Fight! Mayhem! Disagreement Even!
Ok, so maybe I exaggerate and it’s more like a Gentlemen’s discussion. But it is real and it’s all about shifting.
Now it just so happens that when the NASCAR gods visit Infineon (Sears Point for those of us over thirty) it gets broadcast, being in the first half of the season, on Fox. Beside D.W.’s commentary the absolute coolest thing Fox does during that race is put a camera in a car’s foot-well and do a split screen thingy that lets you see the driver’s footwork as he motors around the track. And of course some of the drivers are banging up, and sometimes down, through the gears without touching the clutch.
Now people who’ve driven a manual transmission built for the street might wonder how they do that. The answer is the race transmission (a dog-box) they use is a bit different than the one in your daily driver. Since I happen to own a racecar, with a Jerico racing transmission, I have the opportunity to happily bang up and down the gears, just like the NASCAR guys, with or without the clutch.
The question is… should I go clutchless?
To be able to discuss it intelligently you first have to know what’s going on inside the drive-train. We need to quickly cover the difference between a race transmission (excluding the exotic F1 style paddle shifters) and the transmission in a daily driver. These can be broken down into three basic things.
First, they use straight cut gears instead of helical gears (see the picture).
The largest single reason to use helical gears in a daily driver is to reduce noise, and we don’t care much about that in a race car. In fact, your street car usually does have one straight cut gear in it. Reverse. So if you were to imagine the sound of going a hundred twenty or so in your car’s reverse gear you get the idea of what a Mazda GT sounds like from inside with the Jerico.
The second difference, and this one is huge, is the lack of a synchronizer mechanism.
To understand what the synchronizer does we first have to dispel a common myth. When you move the shift knob from first to second you are not disconnecting one gear and connecting another. All the gears in the transmission are permanently meshed together. It’s just that the gear on the output shaft is free to spin on that shaft. If the car is in neutral, all (four in my case) gears on the output shaft can spin as they like, (as long as it’s the same speed as the lay-shaft, technically.) What happens when a gear is selected is that you are moving a collar on the output shaft, that has teeth called dog’s teeth (on the dog collar a.k.a. dog-box, you get the idea) that bind that particular gear to the output shaft, forcing the gear to rotate at the same speed as the output shaft, which binds through the gear to the layshaft, to the input shaft, clutch, engine, etc… If you are having trouble envisioning this I recommend the site “How Stuff Works” which has more detail and a great animation of a simple transmission in action.
So, what the synchronizer does is to press against the freely spinning gear, before the dog’s teeth (on the collar which is what you are really moving with the shift lever) engage; which will get the speed of the gear and the speed of the output shaft to be the same. This rewards a slow shift, since the more time it takes to complete a shift the closer the match. By eliminating the Synchro, a race transmission sacrifices some drive-ability and longevity for the opportunity to spend less time between gears.
The third and final difference is a larger tolerance between the teeth themselves and the receiving end attached to the gears on the output shaft. The race transmission has far more “slop” between teeth and receiver.
Now we’ve all ground a gear now and again. What’s really happening is that the Synchro, for whatever reason, didn’t match the speed of the free spinning gear with the speed of the collar and so the teeth are sliding across the receiver rather than getting set in place. They drag, grind, and in the end, probably, finally, pop in place.
This is why a double clutch (clutch out, in neutral, blip the throttle to spin up, then push the clutch back in and select a gear) works when you are having trouble selecting a gear. A double clutch works in the race transmission as well. The better matched the speeds are, the easier the teeth pop into place. But in the race transmission, the extra “slop” between the teeth and receiver make it far more likely that, with a firm pull, the teeth will engage even if there is a difference in speed. One rule then, with a race transmission, that everyone agrees with, is to select a gear quickly and firmly, don’t dawdle. Most race transmission damage comes from shifting too slowly.
Beyond that, there are some different ideas out there.
Clutchless Downshift
I don’t do it. In fact I double clutch on the downshift and skip all the intermediate gears.
If I was to do it, the technique is straight forward enough. You want to pop it out of gear while the pressure on the dog’s teeth is minimal by doing it as you lift. If the car isn’t accelerating or decelerating at that moment it’ll pop out smoothly. With the car in neutral and slowed enough for the gear you are going to select, blip the throttle to spin up the gears speed over the shaft speed for the gear you are going to, and as the RPM drops back down from the blip they will match and the car will plunk down into the gear just so. The biggest and most common mistake here is to try too soon. You can get the car out of gear, brake, brake and brake some more before the blip will get the gears spinning fast enough to match the output shaft for a lower gear. Some drivers avoid this by going down through each successive gear. With a number of fourth to first corners out there that just seems to me to be begging for trouble. Cultivate patience, and then shift just before you need the gear (throttle application) is my preference.
Now the only reason to downshift in the first place is to be in the right gear for acceleration when the time comes. On the street some people aren’t aware, but a race car driver knows, that compression braking (using the engine’s compression to slow the rear wheels) is a very poor technique since it usually involves only two tires and will unbalance the car under threshold braking.
That said; just what is the advantage of a Clutchless downshift? To me it’s just three words, left foot braking.
The traditional heel and toe style reserves the left foot for the clutch while the right does double duty by controlling the brake pedal with the ball of the foot and the throttle with the side. If you don’t use the clutch the driver is free to concentrate his left foot on brake and right on throttle as well as gain the most excellent ability to modulate brake and throttle in opposition to each other (ease the brake off while easing the throttle on). Techniques like trail-braking work better with the superior control you get by freeing your left foot from the clutch. The downside is that if you can’t match the transmission perfectly, any shock transmitted through the rear tires as you downshift is going to unbalance the car. If your rear tires are already at 99% of grip and you ask for another 2% by plunking down a gear, what you’ll get is a spin.
