floor levelness

Hi,

This is a great course. Haven't finished the whole course yet but a topic that I have always had problems with and not heard addressed yet is garage or measuring surface flatness. I jumped ahead to ride height and even there you speak about measurement from hub to fender not ground level up to a fixed point on the car at each corner. My floor, and I would guess most residential poured cement floors are about as level as the ocean. Any suggestions for compensation that is not ridiculously expensive? never mind- see working example, step 2 Equipment setup. Thanks.

A trick I read about and have used for cheap and clean slip plates is to place 2 linoleum tiles beneath the tires with table salt to act as ball bearings. Worked a treat. Just tiles under rear wheels to compensate for height change.

As far as measuring ride height, the reason we use the hub centre to the guard/fender lip rather than the ground is because it eliminates the effect of differing wheel and tyre diameter which is useful for the likes of a coil over manufacturer who is selling a kit that will go on cars with perhaps 16"-18" wheels. If you're only measuring on your own car and the tyre/wheel diameter is fixed then you could measure from the floor but my preference is from the lip of the rim to the guard lip (this requires a suitable offset though so that the wheel lip and guard lip are in reasonable proximity.

The table salt idea is a good one. Hadn't heard of that before so thanks for sharing.

Well the attached photos will show my problem. (hopefully the attachment file function is working?) The front fenders/wings are attached to the hub, not the body. So it is not a fixed point adjustable via the coil overs. Suggested height measured behind the front trailing lower wishbone arm is 120mm, to side of car not floor. Rear is 130mm, so slight rake, measured at front edge of fender/wing. A nagging concern of mine is the spring compression from side to side is not the same to achieve equal ride height (from ground). Should this be an issue?

As far as priority goes which is most important? Ride height, equality of spring compression/travel, or corner weight adjustment. I understand that moving the weight of the car via spring adjustment is not really corner weight adjustment.

Ah right, I now understand the issue. In the ideal scenario you'd get the ride height set where you want it to be and then make final adjustments to the spring platforms based on corner weights (We'll be doing a corner weighting course in the new year). Usually for circuit racing we're aiming for a 50% cross weight.

Don't worry about the equality of spring compression - It's a common myth that preloading a spring will affect the ride quality or operation of the suspension but that's not true if you're running linear rate springs. For an 8kg/mm spring, it will compress 1 mm for each 8kg you add. This means that even when you've compressed the spring to the point it's almost coil bound, adding a further 8kg will still compress it a further 8kg. In this way the spring preload (compression) will not affect the suspension operation at all and is the correct way to adjust ride height.

Thank you for the information. Enlightening as usual.

Most basic means of checking the floor, or rather the places you will be placing the plates, for level is to use a clear plastic tube and some vegetable dye.

In an open tube the fluid will be level, so by measuring the distance from the floor to the fluid level at, for example, LF to RF positions you can quickly see what the difference is, then do LF to LR to check that (NOTE, you need to re-measure the LF as it will alter if the latter level is different). Then LF to RR, ditto.

This will tell you the difference in floor level compared the the datum, the LF, and you can then compensate for any differences.

Oh, another 'old school' trick was to use 2 or 3 plastic bags under the steering wheels to make them easy to pivot.

Personally, I'd first check the ride height(s) at the chassis, or hard suspension points, as it isn't unknown for wings/arches to be tweaked slightly from the factory, let alone after settling or fettling after 'incidents'.

Once you confirm they are correct, or at least known values, it does make a much quicker quick setup check.