brake balance testing- strange results

[nomis3613]

Hi All,
I've been measuring stopping distance to try and find the best brake balance settings, and it's thrown up a strange results. Here are the brake balance settings (f,r) and the stopping distances (for reference, car is bmw 2002 turbo, sport medium tyres, sport brakes, no aero).

First, increasing the front brakes' strength:
2,0 = 92.5m
3,0 = 92.0m
4,0 = 93.0m
6,0 = 93.5m
I was a bit surprised that the optimal braking strength was so low (doesn't give more range for adjustment. But otherwise, this seems totally normal to me, the shortest stopping distance is when the tyres are held at their optimum slip speed, but then the distance increases for higher strengths as the ABS kicks in to avoid locked tyres. Also, the results were consistent with the sound- slight screeching for 2, a bit more for 3, then heaps for 4+. All good, lets move on to the rears...

0,1 = 96.0m
0,2 = 95.0m
0,3 = 93.5m
0,4 = 93.0m
0,5 = 92.0m
0,6 = 92.0m
0,7 = 91.5m
...(skipped a few to save time from here on)...
0,9 = 90.5m
...
0.15 = 89.0m
0,24 = 88.0m

What on earth???? The rear brake strength is maxed out and still it's not locking the wheels! (no screeching sounds for any of these tests either) This totally contradicts real life (rear tyres need less brake strength than front tyres to lock) and also Scaff's guide (static weight and weight transfer vs brake controller).

Any ideas??

After this, I switched to Racing Medium tyres and although I didn't measure any stopping distances, from listening to the screeching the results followed the same trends as the Sport tyres: front tyres locking at a fairly low brake setting (but slightly higher than Sport tyres) and the rear tyres not even locking at maximum setting. (there was also dualshock vibration when braking with the Racing tyres which I did not get when running the Sports tyres- wonder what this means?)

Thanks in advance,
Simon

 

[nomis3613]

Update: I've tested what happens with the RUF 3400S and the Bentley Speed 8. Same thing happened, so the weird rear brake results are not just for prehistoric european sedans...

 

[PF]

Good work Simon. Have you compared these results with the data given in these threads? I haven't read them in a couple of years, but am sure you'll get some kind of useful comparison from their findings.

 

[Leonidae@MFT]

Also, try this theory of yours out with heavier cars such as Viper, Audi RS6 etc.. also, test how the braking effects cornering.

 

[Parnelli Bone]

How are you able to measure braking distance? I've never been able to figure this out...I always use time (seconds) from 100 to zero mph.

 

[RacecarBMW]

yea same as above how did you measure

 

[mafia_boy]

You can measure via the Test Course fellas. Remember, you have a whole 1500m of track that's seperated by 100m intervals, not to mention you can use the data logger to work this stuff out too. 👍

 

[Parnelli Bone]

You can measure via the Test Course fellas. Remember, you have a whole 1500m of track that's seperated by 100m intervals, not to mention you can use the data logger to work this stuff out too. 👍

You mean the analyzer?

 

[mafia_boy]

It may be the analyzer Parnelli to tell you the truth, it's been a while since I've used it but I thought it said data logger. 👍

Maybe another difference between PAL & NTSC??

 

[nomis3613]

Thanks for the replies!

Have you compared these results with the data given in these threads?

Thanks for the tip, I've had a look through the thread and can't find anything definitive either way. Scaff believes that the brake balance controller (BBC) is directly proportional to braking force (cos he uses the static weight balance when tuning brakes) which is different from my results. However, here his results are:

No BBC fitted - 85m
Default setting 3 / 3 - 85m
Extreme front bias 24 / 1 - 100.5m
Extreme rear bias 1 / 24 - 85.6m
Scaff's setting 5 / 3 - 82.8m
Ducks request 1 3 / 5 - 85.2m
Ducks request 2 5 / - 84.1m​

I reckon that if he tested 5/24 (optimum front brake, max rear) the stopping distance would be even less than 82.8m (which would support my results), but this is just hypothetical. Is Scaff around and able to dust off his testing gloves??

Something else I found by Scaff (PS I totally respect his knowledge and theories, not having a personal attack or anything, just trying to improve the understanding of how the BBC works) here:

The very active ABS in GT4 is also one of the reasons why setting a stupidly high rear brake bias does not cause massive car instability, which would be the result in the real world.​

Hmmm...I don't think so. ABS can be clearly heard as a staccato screeching (as opposed to normal braking which has a "smooth" constant screech). I have not been able to cause ABS in rear brakes, even with the BBC maxed out for the rear.

Also, try this theory of yours out with heavier cars such as Viper, Audi RS6 etc.. also, test how the braking effects cornering.

Sure, I'll check heavier cars sometime.

How are you able to measure braking distance? I've never been able to figure this out...I always use time (seconds) from 100 to zero mph.

Yep, using the data logger, subtract the track distance (numbers along the bottom of the logger) where you start to brake from the track distance where you stop braking. (GT4 trivia: the data logger measures in 0.1m increments, but the vehicle speed is only calculated every 0.5m, so any data logger calculations will always be to the nearest 0.5m. Impress your friends with your knowledge!!)

Actually, my braking times are 200 to 100km/h to reflect that you never need to come to a complete stop on a racetrack. And I actually test by braking from 210 to approx 90km/h but only measure the 200 to 100km/h section (like professional real-world tests). This makes the measurement more reliable, since the transient effects at the start and end of braking do not effect the test. Also, for consistency, I do not downshift during braking or try to use threshold braking (I just slam on full brakes each time).

