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differential balance wheelrates

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#1 Robert Fleurke

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Posted Mar 21 2016 - 04:03 PM

Quote

You can increase the rotation by altering the wheelrates/bars (but to increase the speed of the rotation will need a different diff).

Quote

You can run an aggressive diff with a understeering mech balance.


Quote

The diff can't override the wheelrates in turning the car, the diff changes the speed of the rotation nothing more.


Quote

You must understand the difference between oversteer and over rotation with the diff, if you dont get this point...you won't understand.


#2 JonnyA

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Posted Mar 22 2016 - 03:05 AM

https://youtu.be/KDFclOrzXeQ

#3 Robert Fleurke

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Posted Mar 22 2016 - 06:51 AM

These were some quotes by Anonymous to understand what the diff does, it doesn't change the balance, just the speed of the rotation. To change the balance touch the wheelrates and bars.

Just some info to all who are interested in setting up, for more understanding. ;)

#4 Saiph

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Posted Mar 22 2016 - 12:40 PM

View PostJonnyA, on Mar 22 2016 - 03:05 AM, said:

:roflmao: :hithead:

#5 Pete Gaimari

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Posted Mar 22 2016 - 12:43 PM

View PostRobert Fleurke, on Mar 22 2016 - 06:51 AM, said:

These were some quotes by Anonymous to understand what the diff does, it doesn't change the balance, just the speed of the rotation. To change the balance touch the wheelrates and bars.

Just some info to all who are interested in setting up, for more understanding. ;)

That's true, but changing the balance also changes the speed it will rotate.

#6 John Woods

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Posted Mar 22 2016 - 05:00 PM

Some quesses and.guestions from beyond understanding...

Quote

You can increase the rotation by altering the wheelrates/bars (but to increase the speed of the rotation will need a different diff).

So, rotation around the vertical axis of center of mass?
(That is, turning the car right or left)?
The CoM does move away from static center, sort of rotating off-center, while the car is in motion, in response to gravity and loads on suspension such as lateral load.
What different diff?

More aggressive or less?

Quote

You can run an aggressive diff with a understeering mech balance.

30/30/6?
:D

Quote

The diff can't override the wheelrates in turning the car, the diff changes the speed of the rotation nothing more.

Okay. Diff only effects speed of rotation.

Quote

You must understand the difference between oversteer and over rotation with the diff, if you dont get this point...you won't understand.


Wait...over rotation caused by the diff? But in above it states diff only effects speed?

This is interesting stuff. Where is it from? Is there more?

Edited by John Woods, Mar 23 2016 - 07:22 AM.


#7 Robert Fleurke

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Posted Mar 23 2016 - 07:34 AM

View PostPete Gaimari, on Mar 22 2016 - 12:43 PM, said:

View PostRobert Fleurke, on Mar 22 2016 - 06:51 AM, said:

These were some quotes by Anonymous to understand what the diff does, it doesn't change the balance, just the speed of the rotation. To change the balance touch the wheelrates and bars.

Just some info to all who are interested in setting up, for more understanding. ;)

That's true, but changing the balance also changes the speed it will rotate.

Yes, but to point out the difference between diff and mech grip, Anonymous likes to keep the term over/understeer for mech grip (balance), and over/underrotation for differential. These are two different things.

Differential settings do not change the balance or mechanical grip, it only changes the drivability of the drivetrain (think traction). Mechanical grip is the grip between the tires and the track, provided only by the suspension and tires.

Edited by Robert Fleurke, Mar 23 2016 - 08:06 AM.


#8 Robert Fleurke

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Posted Mar 23 2016 - 08:52 AM

View PostJohn Woods, on Mar 22 2016 - 05:00 PM, said:

This is interesting stuff. Where is it from? Is there more?

He wants to remain anonymous, but one should respect his authority. There is one more quote so far, but it is useless.

Quote

I was going to try and explain (poorly) how a helicopter works when moving in a direction while pointing, to explain diff and mech grip.

As for your other questions just note the difference between mechanical grip, and differential. The diff cannot override the balance or wheelrates, it only changes the drivability of the drivetrain.

In a way you can say mech grip rotation is mostly controlled by the steering wheel, and differential rotation and traction by controlling pedals. (just my philosophical line of thinking)

Personally, I like a soft neutral balanced car (slightly oversteer maybe) -if I can get away with it, regarding track characteristic- with a reasonable agressive diff like 45/60/1 in general (30/85/1 for 65/F2 mods). The slight oversteer will allow you to push into the corners a bit more if needed, and with the diff (pedals) you can correct slight mistakes in steering/lines. That's how I visualize/theorize it for myself.

Edited by Robert Fleurke, Mar 23 2016 - 11:26 AM.


#9 John Woods

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Posted Mar 23 2016 - 12:01 PM

In Grand Prix Legends, what diff settings are slowest/fastest with respect to rotation speed?
Most aggressive = fastest = ?
Least aggressive = slowest = ?

