SQL Server 2012 :: Select Top X% From Group Based On Total?

What I need to do it select the top 80 percent of records per group based on the group total. To be clear I am not trying to just grab the top x percent of rows.

Table 1:

DealerID RepairID
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
1 10
2 11
2 12
2 13

Table 2:

RepairID Tire
1 225/65R17 102T
2 225/65R17 102T
3 225/65R17 102T
4 235/60R18 102V
5 235/60R18 102V
6 235/60R18 102V
7 235/60R18 102V
8 205/55R16 89H
9 205/70R15 89H
13 225/65R17 102T

Table 1 has the total number of repair orders per dealer. This can be obtained by simply grouping on DealerID and counting the number of RepairIDs.

Table 2 has information on some of the repair orders and it is needed to select the top 80% of tire sizes. This table will be joined to Table 1 and grouped by DealerID and Tire.

Desired Output:

DealerIDTire RepairsOfThisTireRepairCount PercentOfTotalRepairOrders
1 235/60R18 102V4 10 40
1 225/65R17 102T3 10 30
1 205/55R16 89H1 10 10
2 225/65R17 102T1 3 33

The equation I am given to calculate the top tires per dealer is as follows: Total # of tires for the size / Total # of repair orders per dealer.

Here is what I have so far though I think I might have to rewrite all of it.

SELECT
DealerID ,
COUNT(RepairID)
INTO #TotalDealerRepairOrders
FROM
dbo.Table1
GROUP BY
DealerID
SELECT

[code].....