Tyre widths

[James.Burton]

I have 13 x 8J wheels all round (it came like that)

I’ve been using ZZS
185 up front (yes they pull wide over the rim)
215 rear
1.1 bar (18psi) all round

Tried 215 all round as they are the recommend size for the rims.
Front now pushes wide.
I’m a relatively fast, but strictly road driver

What’s going on?
- I can image too much tyre reducing downward pressure
- But the racers go for 8J up front, so is it the softer rubber they use? Or full on trial braking?
- could I just try dropping pressure a bit further?

[DCL]

Any change will alter the balance of the car so you really need to go back to basics and set it up for the new tyres. Lots of things change, for example the larger front tyres are heavier so spring and shock requirements will change, contact patch will be different, camber will need adjusted, antiroll bars will work differently etc etc. the list is pretty much endless. They're all small things but may add up to a bigger problem.

But to fix the issue I would make sure the ride heights and rake are correct, then lower the front (if you have clearance) to tweak out any understeer. And you'll probably have to run lower pressures on the front, or higher on the back (depending on where they are).

[HustleRussell]

If you’ve bunged 215s on the front without any other setup changes (and depending on tyre profiles…) you have probably increased the front tyre radius, increasing the front ride height and probably ending up with negative rake.

I thought 6J fronts were typical, with 175s or 185s.

[James.Burton]

Thanks for the thoughts.
I corrected the rake, but that’s the only change I made

[HustleRussell]

How did you correct the rake?

There is no information I can see here about your car and what you have done to it so far?

[James.Burton]

It's a LHD VXi (I live in Austria), with Nitron adjustable road suspension.

Adjusted by lifting the front off the ground and winding off some of the preload there, and then lifted the back and wound some on there (although I think this has led to the chassis hitting the dedion tube in some jiggly road moments - so may have to drop the whole car sacrificing road clearance for less knocks).

Still wet sump, and for road I think I'll leave it there.

Clearance now:
- A coke can under the sump (just - wasn't quite before)
- Chassis rail height just in front of rear wheel approx 13mm higher than at the middle of the car where it goes from square to round. (roughly 150mm, and 137mm)

Edited by James.Burton on Monday 28th June 16:12

[Tazio77]

I run a VX too and have never seen the need to run 8 inch fronts, and in my experience yours seems to be quite a unique set-up, so there are few if any people around who can give you any advice as to what will work with your set up. I suspect if you were running a normal staggered set-up of 6 inch fronts and 8 inch rears things would be different as there is quite a lot of experience around as what works with that set-up.

[Murph7355]

Very over-tyred at the front.

It washing out must be down to suspension geometry.

Rather than try and work around this, I'd recommend getting narrower front rims and tyres and working from there.

[braddo]

How many miles have you done? Don't tyes usually need a few hundred miles before they perform properly (something about release agent in the rubber?)?

I would spend some time getting some miles on the tyres before you spend time on potential geometry changes or changing tyres again.