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JasonB
25-11-2017, 14:06
I used to race off-road R/C cars competitively, and one major tuning option was to limit suspension travel extension (think bump stop, except it limits extension rather than compression). This was handy for keeping the inside wheels on the ground on off-camber turns, or being able to maintain contact with the surface when cresting a hill at high speed, etc. Droop limiting was implemented in one of two ways:

1) (yellow circle) A screw located at the inner hinge pin of the suspension arm. By extending the screw downward, the button-head (on the underside of the arm, which you can't see) would press against a tab on the chassis, reducing overall available extension.
2) (red circle) Washers that could be placed inside the shock bodies between the piston and the bottom of the body. More washers = less available extension.

245952

I was just curious how a similar effect is achieved in PCars (and racing in general), or if chasing that effect is a bit of a moot point due to factors I don't understand or am unaware of.

Motor City Hamilton
26-11-2017, 17:47
I too raced R/C competitively for about 20 years. Droop limiting was used mostly on off-road cars. I have a friend, Jeff Villemure who raced R/C with us and now races full scale off road cars. There is a ton more suspension travel in an off road car so droop limiting becomes more useful. Look at say a 1/12th scale pan car where the suspension movement is more like an F-1 car in real life. The suspensions are usually more stiff so you rarely top out the suspension making droop screws less important in tuning.

Phos
27-11-2017, 07:02
Only full size droop limiting I know of are position sensitive shocks having droop sections of travel, but even then they're primarily there to prevent the suspension from extending too violently and to take up extra impact on landing.

I think race cars don't need it because they can dial in anti dive and squat into their suspension, plus their suspensions are a lot harder, they don't seem to need as much travel. If an inside wheel lifts, it probably wasn't doing much. Are RC shocks just friction snubbers? Could also be that full size car shocks have more going on.

JasonB
27-11-2017, 12:23
I too raced R/C competitively for about 20 years. Droop limiting was used mostly on off-road cars. I have a friend, Jeff Villemure who raced R/C with us and now races full scale off road cars. There is a ton more suspension travel in an off road car so droop limiting becomes more useful. Look at say a 1/12th scale pan car where the suspension movement is more like an F-1 car in real life. The suspensions are usually more stiff so you rarely top out the suspension making droop screws less important in tuning.

Makes sense, thank you for the explanation. What strategy is used to prevent wheel-lift on undulating sections and off-camber sections? That's one area where I seem to be struggling with setup.


Are RC shocks just friction snubbers?

I'm not quite sure what you mean by "friction snubbers," but in high-end RC cars, the shocks are extremely tune-able. They're oil-filled, and can be built to suit a number of situations by changing:

- oil weight used
- spring rate used
- build process (emulsion vs bladder vs vented)
- shock location and angle
- droop/limiting in both directions
- pistol hole size, number, and shape
- advanced piston options that allow a higher rate of flow in one direction vs. the other (such as allowing quicker rebound vs compression)

bradleyland
27-11-2017, 13:29
Makes sense, thank you for the explanation. What strategy is used to prevent wheel-lift on undulating sections and off-camber sections? That's one area where I seem to be struggling with setup.

Wheel lift can't always be avoided. A car must be tuned to deliver the best possible performance across the entire circuit. In race cars, this means that the fastest setup is frequently sub-optimal for sections of the track with a lot of contour. Having said that, you can try:

- Reduce ARB stiffness
- Increase ride height and soften springs (remember to re-tune your dampers)

Basically, you want more compliance out of the suspension, and less stiffness. The trade-off is that you'll end up with a car that doesn't transition as well, and may ultimately have less grip in the sections of the track that are smooth and flat.

At a circuit like Knockhill, this is a good trade-off, because the circuit is so bumpy and the majority of the turns have significant contour. At a circuit like Laguna Seca, it's a poor trade-off, because lifting a tire over the corkscrew won't negatively impact lap times, while loss of grip in the flat corners will.

Just remember to re-tune your dampers!

Phos
28-11-2017, 02:04
Friction snubbers a re simple form of damper that just uses friction to dampen bouncing.

Oomph
28-11-2017, 02:24
I too raced off road 1/10 electric buggies for about 8 years in the 90ís. droop was a big thing. But one suspension trick that I used a lot was rear anti squat or rear anti dive. Basically rear caster created at the inner hinge pins and rear bulkhead. A few degrees would assist with more rear grip on power due to the rear not squatting down on weight transfer instead that transfer going to the wheels. Kind of miss those days.