Skidding round roundabouts! - accidentally

[growla666]

I've just had some new wheels and alloys put on my SL320 and was shocked the other day when I took it out for a drive. The conditions were: Mostly dry with some dampness on the roads, temp about 6C. The car was driven from cold and within 2 mins I could feel the back end sliding, the traction light kept flashing especially if I accelerated a bit briskly from a stopped position. Even worse as I drove round a large roundabout in Rickmansworth, the back end snapped out and I found my self going sideways un-expectedly. Ok so not a problem as there were no other cars around otherwise it could have been expensive. Thing is the tyres are brand new. They're sitting on 18 amg replica split rims. I never had this prob with the 16 original tyres and wheels. My father in law reckons the new rubber is cheap and too hard which is why I've got really poor traction. Does this mean I'll have buy new tyres or will the problem go away when I've worn them in a bit more. I've done 70 miles on them since fitted. Anyone else had the same snags?:???:

 

[Flying Scot]

your tyres maybe just a bit green give them a few more miles to wear off the mould release compound before you bin them what size tyres and what make and model are they?

 

[Blobcat]

How much wider are the new tyres as this has an effect. Wider tyres generally work better in the dry

 

[Dan996]

Its also becauase you have bigger rims there for smaller profile tyres this means the tyre has less give on the road its more solid. thats why tyre usually getter wider the bigger you go to give more grip. a smaaler rim means bigger tyre profile the tyre can then move more in the trye wall which then bites into the road. im pretty sure im right anyway.

 

[television]

Also what wheels have you fitted, if you have deviated more than a few mm on the ET your ESP will be a long way out and aggrivate the situation. You cant just fit any wheels to a 129,

Other than that you have only got one roundabout in Rickmansworth

Malcolm

 

[BarryG]

Couple of bags of sand or cement in the boot will help till the tyres settle down.

Barry

 

[daveenty]

Matter of interest, what make of tyre?

Some have a considerably harder compound than others making the conditions you describe a reality in any dampness.

Mine are Conti's and are not brilliant in these cold/damp conditions.

A light right foot helps, though does take the fun out of it

 

[Sprint'n'Go]

2 things spring to mind.

What pressures are you running the tyres at? a faulty gauge may have inadvertantly over inflated your tyres causing the skitishness. Possibly try running the pressures a few psi lower to allow a reasonable footprint with the larger tyres.

point 2 is to remember that the roads may have been gritted at this time of year and in my experience a drying but damp road that has been previously gritted can be quite greasy.

Other than that, as mentioned above I too have taken time to gain confidence in some of the new tyre sets I have had over the years, some can be especially waxy to begin with, wait and see.

 

[Blobcat]

I've just had some new wheels and alloys put on my SL320

That maybe your problem, you need some tyres....

 

[growla666]

Tyres

Tyre brand = Fullrun HP199's, and no, I've never heard of that brand before either. Television, the ET is exactly right fr 129's, I checked before I bought em. Will have to check pressure tomorrow as I'm driving 200 miles to check out a C250D.

 

[television]

That maybe your problem, you need some tyres....

I think he has new tyres on these 18" wheels we should know what the ET is as I said earlier you cant deviate by much without upsetting the ESP, this is a well known fact.

Malcolm

 

[turnipsock]

Flying Scot has a point, new tyres do need a bit of bedding in.

 

[growla666]

They are brand new tyres......only done 70 odd miles in them

 

[television]

They are brand new tyres......only done 70 odd miles in them

What wheels did you fit, the ET ??????

malcolm

 

[turnipsock]

They are brand new tyres......only done 70 odd miles in them

Yes, but you need to round of the corners before they really start to grip. New tyres are pretty crap until you have done a few miles on them.

 

[slim_boy_fat]

The biggest issue is probably the road conditions not the tyres. Saying that i have never heard of that type.

I generally stick to a reasonable brand, you atleast buy with some confidence.

The increase in tyre width doesnt actually give you any more contact patch in terms of area.

As has been suggested check the pressure, you may find you might be able to knock a few psi off the tyres.

Let them bed in a bit more.

If it continues you might be better looking at some decent brand tyres.

 

[Parrot of Doom]

I could feel the back end sliding, the traction light kept flashing especially if I accelerated a bit briskly from a stopped position. Even worse as I drove round a large roundabout in Rickmansworth, the back end snapped out and I found my self going sideways un-expectedly.

You say this as though its a bad thing.

 

[mioba]

totally agree with the bedding in idea.

new tyres have shiny rubber, once this has worn through a bit you thrigh to the slightly "tackier" stuff, ie more grip.

 

[television]

I am surprised that know one else here ask's about the ET, Its in big words in the hand book, we know the wheels have been changed to 18" but the ET ?
It is not a case of the ESP not working,it can have an adverse effect if the ET is wrong.

malcolm

 

[Bolide]

All we have to go on is that you have 18" wheels with "Fullrun" tyres, that the car was OK on the original 16s and that it's now not OK. Details, like rim width, tyre size, wheel offset & etc, would help. ET varies with rim width so it may be incorrect

You've increased the effective spring rate (due to stiffer sidewalls), possibly changed the position of the contact patch, increased the size of the contact patch and (probably) increased the unsprung weight. All of these changes will make traction worse. I'd expect a wider, stiffer tyre to give poorer traction and a worse ride at all times though it may give better ultimate grip in particular circumstances

In general, I'd expect that changing good 16" tyres on Mercedes alloys for a set of Taiwanese Ditchfinders on cheap 18" rims would give exactly the effect you describe. The situation may improve as the mould release agent disappears and at higher temperatures

Nick Froome
www.w124.co.uk