The "S" value is a rating measured in kg and represents the maximum vertical load which can be applied to the Towing Jaw/hitch. This is also known as the "nose load".
All type approved towing brackets must also show this value on their respective manufacturer's label. The vehicle manufacturer's hand book will also give the maximum "S" value which can be applied to the rear towbar mountings; the actual vertical load which can be applied to the hitch is the lower of the two values.
With regard to the trailer nose load, this should not be confused with the GVW (Gross Vehicle Weight) of the trailer. The nose load of a trailer is the amount of weight that the trailer exerts on the vehicle's tow hitch. Therefore a hitch which has an "S" rating of 260kg is capable of a nose weight of up to 260kg (subject to the towing vehicle's towbar limits - these are normally significantly lower), and has no reference to the total weight the towbar is capable of pulling. This metric is defined by the "D" rating; see below for details.
Please click here for more information (link opens external website in new window).
The "D" value is a rating measured in kN which reflects the dynamic loading limits between a towing vehicle and a trailer. (Wikipedia)
The "D" value of a Towing Jaw determines the gross weight combination of the towing vehicle and the trailer that can be used with that particular jaw.
The "D" value is calculated as follows: D = 9.81 × (T × C) ÷ (T + C)
T = Towing Vehicle Weight - GVW
C = Trailer Weight - GVW
9.81 = Gravity
For example, a towing vehicle of 3500kg GVW combined with a trailer of 3500kg GVW would require a towing hitch with a "D" value of:
9.81 × (3.5 × 3.5) ÷ (3.5 + 3.5) = 17.167
Historically, the maximum GVW of an LCV was 3500kg and the maximum GVW for an over-run brake system is 3500kg - hence why a "D" value of 17kN is still common.
Important Note:
If a Towing Jaw with a "D" value of 17kN is fitted to a towing vehicle having a GVW greater than 3500kg, then the permitted trailer weight will decrease accordingly. Use our calculator below to work out what you are permitted to tow.
The TP22 supplied by TRAILPARTS Ltd is rated to a "D" rating of 20.2kN. This allows the TP22 to be safely and legally fitted to the newer, larger specification LCV's with a GVW of 5000kg whilst still allowing them to tow trailers up to 3500kg GVW.
Use the below tables to calculate the "D" values, the maximum trailer GVW, or the maximum towing vehicle GVW. These tables are based on standard UK trailers up to 3,500kg GVW. NB: you will need Javascript enabled in your browser in order to use the below calculators.
Calculate required hitch "D" value
Calculate maximum trailer GVW
Calculate maximum towing vehicle GVW
Notwithstanding the above information, the responsibility of ensuring the correct vehicle and trailer combination rests entirely with the user. Please click here for more information about matching the trailer with the towing vehicle (link opens external website in new window). Further information can be found on the National Trailer & Towing Association website.
Information correct at date of publication 27th September 2018. While we have done our best to ensure that all information above is accurate, TRAILPARTS Ltd cannot be held responsible for any decisions made based on the information given. E&OE.
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