High speed stability

[Q102]

Currently in Germany so had opportunity to give it the beans.....  up to 110mph car felt ok, towards 120 not so happy feels too floaty and unstable.

Driven my old XC60 over here roack solid at 130mph!

 

 

 

[Ootohere]

Horses for courses then, or different shoes.   Did you have the tyre pressures set at a nice pressure at the higher speeds.

[Q102]

Tyre pressures were checked and set on the eco setting -2.5 front & 3.0 rear. Only me in car and maybe 50kg luggage in boot.

It's was the rear of the car that felt floaty.

[BillyJim]

No such issue with my 280. In Germany I regularly took it up to the vehicle's restricted limit (digital speedometer indicates 256 km/h) and it's always been as stable as a rock, regardless of whether it's light or heavily loaded.

The advantage of having DCC and Haldex, I guess.

[philsmith]

Driven at up to 140mph in Germany and car was solid as a rock, felt the same as doing 40mph.

As Billyjim said maybe the setup of the 280 helps.

Edited 22 September, 2017 by philsmith

[MartiniB]

for speeds >170kmh necessary Sport suspension or DCC in Sport mode,

in DCC's Normal mode felt uncomfortable too

 

[BillyJim]

Nope, I set DCC (individual) to Comfort on the autobahn, otherwise Normal. Rarely feel the need to use Sport.

[Super280]

DCC set to sport is the solution for stability.

 

Probably the computer changes DCC to harder setting at high speed?

[Gross9661]

We are also currently in Germany and had  a good blast of 100mph on the A7 motorway. Felt rock solid but not sure I'd want to go much faster than that

[Ootohere]

If a car feels floaty and the tyre pressures are at an Eco pressure then smart money might be on adjusting those pressures downwards, 

but not so low as to have tyres overheating at speed if there is a chance of that and no onboard pressure monitor.

A few psi can make a big difference.

 

Q102,

what tyres are on your car, brand and size?

[roo]

I'm guessing that the eco pressures are not meant for such high speeds, which are not eco in the slightest.   High pressures cause the tyres to sit high and give less grip in certain conditions (high speed, rain).

[BillyJim]

Ha ha! I feel ... the need ... for speed spiel. Time for BillyJim to spout more crap!

 

The higher eco tyre pressure rating is probably close to ideal. The recommended eco tyre pressure is set higher to facilitate the best rolling resistance of the tyre. Reduce the tyre pressure and you increase the rolling resistance, negating any fuel efficiency afforded by these "low rolling resistance" eco tyres. AFAIK all Superb III's come shod with "eco" tyres, even the 280. 

 

At high speed you are putting an exceptional strain on the tyre, particularly the side wall, which leads to increased deflection. This results in the tread having a larger footprint and contrary to popular belief that is not a good thing - it adversely affects steering/handling (increased slip angle), rolling resistance (more energy needed to rotate the tyre) and grip in the wet (the blocks and sipes can't compress to expel water as efficiently, increasing the risk of aquaplaning). High speed has the same effect on a road tyre as hauling a heavy load. By increasing the tyre pressure you add support to the sidewall to help reduce the deflection and thus maintain an efficient footprint.

 

 

There's an article about it here if you want to read more.

 

In a nutshell - for high speed driving, reducing tyre pressures is the wrong thing to do.

 

Personally I set my "eco" tyres to the higher eco pressures, not for the economy but for the short bursts of high speed. Even in Germany I have yet to find an autobahn where, in the daytime, I can actually safely sustain max-V for anything more than a couple of minutes to thus warrant driving on otherwise over-inflated tyres.

[Ootohere]

Why so many fit lower profile tyres rather than balloon sidewall tyres, (balloon tyres are nice for touch parking and potholes though...)

and why ECO tyres are not always appropriate fitments as OEM other than because Car Manufacturers are needing lower Co2 g/km & 

mpg figures.

 

But the OP was finding the car floaty, especially at the rear, so a few psi is not the same as letting the tyre pressures run at too low pressures when there is heat in the tyres.

It is just a bit of trial and error if you have a pressure gauge and means of re-inflating tyres, or can go re-inflate at a filling station.

Maybe like DROPPING THE REARS BY A FEW PSI to nearer the front pressures since there is no load being carried.

Short burst are rather different from running at higher speeds over longer distances.

 

As some will know that drop tyre pressures in winter for conditions they might meet, you need to get that pressures back up when on black top again.

Or those that do track driving will likely know the affect of pressures, heating up on some tyres, and handling.

 

Tyres are rather important obviously, and pressures very much so, "probably close to idea" is really not 'good enough'!

 

 

OT, but, When Owners reported 'Pulling to the left' with badly aligned cars from the factory, Skoda / VW blamed the directional Dunlop Sport Maxx or Continentals which have XL sidewalls & appoved fitting 'under warranty' the physically taller but still marked 205/40 R 17 Pirelli Zero Nero with stronger sidewalls, 

this certainly disguised the badly aligned steering on right hand drive cars & the pulling to the left,

but then traction was crap and handling floaty.

Funnily Skoda VW or employees of them or Dealerships would bad mouth the Dunlops / Continentals but keep fitting them for the 4 years of the cars production.

That car comes on standard 205/40 R 17 tyres, not ECO, it would have been good to see them also do it in the sister car a Polo GTI which came on 215/40 R 17 as OEM & without 25kg Ballast on the rear crash bar and no spare wheel as standard but the battery in the boot and see how the tyres stood up.

 

Edited 23 September, 2017 by Headinawayoffski

[Q102]

Car has the standard 17" rims & tyres. Fitted with Pirelli P7 tyres.

I'll have a few crate of beer in the boot on the way home to load it up

Edited 25 September, 2017 by Q102