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Kirkham Motorsports

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  #1 (permalink)  
Old 07-30-2020, 10:20 AM
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Default How not to brake for a corner, newbies pay attention

Hi,

It is important not only to show the good things that you have done, but also the bad. While at Lime Rock Park last week I was experimenting with the track, trying to get familiar with it and trying new lines. I was coming into Big Bend, turn 1, and new that the closest cars to me were several hundred yards behind. so, I came in a little faster and deeper then previously and rather than smoothly engage the brakes, I stabbed them. This video will show how quickly things can go wrong with these cars. I just about broke my right thumb fighting the skid and once I had the car pointing straight I took it off into the grass to get out of the way of any oncoming cars. The curb to the inside is quite high and upended the car some when the tires hit it.

It is also probable that I did not blip the throttle when downshifting from 3rd to 2nd, as when listening to the video I do not hear a little rise in the rpms while I am downshifting. That would also explain why the rear locked up as well.

Watch and learn. People on this site are not kidding when we say that these cars can switch ends in a hurry.

https://youtu.be/C7587fT5j18

Jim
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Last edited by 1795; 07-30-2020 at 01:31 PM..
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Old 07-30-2020, 12:36 PM
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Originally Posted by 1795 View Post
Hi,

It is important not only to show the good things that you have done, but also the bad. While at Lime Rock Park last week I was experimenting with the track, trying to get familiar with it and trying new lines. I was coming into Big Bend, turn 1, and new that the closest cars to me were several hundred yards behind. so, I came in a little faster and deeper then previously and rather than smoothly engage the brakes, I stabbed them. This video will show how quickly things can go wrong with these cars. I just about broke my right thumb fighting the skid and once I had the car pointing straight I took it off into the grass to get out of the way of any oncoming cars. The curb to the inside is quite high and upended the car some when the tires hit it.

It is also probable hat I did not blip the throttle when downshifting from 3rd to 2nd, as when listening to the video I do not hear a little rise in the rpms while I am downshifting. That would also explain why the rear locked up as well.

Watch and learn. People on this site are not kidding when we say that these cars can switch ends in a hurry.

https://youtu.be/C7587fT5j18

Jim
So right and fortunate. Light weight and high power, It all happens too fast.

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Last edited by desgros@vtlink.; 07-30-2020 at 12:42 PM.. Reason: spelling
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Old 07-30-2020, 12:37 PM
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Wow - that was scary to watch and I can't believe how quickly it happened, and seemingly without warning!!! Glad everything turned out okay except for maybe some extra cleaning of the racing suit? Thank you for sharing - it makes you realize how quickly these cars can "turn" on you.
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Old 07-30-2020, 12:44 PM
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What's amazing is the amount of thought that I had during those few seconds. I was planning, thinking about where the other cars were and where I wanted to be and had time to decide that I should get the car off the track to the outside and drove it onto the grass to get out of everybody's way. I think that it was more reaction time than anything else. I just reviewed the speed on the video and I was doing 88 mph when the spin started. Things happen fast when you are going fast.

What allows me to race is that those things will make me think that I do not want to do that again, but they do not scare me enough to stop racing. I came off the track after that lap to check the underside of the car to make sure nothing was damaged, which luckily nothing was, and was back out driving fast for the next session.
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Old 07-30-2020, 12:55 PM
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It is also probable hat I did not blip the throttle when downshifting from 3rd to 2nd, as when listening to the video I do not hear a little rise in the rpms while I am downshifting. That would also explain why the rear locked up as well.
I watched your video several times and that's what I came away with thinking. Now, if anyone would know, it would be Morris. Hopefully he'll spot this thread.
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Old 07-30-2020, 01:12 PM
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Hi,

... It is also probable hat I did not blip the throttle when downshifting from 3rd to 2nd, as when listening to the video I do not hear a little rise in the rpms while I am downshifting. That would also explain why the rear locked up as well ...


Jim
I am not sure which was the greater whoops, Jim. Stabbing the brakes or down shifting without matching engine rpm and vehicle speed. Intuitively I want to say the down shift without matching the engine rpm to the vehicle speed but I am not smart enough about those things to know with any degree of certainty.

Great learning experience, thanks for sharing. Quite a ride and great recovery!


Ed
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Old 07-30-2020, 01:21 PM
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It looks like a combo of both caused the rear to get light and then break loose as the clutch was released without rev matching.
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Old 07-30-2020, 01:34 PM
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Jim,
I doubt it was the braking, unless you already noted it pulling hard or lockup under braking previously. Is your car equipped with a brake bias adjustment? Like you summarized, not rev matching more than likely caused the hard clutch engagement and rear end to lose traction. Do you heal and toe routinely under braking/downshifts? Or are you simply blipping the throttle on downshifts where braking isn't needed?

