might be this will be handy and more readable

with cte as (

SELECT DISTINCT t1.DealerID, t2.tire,

TotalRepairs = SUM(1) OVER (PARTITION BY t1.DealerID),

RepairsOfThisTire = SUM(1) OVER(PARTITION BY t1.DealerID, t2.tire),

PercentOfTotalRepairOrders = ROUND((SUM(1.0) OVER(PARTITION BY t1.DealerID, t2.tire)/SUM(1.0) OVER (PARTITION BY t1.DealerID)) *100,0)

FROM dbo.Table1 t1

LEFT JOIN dbo.Table2 t2

ON t2.RepairId = t1.RepairId

)

SELECT * FROM cte

WHERE tire IS NOT NULL

ORDER BY PercentOfTotalRepairOrders DESC

since you are using Sql 2012 you can use Lead or Lag function to calculate Total percent by Dealer Group and you can get the desire result

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