- 370
yes it would, but then the release date wouldve been delayed, lol
djaft3rb3ats
djaft3rb3ats
noob question about ride height
- Thread starter MADTJ
- 114 comments
- 5,848 views
- 58
doormeister
I know the discussion has gotten past this post, but I just got back from the weekend and had to correct a mistake here. The least shift in CoG should occur when the CoG is between the points of reference (where the springs contact the underside of the body??), and if the CoG is BELOW the points of reference(?), tilting the car back would actually move the CoG AWAY from the rear tires, so if the CoG is below the axles, you could actually tilt the nose down/rear up to move the CoG closer to the rear wheels, but the CoG would move AWAY from the rear wheels as the car accelerates and the body rotates back. How often the CoG is below the point where the springs contact the body is something I am at a loss for. This may occur with some frequency on F1 cars, but I really have no friggin idea...
- 370
lo, gj confusing the rest of the world
djaft3rb3ats
djaft3rb3ats
- 2,208
Okay, here are the results of my little ride height and rake versus top speed tests on the Test Track, using the Pescarolo '03 with stock power. I used a 2.00 final drive, Autoset of 1, and automatic transmission. I tested for various amounts of rake, all at the lowest front ride height setting:
55/65: 241
55/75: 239
55/85: 238
55/95: 229.3
55/105: 228.9
I didn't expect this. I thought the reduction in speed would be progressive as you increased rake, but that isn't the case at all. Looks like 30mm difference is the sweet spot on this car, huh?
Question is, how does this relate to downforce? All this does is show how the increased frontal area caused by jacking up the rear end slows the car down. Without a "downforce gauge", how do we know how rake affects DF?
It looks like we can only determine that by strictly subjective testing on a high-speed track. Seems like the Super Speedway might be good for that. Maybe I'll try to test for lap times with varying amounts of rake.
Oh, by the way, I saw a discussion on a thread somewhere a while back about the effect of ride height on top speed, with some claiming that it made a difference, so I tried testing with no rake at all, but with varying ride heights:
55/55: 242
65/65: 242
75/75: 242
85/85: 242
95/95: 242
105/105: 242
So much for the idea that ride height affects top speed...
55/65: 241
55/75: 239
55/85: 238
55/95: 229.3
55/105: 228.9
I didn't expect this. I thought the reduction in speed would be progressive as you increased rake, but that isn't the case at all. Looks like 30mm difference is the sweet spot on this car, huh?
Question is, how does this relate to downforce? All this does is show how the increased frontal area caused by jacking up the rear end slows the car down. Without a "downforce gauge", how do we know how rake affects DF?
It looks like we can only determine that by strictly subjective testing on a high-speed track. Seems like the Super Speedway might be good for that. Maybe I'll try to test for lap times with varying amounts of rake.
Oh, by the way, I saw a discussion on a thread somewhere a while back about the effect of ride height on top speed, with some claiming that it made a difference, so I tried testing with no rake at all, but with varying ride heights:
55/55: 242
65/65: 242
75/75: 242
85/85: 242
95/95: 242
105/105: 242
So much for the idea that ride height affects top speed...
- 466
Perhaps I am misreading the data, but it looks like 10mm was the fastest, no? Also, technically, you shouldn't need downforce to go fast, assuming the car is set-up relatively stable. Picture an arrow shot from a bow (the Auto Union V-16, for example). The only time the arrow would need downforce is when it tried to negotiate a higher "g" turn. Down(would)force its skinny little arrow tires into the pavement, giving them the necessary grip to drag the rest of the arrow through the turn. If your top end (no rake, no airfoil DF?) is 242, it doesn't seem like the banked corners are enough to slow you down without DF, that using it would increase speed. I think the best test would be a track where the car has to slow down for the turns, Deep Forest, Midfield and Laguna Seca, come to mind, and probably something in Driving Park and City Courses. A B-Spec driver might be a good way to eliminate subjectivity and you can fast forward him.Zardoz
- 2,208
Zardoz
That's what I was referring to. Going from 30 to 40 knocked off 9 MPH. All the other increases in rake made very little difference in top speed.
I thought we would see a proportional reduction in top speed. Instead we get one change making an enormous difference, which seems a bit odd, when you think about it.
- 370
Zardoz
correct me if im wrong or misinterpreting the data, but with high speeds come air ay high velocities. since there are no body kits or side skirts for the cars, there are plenty of spaces where air can infiltrate the bottom of the car, casuing it to have a slight lift and therfore the jittery feeling and a lack of grip (to a certain degree as is also limited by PD), what im getting at is that df is completly necessary, its just the amount that matters. for example, the LMP cars have less air going underneath the car cause of the body hit it front, it deflects the air upwards and away from the bottom of the car
djaft3rb3ats
- 2,208
djaft3rb3ats
If PD is really being accurate in their modelling, it seems like the lack of side skirts would pretty much negate the underbody ground effects, because, as you and rk have said, it would allow air to be pulled in from the sides and relieve the negative pressure under the car, cancelling out the "venturi effect" and resulting in no additional downforce to speak of.
I doubt that PD is pretending that we're lowering the side skirts as we raise the rear ride height.
So if we're getting any additional downforce from lowering the nose and raising the tail, is it all because PD is modelling for top-of-body air pressure as we turn the car into a wedge? We know for sure they're modelling for increased frontal area, because of how much the wedge effect slows the car down.
- 466
On my most recent tune, the TVR 350C, I tried in vain to keep body rake to 10mm. When that didn't work, I tried half of the remaining range, 15mm, still not good enough. I cannot say if the 30mm I settled on limits top end, but I couldn't have driven it 180mph on the first fast stretch at Nürburgring without it. Which reminds me, I forgot to include my auto set value...Zardoz
LMP cars don't have sideskirts-heck neither did Group C cars. But they still benefit from rake. Sportscars normally run 10mm of static rake, IIRC, for ground effect. F1 does it too, and they have high ride heights to start with, as well as small floors.
My guess for the top speed dropping a ton, is that it just goes over the edge of being efficient. In real life terms that'd mean flow seperation among other things, but in GT4 it probably just means that too much rake=no worky.
My guess for the top speed dropping a ton, is that it just goes over the edge of being efficient. In real life terms that'd mean flow seperation among other things, but in GT4 it probably just means that too much rake=no worky.
👎Zardoz
Depends which GT4 theory you subscribe to. Seeing as there isn't any conclusive evidence of the 'increased downforce due to body rake' theory in GT4 - the other theory of why lifting your cars bum helps on the bumpy tracks is that it stops your rear end bottoming out. This bottoming out tends to happen most noticeably for fast cars with high downforce (eg F1, minolta toy etc.) with low ride height. When the cars bottom out, they become jittery because they are banging their asses along the road - not ideal for car balance. Jacking their bums up stops this dragging - and hence makes them smoother and more stable at high speeds.
The other interesting point to note is that this seems to affect PAL users more than NTSC users. As demonstrated by PALs B-spec problems with sarthe II. If you set up your F1 just 'right' b-spec bob will do all kinds of fun stuff down the back straight.
- 370
im confused in one point. i understand the rake theory and all that, but if i increase the back by 30mm, do i need to strengthen the springs too or do i just leave it, that question has been buggin me and no one really has said anyting about it, (or else im blind)
djaft3rb3ats
djaft3rb3ats
djaft3rb3ats
Yeah not sure if its been mentioned. I tend to soften my rear springs more related to how i want the balance to operate - ie soften them if you are struggling for rear traction (eg oversteer). Admittedly this is a vastly simplified view on how to tune a cars balance - but it tends to work. You shouldn't soften them too much tho, as then the car may start bottoming out again which puts you back at square uno.
oh and was the "playstation" car the pescalaro whatever? I haven't bought this yet so have never driven it. maybe that's why these cars tend to get better tire wear - because their default setup is smoother and therefore not as harsh on the rear tires.
- 466
Thank you TJ, it was this car that first clued me that ground effect downforce was simulated in GT4.MADTJ
In this context, try to think of ride height adjustments as the little detent stops on your lawnmower where the wheels connect to the body. Every detent is a 10mm adjustment. You can quickly see that what is most affected is how high that part of the body is held off the ground. These days I always catch myself wondering if lawnmowers mightn't benefit from a little rake like cars in GT4, but of course you have time to let your mind wander while mowing a lawn.djaft3rb3ats
Now
Once you have jacked your rear suspension, you do have more room before the chassis bottoms, which could allow you to soften your rear springs to allow more travel as Zardoz mentioned, however, my cars springs are tuned for steering bias only, I always test at Nürburgring, and if it lands the Quiddelbacher jump without skidding off the road (the sure sign of overly compressed suspension, the simulation is that of sliding on your chassis), you are good to go. While doing so, I have found that a front ride height of midrange, or default if it is not one of those "slammed" cars, always clears the hump landing, so the jacked rear does as well. Softening the rear would make my car too pushy or "understeery".
- 370
so rk, what u are telling me is that a high spring rate in the back creates oversteer (to a certain extent) and that while increasing my rear by say, 30mm, then i should also in effect increase the spring rate. if what i said sums up what u just said, then my next question to you is for spring rates with rake included, what increments should u increase the spring rate by, is it the same concept for regular tuning or is there sumtin special that u must do ir take into consideration?
thanks rk for ur insightful post.
im looking forward to ur next one
djaft3rb3ats
thanks rk for ur insightful post.
im looking forward to ur next one
djaft3rb3ats
- 2,208
Zardoz
Maybe we don't know, after all. Maybe we've been completely wrong about this, and PD isn't modelling for chassis downforce at all.
I finally ran the test on Super Speedway that I've been threatening to do. I used the '03 Pescarolo Courage, with stock power (840 HP), stock suspension and LSD, ASM and TCS at zero, and R2/R2 Hard tires. I used a final drive of 2.52 with the Autoset at 1, and AT.
