Hey Tom, F&L GoR a question

[Catwood]

Lots of talk on brakes recently.

What's the educated guess on the amount of grip in terms of Gs that a good Toyo can handle in straight line braking? I'm pulling about a G now with occasional slippage (seen as an upward spike towards +Gs) I suspect in the rear. (the slippage may be bumps in the track also)

In other words, how much brake can I add until the tires become the limiting factor.

 

[Tom F&L GoR]

I don't think I'm educated enough to know that one. Magazines write about cornering Gs just over 1.0 on street tires, so I would have guessed that braking (or cornering) with racier tires would be higher Gs. If you have an accelerometer, how high are cornering Gs?

I'm going to guess again and say braking could produce higher Gs than cornering because in a corner, the rear wheels are also asked to push as well. Therefore they can't devote all effort to one direction, which in braking they could.

But then again, wheel alignment under cornering is designed for best cornering. Under extreme braking you might produce toe out and more camber, which may limit braking... (I don't think people get an alignment for best braking.)

The obvious dumb answer to how much brake to add - can you lock them up now? If yes, then you have enough brake and need more tire.

If you have the equipment to try again, leave the clutch engaged. Asking the rear brakes to also decelerate the engine will lessen their impact on decelerating the car weight and you can perhaps judge whether the rears are locking or not.

Lime Rock Park in Connecticut has a 140MPH to 70MPH (I think 70, but I am never looking) and under braking my car dances. As each tire rises and falls over the uneven pavement it gets more and less grip. It's very interesting how it affects the yaw of the car - happens quickly enough I can't really keep up with it, but happens sufficiently to each wheel that on average the car stays straight.

Iridium on this board has experience with Toyos, Vipers, 40mm rears, and an accelerometer. We'll have to page him, too.

 

[Catwood]

I'm showing 1.5Gs cornering and only 1G in braking as a peak. Part of that could be skewed due to banking both on camber and off camber on the track and downhill braking. My hardest and longest brake zone is from mid 140 to ~90ish and I seem to get pretty a pretty consistent negative rise to 1G.

The Accelerometer has to remain flat to ground or else it will add or subtract a false value. This is hard to do on a course going over hills, with banking and the pitch of the car itself.


I suspect I could lock up the tires but my fear is and always would be only one tire. I do stand on the brakes pretty hard and have locked up one or two. That's more a problem when the pads haven't come up to temp and tend to be a bit more grabby. Once they heat up they seem to have a nice transition in bite. I'm also not one to slam them down but more of a quick press and build pressure. Although I tend to brake fairly late, I also have a tendency to over brake. As I gather more data I'll be able to correct. One thing I did learn from the first time to the second time was that I could go harder on the brakes. My deceleration ramp is now quicker. However my peaks braking Gs did not seem to increase even with a more aggressive pad.

The alignment for braking is an interesting comment and a cause for something to consider.

I'm always in gear during braking but I have the bias valve. I appreciate the dancing aspect and have faced that several times. The last time out I took 1/4 of a turn out and the rear settled down quite a bit. I always thought I was on the verge of rear locking. I probably could have taken some rebound out of the rear shocks also but didn't for fear of the effect of cornering.

I'm fasinated by all the little nuances that truely have an effect and one of the reasons I haven't jumped on making major changes.

I don't think I'm educated enough to know that one. Magazines write about cornering Gs just over 1.0 on street tires, so I would have guessed that braking (or cornering) with racier tires would be higher Gs. If you have an accelerometer, how high are cornering Gs?

I'm going to guess again and say braking could produce higher Gs than cornering because in a corner, the rear wheels are also asked to push as well. Therefore they can't devote all effort to one direction, which in braking they could.

But then again, wheel alignment under cornering is designed for best cornering. Under extreme braking you might produce toe out and more camber, which may limit braking... (I don't think people get an alignment for best braking.)

The obvious dumb answer to how much brake to add - can you lock them up now? If yes, then you have enough brake and need more tire.

If you have the equipment to try again, leave the clutch engaged. Asking the rear brakes to also decelerate the engine will lessen their impact on decelerating the car weight and you can perhaps judge whether the rears are locking or not.

Lime Rock Park in Connecticut has a 140MPH to 70MPH (I think 70, but I am never looking) and under braking my car dances. As each tire rises and falls over the uneven pavement it gets more and less grip. It's very interesting how it affects the yaw of the car - happens quickly enough I can't really keep up with it, but happens sufficiently to each wheel that on average the car stays straight.

Iridium on this board has experience with Toyos, Vipers, 40mm rears, and an accelerometer. We'll have to page him, too.

 

[REDSLED]

I'm fasinated by all the little nuances that truely have an effect and one of the reasons I haven't jumped on making major changes.

Carl, I can think of another reason and it is a 5 letter word that starts with a "P" and ends with a "Y"

Why not ask the racers who actually drive the same track that you speak of and drive GTS race cars? Hmmm..... You can run 1:30's at WSIR with your stock set up on Pilot Sports no less! Turn 8 and 9 are the keys to this.

 

[Catwood]

Sled...you're my idol and when I grow up I want to be just like you (except for the Principle part)

Actually I think my problems are all the turns but 8.


The next time we are Willow together let's put my data acquisition system in your car and see the differences.

Carl, I can think of another reason and it is a 5 letter word that starts with a "P" and ends with a "Y"

Why not ask the racers who actually drive the same track that you speak of and drive GTS race cars? Hmmm..... You can run 1:30's at WSIR with your stock set up on Pilot Sports no less! Turn 8 and 9 are the keys to this.

 

[Tom F&L GoR]

I may have to learn something about this.

Here's a link to an AX run with a g-meter. The driver achieved 1.3 - 1.4 cornering Gs and 0.9 braking Gs.
http://www.napylon.com/short1099.htm

Here's another. 1.2 cornering, 0.85ish braking.
http://www.performanceinsider.com/articles/articleDetail.cfm?articleID=64

About halfway down is another with 1.5-2.0 cornering, 1.0 braking.
http://www.advantagemotorsports.com/WS.htm

I suspect it's the wheelbase is longer than the car is wide. In cornering, the lateral weight transfer leaves a greater percentage of weight on the inside tires than braking leaves on the rear tires. Consequently in cornering you get more total work out of the four tires than in braking. It might also be that the front tires are often smaller than the rear tires.

If you get more data, please share. To see if the above theory has any merit, you would have to measure ride height at each corner and translate that into pavement load. Good luck!

 

[kcobean]

I may have to learn something about this.

Here's a link to an AX run with a g-meter. The driver achieved 1.3 - 1.4 cornering Gs and 0.9 braking Gs.
http://www.napylon.com/short1099.htm

Here's another. 1.2 cornering, 0.85ish braking.
http://www.performanceinsider.com/articles/articleDetail.cfm?articleID=64

About halfway down is another with 1.5-2.0 cornering, 1.0 braking.
http://www.advantagemotorsports.com/WS.htm

I suspect it's the wheelbase is longer than the car is wide. In cornering, the lateral weight transfer leaves a greater percentage of weight on the inside tires than braking leaves on the rear tires. Consequently in cornering you get more total work out of the four tires than in braking. It might also be that the front tires are often smaller than the rear tires.

If you get more data, please share. To see if the above theory has any merit, you would have to measure ride height at each corner and translate that into pavement load. Good luck!

Could it also be that the design of the tread blocks (shape, pattern, etc) and the sidewall construction allows the tire to absorb more energy laterally rather than longitudinally?

 

[Tom F&L GoR]

I believe the Toyos are roughly square tread blocks and would have similar stiffness in either direction. I could be wrong, but cornering will load the outside sidewall differently than the inside and the resulting contact patch always looks like a teardrop. In braking it looks more like an oval, and could be (?) better distribution of contact pressure. Interesting question, I hope we find out more about it.

 

[Catwood]

Mine were shaved and used. Not much in terms of "tread block". More like a thin grove around the tire in a few places.

I believe the Toyos are roughly square tread blocks and would have similar stiffness in either direction. I could be wrong, but cornering will load the outside sidewall differently than the inside and the resulting contact patch always looks like a teardrop. In braking it looks more like an oval, and could be (?) better distribution of contact pressure. Interesting question, I hope we find out more about it.

 

[SoCal Rebell]

Sled...you're my idol and when I grow up I want to be just like you (except for the Principle part)

Actually I think my problems are all the turns but 8.


The next time we are Willow together let's put my data acquisition system in your car and see the differences.

There are actually 2 lines around turn #8, the line you take and the "race" line, IMO the race line is faster and requires precise braking to hit it right but can knock a full second alone off your time. Last time out with you, you were off line in a few places. Let me know next time you go and have time for me

Let Jonathan show you Buttonwillow, I'll show you Willow Springs

 

[Catwood]

No brakes in 8, do you mean turn 2? I think I give up alot there, especially for the amount of time spent in the turn

 

[SoCal Rebell]

No brakes in 8, do you mean turn 2? I think I give up alot there, especially for the amount of time spent in the turn

I already showed you the correct line in #2 you can only go as fast as your tires allow, you should be in a 4 wheel drift, mid track decreasing the radius at the 2nd "Dunlap" sign, full gas at that point. Into #8 no brake just breath the gas to transfer weight to the front to turn on street tires. Instead of tracking out on #8 into #9 you track in full throttle in a straight line to track's end and brake hard and at tracks edge turn right to the apex of #9. In a race this protects your inside from a pass and is actually faster since you're flat on the gas to the edge, it takes some getting used to and you have to be exact in your braking point.

 

[Catwood]

Ah...I see. Stay in and cut across braking towards #9 turn in point. When I track out I do wait along time before turning into 9. I think I see what your doing and can see how the momentum cars could get inside...interesting change. scary to think but interesting.

 

[SoCal Rebell]

Ah...I see. Stay in and cut across braking towards #9 turn in point. When I track out I do wait along time before turning into 9. I think I see what your doing and can see how the momentum cars could get inside...interesting change. scary to think but interesting.

Yup that's it, John Dearing showed me that line, took me a couple of sessions to get used to it because it is scary, you are carrying all that speed into #8 and then staying flat out straight to tracks end. You are carrying alot of momentum that's why the braking part is important, especially in a non-ABS car, I locked them a couple of times and thought I was gonna go straight off #9 but that's when I was learning and braking early and had wiggle room. When you get it right it's easy, you fly, brake hard the weight transfers for the turn and you're right back full on the gas as soon as the car turns for the apex of #9 and track out. With my 3.55 gears I was in 4th the whole time, you may have to experiment with downshifting to 3rd for the turn or maybe the torque will pull you through with the 3.07 gears.