Axle Length Calculator Holden / Ford / Parallel CW – Measure the width of your trailer body. BS – Measure the offset of the rims being used “with tyre fitted”. TC – 40mm Gap used on calculator as Standard. CW: BS: Axle Size Tip to Tip (mm): Send Dexter CW – Measure the width of your trailer body.BS – Measure the offset of the rims being used “with tyre fitted”.TC – 40mm Gap used on calculator as Standard. CW: BS: Axle Size Tip to Tip (mm): Send