I started in B-Spec mode, with the speed setting at "3". I ran ten laps per session, and recorded the best single lap per session. I began with no chassis rake at all and progressively raised the tail, as I did on the Test Track. With the DF settings at their minimum of 38/53, I got these lap times:
55/55: 30.953
55/65: 30.909
55/75: 31.050
55/85: 31.021
55/95: 31.094
55/105: 31.170
I then switched to A-Spec mode and, with the DF still at minimum, got these times:
55/55: 30.325
55/65: 30.785
55/75: 30.831
55/85: 30.872
55/95: 30.854
55/105: 31.048
Next, I went back to B-Spec and ran just one no-rake session, with the DF turned up to 51/72:
55/55: 29.903
Then one more session in B-Spec, with the DF at its 63/88 maximum:
55/55: 29.323
Now A-Spec, DF at 51/72:
55/55: 29.651
Finally, A-Spec with the DF maxed at 63/88:
55/55: 29.001
The results do all the talking. It doesn't look like PD is modelling for chassis downforce at all, does it? What do you think of my using the Super Speedway as a test venue? Is its speed and simplicity conducive to a good test, or should we also try this same sort of experiment on a road course? If so, somebody else will have to do it, because I've seen enough...
- 466
Chassis down force, by its very nature, CAN'T make a car faster. The super speedway hia only high speed, banked turns, granted the one turn requires most LMP cars to slow from 200+ to negotiate it, but it is hardly a test for "traction," which is the ONLY thing chassis downforce can improve. The test runs you have posted are very well rounded and complete, however, I bet the lateral G-force gauge never even went past the first "tick" mark, or one G.Zardoz
rk
Actually what I had hoped to convey is that spring rates and ride height are almost completely independant of each other. They only interrelate if a low rate and/or low height cause bottoming, in which case you must adjust one or both. Since changing the spring rate will alter the steering bias, you must compensate (usually) in other areas of adjustment, like: opposite end springs, stabilizers, wing DF and in extreme cases weight distribution; sometimes tweaking the LSD will compensate enough. I always add my front and rear rates, divide by 2 and apply that figure to both, then adjust for bias if necessary. I then test with my desired ride height, and if all is well, I complete a lap at the 'Ring, and I rarely change ride height to compensate for bottoming, the exceptions would be the cars that come fully slammed (bottomed), like the Poly F1 and Amuse Carbon.djaft3rb3ats
Also, I got your message but can't access my memory card over the weekend while my son is here, he is very into his Lego's Starwars game...I'll send the tune along when I am able, didn't I post my Alpine tune? You get the "good" one by buying the sad one and winning the Alpine race in French Hall.
rk
The whole point of the second stage of his testing (ie the increased downforce with no change in rake section) was to show that this did have an effect on lap times (ie making the car faster). With respect to your general comments on this topic (ie having a pretty good idea of what you are talking about), i would assume that you are thinking that Zardoz's test was done on the test course 👎 - not the super speedway (the tight oval - where downforce is probably the biggest contributor to fast laptimes) - where i would happily field your bet that the lateral Gs would get way above 1 (given the lap times he was running). Because the lap times seem to increase as the rake is increased - it would appear that rake has no impact on DF - and therefore that the bottoming out theory for why raising your race cars bum proves more stable (and often quicker) would be correct.
- 370
oompff, i think we have stumbled across a road block
djaft3rb3ats
djaft3rb3ats
djaft3rb3ats
not a road block persay. just time to take into account the fact that GT4's physics doesn't model everything we would like it to. The unfortunate thing for the GT guys is that they are always used as a benchmark for the genre and are therefore always expected to have everything. it is a testiment to their efforts that after this long they are still releasing stuff that is at the pinnacle of their genre.
- 2,208
I just checked it, and, for the record, the lateral G-Force gauge buries itself at 2 immediately upon entering both turns, and stays there all the way around until you're almost completely out onto the straight.
I should also add this: The lap times aren't the only indicator. The subjective "feel" was just as conclusive. With the DF settings at minimum, I felt no additional traction at any increased rake settings. The car felt the same around the turns whether the ride height settings were 55/55, 55/75, or 55/105.
Then I set the RH at 55/55, and increased the DF setting to the halfway points of 51/72, and took off. Halfway around the first turn I muttered to myself "Oh...my...God". The difference was instantly apparent, even at the midway settings. At full downforce I was glued to the track. It was as if I had changed cars or something.
I should also add this: The lap times aren't the only indicator. The subjective "feel" was just as conclusive. With the DF settings at minimum, I felt no additional traction at any increased rake settings. The car felt the same around the turns whether the ride height settings were 55/55, 55/75, or 55/105.
Then I set the RH at 55/55, and increased the DF setting to the halfway points of 51/72, and took off. Halfway around the first turn I muttered to myself "Oh...my...God". The difference was instantly apparent, even at the midway settings. At full downforce I was glued to the track. It was as if I had changed cars or something.
So it would appear that downforce is merely a function of the two controllable front and back values. So while rake does have an undeniable indirect effect on grip (in relation to how the physics models bottoming out), it doesn't have anything to do with downforce. Thanks for testing it Zardoz.
- 370
yeah, thanks a lot for u research and stuff
djaft3rb3ats
djaft3rb3ats
