Driveline Drag?

[Paul Mason]

I've noticed a few times when out (long drive at the weekend so noticed a few times) that the car doesn't seem to roll when stopped on a slight incline - not talking about a steep hill, but inclines when sat at lights/roundabouts etc. where in a normal car I would perhaps be holding on the brake/handbrake.

Over Xmas when the car was up on stands, front wheels spin no bother (aside from the normal build up of surface corrosion when the cars not been moved). Rears have much more resistance, but put this down to LSD/gearbox resistance (Titan and Type 9 respectively).

Car easy enough to push back and forth on the flat so potentially nothing to worry about - just wanted to check whether I need to look at anything (handbrake seems to work all OK)?

Thanks in advance

Paul

[Ivaan]

If the brakes were binding at all, you'd hear it when rolling back and forth.

The weight of a tin top compared to the 7, will probably increase the downhill roll.

My 7 tends to be easier to move after a blat, than before. Could be the viscosity of hot oil, compared to cold?

Nothing to worry about.

[Jonathan Kay]

Rears have much more resistance, but put this down to LSD/gearbox resistance... 

You could explore this a bit both on stands and on the road by declutching.

Jonathan

[Paul Mason]

Hi Jonathan, hope you are well. Declutching on the move there seems no massive slowing force, though I do mainly slow with gear changes as opposed to brakes. The issue seems to be when stationary, car doesn't roll as I would expect. Hope that makes sense

[Paul Mason]

Hi Jonathan, hope you are well. Declutching on the move there seems no massive slowing force, though I do mainly slow with gear changes as opposed to brakes. The issue seems to be when stationary, car doesn't roll as I would expect. Hope that makes sense

[Jonathan Kay]

Double declutching!

;-)

Jonathan

[Jonathan Kay]

Nobutseriously... how about declutching when it won't quite roll on that slight incline and seeing if it then does?

Jonathan

PS: All well here, thanks. Third performance of Galileo tonight, tickets still available but not that many!

[Paul Mason]

I generally sit in neutral, would declutching produce a different result if already in neutral (he says embarrassed not knowing the answer) 

[SLR No.77]

Toe in/out and camber has an effect on rolling resistance.

[Paul Mason]

Aha, that may well be a very good point Stu, the car does have a quite a lot of camber and toe out I think (my memory of the suspension set up sheet/details that came with the car is a bit fuzzy so I can check tonight). It has been set to be more track orientated prior to my ownership. Thank you muchly

[Jim 123]

I notice that mine will stay put where my tintops will roll on the same piece of road.  I put it down to several differences e.g. lots of lightness, very low centre of gravity, big sticky tyres on low pressures with lots of rolling resistance, and Stu's point about quirky steering geometry of Sevens.

[andy couchman]

...and tyres have a rolling resistance made up I guess partly of friction against the road but also compression and expansion of the tyre sidewall and the tread 'pinching' on the road. Hot tyres may also 'stick' to the road a little.

So I guess we have:

- tyre friction/stiction/whatever

- resistance in the wheel bearings, brakes (more so with discs than drum brakes?), halfshaft CVJs (are live axles better in this respect?), diif (various bits), propshaft UJ's and gearbox (straight cut gears improve that a bit by reducing friction)

...it's a wonder they move at all!

Andy

[Paul Mason]

Thanks all, by the sounds of things, nothing out of the ordinary and just another one of the 7's curiosities I need to get used to! Stu, to your point earlier front camber at 1 and 3/4 negative, castor 3 and 1/2 degree, 1 mm toe out. Rear is 2 and 1/4 negative camber, 2mm toe in. Ride height 5 and 51/2 inches front and rear. I must confess to not knowing really what that means! Not sure when it was done either, so the Great British roads may well have changed those settings too!

[SLR No.77]

Paul, in a straight line castor angle won't have a great deal of effect. However negative camber will - a tyre that is leaning over will try to turn in the direction of lean therefore the tread will need to scrub sideways slightly in order to move forwards. Try rolling a loose wheel to see the effect. Likewise with toe in or out the tyre will again need to scrub sideways to enable forward movement.

My SLR originally ran ACB-10s (crossplies) and was set at zero degree camber all round and zero degrees toe, it was noticeably easier to roll forwards than it is now with CR500's and the relevant  camber and toe settings. 

Stu.