one. Low profile tyres will exacerbate that.

So for that reason, in that situation, low profile tyres won't be the best.

[Hol]

300bhp/ton said:

On the flip side I've read/watched stuff in the Subaru world that said and claimed low profile tyres made the cars handle better.

That's an interesting comment, if true - as back in 2000/2001 those of us (on Scoobynet) who tracked their cars pretty much all agreed that the Classic Impreza's handled better overall on the 16in wheels, rather than aftermarket and factory upgrade 17's and lower profile tyres.

In fact the P1 Impreza had to be fitted with specially designed coil springs to the otherwise factory STI inverted shock absorbers to help it cope with UK roads and 205/45/17 tyres.

However, the later generation of cars all came with 17's as standard, to allow for bigger/heavier brakes by Brembo.


No tyre is the same though and two tyres the exact same (physical) size from different manufactures can have totally different flex and load ratings.

[XOP]

To the best of my knowledge bigger alloys will have less side wall flex for a similar tyre on a smaller rim with a bigger sidewall.
However smaller alloys will weigh less. Less mass to spin up and slow down will lead to greater acceleration and braking. Plus greater deformation allows the tyre to create a bigger footprint for greater grip. On the downside a tyre that deforms easily will have a higher rolling resistance and use more fuel plus struggle to achieve the same top speed as a stiffer tyre. In corners the stiffer tyre on low profile alloys deforms less and alows less roll, being more stable in cornering.

Like most people I agree that there's a compromise on all of these properties to get the wheel and tyre that's best for you.

[Kawasicki]

TheJimi said:

We're at crossed purposes. Re-read my posts please.

I'm talking about a driver who's default driving style is an aggressive one. Low profile tyres will exacerbate that.

So for that reason, in that situation, low profile tyres won't be the best.

Yes, I agree that we are at crossed purposes.

Can we agree to say a digital driver rather than aggressive driver? A digital driver will be worse off with low profile tyres when he first steers as he will get more response, though I think he might be better off with low profile tyres if he steers back , again digitally, the other direction.

Anyway, I like low(ish) profile tyres, for the same reason I like fast(ish) steering racks, or taut(ish) body control.

[gizlaroc]

mwstewart said:

Very interesting. On 18's my E46 rides better over crap surfaces but handling wise lost the precision of the 35/30 profiles. The back end hasn't broken loose without me driving in a way where I expect it to, and I have all ball joints from the CSL rather than the std mix of rubber bushes & ball joints.

It is quite possible your RTABS were worn, which is a common problem.

No, bushes were fine.

I'm not talking about the back end breaking loose, it was just that over poorer surfaces you could feel it not biting as well on the 19s.
Much the same way as it does if you simply over inflate a tyre.

[300bhp/ton]

2Btoo said:

Miglia 888 said:

Article from Car & Driver magazine, testing different sized wheels & tyres on the same 2010 VW Golf.
As you'd expect, the largest wheel / lowest profile tyre option isn't necessarily the sweetspot, particularly if acceleration and/or fuel economy are important factors for consideration:
http://www.caranddriver.com/features/effects-of-up...

Interesting article, thanks.

I agree an interesting article. But on reflection I think their conclusions are flawed and seem to centre around tyre width rather than rim diameter.

[2Btoo]

300bhp/ton said:

2Btoo said:

Miglia 888 said:

Article from Car & Driver magazine, testing different sized wheels & tyres on the same 2010 VW Golf.
As you'd expect, the largest wheel / lowest profile tyre option isn't necessarily the sweetspot, particularly if acceleration and/or fuel economy are important factors for consideration:
http://www.caranddriver.com/features/effects-of-up...

Interesting article, thanks.

I agree an interesting article. But on reflection I think their conclusions are flawed and seem to centre around tyre width rather than rim diameter.

True, but the observations about grip, noise, MPG etc apply regardless; the comments about width seemed to be more in their conclusions.

[HustleRussell]

Essentially I agree but please stop using this word. I don't see how a tyre can exacerbate any input from the driver, only attenuate it to a lesser or greater degree.

TheJimi said:

exacerbate

[300bhp/ton]

2Btoo said:

True, but the observations about grip, noise, MPG etc apply regardless; the comments about width seemed to be more in their conclusions.

I'm not saying they don't, only their data doesn't really support this conclusively.

e.g. the 235 width section tyre had more lateral grip than a 195 section tyre. But they portray the results as the 19" tyre had more grip than the 16" one.

I know it would be much harder to do, but seeing a test where the rim width and tyre width remained constant and only the profile changed for varying rim sizes, while maintaining the same rolling radius, would in my opinion be an interesting read.

[HustleRussell]

The structure of the tyre's reinforcement bands, and the camber the vehicle runs will have a significant hand in cornering grip.

[matsoc]

Without altering the suspension geometry the rolling diameter and the contact area on the road surface should always remain the same: that is why is not possible comparing tires with same width and different wheel diameter on the same car: on the same set up the larger wheel must have a greater width and a lower profile. The lower profile will make the shape of the contact area change, decreasing its length, so the tyre will need more width to get the same contact area.