"Helper Springs"

[Anddenton]

Be interesting to see if a driver a front seat passenger would bring the front end down a bit. Also could the roof box be mounted a bit further forward?

[SB1962]

As I said earlier I'm surprised how low mine (& the previous Oct 4x4) gets just with the boot full. I've not weighed the stuff going in the boot but when half of the boot is a dog cage & a small border terrier & the rest the usual camping gear I've always carried in my cars the difference between previous cars & the Skoda are very noticeable. The 3 bike carrier with 1 to 3 bikes doesn't really make a big additional difference - neither does the roof box. I've got a trip coming up later this month so I'll take measurements & pics. From memory it's not quite as bad as the OP's but, as said, markedly worse than previous marques I've had.

[splat]

I think you are missing a couple of things:

- The payload should include everything; you should NOT exclude a 75kg driver weight.

- Your nosewight and roofrack weight should include the racks; you can't put 75kg of load in a roofbox which itself weighs 20kg.

I suspect this will increase your calculations by at least 100-150kg.

It looks like there is a translation error in the brochure with regard to payload and kerbweight; its kerbweight that includes a driver at 75kg. See http://en.wikipedia.org/wiki/Curb_weight - this explains both the US and EU definiitions.

The weight should be evenly distribted. Load it all to the rear and you'll loose steering grip. Things overhanging the rear bumper will make this worse.

Hope that helps!

[The Ships Cat]

The Ships Cat

Did the ride (unloaded) feel noticeably stiffer with the MAD springs? How did you get on with insurance and warranty (if you took the trouble...).

I did not notice much difference in the ride , 90% of time car loaded with spares , insurance not a problem , warranty did not really apply as doing over 40,000 miles a year so ran out after 18 months.

Edited 8 October, 2011 by The Ships Cat

[Rab-k]

Thanks for all the replies.

I've come to the inevitable conclusion that 4 bikes hanging off the back-end is not for the Octy, without a little help...

Therefore my choices, should a similar load configuration be required in the future, are:

1) Fit the MAD Helper Springs, or

2) Go for a narrow roof box, single roof mounted bike carrier for the heaviest bike, and limit the rear end to 3 bikes only.

Or, following a trip to my local public weighbridge to check out the loads, both options 1 & 2. (Be interesting to see just what the rear axle and tyres are coping with).

What I'd also love to know is what vehicle and nose weight limitations those nice people at Thule had in mind when they designed that sodding bike carrier...

Edited 9 October, 2011 by Rab-k

[Rab-k]

Ok all you physics buffs out there - to calculate the actual weight of the bikes/carrier, taking into account the lever effect, will the following method, (using a car jack and bathroom scales), work?

[Rab-k]

Tried the method outlined, and the results were quite surprising...

Amazed at the 25% increase in the load due to the lever effect. Guess I'll have to stick to 3 bikes and try to flog the 4th bike extension on fleabay.

Now, if only SUK CS would get back to me re. the helper springs and warranty.

Thanks again for all the replies.

[thewez]

Ok its the moment generated from the off set load thats the issue.

Say the tow ball is 300mm from the tow bar bracket.

So say the max tow ball weight is 75kg thats a moment of 75 x 300 = 22500 kg x mm

Now lets assume that the bike rake is 750mm wide and that the 60kg weight of the bikes opperates at mid width 375mm.

ie 60kg x (300mm + 375mm) = 40500 kg x mm the moment on the tow bar due to the bikes and bike rack.

in other words you'd need a tow ball weight of 135kg to give the same moment. This equates to 1.8 times the max design load of 75kg...

Hope this helps.......

[London Les]

Your experimental method looks iffy to me. If the line of action of the jack is different to that of the load from the bikes, then if you achieve the same moment on the car then the loads will be different but not representative of the loads in the car springs.

[London Les]

The vertical load in the rear springs is:

Bike load x offset from front wheels centres / wheelbase I.e. 2.578

The load in front springs is the bike load minus the vertical load in the rear springs - this is a negative number as the total reaction of both front and back wheels has to = the bike load.

[Rab-k]

Ah jeez, all I need now is E=MC2

Sorry chaps, but you're speaking to a complete idiot when it comes to such things. My Physics education was getting kicks out of the VDG machine by sparking your finger off the nose of the person nearest to you. Beyond that...

I'll pop over to my local public weighbridge tomorrow and do all four corners on the deck, then rear axle only with/without the bikes/rack and see what the difference is.

I'll post my findings here and see what, if anything, you geniuses can make of them

Damn, never thought a simple bike rack on a car could be so complicated...

Cheers