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Old 03-09-2011, 03:29 PM   #1666
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Without a section of the suspension arm cantilevered inboard past the inner hinge pin (like the losi sedans) the easiest way is going to be with external shock limiters on the shock shaft. You can use o-rings or maybe a 1/12 scale front spring over the shock shaft instead of a solid limiter (think "helper" spring). If the spring is too short to limit the travel in the range your looking for just add some solid spacers so the "helper" spring becomes effective sooner in the travel.
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Old 03-09-2011, 03:32 PM   #1667
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Its something I've always pondered about as well, so don't feel bad. And yes... Vehicle Engineering student here .

I think the reality is the gains we get from letting the car flop around all over the place are much greater than what amount of traction is lost from the chassis hitting the ground. My car rubs the sides all over the place and it still feels pretty awesome (despite my head telling me it shouldn't work that way).

I know in the Nitro TCs and 1/8 cars they have screws that limit the upward travel of the suspension. I've never had any experience playing with it though.

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Old 03-09-2011, 03:33 PM   #1668
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sounds cool i could do such a mod easily. so there are no suspension arms that have build in adjusters for upwards travel like there is one for droop?
i wish i could remember the software that porsche's racing team used in one demo at uni. it was so many years ago but they had an awesome software that simulated exactly how suspension and tyres behave under cornering. i never had to use it really so i did't keep any info. But yes, it should not work like this but sometimes you gotta tolerate it because the overall setup gives an advantage on other things. Big sized cars have reinforcement on parts that might touch the ground anyway, which is a luxury we don't have in small cars. I have 2 nitro 1/10 TC and they don't have adjustment for travel. Maybe only the 1/8 have it but i don't own one and i have never seen one in person.
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Old 03-09-2011, 03:34 PM   #1669
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None that I know of for our car, but I have not taken the time to look either.

-Korey
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Old 03-09-2011, 03:38 PM   #1670
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uptravel screws are terrible in nitro sedan btw, Its like going from a 28 lb spring to infinite rate (not really but for instructional purposes only). So when used in the front, once you touch the upstops you get massive understeer. So you end up with more grip without them even though your bottoming.
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Old 03-09-2011, 03:46 PM   #1671
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Pretty much how I figured it would work out haha.
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Old 03-09-2011, 03:55 PM   #1672
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Quote:
Originally Posted by omegaf View Post
It is true to a certain extent. The chassis hitting the ground will definitely bounce off hard. However, when the suspension bottoms out and the spring compacts, the tyres still absorb part of the bump. it is a lot better to have the suspension bottom out and let the tyre absorb the bump than let the chassis take the hit. I do see your point though. I might try a simple mod for suspension travel if i can come up with a good idea.
When the chassis hits the ground the car isn't unsettled as much as you should think. Because the reduction in load is caused by the chassis the reduction is spread over multiple tires. If all the load was taken away from one tire you will notice it.
When the suspension bottoms out on one part of the car the springrate changes dramatically because the wheel (foam,rubber) has already been compressed quite a bit. This sudden change of springrate will upset the car more then a chassis hitting the ground because the wheel will break traction instantly.

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i will put an example scenario so you all understand why i think there is a problem.

say you are traveling on a straight line and there is a speed bump ahead vertical to road. (race tracks will not have that but it is still a viable scenario for a basher)
At this point, with the current set up of the car, the wheels will get pushed all the way up and off the ground and then the chassis will hit the bump and send the car flying.

If we are able to adjust suspension travel so that it doesn't allow the chassis to touch, then the outcome changes. At that point, the wheels will not get pushed upwards above the chassis but they will instead take the hit instead of the chassis. The wheels being made of plastic and foam are able to absorb the impact much better than the aluminium chassis. The end result will be less of a jump or no jump at all depending on the speed of the attack.
The added benefit will be no damage to the chassis (and i do not mean just scratches.)

