thoughts about track rims and tyres

[Bealo]

So am i correct in saying that the ideal size is 19 x 9.5 et28 all round with 265/30/19 cup tyres???

Look forward to hearing your comments of the extra grip at the front on trackdays. :thumbs:

[shimmy]

Here's a photo of BBS ch's 19 x 9.5j et28

the 9.5J look spot on, i think you missed a trick not getting 9.5J all round making tyre wear and wheel swap dead easy (although you loose that 0.5 inch of rear grip)

[TANKSLAPPER]

Here's a photo ofthe BBS ch's 19 x 10j et20




Here's a photo of BBS ch's 19 x 9.5j et28





you can see the difference, both have 265 cups on. The second picture is just road legal AND A mot pass. As the other, well, your nicked LOL

[TANKSLAPPER]

i might come by your place next month and see how it looks if thats ok, maybe after a visit to Racoon and Brands:thumbs:

Shimmy, You are always welcome at my place, just pm me first.

:thumbs:

[shimmy]

I must say, it look the dog bollocks. The tyre is about 2mm outside the front wheel arch with a 2.5 dergrees of camber. I only have 2-3mm between the strut and the tyre.

A very tight fit, if it rubs on track I will increase the spacer size. I reckon this is the best fit for 19" s it's a petty BBS don't do them in 18" in 9.5j

I will put some photo's up over the next day or so.

sounds real close to me. be careful and if you see any black smoke STOP

what is the gap like between the strut and tyre at the front? OEM runs about 5mm away. My guess is you need more clearance to the arch so see if you can reduce the spacer as you dont wanna run any more camber on road really, as -2.5 will shag the tyres pretty quick anyway

i might come by your place next month and see how it looks if thats ok, maybe after a visit to Racoon and Brands:thumbs:

[Bealo]

Great R&D guys :thumbs:

I'm watching this with great interest.

[TANKSLAPPER]

I've just changed my wheels and tyres over

On the rear I run currently BBS ch's 19 x 10j et20 with 265 cups

On the front I just bought BBS ch's 19 x 9.5 et40 with a 12mm spacer which is = to an et28 with 265 cups

I must say, it look the dog bollocks. The tyre is about 2mm outside the front wheel arch with a 2.5 dergrees of camber. I only have 2-3mm between the strut and the tyre.

A very tight fit, if it rubs on track I will increase the spacer size. I reckon this is the best fit for 19" s it's a petty BBS don't do them in 18" in 9.5j

I will put some photo's up over the next day or so.

[shimmy]

UPDATE

at Simpsons yesterday i got the geo redone and test fitted and ran some CSL rear rims on the front.

We had to get the geo out to -3 camber at the front to get he tyre under the arch. It just touches the wheel arch liner on full lock but seems to miss everywhere else, especially on track damper settings.

Need to test it at the next dry trackday before deciding if its worth getting 4x 19x9.5 (or18x9.5). At the moment with the et27 the rim is 5mm further off the shock then OEm front rim so i can go 5mm back in therefore my estimate of a new front with et32 is about right

With an et32 you should be able to run at -3 camber on track and even maybe -2 camber on road witht he same 4 rims all round.

[_Nathan_]

Shame because the BMW BBS WTCC 17 inch wheels come up regularly and are cheap

[shimmy]

17s won't fit over the brakes will they?

def not over APs,

not sure about stock brakes but you wouldnt want to be on track with those anyway :smokin:

[_Nathan_]

17s won't fit over the brakes will they?

[The Gorilla]

Hi,

Shimmy- I can see what your saying
but I was working on the basis that
the standard CSL fronts at the tyres-

235 35 19 and pending on which make of tyre
are O/A Diam of 647mm.

265 35 18 and again pending on which make of tyre,
Diam of 642.7mm.

Even allowing for the increase in the ET
the O/A diam is almost 5mm less, so
rolling the arch should make it work ?

While on this subject has anybody ever run
17s with say a 40 profile side wall and then
firmed the suspension right up tight for track
work ?

A 265 40 17 comes in at 643.8 mm so O/A
Diam is good, and increased side wall profile
gives a little 'suspension' via the tyre to compensate
for the harder damper setting, and I think a car would
ride much better in the corners due to the tyre side
wall compensating and assisting for the progressive roll in and
then out again for good cornering, while being a bit stiffer
for the straights.

This is very much akin to current F1 suspension.

Although 30/25 and even 20 profile tyres might
look the dogs, any surface change is more or
less transmitted straight to the suspension as the
the tyre side wall has such a small margin
from which it is able to absorb.

Also explains in part why the majority of 18'' slicks
go 650 upwards.
Porsche are 650 fronts and 670 rears I think,
and they handle OK ishhhhh.

I ran 230 625 18 slicks once on a
e30 m3 and it was bloody awful.

Always looking at the inner wheel beading
and the way the tyre is located to the rim
for Track Wheels, as if the tyre starts rotating
on the rim, which can and does occur it will
cause untold issues.

Regards,

The Gorilla.

[shimmy]

Hi,

Shimmy- just my quick calcs before I dash out.

Some guys run the rear CSL rims on the
fronts which are 9.5 J ET 25 if I remember.

So at ET 20 your 5mm more ET would push the
rim out about 2/3mm more.

At around 3.5 to 4 degrees camber an
an ET 20 9.5 J rim might need the standard
front arch lips well rolled, but it should
go.

The gain in extra O/A track width on the front
will also help turn in but the trade off, and there
always is, that front tyre scrub radius will increase.

Regards,

The Gorilla.

Gorilla

Thanks but it is def worse than that as OEM rears are et27 (fronts et45). The difference between et20 and et27 is a straight 7mm as the face of the wheel hub is moving 7mm one way. Therefore the ROTA rears on the front will foul the arch by 7mm more than OEM rears, so i am not sure if they will fit without rolling arhces or even with:whistle:

[The Gorilla]

Hi,

Shimmy- just my quick calcs before I dash out.

Some guys run the rear CSL rims on the
fronts which are 9.5 J ET 25 if I remember.

So at ET 20 your 5mm more ET would push the
rim out about 2/3mm more.

At around 3.5 to 4 degrees camber an
an ET 20 9.5 J rim might need the standard
front arch lips well rolled, but it should
go.

The gain in extra O/A track width on the front
will also help turn in but the trade off, and there
always is, that front tyre scrub radius will increase.

Regards,

The Gorilla.

[shimmy]

What reason do you see the et20 being a problem shimmy?

well my calcs (bear in mind i am new to this stuff) show that my rear CSL rim 19x9.5 et27 if put on the front will foul the arch if a camber of say -3 is not used

Now if you bring the et down to 20, thats 7mm further out which means it will foul even worse unless a -3+ camber is used, god knows how much


but saying that Nathan is using et14 but i guess he will run a massive camber for race circa -4/5 anyway

:smokin: