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2Addicts | BMW 2-Series forum Technical Topics Tracking / Autocrossing Bridgestone RE71r 235/45 17 for Auto X

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      06-23-2019, 11:37 PM   #45
TajoMan
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Quote:
Originally Posted by bryan_G01 View Post
Tajo, brake much later and harder. your wheels should be screeeching around every turn.
Thanks for advice. (at least it was too early brake, not too late brake, haha)
I knew in theory but easier said than done.

Much higher speed than auto x kinda got scared.

Now I noticed that the traction control didn't even kicked in.
(left it in sports+. Normally on Auto X, always TC fully off)

Next time....

Last edited by TajoMan; 06-24-2019 at 12:07 AM..
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      06-24-2019, 06:53 AM   #46
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Quote:
Originally Posted by TajoMan View Post
Much higher speed than auto x kinda got scared.
That's a healthy reaction. Matching driving skills to speed is the challenge and what will keep you on the driving surface.
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      06-24-2019, 06:55 PM   #47
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Quote:
Originally Posted by bryan_G01 View Post
Tajo, brake much later and harder. your wheels should be screeeching around every turn.

looks like tons of fun, more like a Time Attack than an autox.


Interesting, the instructors last weekend told me that I need to trail brake as I enter turns and slowly release, inducing understeer with too much speed is actually slow. I mean it sounds cool and is really fun but very hard on the equipment and if I can gain a few tenths by being smoother why not.

Like the vids Tajo!
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      06-24-2019, 09:16 PM   #48
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2 of the tires have abnormal wear.

This happened during the Auto x school in April when I did 26 runs almost back to back.
Front 2 tires were like this. (one is worse)

I saw similar wear from other cars with RE71r as well.
It seems like it's due to overheating the outer edge with lack of proper camber.

I guess I have to keep my eyes on it.
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      06-25-2019, 08:50 AM   #49
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Quote:
Originally Posted by Pairadime View Post
Interesting, the instructors last weekend told me that I need to trail brake as I enter turns and slowly release, inducing understeer with too much speed is actually slow. I mean it sounds cool and is really fun but very hard on the equipment and if I can gain a few tenths by being smoother why not.

Like the vids Tajo!
These aren't incompatible, they are discussing different parts of the braking event. Bryan is referring to good threshold braking (brake onset), and not overbraking to slow more than you need to (keep 'em 'squealing' by maintaining enough speed that they are in slip angle - but some R compounds don't actually squeal much). The instructors advice on trail braking is referring to the brake release point and weight transfer, using the trailing brake to maintain more front weight up to the apex. I'm more familiar w/ tracking than autoX, but I know there are some distinctly different theories or approaches to this, with controversy covering the full range (i.e. trail braking is ideal vs. the worst thing you can do). I've heard from many sources that brake release and weight transfer through the turn are the key issues to focus upon, both timing and how you release.
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      06-25-2019, 04:32 PM   #50
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When you hit the brakes, hit them like you mean it! Stand on them... You should be able to go from 130 to 60 in less than 2 seconds and dip into the apex. As you push your braking reference point further to turning point, thats when your going to want to trail brake into the turn.... It assist with the understeer. You can even learn ho to left foot brake to help.

As shown here in turn 1 of LRP:
https://www.facebook.com/bryanduncan...6219213296457/

same turn, track from in car: https://www.facebook.com/bryanduncan...2585834664262/


Using brakes for weight balance and distro is an entire conversation by itself, but as you progress as a driver, and learn your cars characteristics, knowing how and when to break to setup for a turn is good for a couple of seconds. LRP is my favorite spot as its semi local, and if you mess up 1 turn, your whole lap is wrecked.
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      06-25-2019, 08:35 PM   #51
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Quote:
Originally Posted by Pairadime View Post
...the instructors last weekend told me that I need to trail brake as I enter turns and slowly release...
This is turn-dependent. Some tracks call for very significant trail-braking; in comparison, some call for very little.

At the risk of way too much information, examples follow below. Each is a high-speed, former F1 track.

The first is Mont Tremblant, a track requiring modest trail-braking, including two turns requiring only a short, sharp press of the brakes. The steering wheel is off by 10 degrees to the right in this video.

https://www.youtube.com/watch?v=2e3aaeSGgCI

In comparison to Namerow, note the steepness of the application and especially the release of the brakes in the turn under the Bridge. This despite the fact that both are uphill, straight-line braking zones. The 15 MPH increase in speed accounts for the trail-braking going up the hill to Namerow.




In contrast, Watkins Glen is a very heavy trail-braking track, as shown in the video and the data traces that go with it.

Look how far this professional driver trail-brakes across the track going into many of the turns; he's holding the car at the very edge of the tires' adhesion.

https://youtu.be/NMdnioBa0E

The brake trace of the turns where the driver is trail-braking or more across the width of the track shows just how much and how long he's trail-braking. The reason for the jaggedness of the brake pressure while trail-braking is because in addition to slowing the car as necessary, he's also steering the car with the brakes. That is, the rising and falling brake pressure is keeping the car on a smooth and perfect arc from the turn-in point to final brake release.

At the turn-in point, the car has been slowed only enough to allow it to turn in while maintaining the desired line.

From 1:03 to 1:07 in the video, the data overlay shows the driver using a rising and falling throttle to effect the same type of result, thereby allowing the car to smoothly turn down to the curb in the Carousel. In this car, pressing and releasing the throttle one or two credit card thicknesses was enough to produce the desired result.




Here the driver is shown using the brakes for ~460' going into the Bus Stop, finally releasing them just before he climbs up onto a significant curb at 90 MPH.

The purpose of this breakdown of the Bus Stop's braking zone is to show (generally) how a professional race car driver uses the brakes, especially the throttle-to-brake transition. (Not shown is the transition from no-throttle/no-brake back onto the throttle, which also has a "knee" in the throttle trace (i.e., the driver eases onto the throttle for ~1/10 of a second before fully opening it; on this lap, he reached full-throttle with the steering wheel turned 72 to the left.))

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Last edited by dradernh; 07-15-2019 at 05:25 PM..
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      07-15-2019, 03:48 PM   #52
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Another Auto X last weekend.
Weather was super hot (95F) but spraying water on tires worked pretty well. (didn't feel greasy)



More and more I Auto X this car, I feel like the car is just way under tired.
For the weight and power, it should be at least 255 or 265 (just like M2 or new Supra)

I got the tires flipped today. Inner half looked almost new. lol
(damn camber...)
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      07-15-2019, 04:50 PM   #53
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Quote:
Originally Posted by TajoMan View Post
Does SCCA put Re71r in different class?
I couldn't find anything about Re71r in SCCA rule book.
They are legal in the street classes. I'd say that most serious competitors run them. SCCA rules say that any 200 TW tires that are widely available to all competitors through retail outlets are permitted. See p. 4 of https://dk1xgl0d43mu1.cloudfront.net...pdf?1458856378

Last edited by Bareiss; 07-15-2019 at 04:51 PM.. Reason: To add additional information
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      07-15-2019, 05:15 PM   #54
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Quote:
Originally Posted by Bareiss View Post
They are legal in the street classes. I'd say that most serious competitors run them. SCCA rules say that any 200 TW tires that are widely available to all competitors through retail outlets are permitted. See p. 4 of https://dk1xgl0d43mu1.cloudfront.net...pdf?1458856378
Thanks.

I knew it's legal but someone mentioned it's not.

Basically about 80% of serious Auto Xer runs with RE71r. (14% Rival, and 1% etc.)

Now I am wondering about Yoko Advan A052.
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      07-15-2019, 06:58 PM   #55
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Quote:
Originally Posted by TajoMan View Post
Thanks.

I knew it's legal but someone mentioned it's not.

Basically about 80% of serious Auto Xer runs with RE71r. (14% Rival, and 1% etc.)

Now I am wondering about Yoko Advan A052.
Andy Hollis published a pretty comprehensive test of 200 TW tires in the August issue of Grassroots Motorsports. When Andy says something about tires, you can certainly believe him.
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      07-21-2019, 12:39 AM   #56
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Track sprint #2 by TSSCC.





Thinking about doing a full track day.
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      07-24-2019, 12:39 PM   #57
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I have issues with MP4S where I destroy the outside of it due to lack of camber plus the fact that they love to lose chunks of rubber all at once. Might try these as summer tires (I don't do a lot of mileage) that I leave on at the track a few times a summer...
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      07-24-2019, 05:58 PM   #58
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Quote:
Originally Posted by Gepeto View Post
I have issues with MP4S where I destroy the outside of it due to lack of camber plus the fact that they love to lose chunks of rubber all at once.
That's normal. Between the lack of negative camber and the fact these tires don't like the heat generated by running the car on race tracks, reports such as yours have been coming in for years now. The photos are often pretty dramatic considering that owners plan on driving their cars home from the track.
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      07-25-2019, 12:04 AM   #59
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Quote:
Originally Posted by Gepeto View Post
I have issues with MP4S where I destroy the outside of it due to lack of camber plus the fact that they love to lose chunks of rubber all at once. Might try these as summer tires (I don't do a lot of mileage) that I leave on at the track a few times a summer...
Just be aware, this tire is LOUD.
Also, you can't help the lack of camber. It wears only outer half for track or auto x use.
It's a must to flip after a while.

As long as you don't put too many miles, it will be very good track tire.
(it's as sticky as the R comp 10~15 yrs ago)
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      08-01-2019, 11:51 AM   #60
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Why does it seem like everyone is running on 17s? Is it more preferred over 18?
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      08-01-2019, 02:44 PM   #61
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Quote:
Originally Posted by Two4me View Post
Why does it seem like everyone is running on 17s? Is it more preferred over 18?
They're lighter and cheaper than 18s, so they've got that going for them.

When it comes to wheels and tires, the issue with these cars is fitment. My requirement for the track was 255s front and rear, and you can see in my signature what I came up with for a solution.
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      08-12-2019, 11:01 AM   #62
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Another Auto X with CCSCC.
After 130+ Auto X runs, tires still have about 30~40% left.






After this tire, I want to try Yokohama A052.
According to Tirerack's test, it is even faster than RE71r.
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