So yes, adjusting suspension travel so that it prevents the chassis from hitting the ground is important in my book but it may not be important on a race track where such a scenario does not apply. Even so, on a track, allowing lower ride height with less suspension travel will prevent the sides of the chassis from scraping the ground at high speed cornering. Suspension travel is important in the "big world" of car racing and i don't see why it is left out in small scale racing.
Setting up a racecar is all about compromises. When you have just one little bump in the track it's probably better to have the car bottom out over that bump than to have the car absorb the bump and suffer in the rest of the lap.
When you have a very bumpy track you change your spring/damper combination and maybe rideheight to absorb the bumps better. But the car won't be as fast as when you would drive the same lap without the bumps and a normal setup. Because the track is so bumpy it's better to tune in the car so it handles the bumps better because otherwise handling will suffer like a very unpredictable car which doesn't give the driver confidence to push it.

Fullsize racecars (I work in professional racing as an engineer) which utilize ground effects, Formula cars, Le Mans, DTM etc, all have some sort of plate along the centerline of the chassis to protect the actual, mostly carbon, chassis/monocoque, against wear when bottoming out. Most of the time this is a 10mmm thick wooden plate and in full bodywork cars like the audi's shown above combined with Titanium skids on the outer sides of the car.
These kind of cars are setup to hit the ground a couple of times during a lap. You want these cars as low as possible because of the ground effects, their diffuser shaped undertray's work best when positioned low to the ground.
The driver can feel the car skidding across the ground but it doesn't influence the handling dramatically because of the high amount of grip these cars already have.

If you really want to test with this try the O-ring (or any other piece which is able to compress) on the shock shaft. This basically is the same as the bump rubbers we use in fullsize motorsport.

It really is better to have the suspension bottoming out once in a while than having a hugely compromised suspension setup which prevents this.
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Old 03-09-2011, 04:26 PM   #1673
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Excellent post. i know about the real cars as i've had the fortune of working with a Skyline GT and a Viper GTSR (both in the EU GT, the Skyline was I believe from the Norwegian GT championship but retired) many many many moons ago.
Those cars had massive reinforcements under them and they also had metal plates on the skirts around them.
It's because we don't have those in the small cars that i am concerned about the chassis hitting the ground. The other factor is that the small cars do not have an equivalent weight to their big versions so it is not easy to make an analogy in terms of losing traction when the suspension bottoms out. With the big cars, the massive downforce and weight are going to keep the wheels down even if the chassis hits the ground. With the small cars, the chassis is extremely stiff for the weight of the car so when it hits the ground over a bump it can make the whole car jump. A big car would't jump, it would just scrape harder, obviously inertia also plays a role here.
I don't have the means to run a simulation to verify my thoughts and at this point they are just thoughts really. It's just the impression i have based on what i know.
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Old 03-09-2011, 04:31 PM   #1674
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First of all i am not driving a train. if that's what you do for a living, that's your own problem go look at your face in the mirror and laugh but otherwise you can stick your sarcasm up your own rear. Maybe you should have considered a mechanical engineering degree like me.
Second, yes, on rare occasions the chassis can hit the ground even in real race cars. You cannot prevent it 100% of the time and there are many reasons why it can hit the ground but the general idea is to use suspension travel to prevent that.
I love how touchy some of you are on the subject. What's wrong? Someone pointed out a flaw in your precious little toy cars?
Gee, who is the touchy one? Mechanical engineers are a dime a dozen (I am one). I think that your title should be "pompous ass". Your degree (if you have one, or did you just pursue one?) does not make you superior to a train driver or any other occupation. If you are so intellectually superior then you should already have the answers rather than ask us mere mortals.

If you really had a handle on your engineering then you would find it obvious that upstops would unsettle the car more than the chassis drag. If you don't hit the chassis occasionally then you are not utilizing the full range of your suspension. Now stick that up your rear, Richard.
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Old 03-09-2011, 04:35 PM   #1675
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Gee, who is the touchy one? Mechanical engineers are a dime a dozen (I am one). I think that your title should be "pompous ass". Your degree (if you have one, or did you just pursue one) does not make you superior to a train driver or any other occupation. If you are so intellectually superior then you should already have the answers rather than ask us mere mortals.

