XRAY - Model racing cars

I think there might be a lot of other people like me that would like to better understand the specifics as to why to change one of the shock/spring settings over another with the Xray. Most of us don't have the time to do the amount of testing I've been able to do the past three weeks in order to try all of the settings below and take shots in the dark until something works.

I would like someone to please explain the reasoning behind which of the following actions you would perform to the shocks/springs in order to increase/decrease CORNERING grip at either end of the car. Please explain from the perspective of what you would notice in the handling of the car, during corner entry, mid corner and/or corner exit, that would prompt you to choose each of the following setting changes. Please also include any things you've noticed after making a change that was different than expected (and/or changes to steering if you can). If you would do one of these changes in conjunction with another setting not involving the shocks/springs, please note so as well.

Increase grip:
1. Move upper shock position inward
2. Move lower shock position inward
3. Decrease spring rate
4. Decrease shock oil weight or open more holes

Decrease grip:
1. Move upper shock position outward
2. Move lower shock position outward
3. Increase spring rate
4. Increase shock oil weight or open more holes

I'd really appreciate the perspective of the factory guys as well as any others who have a lot of experience in this area and have been able to duplicate their findings successively and consistently. Though the setup books give a good understanding as to what the effect of each of these should be, none of them really give the perspective as to "what to look for" to prompt you to make the change. Putting the cart (what a setting change will accomplish) before the horse (why I should look to make a setting change) in our thinking might help!

Thanks all.

for shock angles

Basicly spring work 100% efficently when the load is applied directly in the direction of the load in this case more upright. This mean angling them downwards will reduce to amount of force needed to compress the sping rate you currently using .

By decreasing the spring rate eithier by changing the spring or shock angle you are making the car create more mechanical grip when it rolls as it is going round a corner. This done be transfering more load on to the out side wheels.

Decreasing the damper oil wt or opening more holes in the damper will reduce the restance to the spring compressing and decompressing.
In theory making the damper react quicker to changes either in a roll or over bumps. Too little damping though, can cause the sping to rebound too much, causing axle tramp or chassis bounce. Not sure how to put it in to context. Seen an american car when it comes screeching to a halt you'll get what I mean.

Note by doing this you increase the tendacy for the car to understeer cause it has more grip on the front end. And it give a lot of grip on the rear end stop it fish tailing. Like wise stiffering the car will cause the car to oversteer and fishtail depending on changes to the f/r.

You also have to take into account the camber intial start piont measured at ride height. With also the rate of camber change as the car rolls. this is done by moving the camber links inwards /outwards of the of the shock tower.
Inwards less agressive camber change this mean the supension has to roll more to increase the contact patch of the tyre with the surface.

you should run this setting when running a soft setup
beacuse the car is rolling more

Outward more agessive camber change this mean the supension has to roll less to increase the contact patch of the tyre with the surface.

you should run this setting when running a hard setup beacuse the car is rolling less

If you run in low grip situation where the tyre surface combination is causing the car to slide about, i,e low grip carpet, polished wood or running rubber tyre on carpet; depending on weather is used or not additive or not runs a softer setup to generate mechanical grip.

And a harder setup if the car has too much grip it grip rolling and or understeering. (though this can be caused by down stop being set too high)

Other thing to take into account are roll centers which isexplianed really well in the setup book.


Also it help not to set a tc car up like an F1 car.
Due grip and load factors of a full scale F1 require the damping and suspenion movement duty to be done by the tyre. the supension in an f1 car is designed to transfer as much aerodynamic grip to the tyres from the wing and body of the car.

Sorry for the crappy English grammer and spelling I went through to many english teacherswhen i was a kid each with bloody different rules on grammer and punctuation. Got fed and talked about cars in class instead.


Sammy

I'm not sure you can really lump changes into "increase grip" or "decrease grip". Static problems can be complicated enough, but the dynamics of a race car chassis setup can be quite difficult to understand. For an answer to these questions I'm going to point you to Hudy's set up book. Lots of good answers in there.

I really appreciate your posts, but I already know what you've said (read all of the xray setup books and then some). What I'm looking for now is, "the perspective as to what to look for to prompt you to make the change" as stated previously.

I would like to know what specific handling characteristics to look for WHILE DRIVING THE CAR in order to figure out which setting change makes more sense to try, according to the descriptions you (and all of the setup books) have provided. Tips on how to test for certain handling characteristics, other than the standard "go a few laps or packs around your track" would be very helpful as well. I hope this makes a little more sense now.

For the F1 ideas, you'd have to read the books to understand the "methodologies", not necessarily the application of those methodologies, which should apply to any vehicle that is raced.

Use the drivers you race againest as a guide. If your racing againest some quick drivers and can't keep up, then figure out where your losing time.

On straights = batteries, motor
Corner entrance = front end set up
Corner exit = rear end set up.

The above is a very general guide but a good starting point.

Use the increase grip / decrease grip rules mentioned above accordingly to alter car.

When you get close to a fast set up the improvements are very subtle. When trying to keep up with faster drivers just look at exactly where you are losing the time, corner entrance, corner exit or on straight.

look at lap times. They are the key to it all. record times, make change to car and see if it is faster or slower. That's what you should be looking for!

Another thing make sure your rear diff isn't too tight it can cause the car to spin out on exit as it locking too early out of the exit.
I have seen peep have this problem when coming from outdoor racing to indoor racing should run it as loose as you can on the rear end for tight coners and tighter for flowing corners.
This has been a big problem for some drivers they try eveything to keep the rear planted only for it to be the diff being to tight for the track.
Xray diffs can be run quite loose with out slipping and also very tight as well
depend on the circumstances.

Sammy

Great piece of work Orca. Assuming the damper angle, spring and oil is all you change your write-up gives some very good starting points and basic principles.

I do want to refine some of the statements with regards to traction. The basic rule of thumb is that softening one end of the car will increase traction at that end of the car. This is true as the weight at that end increases. However, the total grip of the car is actually reduced! Without going into details I don't fully understand myself it is enough the point out that the traction loss at the front (less weight) will be more than the traction gained at the rear under acceleration.

The same goes for left to right. So, if you were to run softer springs all round during cornering the traction provided by the outside wheels will increase, but the traction from the inside wheels will decrease even more actually lowering the overall traction! There is an upside to this however. Traction is in effect the resistance between the tyre and track surface. The resistance between the tyre and the track surface is governed by the resistance coefficient. However this coefficient is not constant. As long as the tyre is not sliding (too much) the resistance coefficient is high and traction will be close to maximum. But once the tyre looses traction the coefficient drops significantly. As a result it is harder to regain traction. In other words you will have to slow down to well below the maximum corner speed to regain traction and therefore you will lose a lot of time. By running soft springs and good damping (possibly more than you would like), you reduce the maximum force that is put on the tyre when entering a corner or when accelerating out. This prevents the slide!

While in Formula 1 cars the aerodynamic grip is the main reason to run a hard setup, it also has to do with maximising mechanical grip. As can be seen from Orca's writeup and my addition the maximum mechanical grip will be gained if weight transfer is minimized AND no sliding is essentially prevented or at least minimized. The same is true in RC racing which explains why hard setups are allways used when running foam tyres. These simply give much more grip than rubber tyres and therefore don't lose traction quite so easily.

Thanks tonyv, i think as this thread has developed we have shown the complexity, theory and attitude required to set up an rc car.

The original post was a request for a simplistic overview of basic suspension theory. However, in replying in general terms huge areas of more advanced theory have to be glossed over in order to explain the basics.