~Steven
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Old 07-30-2020, 01:34 PM
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When I first started autocrossing my VSE ...my first event was at the rolling prairie high school parking lot in northern Indiana. The lot is not really big and it is ancient asphalt with lots of cracks filled. I had on oldish treaded street tires....then it began to drizzle.

I came off a right hander and then there were two or three s curves. I was fine until I hit the s curves then spun comprehensively. I ran that corner five more times and spun again in four of them each time a little further down the course. I decided that with the large engine and only 2000# weight that just letting off the gas too abruptly was like locking the rear brakes.

I solved it by setting up the idle a bit and never letting off the gas much but trail braking. The Hoosier slicks helped too.
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Old 07-30-2020, 01:40 PM
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Originally Posted by eschaider View Post
I am not sure which was the greater whoops, Jim. Stabbing the brakes or down shifting without matching engine rpm and vehicle speed. Intuitively I want to say the down shift without matching the engine rpm to the vehicle speed but I am not smart enough about those things to know with any degree of certainty.

Great learning experience, thanks for sharing. Quite a ride and great recovery!


Ed
Ed,

When you are on the track you do not necessarily know how fast you are going, the speedo is not hooked up. It's more of a sense of how fast you are going. My guess is that coming in at that speed into that corner might have caught me a little off guard and disrupted my normal routine. Not sure that at that speed I could have rev matched it in 2nd gear even if I did blip it. Second Strike for my setup has 88 mph in second gear at about 6600 rpms and I may have been going faster than that when the clutch was let out. I should have kept it in 3rd until I had slowed more.

Patrick,

Morris will definitely be able to add some wisdom to this one.

Jim
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Old 07-30-2020, 01:44 PM
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Originally Posted by CSX 4133 View Post
Jim,
I doubt it was the braking, unless you already noted it pulling hard or lockup under braking previously. Is your car equipped with a brake bias adjustment? Like you summarized, not rev matching more than likely caused the hard clutch engagement and rear end to lose traction. Do you heal and toe routinely under braking/downshifts? Or are you simply blipping the throttle on downshifts where braking isn't needed?

~Steven
Steven,

I heal and toe routinely on downshifts. I think that I either forgot or did not blip it enough. Also, as I stated in a prior post, was probably going to fast to downshift into 2nd at 88 mph probably could not have blipped the rpms that much to speed match. Should have trail braked into the corner more and then downshifted. Thanks.

Jim
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Old 07-30-2020, 02:46 PM
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I used to race with Morris in IMSA and SCCA in the 1980's.
Either you didn't blip the throttle enough or you shifted too soon. Braking didn't look that extreme unless your bias bar was set way to the rear.

Last edited by SwiftDB4; 07-30-2020 at 02:54 PM..
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Old 07-30-2020, 02:53 PM
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I used to race with Morris in IMSA and SCCA in the 1980's.
You didn't blip the throttle enough. Braking didn't look that extreme unless your bias bar was set way to the rear.
The bias bar is set towards a front bias. It was the rear end locking up due to too high of an rpm differential. My initial thought at the time was that I hit the brakes too hard, but I was not able to review the video at the track and it was not until I returned home that I was able to watch it.
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Old 07-30-2020, 03:29 PM
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Looking at the video again you did react pretty well with enough opposite lock to avoid a total spin and get your car off the track safely. I used to race light formula cars with lower power and matching revs on downshifts was pretty forgiving. Our cars with high power and around 2500 lbs weight are definitely touchier with downshifts.
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Old 07-30-2020, 04:24 PM
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Thanks. Appreciate the feedback. I did my race school with Formula Fords and they were way more forgiving than a cobra. the short wheelbase comes into play as well.
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Old 07-30-2020, 04:57 PM
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Glad you're ok, 1795.
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Old 07-30-2020, 05:39 PM
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Thanks Rod. We learn more from our mistakes than we do from our successes.

Jim
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Old 07-30-2020, 06:04 PM
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Hi,



It is also probable that I did not blip the throttle when downshifting from 3rd to 2nd, as when listening to the video I do not hear a little rise in the rpms while I am downshifting. That would also explain why the rear locked up as well.
I concur that the throttle matching was probably the root cause. I listened through it and there was no change in engine sound at the time you moved to the shifter. A case of trailing throttle oversteer.

Happened to me once while I was turning so I exacurbated it by already being "off center".

Rev matching is hard on the Cobra (at least the CSX) because the throttle and brake are horizontally spaced to make it difficult in addition to being vertically offset. It was real easy to miss the throttle
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Old 07-30-2020, 06:29 PM
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The formula ford does not have a limited slip so if you make this mistake you only break traction with one wheel....much more forgiving.
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Old 07-30-2020, 07:05 PM
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Thanks Rod. We learn more from our mistakes than we do from our successes.

Jim
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