Front tyres and handling question

[knk]

My 96 Griffith 500 with PAS currently runs with 205 SO2s on the front, 245 SO3s rear. It has pronounced initial understeer. I am due to change the Fronts soon. Would changing to 225s as seem to be spec for PAS decrease understeer, increase it or make no diference to the handling?

[bjwoods]

my 98 griff 500 (with PAS) has 225's on the front, never really noticed understeer. Have done the Driving developments wetter the better course (fun)
Seems like you have the tyres for a Non PAS car.

Oversteer is always a right foot away :-)

B

>> Edited by bjwoods on Wednesday 9th October 16:42

[CleG]

I thought most the PAS cars came with 225 fronts .. I know mine also has these fitted.

So uping your size to this should be no worries

[davidy]

I thought that early PAS cars can with 215s and later ones with 225s. It may be worth having your camber/toe-in checked when you replace the tyres and either of these will have an effect on understeer (including the rear)

davidy

[CleG]

On Davids point .. My griff was very scatty untill joolz set it all up properly.

There is a large difference in how it handles now.

[Jarcy]

Understeer? TVR? Something other than the tyre choice at fault here I think. I doubt whether 205 SO2 vs 225 SO3 would make so much difference.
My '96 Chimaera 500 (power steering)has 225 & 245 SO3s and seems perfectly balanced. Predictable oversteer induced by feathering of right foot.

>> Edited by Jarcy on Wednesday 9th October 17:27

[knk]

The understeer obviously disappears rapidly with a foot on the gas, but is there on turn in.

[Jarcy]

Turn-in on mine is very crisp(for want of better vocabulary) i.e. it goes exactly where you point it.

[GreenV8S]

quote:My 96 Griffith 500 with PAS currently runs with 205 SO2s on the front, 245 SO3s rear. It has pronounced initial understeer. I am due to change the Fronts soon. Would changing to 225s as seem to be spec for PAS decrease understeer, increase it or make no diference to the handling?

Decrease, but not dramatically. As well as increasing the peak grip slightly, it'll also produce that grip at lower slip angles which will make it feel slightly more responsive. You might consider going to a 205/225 or 225/245 combination F/R. IMO 245 is a little too wide for those rear rims, 225 or maybe 235 work better. Similarly, 205 or 215 are about as far as you really want to go on the front. Also look at the tyre pressures, this affects lateral stiffness (and hence the feeling of initial understeer) significantly. If you're looking for a bigger change, damper rates and geometry changes can be used to make a huge difference.

In any case, slight understeer is normal, in fact desireable. If it's severe enough to cause trouble, there are several ways you can reduce this including changing the tyres. But be warned, as you reduce understeer and promote oversteer you will also tend to reduce traction coming out of a corner and exaggerate power-on oversteer. A good fast safe setup will understeer slightly unless you're accelerating. Shouldn't be severe enough to stop you turning in, except on the very tightest of corners though.

Cheers,
Peter Humphries (and a green V8S)

[Leadfoot]

Could the understeer be down to shot S02's (the idea 'that it's got no tread left so it should grip even better in the dry' doesn't hold true)?
I used to have a 205F/245R combination, now 225F/245R on my PAS Griff. The 225 fronts give more grip, the 205's seemed to give sweeter handling & a more balanced feel on the road - on the track it's 225's no contest.

[GarryM]

quote:
Could the understeer be down to shot S02's (the idea 'that it's got no tread left so it should grip even better in the dry' doesn't hold true)?

I don't understand this but am experiencing it on my Griff. Rear SO2s are down to 2mm on inside edges and they definitely slide more - why is this?

[v8 mark]

I too had this worry, last week. What to replace the worn out S-02's with, read various threads, and decided to go for the Goodyear F1's in 225/50/15 for the fronts. All i can say is what a difference? The car used to twitch all over the place (could be setup?) but now sits sure footed on roads, where it never used too...My only downside is the tyres look too tall on the rims, but they feel so much better. Incase interested bought from (tyre4u.com £220 all in with delivery, not too bad i thought)

[DIGGA]

Tyres are made up of different rubber compounds, and in very simple terms that means the stuff at the centre which forms the structure is tougher, and the tread blocks are grippier. Over simplification I know, but that's basically why worn tyres aren't roadgoing slicks!

Referring to the original point, IMO, on my non-PAS Griff 500, it's always felt better since I changed to 225 fronts.

>> Edited by DIGGA on Thursday 10th October 15:43