Auto Insurance Claims: After-market additions to vehicle, fault insurance, t pay

Question
My car was parked.  Their insurance is paying.  I have liability only.  They are telling me that unless it added to the resale value of the vehicle, they don't pay.  For example, the $800 in tires that I bought in November (the accident was in December), add $130 to the value of the vehicle so that is all they will pay. (Actually, they don't care that the tires cost $800, only that "new tires" add $130).
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I'm sorry, I made a mistake earlier and missed the follow-up.  Is there a formula for depreciating these things?  Is it just straight line from the purchase date to the date of the accident?  Should I get a lawyer if they flat out refuse?
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Thank you.  Why does it matter whether they increased the value of the vehicle?  A $1000 laptop inside the vehicle would be covered, but a $1000 suspension is not. Why?

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Someone else totalled my parked vehicle.  In addition to the resale value of the vehicle, does the insurance have to compensate me for expensive additions such as wheels, $800 tires, lights, and suspension lift?
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HI David,

If your claim is being paid by your insurance company, they may not pay for aftermarket add-ons unless you specifically added them to your policy and paid an additional premium.

If the claim is being paid by the at-fault insurance company then they owe you for all of it.  However, they will owe you for the amount those things increase the value of your vehicle, not necessarily what they cost.

I hope this helps
Richard Hixenbaugh
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Hi David,

Even with a laptop, they would not pay the cost of the laptop. They would pay the depreciated value depending on its age.

Items that are permanantly attached to the vehicle will also be depreciated based on when they were installed.

I hope this helps
Richard Hixenbaugh
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David,

You have never clarified who will be paying the claim. Yolur insurance company or someone elses insurance company.  It does make a difference.

Please re-read my original response.  

You should not need a lawyer. It will simply be a matter of you providing proof of purchase and a description of the items.

Richard Hixenbaugh

Answer
Hi David,

Another option for you.

If the insurance company will not pay you what you think the items are worth, You have the option of removing them from the vehicle, replacing the original parts, them you can sell or re-use the items yourself.

I hope this helps
Richard Hixenbaugh