Now when we first got the Jerico transmissions last season I thought about going to left foot braking, but the question quickly became moot. The pedals in my car are set up perfectly for heel and toe, but for left foot braking, not so good. The first time I tried it, going pretty damn quick into the sunset turn at Buttonwillow, my thigh caught on the bottom of the steering wheel wedging it in place. Not being able to turn the steering wheel is generally a bad thing while driving a race car at speed. I could get the pedals and/or seat moved, and try again, but if I give up where the pedals are now I’ll be forced to left foot it, and if it doesn’t work well for me I’m toast. So I decided not to, at least for now.
I don’t think I’m alone since I don’t know of any of the other Mazda GT drivers going left foot. But I’ll ask around. I’m not sure who, other than T.W. is going clutchless on the downshift; it might be everybody but me and Tom.
Clutchless Upshift
Dave does, Bob does, Mark does, Jim does, T.W. does. I did, but last October I didn’t.
Again the technique is simple. Just like with the downshift you need to get the dogs to relax by lifting the throttle. Not enough to slow the car since that will just put pressure on them in the other direction. The gearbox will pop right out under steady pressure applied just before you lift, as soon as the car is neither going faster nor slower. The difference between the clutchless upshift and the downshift is the lack of a double clutch blip on the way up. It’s all one movement from when you relax the dogs with the lift (really closer to a half lift) to when you plunk it into the next gear in one smooth but firm and quick motion. As long as you don’t lift too much or too little, or squeeze the throttle back on before the car gets back in gear, or especially shift too slowly, it’ll go like butter. If you are slow, the relative speed of the output shaft and gear will mismatch and the shift will officially be blown. If you get on the throttle before the teeth are seated the gear will wind up more than the output shaft and the shift is officially blown. If you get it wrong, badly and a lot, you can hurt the transmission, perhaps even knock out a tooth or two which would put paid to the whole thing and create an expensive mess. But it is easy to get right and the Jerico is very tough. So why not do it?
To me it is, like most everything else, a trade off. You may spend a fraction longer in gear (and therefore accelerating) clutchless than by using the clutch (and even that is disputed) but there are two prices to pay for this party.
First, you can lose everything you’ve gained and then some if you miss a shift during a race. Unless you’re a pro who gets to test for hour after hour you’re all too likely to miss at least one of the hundreds of shifts at some point during the weekend. With my luck, I can count on it to happen at the wrong time. Yes, you can miss a shift with the clutch as well, and nothing will save your transmission from damage if you have bad technique, especially, and without the synchro, I cannot put too much emphasis on this, if you shift too slowly.
The second price comes from considering the transmission in isolation. Anything that causes a shock to the drive-train is going to transmit that shock all the way up and down the system. The race car is an amazing collection of rapidly spinning stuff that’s all interconnected. Anything that makes one thing start or stop suddenly is best avoided, since it’ll make everything else start or stop suddenly as well. This means that the best technique might just vary from car to car, since different cars have different weak links (parts voted 'Most Likely to Break') and the best technique might be to minimize the strain on the weakest part.
With the clutch partially disengaged (and if done right you really don’t have the time to fully disengage the clutch) that banging up a gear is more likely to contribute to wear on the clutch, which is preferred over more expensive, and often race ending, types of drive-train damage. The pretty common exception to this rule would be when the clutch is so weak relative to the rest of the drive train that using it will quickly turn it into a bag of broken glass. So I'd assume most of the NASCAR guys will avoid the clutch even though we use the same transmission. But I’m using it, for the moment, for the same reason I'm trying to avoid wheel-hop or excessive off road excursions or banging into curbs; the theory is that it helps keep the car running so I can finish the race. The big question is whose theory is correct?
Dispute
Tom is the only other person I’m sure uses the clutch on upshift. Mark is adamantly opposed, going so far as to send me a link to Hewland’s notes on shifting which supports his position. On the other hand, the most excellent Skip Barber book, ‘going faster’ supports using the clutch, even with a dog-box transmission, except on high horsepower cars where the clutch is the weak link, or when the ratios are close together. We don’t have the horse power or torque of a stock car, and I don’t recall the last time I needed a new clutch, but our ratios are very close.
The major points in the Hewland piece are, first, that you can’t damage the dog teeth while they aren’t in the small gap of time just before being engaged, and second, that using the clutch in a ‘normal’ shift slows the shift which means more time is spent in that ‘danger zone.’ Everyone agrees this is where damage to the transmission happens.
I’m not really experienced or fast enough to dispute a guy who was winning at a level of racing I’ll never achieve, well before I was born, but I’ll try by paraphrasing Skip Barber (If an expert disagrees, find another expert).
The worry is that if a collar is moving when the throttle position changes; clutch out, it’s going to hurt the transmission. The shift lever, that moves the collar, is moving at the same speed regardless of what your feet are doing. If it takes two tenths of a second to do the throttle lift with the right foot, you can spend the same two tenths on the clutch pedal with your left. Dorsey Schrader points out that he uses the clutch, even when it’s broken, simply to stay in rhythm. In the end Skip Barber recommends using the clutch to swap shock to the drive train for clutch wear, except when they don’t (as mentioned, high HP/Close Ratio, etc).
Our clutch can take it, but our ratios are so close that the throttle lift isn’t even really a full lift. Which to me explains why this is such a grey area for the Mazda GT.
In the end I’m not certain where I’ll wind up. It’s even possible the best technique varies from person to person as much as it does from car to car. What I’ll try to do is flesh this, already way too long, post out with as many opinions and techniques on the subject of shifting as I can find, and put them in future bloggy bits. Or I’ll revise and update this post with any comments the other drivers want to make as long as they don’t start with ‘Paul you ignorant [insert swear word]’
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