Some more info.
I am not using GI. Its also noisy using a vraymaterial.
Is there any way I can make vray put more samples in that area?
up aa up sampes on light.
My light samples are 150 at the moment.
To smooth the shadow I pushed it to 700
At 700 its not feasible to render the scene.
My render settings are
ADMC 1/15 (its at 15 because I was getting some aa issues on the geometry)
Adaptive amount .85
Noise thresh .01
Min samples 8
Light subdvis 150
2/15 should give u good boost. Change adaptive amount to .65 see if that helps.
Its slightly better.
Is there anything else I can do. Is there a way of forcing vray to do more samples on an object or material?
Heya
Well u are doing it wrong lets just put it this way 
1st make 1 render wish shadow invisible to camera for car on black background.
2nd make 1 render with car invisible to camera for shadow pass
3rd post it together in post.
This way you will save many time and get great results.
I think I know what you mean.
1 Render car no ground. normal render settings.
2 render matte car with ground. High samples for the shadows.
3 comp it all.
I remember in mentalray there’s a light portal thing that adds extra samples…
Thanks for the tip.
Yes but 1st point make sure ur matte shadow is still rendering. Remember you still want the shadow to reflect in car…
Any chance to send us this scene for investigation ? You can remove/replace the car-geometry with simplified version , what is important is to get the same issue with the shadows.
Thank you very much in advance.
Hi Svetlozar,
Thanks for looking in to it. Unique Download Link | WeTransfer
In my scene I put the AA samples up quite high to 1/15 because I was getting some noise on geometry edges.
I have actually now rendered the scene. I tried matting out the cars and doing the shadows separately but I got nasty fringing in the comp. In the end I made the cars invisible to camera and rendered all the shadows using different render settings. In the comp I also gave my shadow layer %1 blur.
Thanks for the scene nomads
First I would like to point out that Max Subdivisions = 15 in AA settings you’ve specified are never fired cause the Color Threshold value = 0.01 is too high , so most of the pixels are sampled with 1 , 2 probably up to 5/6 subdivisions and only a very few pixels are sampled with 15 subdivisions. This could be clearly seen in SampleRate render element - as you can see it is mostly in blue which indicates Min-Samples are used , Red color means Max Samples are used.
Images Scale(400%)
Here is how the RBG pass looks like with unchanged settings:
As you probably know DomeLight usually produce a lot of noise and it requires a lot of Subdivisions in order to clear that noise - in case that HDRI image with great difference in values is used noise levels are even higher. HDRI image you’ve used have a lot of very dark and bright spots which makes it difficult for sampling - more samples will be needed in order to produce smooth result.
I managed to clear a lot of that noise by reducing the Noise Threshold to 0.003 value into DMC Sample settings. AA samples are decreased to 1/10 and DomeLight Subdivisions to 100.
With that value of the Color Threshold (Noise Threshold) Vray fires more rays per pixel and the result is better - here is how SampleRate element looks right now:
You can decrease this value even more or increase DomeLight subdivisions to improve image even more but you should have in mind that the render time will increase even more.
Heya
Correct me if I’m wrong but isnt that incorrect? You are using AA to clean up noise that come out from light. Should he not tweakd DMC settings treshold lower or adaptive amount so that more samples get fired by Dome light ? This way his AA should stay low and dome light should render cleaner?
Thanks so much for you time on this. This is very confusing.
What does the VRayDampleRate render element display?
Is it the maximum and minimum combined samples form the image sampler and secondary subdivs?
Have a look here, very indepth explanation on how stuff works including the vray sample rate element. http://forums.chaosgroup.com/showthread.php?76373-V-Ray-Render-Optimization-an-in-depth-Guide-(call-for-Before-Afters)
in short, blue means min samples taken red means max samples taken. In your case, its not firing enough samples to clean as svetlozar pointed out.
There is two ways to solve your problem, one to add more samples to lights, which you did but it does not entirely solve the issue and this is due to the fact that dmc sampler actually takes over some of those samples and throws them away. So as svetlozar pointed out again, you must lower the noise value, in your case 0.01 is too low.
What I would suggest is to set your light to something like 16 subdivs, set your adaptive threshold to 0.9 and noise threshold to 0.005 or lower. By not giving the light many samples, you will force dmc sampler to do more work, but its ok in this particular scene.
Btw I had a look at your scene. So one of the causes of the noise could also be hdr. It had very detailed and contrasted white/black lines that would result it extra noise. I would not suggest to make the texture resolution very high for the lighting dome, instead keep it low and possibly blur the hdr so it contains less sharp detail, less detail less work for the sampling.
For the method I described. If you try it, and look at sample rate element you will see the shadow area below the car is red. This means that there is not enough samples there, where it exceeded the maximum, but more samples were required to create a clean look. I then had to raise the samples to 2/48 at noise 1.0 / 0.002, and got a very clean result but this would probably be quite slow, so you should find a balance 
He lowered the AA sampling and increased the Domelight sampling while reducing the DMC sampler noise threshold in his examples… so why do you think he’s using AA to clean up noise?
The way I understand it now is…
I use the sample rate element the view where the samples are going.
I want the Red samples to go where I need the detail ie noisy shadows and edges etc.
Blue where there is no detail.
Because this scene has soft Hdri shadows I will need lots of DMC samples.
I should be thinking lower AA and higher DMC
In other words.. Fewer Primary and more secondary, but I need to make sure there are enough primary samples in the detailed areas.
I can use the DMC calculator to refine what the max and min samples are.
If I get the equation right I wont need to reduce the noise threshold to far because the secondary sample will have already cleaned up.
I can also help the scene by blurring and reducing the HDRI map in the light,
I usually use three methods to clear the noise in scenes.
1. using AA approach - shooting more camera rays will definitely clear noise coming from the lights too.
2. using DMC approach and tweaking directly light-subdivisions
3. using a combination of both - i.e. adding more light-subdivisions and shooting more camera-rays.
In this situation I have lowered AA sampling cause when I changed Noise Threshold value I decided that Max=15 subdivisions are too much to get the results I am looking after.
Since Noise Threshold value in DMC settings is changed to a lower value I do not need such high value for the DomeLight subdivisions and I decreased this value as well.