Seems on fast long straight tracks with big turns we would want slower diff, quick tracks with short straights and lots of turns the preference would be for fast response diff? Or is that not the priority/purpose?

Anything about how to match suspension and diff so they work together?

Edited by John Woods, Mar 23 2016 - 12:02 PM.


#10 Pete Gaimari

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Posted Mar 23 2016 - 01:01 PM

Loose on the coast side (high number) will rotate the fastest.

Tight on the power side(low number) will rotate the fastest.

So, a diff setting of 30/85/1 will rotate fast on power and coast. Which is why it's harder to drive.

I left the clutch setting out on purpose, but they affect both sides.

#11 John Woods

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Posted Mar 23 2016 - 04:42 PM

My theory for awhile, (just realizing while running 30/85/6 for a few laps around Spa67), has been to go into coast by quickly lifting the throttle while accelerating after braking, so the rear settles onto the cushion as it rotates, then as soon as that happens go back on power and grind the front as little as possible into the turn, using tire sounds for feedback.

One benefit of faster diff is being able to correct errors soon enough to catch things when a slower diff would not have helped?
Another is quicker twisty capability thru some esses?
Quicker changes of direction?

Now it makes sense why it is suggested newbies start with 85/30s. Had always thought it was only about stability, but now realize the stability was because of slower diff.

Thanks, Pete, your answers helped to get a grip on this.
And RF and Anon also.

now off to try 30/85/1.
:)

#12 Warren Hall Jr.

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Posted Mar 23 2016 - 06:57 PM

You guys are diving me nuts with all this diff locking stuff. It's pretty simple. If you are in an under powered car with a locked diff you will under steer badly under power. If the car you are in is high powered a locked diff will light up both rear tires and spin out. A balance of locked or not has to be found and it won't be the same for every driver. The effects of a locked diff or an unlocked diff can be mitigated with springs and sway bars. When coming out of a turn and all you do is spin the inside tire you need more locking but not so much locking that you can't get the power down early without getting sideways. Some tracks that have high speed sweepers will need a bit of locking to keep the car in a drift so you can make the turn.
Have you ever seen a Saab 96 with welded spider gears( a fully locked diff) try to run on a 1/4 mile oval? It's pretty funny! Same with a VW Bug trying to do the same thing. The Saab would'nt turn at all and the VW turned way too much.
The Torsen diff is popular for a reason.
Warren

#13 John Woods

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Posted Mar 24 2016 - 11:17 AM

The more you know, the more I forget.

Until this discussion had thought 30/30/6 is the tightest diff possible. That is, with the most locking, thinking for some forgotten reason that is the setting that if I could drive better would be the fastest. No idea where that came from now...it was too long ago...but think it started with some of Alison Hine's comments and that Nate Hine wrote Race Engineer with a 20/20 diff option. (Why do that except for a good reason)?

Now this new idea, (for me anyway, thank you all again), of speed of rotation being caused by the diff is big fun to think about and see how it can be applied to GPL.

There is only one diff and one effect, compared to four springs, four tires, two anti-roll bars, and at least three, seven or twelve centers of gravity that are said to add up to one big Center of Gravity and all of that is either static or dynamic. And then there's roll centers and front and rear toe.

Seems easier to check diff effect because speed of rotation is a display feedback and FFB variable. It is not required to imagine what is happening at the rear or the tire's slip angles or analyze tire temps.

Now knowing what to look for, the effect now seems obvious.

I think, maybe, pretty sure, it could be, but still just questions and guesses.

Edited by John Woods, Mar 24 2016 - 11:50 AM.


#14 Robert Fleurke

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Posted Mar 25 2016 - 07:26 AM

View PostWarren Hall Jr., on Mar 23 2016 - 06:57 PM, said:

The effects of a locked diff or an unlocked diff can be mitigated with springs and sway bars. When coming out of a turn and all you do is spin the inside tire you need more locking but not so much locking that you can't get the power down early without getting sideways. Some tracks that have high speed sweepers will need a bit of locking to keep the car in a drift so you can make the turn.

Thanks for this quote.

#15 Robert Fleurke

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Posted Mar 25 2016 - 07:51 AM

I try to setup to achieve maximum grip of the tires (mech grip), with a neutral/slight oversteery balance. In GPL reality it means for me having slight higher reartemps than the fronts, and slightly higher rear pressures than the fronts (for 65/67).

Sometimes, when I don't want to touch the (base) suspension setup anymore, but just look for slightly more rear temps, can adjust it with a slighly more agressive diff (instead of stiffer rear wheelrates/rear sway bar). Anonymous says I should change the balance (wheelrates/bars), but for me it works at certain tracks.

So, I'm trying to find that setup that doesn't turn to understeery during a race, which can easily happen when you start to push more into the corners (change your driving). I like to have that little margin/room to push a bit more, at times, in a race. The most important thing is you can handle an agressive diff, you need to have very smooth throttle/brake control, so it won't cost you time instead.

