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How To Stop The Thundercars Bottoming Out...


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#1 Dark - guest

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Posted Feb 01 2011 - 03:48 AM

Hi Guys,

It seems that everytime i take the Thundercars out for a spin they seem to bottom out on the most minor of compressions. So do we have any Thundercar drivers out there who have solved this issue or any setup gurus with suggestions on how to solve the problem?

#2 Burnsy865

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Posted Feb 01 2011 - 03:03 PM

Drive slower Stewart  :lol:     How low are you running these things, I find that any track with a bump anywhere I have to raise the ride height and usually run the rear a little bit higher than the front. They are heavy cars and this is not the best solution but it works (not always though) for me. You drive much quicker than me so it would be happening in more places for you though  :o , I will be watching this thread to see what I can learn too. :unsure:

#3 Dark - guest

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Posted Feb 02 2011 - 03:53 AM

That was my first thought Craig, i raised the ride heighht to 3 inches front and rear from 2 and it made little difference. I'll try maxing it out to see if that helps.

If i can ge them to stop bottoming i'm tempted to run them through what circuits i can :think:

#4 Saiph

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Posted Feb 02 2011 - 06:54 AM

As you've found Stewart, I don't think that simply adjusting the ride height will help with grounding. If the suspension is too soft or has too much travel, then the bodywork doesn't really care if it has to travel an extra inch to hit the floor, it's still going to do it. And as Craig says, the extra weight of the TCs doesn't help things.

Although I haven't got around to experimenting with the Thundercars yet, I can remember going down this route when I was trying to do my TotalRank times at the Pantsring, trying to figure out how to stop the cars from swapping ends at high speed.

I suspect we'll have to go back to basics. First, max out ride height, then max out the bump rubbers to see if restricting the travel will help. If (as I suspect) it doesn't, then we'll have to try steadily increasing the spring rates at both ends of the cars. If the stiffer setup loses grip, then we'll just have to compensate by running a little extra wing. But then that raises the question of whether the wings will force the suspension to compress more!  :D  Ah, the fun of exploring GPL setups!  :D

Edit: My experience with the GT cars gives me a little hope though. I used to think that generally if you kept stiffening the springs enough to stop grounding completely, the car(s) would be so stiff as to be undriveable. But obviously the GT cars have very stiff setups, and they are just as much fun to drive as any of the other GPL mods. Possibly their physics have been tailored a little to work better with stiffer setups, so maybe it won't work as well with the Thundercars, but I suppose we'll just have to keep experimenting and find out.

Edited by Saiph, Feb 02 2011 - 07:01 AM.


#5 Dark - guest

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Posted Feb 02 2011 - 07:14 AM

Interesting, thanks for your insights Keith. How about as an experiment maxing out the ride height, bump rubbers and spring rates because if it bottoms out still like that then its never going to be cured?  :unsure:

#6 FloP

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Posted Feb 02 2011 - 08:21 AM

View PostDark, on Feb 02 2011 - 07:14 AM, said:

How about as an experiment maxing out the ride height, bump rubbers and spring rates because if it bottoms out still like that then its never going to be cured?  :unsure:

At least you'd still have the dampers to play with, and I think they should have more influence than the ride height itself - but I'm no expert, either.

#7 Dark - guest

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Posted Feb 02 2011 - 08:25 AM

Hmmm ok, what would you try first the FloP?

#8 Border Reiver - guest

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Posted Feb 02 2011 - 09:07 AM

The GTs need stiffer springs because they are dealing with more mass, and so to get the same overall suspension travel you need to provide more resistance.

Some of the ambiguity comes from imprecise terminology and to some extent the fact that there are two different kinds of lbs in the US measurement system for weight (mass) and force. The car is weighted in lbs (mass) and the springs are measured in lbs (force) and these are not the same thing. With suspension, I think the thing you are looking for is how much the springs compress when you apply a certain mass to them. If a mass of 100lbs compresses a given spring by 1 inch, then putting a mass of 200lbs on the same spring with the same restoring force would now compress the spring by 2 inches. In order to get a 1 inch compression for the 200lb mass you would need to double the restoring force of the spring in that case. So, if you have a car that is twice as heavy as an F1 car, then you would expect to need (roughly) twice as stiff springs compared to the F1 car to get the same overall suspension movement.

If the mass of the car is too great, (and in the case of the Thundercars you also need to remember that at speed downforce is also adding to the effective mass of the car), such that the restoring force of the springs cannot hold it up, then you will have no suspension travel left and so you'll be sat on the bump stops. Raising the ride height might keep the belly of the car off the road at this point, but in any case you have no suspension left, so you are effectively using very stiff springs from the bump stops.

