OlivierWierda

In my free time I do a lot of simracing with GT3 cars in Assetto Corsa Competizione, which, as far as setup goes, is mostly realistic, and as the game offers telemetry data in the form of MoTeC log files, you can inspect the inner workings of a car, and setup quite well.

What quickly becomes apparent is that bumpstop range (the range of upward suspension travel before the bumpstop engages), and bumpstop hardness (bumpstops are mostly a rubber like compound with different hardnesses), are some of the most important parameters to getting a car to go "fast".
Just like our 1:10th Touring Cars, the modern era GT3 cars rely heavily on aerodynamics for their performance, but what seems counterintuitive at first, becomes logical when you consider the importance of aerodynamics: bumpstops are not used to "stop bumps", but are used to stabilize the ride height under extreme aerodynamic loads.
This can help with many issues, it can stop the car from bottoming out under high load, it can help to achieve set rake angles under high load, it will allow running the car softer and lower while maintaining ride height, and it adds another layer of "progressiveness" to the suspension of the car, which can help to fine tune it for specific conditions.

There is however a key difference between GT3 and 1:10th touring cars, and that is ground-effect, or under-body downforce generated by the front splitter, flat floor, and rear diffuser, these are all areas that are unexplored, or simply not allowed in the rulebook of RC Touring Car racing.

Still, with the introduction of all kinds of boutique, aerodynamically designed bodyshells, that generate a boatload of downforce from the shell alone, I think bumpstops are something that is worth exploring, and my question is, if there have been any experiments, chassis, or "option" parts that have tried this?
When I google "RC Bumpstop", some results show up, but mostly for off-road, and I have never seen any mention of bumpstops in setup sheets.

bertrandsv87

iTrader: (2)

Only the Awesomatix A700 chassis offers the bumpstop option, eventhough racers rarely use it...I use it on my A700 cars to stop my cars from bottoming out on crc black carpet: no more braking effect on the ground and no more tire rub on the body...I set it up to have the bumpstop engage at 1mm rideheight. Try it....

gigaplex

iTrader: (2)

Rubbish. Pretty much any conventional shock TC can have tunable bump stops by using different grades and thicknesses of orings on the outside of the shock.

tortoise 1

There's a massive loophole in the aero rules for rc touring cars which negates a lot of the benefit of traditional bumpstops.

On a real car the body is fixed relative to the chassis.

But on a modern rc touring car the body is free to move up and down by several mm and body upstops are used. I.e you have bumpstops for the bodyshell which allow it to be lowered, especially on outdoor tracks with no ride height restriction.

When Colin Chapman of Lotus designed an f1 with a shell which moved relative to the chassis to get round ride height rules for ground effect. It was quickly banned as a movable aerodynamic device so I am not sure why it is allowed in rc.

bertrandsv87

iTrader: (2)

That's a Mod not a purposefully designed bumpstop system, and those O rings get mushy overtime, impeding shock function, ruining everything.....WOW....Let's not feed the confusion...

Sir 51D3WAYS

Because the bump stop is the chassis plate itself. It's rather difficult to engineer such subtle effects as you describe at our scale. Plus, the shocks themselves are a bit rubbish in general.

It's also not really known how much the downforce affects the suspension loading/remaining stroke. We are talking about a very thin, flexible material that can cave in under not a lot of force that is mounted on some fairly soft body posts. How that translates into force on the tyres is also very debatable.

DesertRat

iTrader: (2)

You cannot generate any sort of useful ground effect in an RC car, its going too slow and has no way to 'seal' itself against the ground. You can't even get ground effect from something that runs on a perfectly smooth surface like a carpet oval car or even wing slot car. There's just too much of an opening at the bottom of the body relative to the volume inside of it. Aerodynamic efficiency in RC is all about shape and wing downforce.

tortoise 1

The lower you can run the shell , the more down force it will produce. When you lower the shell it prevents air from getting underneath.

It might actually be a case of avoiding lift rather than generating downforce but the effect is the same.

A Shell that is set 3mm above the track with body upstops to prevent it from bottoming out generates a lot more steering and grip than a shell set at 9mm above the track without upstops.

Fastfreddy74

Erm, 1:1 racing cars bumpstops are basically big o-rings made of rubber, silicone, teflon if you need an harder material; sometimes there are additional springs but that's it. Anyway, the purpose and end result is the same.

IndyRC_Racer

iTrader: (9)

The biggest issue with lowering or "slamming" an r/c body is that most organized r/c racing has minimum ride heights which typically include the body being mounted. You cannot have the sides of the body lower than the chassis when going through pre-race inspection/tech (at least in most forms of carpet racing). TC classes usually have a minimum of 5mm ride height.

Also r/c racing often times has minimum/maximum roof heights as well. Therefore even if you could slam the body straight into the ground, the top of the roof may now be too low to be legal. Also since most organized racing may require cutting of the body at the mold/seam line, you may be limited in how much you can effectively mount a body higher or lower. These chassis & body minimums or maximums help to ensure a level playing field for all racers and manufactures.

Often times it isn't about having the best theoretical aerodynamically superior body, but having a body that fits legally into the class rules.

glennhl

iTrader: (16)

I find what the OP wrote extremely interesting. There are oval racers (full size cars) that basically lower the car down on the bump stops and use them instead of springs. I think it's crazy, but it works.

glennhl

iTrader: (16)

Actually the chassis is the up stop for setting droop. The down stop is either built into the shock or on the A800 the top part of the P12X.

tortoise 1

Ride height restrictions in the uk only apply on carpet, where it is usually 5mm. Outdoors on tarmac you can slam the shell as much as you like as long as it is an approved shell cut to the lines. The days when roof height used to be measured by scrutineers are long gone.

setting the front of the shell lower than the chassis is not unusual..

on carpet where the 5mm ride height rule applies, that is still lower than you would typically need to run a rigidly fixed shell to prevent it from rubbing on the track so using a floating shell with body upstops still allows the height of the shell to be reduced.

Nerobro

iTrader: (2)

bump stops, are springs. The original Mini used cone shaped rubber springs (with some fluid inside for damping)

Assuming they're a useful spring rate, springs are springs.

mr.rev

Not everywhere. Certainly not on any big race.