PS: ppl often think I have a secret setup advantage etc., but the biggest difference will be your driving and lines. When I share setups, most ppl say they are undrivable! :D Only someone like Iestyn Davies would beat me with my own setups! I think it's mainly about being able to handle an agressive diff setting.

Edited by Robert Fleurke, Mar 25 2016 - 07:54 AM.


#16 John Woods

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Posted Mar 25 2016 - 08:32 AM

View PostWarren Hall Jr., on Mar 23 2016 - 06:57 PM, said:

...and it won't be the same for every driver.

:)

Won't be the same because we all have our own style and technique based on how far along we are with developing our driving skills.

The better our skills at tossing a car around, the more likely we will prefer a looser, oversteery setup that when well balanced allows easy counter-steering to hold the tires in slip/drift and keep the car on the line and on the edge.

Earlier commented maybe looser for tracks with lots of tight corners and tighter for big tracks with long sweepers...but now thinking that is not right and a better approach is to always run the quickest diff that is comfortable regardless of the track map.

Agreeing Anon is correct that suspension setup and diff are separated, it seems better to tune the suspension first, then tune the diff to that, rather than fight against the diff or compromise grip in order to make a diff setting work.

#17 Pete Gaimari

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Posted Mar 25 2016 - 10:30 AM

It's a balance between the two. I can use the loosest diff setting which should have the fastest rotation (oversteer), and make the car understeer with the mechanical setup.

#18 Pete Gaimari

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Posted Mar 25 2016 - 10:35 AM

View PostRobert Fleurke, on Mar 25 2016 - 07:51 AM, said:

I try to setup to achieve maximum grip of the tires (mech grip), with a neutral/slight oversteery balance. In GPL reality it means for me having slight higher reartemps than the fronts, and slightly higher rear pressures than the fronts (for 65/67).

Sometimes, when I don't want to touch the (base) suspension setup anymore, but just look for slightly more rear temps, can adjust it with a slighly more agressive diff (instead of stiffer rear wheelrates/rear sway bar). Anonymous says I should change the balance (wheelrates/bars), but for me it works at certain tracks.

So, I'm trying to find that setup that doesn't turn to understeery during a race, which can easily happen when you start to push more into the corners (change your driving). I like to have that little margin/room to push a bit more, at times, in a race. The most important thing is you can handle an agressive diff, you need to have very smooth throttle/brake control, so it won't cost you time instead.

PS: ppl often think I have a secret setup advantage etc., but the biggest difference will be your driving and lines. When I share setups, most ppl say they are undrivable! :D Only someone like Iestyn Davies would beat me with my own setups! I think it's mainly about being able to handle an agressive diff setting.


Aggressive diff settings are easily handled when throttle is used with braking. That's easy to understand by RF braking with those loose diffs.

#19 Robert Fleurke

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Posted Mar 25 2016 - 10:49 AM

Yes, you can use a understeery setup with a "loose" diff.

But normally you'd try to find the balance first, finetuning the base setup if you have one, for a specific track. Personally I just use the weight ratio as a guidance for the wheelrates ratio, and even for the amount of, since I like to run quite soft if I can get away with it. (recently more experimenting with stiffer setups)

And you will find you will use quite the same like diffs. It evolved here from 85/45/5 to 60/45/1 to 45/60/1. But sometimes I will use 60/60/1 for example. It's more finetuning your choice of diff for a track. Sometimes I finetune to 50/55/1 for example, with GPL Setup Manager. I do remember at Brands  Hatch 1967 it was a very fine line to find my optimal diff settings in combination with the car balance and tire parameters, in the Brabham.

But normally you can use your favo diff at most tracks, I would say. Surely, with agressive diff you will avoid understeer way more easy than with a more conservative diff, surely with the same suspension setup.

I have to use throttle for stabilizing the car under braking, therefore using down to 48% brakebias in quali/hotlap trim. For races mostly 49/50%.

Edited by Robert Fleurke, Mar 25 2016 - 10:52 AM.


#20 Pete Gaimari

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Posted Mar 25 2016 - 11:47 AM

I agree Robert. When i was LF braking and using throttle with braking my favorite diff was 45/85/1. When switching to RF braking I couldn't handle that diff setting anymore without completely screwing up the rest of the setup. I actually learned RF braking with 85/30/6. It was terrible and the car wouldn't turn for beans, but I did get used to RF braking. I then went to 85/45/5 and that was much better. Now I use 60/45/1 almost everywhere with RF braking, and adjust the rest of the setup for each track.

My brake bias was 49% with LF braking. At first with RF braking I was using 57%. It was also terrible and I had to be careful to not lock up the front tires. I gradually moved it forward as I got used to RF braking and use 53% now. Any more forward than that and I have a hard time trail braking to the apex. With no throttle used with braking now I can use a lot less brake pressure to stop. I also get better fuel mileage.

I'm actually very close to my LF braking PB's, but it's more work RF braking when close to my limit. It's more fun, but more work too.





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