Brake bias

[Kees Veenstra]

Hi All,

I’m currently optimizing my car setup for the Sprint car at the Curvelo circuit. Using the time trial mode it’s possible to use the setups of the ghost cars. What strikes me is that most setups use a brake bias around 57/43. When I do the same, I instantly loose the back of the car when I touch the brakes in a straight line. Therefore, I need at least a 62/38 brake bias to brake in a straight line without spinning out.

Anyone could shed a light on this? It’s not related to the brake pressure since I use the same as the time trial setups.

Cheers,
Kees

 

[UMC 22]

Anyone could shed a light on this? It’s not related to the brake pressure since I use the same as the time trial setups.

Actually, it probably is entirely related to brake pressure... namely the pressure you are applying to the pedal.

The reason you spin out is because by pushing the bias more towards the rear you are increasing the chances of the rear wheels locking under braking. If they do, you start to lose the rear of the car. To counter this you need to "feel" the point at which the wheels start to lock and modulate the brakes to prevent it happening... kind of like manual ABS. You can lower the brake pressure in the setup to help with this, but many drivers will just use their own foot to do the job.

One reason for moving the bias towards the rear is because it can help reduce understeer and to get the car rotated. That's generally the reason I do it on with many cars, including the Sprint Race. I was running 60/40 which worked well for me, though it did directly cause the exact kind of spin mentioned above in the second race yesterday.

On a final note, I would not put too much faith into setups downloaded from time trials. The time trials give you perfect ambient racing conditions, and totally ignore fuel use and tyre wear. So while a setup may be good for wrenching a car around a track as quickly as possible in "perfect" conditions, they are not necessarily any good for actual racing conditions.

Oh, and setups don't make you fast. Practice makes you fast.

 

[Gordie Gunn]

though it did directly cause the exact kind of spin mentioned above in the second race yesterday.

Funny you should mention that because I had the exact same issue in race 2 and found it a bit odd. Having not changed anything in the setup it was unexpected. Of course it could be an issue with track state, perhaps it's reset after each race and with only running a 5 minute superpole there may be far less rubber down.

 

[UMC 22]

Funny you should mention that because I had the exact same issue in race 2 and found it a bit odd. Having not changed anything in the setup it was unexpected. Of course it could be an issue with track state, perhaps it's reset after each race and with only running a 5 minute superpole there may be far less rubber down.

That may well be it. I did feel like my car was twitchier under braking than the first race. I know AMS 2 has track progression, but I'm not entirely sure how it works with regards to session lengths. I would expect it to reset after a trip to the lobby, but whether there is a difference between having 45 minutes of practice/qualy before a race and just 5 mins, I don't know.

But at the same time I was pushing harder trying to gain on the guys ahead at the point of my spin, so it was mainly driver error on my part. The top 7-8 drivers were covered by less than 0.8 seconds in qualy, so catching each other was a case of either waiting for mistakes, or trying to eke out a few hundredths wherever possible.

 

[Gordie Gunn]

But at the same time I was pushing harder trying to gain on the guys ahead at the point of my spin, so it was mainly driver error on my part.

That's what I was thinking until you mentioned the same issue.

I'm sure I read somewhere that the track state is persistent from practice through to race so it most likely resets after.

That said, quali times were similar so perhaps it was a case of over eagerness after all

 

[fwyflyer]

The same issues occur with the Camaro SS... This latest patch to the tire model certainly added some to the handling, but this rotation under braking has got to be rectified as does the rotation under moderate acceleration. Adding more forward brake bias to default values of 64/36 diminishes the behavior. But, the real car has absolutely no issue repeatedly braking in a straight line from 70 to 0 in about 147 feet. And, the real car accelerates hard in a very straight line as well.

 

[tomythto]

Being an hunderds of hour sim racer, I could not even hold straight the car at first in AMS2. Even refunded within 15 minutes, later bought again because of the community reviews. Setups may do the job to a point but default setups suck imo.

 

[Chico Ingles]

I think you still should try low the brake pressure to 78% and lighten your foot...

 

[JoelGL]

Actually, it probably is entirely related to brake pressure... namely the pressure you are applying to the pedal.

