thoughts about track rims and tyres

[shimmy]

http://www.rotashop.co.uk/?gclid=CML...FWlr4wodTwhVMA

thye have a big selection of replicas

Rota drift weigh 9.5kg each, £850 for 4 18x9.5 approx

[shane@mbtech]

Originally Posted by shimmy

http://www.rotashop.co.uk/?gclid=CML...FWlr4wodTwhVMA

thye have a big selection of replicas

Rota drift weigh 9.5kg each, £850 for 4 18x9.5 approx

I might be guineau pig

[shimmy]

Originally Posted by lawsy

I might be guineau pig

check out this uk site

only trouble might be et20 only for 18x9.5J E46 versions


http://www.rarerims.co.uk/alloys_sub...=22&RangeID=77

[shane@mbtech]

Originally Posted by shimmy

check out this uk site

only trouble might be et20 only for 18x9.5J E46 versions


http://www.rarerims.co.uk/alloys_sub...=22&RangeID=77

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

[shimmy]

Originally Posted by lawsy

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

[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]

Originally Posted by 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.

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

[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.

[_Nathan_]

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

[shimmy]

Originally Posted by _Nathan_

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