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Can some one shead some light on what is the recommend offset for Autocross on a FWD car?

that seems a rather vague question.
this is offset.

The rules used to state that the tyre was not supposed to extend beyond the fender. Really, the wider it is should be better for handling around corners as the car becomes more stable. Trade off in autocross is the car now has to turn more which I think is one of the main reasons smaller cars like swifts, civics etc do well, they have the same stability and can have a smaller angle into corners and can therefore maintain higher entry and exit speeds. Especially through chicanes.

So pete which rim would be better for autocross 15x6.5 35+ or 15x6.5 42+?

When I was looking for rims to put the R compound tyres on I looked for 7" rim and just so happened to get 15x7 +35 or maybe +37. The road rims I have are 16x7 and the same offset.

offset depends on your driving style. Low offset all around will corner well but steering is twitchy on the straights. Low offset in front alone gives you oversteer but steering is still twitchy.
If you have different offset wheels you should try the combinations during the bycc to see which you prefer.

Moses your question really is vague....there is no best offset or one particular offset that anybody here can recommend for you.

As for your second question the +35 would be better than the 42 since it widens the track of the vehicle and hence would improve handling.

A pretty decent combination for a car like urs would be 15x7" +35 offset with a 225/45 tire or a 205/50 tire. Problem with that is, mainly expensive JDM racing wheels like the enkeis come in that sizing and hence $$$

So i should use the +35 instead of the +42 for autocross?

whichever rim gives you a wider track

The widest track that would not foul your body work or inner fender and one that will seat your tire adequately.I am on a 15 x7.5 +38 on my corolla and it holds 225 nicely without rubbing. the volk replicas i have are a 15x6.5 with a +40 offset and i tried this combo with 225 in the front and 195 in the rear.Made for alot of oversteer on turn in due to the difference in foot print front to rear.

is that a winning combination?

With time and effort and seeing which setup helps my car the most would make it.

Well the guy asked for the best recommendation. So are you recommending the best option to him, or showing him your trial and error process?

from the 2013 rules

1. TYRES:
a) Any tire which is OE on a car eligible for Stock Category may be used.
b) Tires up to and including a width of 225.
c) Tires must have a minimum tread wear rating of 140.
d) Tire must fit the allowable wheels and fender wells without modification.
e) Any wheels up to 7.0" in width that fit over stock brakes

so yeah, run the widest track you can, while staying within the above rules
If your current rims don't give you maximum track width, it may be cheaper to run spacers than buy new rims (within reason)
To maximize your contact patch, look for tyres with less of a sidewall bulge. A stiffer sidewall means less deformation under hard cornering
Look also at your camber. A bit of negative camber will help with cornering, as again you will have a more positive contact patch under hard cornering
Be mindful of tyre pressures as well. High tyre pressures (say 10 psi over stock) will also reduce sidewall deflection under hard cornering, and maintain a better contact patch.
Walk with some chalk, and make a nice broad chalk mark around your sidewall, up to the edge of the tread. The less chalk you rub off, the better
I hope this helps

10psi above stock is way too hard in my opinion. Yes when you do research on the internet about autocross/time attack etc they always recommend figures like that however, you need to be mindful that the surface they use over there and the surface we use at ARC is completely different.

From my experience, the surface at ARC is almost gravel like and as such very very loose compared to the nice smooth, clean, grippy surface that is used in most car parks for autocross events abroad.
In my opinion, once you go too high with your tyre pressures at solodex you begin to under steer a lot on the loose surface. My recommendation, set the tyre pressure's to the manufacturer recommendation found on the door jam of the vehicle, then look for roll over and increase if necessary.

jamb, not jam
jam is what you get in your toes after a long day at dex

http://www.willtheyfit.com/index.php?wi ... 40#content

Things to keep in mind:

Wider track in front helps reduce understeer. Make it overly wide and the car becomes unstable in corner entry, especialy with some trail braking.

wider track to the rear helps reduce oversteer. Again make it too wide and the thing wont want to turn.

Increasing overall track will give more grip front and rear. As was said previously, wider then better... use the website i gave to check new specs against what u currently have. give those rear fenders a roll, get camber plates and let the widest wheel/tire combo with the most aggressive offset that could work.

Also, as someone said tire pressure. higher pressures infront adds oversteer. ( in my civic days i ran 38f34r ) and the reverse is also true. Just keep in mind going too low will cause too much tire roll and the tire can peel off the rim. aka focus ST on sunday.

The type of offset differences you are looking at with stock rims will have a negligible effect on performance as compared to aftermarket rims that can approach +10 or even 0 offset. Don't go mixing f/r with different offsets if you are trying to build a stable, predictable setup. More concentration on your tire pressure, toe and camber would have a much more noticeable effect on handling than pushing for lower offset wheels. But I would concede, as others mentioned... get as wide a track as you can, within reason... +35 is common. But amongst the highest offsets on an OEM car is +42 ... an offset offered on the OEM type R for reference and that setup is ideal for autoX and road racing... so both are great. Beyond +35, would put excess pressure on the outer portion of (some) rim's spokes which can possibly fatigue the rim faster than an OEM-esque offset.

Not that we are running 1 or 2 hour races, or even multiple laps so increased forces on the rim might not be such a factor with a 8 or 12 race schedule for the year... but ultra low offsets are for race cars, on race tires... guys that want to run 245's on a fwd because THAT'S how fast the circuit is . Other than that... ultra offsets are for style... stay with 35 or 42 unless you wanna baLL OUt.