The reason you spin out is because by pushing the bias more towards the rear you are increasing the chances of the rear wheels locking under braking. If they do, you start to lose the rear of the car. To counter this you need to "feel" the point at which the wheels start to lock and modulate the brakes to prevent it happening... kind of like manual ABS. You can lower the brake pressure in the setup to help with this, but many drivers will just use their own foot to do the job.

One reason for moving the bias towards the rear is because it can help reduce understeer and to get the car rotated. That's generally the reason I do it on with many cars, including the Sprint Race. I was running 60/40 which worked well for me, though it did directly cause the exact kind of spin mentioned above in the second race yesterday.

On a final note, I would not put too much faith into setups downloaded from time trials. The time trials give you perfect ambient racing conditions, and totally ignore fuel use and tyre wear. So while a setup may be good for wrenching a car around a track as quickly as possible in "perfect" conditions, they are not necessarily any good for actual racing conditions.

Oh, and setups don't make you fast. Practice makes you fast.

Pardon going bit OT, but what about the rear looses when 'releasing' brakes (experienced this w/ both AMS2 Ginetta GT4 or R3E C-Klasse DTM '05)? I've had the impression that as this should transfer weight to the rear, it would give it back more grip. Got used to this with other cars, primary GT cars, in corners as I turn and has worked well... but not w/ these cars mentioned, so far. How do you suggest to address this (maybe lifting front height)? And which cars are more prone to this? Cheers!

 

[wolftree]

Time Trial setups are meant for hotlapping, not racing. An aggressive brake bias will give you lots of rotation when entering corners but might be too inconsistent for longer stretches. In the end, brake bias settings should be adjusted to your individual skill level and driving style, sometimes even on a corner-to-corner basis. This is why even fixed setup online races allow brake bias adjustments.

Pardon going bit OT, but what about the rear looses when 'releasing' brakes (experienced this w/ both AMS2 Ginetta GT4 or R3E C-Klasse DTM '05)? I've had the impression that as this should transfer weight to the rear, it would give it back more grip. Got used to this with other cars, primary GT cars, in corners as I turn and has worked well... but not w/ these cars mentioned, so far. How do you suggest to address this (maybe lifting front height)? And which cars are more prone to this? Cheers!

This is a pretty comprehensive description of combating oversteer in cars with various drivetrain configurations:

Oversteer - what is it, and how to control it

Oversteer is invoked when the rear of the car loses adhesion in a corner before the front, resulting in the 'back coming out'. It can be fun or dangerous.

drivingfast.net

The Ginetta G55 is a front-engined car, so if you are losing the rear when coming off the brakes and turning in you are likely going in too fast and need to brake earlier/harder.

The R3E Mercedes DTM 2005 has a bug with excessive engine braking that makes it spin out when you lock the brakes no matter what value you set the brake bias (confirmed by Sector 3). You can still drive it but it's not a very good car for trying to learn braking.

 

[acidburn82uk]

Pardon going bit OT, but what about the rear looses when 'releasing' brakes (experienced this w/ both AMS2 Ginetta GT4 or R3E C-Klasse DTM '05)? I've had the impression that as this should transfer weight to the rear, it would give it back more grip. Got used to this with other cars, primary GT cars, in corners as I turn and has worked well... but not w/ these cars mentioned, so far. How do you suggest to address this (maybe lifting front height)? And which cars are more prone to this? Cheers!

That my friend is lift off oversteer... instead of jumping off the brakes, try bleeding off the pressure and trail brake. Some cars you have to be very careful how you come off the brakes.

 

[JoelGL]

That my friend is lift off oversteer... instead of jumping off the brakes, try bleeding off the pressure and trail brake. Some cars you have to be very careful how you come off the brakes.

Thought lift-off oversteer was with the accelerator

 

[Günthar Rowe]

Thought lift-off oversteer was with the accelerator

and maybe too much diff preload

 

[Playerone11]

Wrong setups make you slow, for sure. Even with practice.

 

[ozziecoops]

i always use more front than rear it helps with the rake of the car.