KPRA measurement conversion to TT length?

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dtombaug

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Sep 14, 2020
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I know how the KPRA works for 5ers and trucks, but what is the equivalent for TT? I have 32 foot TT and I've been avoiding roads with KPRA warnings less than 32' . I was just wondering if there is a rule-of-thumb that says 30' KPRA would be equal to 32' TT. So KPRA +/- 2'? I Hope I'm explaining this clearly enough.




If this needs to be in a different section, please move - I'm thinking this is the right section because it does relate to towing.
 

Lou Schneider

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KPRA is the King Pin (or hitch ball) to Rear Axle length. It's what determines how far the trailer axles will offtrack to the inside of turn and that's the objective of the KPRA limits. The overall length of the trailer is largely irrelevant to how it will track around a corner. On a tandem axle trailer the rear axle location is midway between the two axles.

You can measure the KPRA distance on your trailer, or just assume like with most RVs it's 50% to 60% of the overall trailer length. On a pull trailer the hitch location behind the rear axle partially cancels the offtracking because the overhang moves the hitch towards the outside of a corner. But the above estimates should do.
 

dtombaug

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Sep 14, 2020
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Lou, thank you. I'm aware of what KPRA is and I was wondering about the correlation to a TT. But I believe you answered it though. So on my TT I would measure from the hitch to the middle of the two axles (or close). that would be (just a guess right now) somewhere between 15' - 18'.

On a side note: I've done google streetview on a couple of KPRA 30' roads and those seem to be very "tight", putting it politely.
 

Gary RV_Wizard

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Right, the ball-coupler to axle-midpoint distance is the TT analog of the KPRA distance. In other words, the pivot-arm of the trailer. However, the value isn't really comparable to a 5W KPRA because of the off-tracking that Lou described. Thus the state KPRA regs/values don't apply to TT's and you can't really make judgments based on them.
 
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dtombaug

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Sep 14, 2020
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Thanks guys. I was wondering about that and I have been using them as guides. So I check the state KPRA and then do like streetview and google earth to check them out. I found that if the KPRA is 30', that is usually at the edge of my comfort level for taking the trailer.

thanks again.
 

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