 

[TOURNIQUETFAN]

You should try the heaviest of the heaviest, the Tank:idea: Car.

 

[Parnelli Bone]

It may be the analyzer Parnelli to tell you the truth, it's been a while since I've used it but I thought it said data logger. 👍

Maybe another difference between PAL & NTSC??

I never use it, except during the TCV5 to calculate top speed. In GT3 it was called an Analyzer or Track Analyzer. It was way more detailed (including frame-by-frame replay pictures if I remember correct).

Thanks for the replies!

Thanks for the tip, I've had a look through the thread and can't find anything definitive either way. Scaff believes that the brake balance controller (BBC) is directly proportional to braking force (cos he uses the static weight balance when tuning brakes) which is different from my results. However, here his results are:

No BBC fitted - 85m
Default setting 3 / 3 - 85m
Extreme front bias 24 / 1 - 100.5m
Extreme rear bias 1 / 24 - 85.6m
Scaff's setting 5 / 3 - 82.8m
Ducks request 1 3 / 5 - 85.2m
Ducks request 2 5 / - 84.1m​

I reckon that if he tested 5/24 (optimum front brake, max rear) the stopping distance would be even less than 82.8m (which would support my results), but this is just hypothetical. Is Scaff around and able to dust off his testing gloves??

Something else I found by Scaff (PS I totally respect his knowledge and theories, not having a personal attack or anything, just trying to improve the understanding of how the BBC works) here:

The very active ABS in GT4 is also one of the reasons why setting a stupidly high rear brake bias does not cause massive car instability, which would be the result in the real world.​

Hmmm...I don't think so. ABS can be clearly heard as a staccato screeching (as opposed to normal braking which has a "smooth" constant screech). I have not been able to cause ABS in rear brakes, even with the BBC maxed out for the rear.

During testing of TCV4 and TCV5, I noticed Adamgp had a habit of setting his rear brakes to max, while leaving the fronts stock or near-stock. Wasn't sure why he tuned this way, but the results above show there clearly is no advantage, which was my opinion after driving his cars around, so +Rep as usual. 👍

Sure, I'll check heavier cars sometime.


Yep, using the data logger, subtract the track distance (numbers along the bottom of the logger) where you start to brake from the track distance where you stop braking. (GT4 trivia: the data logger measures in 0.1m increments, but the vehicle speed is only calculated every 0.5m, so any data logger calculations will always be to the nearest 0.5m. Impress your friends with your knowledge!!)

Actually, my braking times are 200 to 100km/h to reflect that you never need to come to a complete stop on a racetrack. And I actually test by braking from 210 to approx 90km/h but only measure the 200 to 100km/h section (like professional real-world tests). This makes the measurement more reliable, since the transient effects at the start and end of braking do not effect the test. Also, for consistency, I do not downshift during braking or try to use threshold braking (I just slam on full brakes each time).

So in layman's terms you do your testing how? I mean, where on the Test Curse do you actually do your brake testing? Is there a particular spot you start braking? Or is it just whatever speed you happen to be carrying?

 

[nomis3613]

So in layman's terms you do your testing how? I mean, where on the Test Curse do you actually do your brake testing? Is there a particular spot you start braking? Or is it just whatever speed you happen to be carrying?

Hi Parnelli, actually I use the circular track on Twin Ring Montegi (cos it's a shorter lap so there's less time to wait before getting the results). Same deal as Test Course, though, get up to the required speed at the start of the straight and them slam on the brakes. I take care to be on the same line (how low or high you are in a corner), but not so worried about distance along the track because it's all just one long straight so that doesn't make a difference. It usually works out similar within 20m though anyway.

Repeated tested with the same settings gives the same result, so I'm confident this method works.

 

[Parnelli Bone]

Hi Parnelli, actually I use the circular track on Twin Ring Montegi (cos it's a shorter lap so there's less time to wait before getting the results). Same deal as Test Course, though, get up to the required speed at the start of the straight and them slam on the brakes. I take care to be on the same line (how low or high you are in a corner), but not so worried about distance along the track because it's all just one long straight so that doesn't make a difference. It usually works out similar within 20m though anyway.

Repeated tested with the same settings gives the same result, so I'm confident this method works.

Cool. I should figure out how to do this. I always just drive to 100 mph, slam the brakes while downshifting at the appropriate moments, and then compare the time it took from 100 mph to zero mph (by pausing). Didn't know there was a reliable way to calculate distance. 👍

 

[PF]

If you're doing a statistical analysis PB, surely you should be using AT, not MT, to make the results more consistent.

 

[nomis3613]

If you're doing a statistical analysis PB, surely you should be using AT, not MT, to make the results more consistent.

Actually, if you don't start braking in the same gear each time and don't downshift it's fine to use manual. I get the same results (down to 0.5m, the minimum resolution that the data logger is capable of) every time using MT.

 

[Parnelli Bone]

If you're doing a statistical analysis PB, surely you should be using AT, not MT, to make the results more consistent.

Yea I see what you're saying, and I've thought about it. My results don't have to be super accurate, as I'm not officially posting results here at GTP; I merely use brake testing as I review cars for my website. Using automatic trannies might make a tad bit of difference, but I'm more interested in getting a figure that's in the ballpark.

Plus, I like imagining each car I drive in GT4 really is an automatic or a manual. I don't like switching around from one to the other in the same car...it makes the game feel fake to me.

Plus, I'm pretty consistent with my tests. I've been playing Gran Turismo for years, and can nail downshifts fairly accurately without hitting the RPM limiter.