If you really had a handle on your engineering then you would find it obvious than upstops would unsettle the car more than the chassis drag. If you don't hit the chassis occasionally then you are not utilizing the full range of your suspension. Now stick that up your rear, Richard.
A dime a dozen eh? Ok, if you say so. Perhaps you mean the ones that actually bought their degree. Funny you would call me a pompous ass but ignore the comments from the other about me without knowing anything about my background or education. I never said I am intellectually superior. I had a question and I was hoping someone with experience can give me some insights. I laid down my thoughts on the matter, prove me wrong if you can.
If you chassis bottoms out by the way, then by definition you are not using the full range of your suspension. Now, you stick that one up your rear Charlie!

(did you really have to make a new account to cuss at me? and then you come here and pretend you are the better man? ?
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Old 03-09-2011, 04:42 PM   #1676
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Yes, I created an account just to point out your immaturity. No more replies will be made to your drivel.
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Old 03-09-2011, 04:43 PM   #1677
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good to know. it's not like you added anything constructive to the debate.
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Old 03-09-2011, 04:49 PM   #1678
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Quote:
Originally Posted by omegaf View Post
Excellent post. i know about the real cars as i've had the fortune of working with a Skyline GT and a Viper GTSR (both in the EU GT, the Skyline was I believe from the Norwegian GT championship but retired) many many many moons ago.
Those cars had massive reinforcements under them and they also had metal plates on the skirts around them.
It's because we don't have those in the small cars that i am concerned about the chassis hitting the ground. The other factor is that the small cars do not have an equivalent weight to their big versions so it is not easy to make an analogy in terms of losing traction when the suspension bottoms out. With the big cars, the massive downforce and weight are going to keep the wheels down even if the chassis hits the ground. With the small cars, the chassis is extremely stiff for the weight of the car so when it hits the ground over a bump it can make the whole car jump. A big car would't jump, it would just scrape harder, obviously inertia also plays a role here.
I don't have the means to run a simulation to verify my thoughts and at this point they are just thoughts really. It's just the impression i have based on what i know.
Unless your track is particularly bumpy or your car is setup wrong, the chassis will only make contact with the ground when banging across a curb.
I'm sure you're all great at the real thing, but don't forget the laws of physics do not scale unlike our RC cars.
One guy on the Xray forums pointed out that the roll bars should be next to useless because they would need to be 3mm thick to compare with the real thing
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Old 03-09-2011, 04:57 PM   #1679
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Unless your track is particularly bumpy or your car is setup wrong, the chassis will only make contact with the ground when banging across a curb.
I'm sure you're all great at the real thing, but don't forget the laws of physics do not scale unlike our RC cars.
i agree. i just don't have experience on the track with these things which is why I am asking for all this info. It is precisely because the 1/10 scale cars are scaled in size but not in weight that I am so confused about. I am mostly thinking of the aluminium chassis on my nitro cars. It is very stiff and barely flexes at all unlike a real chassis that carries 1000kg. That's why I am led to believe that hitting the ground will just make the whole car jump as opposed to a big car which would flex due to the weight and inertia.
I am not an expert in the real thing by any means. I am not an automotive engineer, I just go by a few things I know and experienced. That's why I asked for an explanation and some people provided very nicely. I am not 100% convinced but I am starting to see the logic behind it. I would love to experiment a bit on the matter if i get the chance and share my findings.

Many thanks to the guys who tried to clarify things. We shouldn't take the thread more off the topic though.
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Old 03-09-2011, 04:59 PM   #1680
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Quote:
Originally Posted by Skiddins View Post
Unless your track is particularly bumpy or your car is setup wrong, the chassis will only make contact with the ground when banging across a curb.
I'm sure you're all great at the real thing, but don't forget the laws of physics do not scale unlike our RC cars.
One guy on the Xray forums pointed out that the roll bars should be next to useless because they would need to be 3mm thick to compare with the real thing
That person probably didn't factor in that the mass of a 10th scale car is far less than a 10th of the mass of a 1/1 scale car

Imagine a full sized car that weighs 32 pounds, including the driver.
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