When you change direction in the car, left or right, up or down, or accelerate or brake, the momentum of the car body wants to keep going the way it was going and this produces a force proportional to the car body mass and the rate of change. The springs have to be capable of providing an almost equal force to resist and damp this change to return to approximately the static case. As they resist this change they compress, but they can only do this up to their total available travel. Larger mass car bodies have larger momentum and so produce larger forces which must be counteracted with larger springs.

The spring rates required are therefore relative to the mass of the car in question, so settings that are normal/average for a 67 F1 car would be very soft and ineffective for a GT car, or conversely normal/required settings for a GT car would be far too stiff for the 67 F1 car, but for the cars they are intended for both are correct. In relative terms, when using the setups that are correctly scaled to the mass of the cars in question, the amount of body movement when cornering or braking would also be approximately the same, and the physics of what is going on is certainly the same for both cars, as I am sure someone once said "you cannae change the laws of physics". ;)

Rob

Edited by Border Reiver, Feb 02 2011 - 09:17 AM.


#9 FloP

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Posted Feb 02 2011 - 11:26 AM

View PostDark, on Feb 02 2011 - 08:25 AM, said:

Hmmm ok, what would you try first the FloP?
It depends on how severe the bottoming is and in how many places it occurs. As long as it happens only once or twice per lap (e.g. at the Ring), I would try to eliminate this effect by using more bump rubber. If, however, the car bottoms out five times a lap and you basically drive on the bump stops in every other corner as Rob explained so well, I think it's more a question of proportionally increasing all spring rates and bump dampers.

It certainly doesn't hurt to increase the static ride height along with the suspension stiffness as well. This way, the suspension can provide more resistance and can be compressed further before hitting the bump stops. Since the reaction force is proportional to the product of the stiffness times the compression, increasing both at the same time should allow you to eliminate the bottoming with the least change in any one setup variable.

I hope the above makes at least some sense! ;)

#10 Dark - guest

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Posted Feb 03 2011 - 04:07 AM

Thanks Rob and FloP.

So may be a good rule of thumb is to find out the weight of a 67 F1 car and a Thundercar and stiffen up the Thundercar in proportion to the 67 F1 car settings :think:

#11 Border Reiver - guest

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Posted Feb 03 2011 - 04:26 AM

As a starting point that is an excellent first approximation. :) The weight distribution might be slightly different between the two so you may need to slightly readjust the front/rear balance and then re-trim the settings on the ARBs, but for total springing that would be a good starting point.

Also remember that at speed the TC will in effect be heavier due to downforce, and the more downforce you crank on the more extra springing you should need to add to compensate, so being slightly on the high side for spring rates would make sense. It is only a guess, but I'd have thought you'd always be better to have the spring rates slightly higher than actually needed, since although you are potentially not maximising the grip you could possibly have, at the same time you are much less likely to ever hit the bump stops that way or to ground the car which overall would certainly lose you more time.

Also remember that as real racing cars got more and more downforce, their suspensions became much stiffer to be able to deal with the rising forces involved. I know that I read that Villeneuve hated the cars of the early 80s as they got so stiff to deal with the downforce they generated that driving them was like getting continuously punched in the back.

Rob

#12 Dark - guest

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Posted Feb 03 2011 - 05:18 AM

In that case maybe a better settings base would be a 69 F1 car :think:

I'm assuming that the Thundercars achieve more downforce with speed due to a bigger wing area and i'm also hoping that the car choice screen in GPL will have the weights listed in the info. Does anyone know this for sure?

#13 Border Reiver - guest

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Posted Feb 03 2011 - 07:09 AM

The car setup screen will tell you the static weight of the car, with fuel, but obviously not the effective weight at speed.

I don't know that this "aero weight" is written down anywhere I am afraid. Obviously it depends on the speed of the car and the wing angle in use. It should be perfectly possible to calculate based on a few given parameters what the effective weight would be at say 120mph, which is relevant for cornering in "average" turns or at 200mph to know the maximum suspension loading for the ends of straights. I am intending to write an excel sheet or similar to calculate all of this stuff where you input the car/mod you are driving, the wing angle set and the speed to use for the caluclation to help assist with car setups, but again it is another thing on my to do list that has yet to float up to the top.

Rob

#14 thomass

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Posted Feb 03 2011 - 07:10 AM

From my head the setup screen shows the overall weight of the car including the fuel? Top right corner?

Thomas

#15 Dark - guest

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Posted Feb 03 2011 - 07:35 AM

Bonza! thanks guys.

That will be a useful tool Rob  :thumbup:




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