I went to school for automotive technology and this is a common misconception/mixup. Actually, helical cut gears are stronger, however they create a lot more heat because of the axial thrust and radial thrust they produce under especially high torque. The bearings in the transmission, then, must be that much stronger to withstand especially the axial thrust loads. However, the gear itself is strong because the area of the base of the gear tooth is much larger than the area of the base of a tooth on a similar in size straight cut gear It may seem backwards then that straight cut gears are used in high torque applications, such as semi trucks and race cars. This is because straight cut gears run much cooler because they do not create axial thrust loads. The other advantage is the bearings and the transmission case does not have to be designed to withstand the axial thrust loads that helical gears produce. This lightens the transmission and is cheaper to manufacture. Straight cut gears in and of themselves are a bit cheaper to manufacture as well. The best of both worlds is a herringbone cut gear, which has a V-shape to its teeth which means it has a large surface area for strength, but has no axial thrust load. These types of gears are used in applications such as high end supercars and hypercars. This cut is very expensive to manufacture.
Ryan Vincent Before I piped in on the axial thrust of helical gear sets, I wanted to check if anyone hit it already. You did and well stated. I can only add that the axial thrust also costs efficiency as it absorbs power (the heat you mentioned).
xXxMartin96xXx I think he reads off a script because he doesn't know much about mechanics or electronics. The other time a few weeks ago Scotty kilmer fucked him up for good on a video
I drive a semi truck and most of the time, I am floating the gear, I drive a 10 speed tranny, with a air flip between 1 through 5 and 6 through 10. Usually, only when I stop do I use the clutch. In heavy sudden traffic, hard on the brakes, then double clutching is handy, but then, you can always clutch out of gear, and then match revs with truck speed and float it into gear. Much like a race car, the semi doesn't have synchros and has straight gears. Unlike a race car, this is not for slamming gears to take off and race, this is to pull 80000lbs up grades as steep as 7%. Just like a race car, the semi whines, but that again is the straight gears. Great videos guys, keep them coming. Would love to take my performance driving to the next level, but sadly, I drive over the road, all 48 states. On the road almost all month.
I want to point out that "straight cut gears" does not mean "no synchros" and crash boxes can have helical gears. Some mixed messages on this nomenclature in the video.
They are talking about 3 different gearbox types: Synchro gearbox where the syncro's's are a brake that synchronizes the speed between the input and output shafts ( double clutching will protect the syncro's) : Dog box where the gear teeth are constantly engaged but there are dog clutches that engage as in all motorcycle gearboxes and heavy truck applications: A crash box is gear on gear engagement of either straight cut gears or helical cut gears it really doesn't matter but they will not engage unless the driver can synchronize the speeds of the input and output shafts at the same time. Double clutching is crucial for crash boxes but thats a whole different subject.
shifting too fast in a normal transmission will wear out your synchros taking a little bit more time between shifts (like .2 of a second) will extend the life of your gearbox I have a spare trans so I've just been thrashing on it lol
So the reason straight cut gearbox is more expensive: *bespoke, more reliable, low demand* In reality, they are much cheaper to manufacture, require less material and are simpler. Herringbone cut gear, is another dog, V-shaped cuts, super expensive to make but supposedly best of both worlds -- these are for hypercars, are stronger, don't have axial load so run cooler.
2:00 Straight-cut gears don't mean you can't have synchros/baulk rings. You're thinking of sliding-gear transmissions, where the whole gear slides in and out of mesh - which use straight cut gears, but are not the only sort of box that uses them. But there's constant-mesh gearboxes that use straight cut gears, and use synchros.
good video, but its a bit misleading when your talking about the cut of the gears and shifting. the cut of the gears has nothing to do with gear engagement, because they are all in constant mesh. you can have a dog engagement box with helical cut gears, or a syncro box with straight cut gears, its just that usually straight cut goes with dog engagement for racing, and helical goes with syncro for street use. showing and talking about exactly how the dog engagement and syncro engagement differ would be usefull, i do appreceate you sort of show the shift forks sliding and engaging the syncro and dog rings, but i dont think allot of people are going to grasp how that actually shifts the transmission. original transmissions as you mention did actually have sliding gear engagement, instead of dogs or syncros, in this case the gear cut would affect engagement. there are a number of different ways manual transmissions work and have worked in the past. most heavy duty truck transmissions work similar to a dog box, as in the gears are in constant mesh and engaged via a sliding clutch, except instead of a dog ring they have a sliding splined clutch that engages the center of the gear. they also have 2 counter shafts to add strength, and are usually straight cut as well as being generally huge compared to automotive transmissions. also, helical cut gears are actually stronger than straight cut given the same size and matereal. there is more mesh surface and thus more strength. the problem is helical cut gears create allot of linnear force as power is applied, because the angle of the gears and their tendency to push in the opposite direction from echother. this linnear force stresses bearings, cases and other components. thats why racing transmissions are generally straight cut.
I understand what your saying , straight cut gears will make the overall gearbox stronger and last longer under load , it's not the actual gear itself that is stronger
Could rally a automatic long term ? Especially if the automatic has a manual mode to request overiding the transmission for ideal gears for any given situations on the rally stage
I have a racing question. I race a Pontiac sunfire 2004. Other drivers have their auto tranny locked just like you would with a rear drive car. I dont know how to do this. Any help would be appreciated. Doug
Hey guys, I am curious about the clutch use with that sequential gearbox. I have watched your video about down shifting without the clutch in a street car but I would still need to clutch to up shift with a stock type transmission. Would the sequential gearbox in this video shift the same way aside from using sequential vs H pattern for changing gears? The mention of flat shifting on pressure to the shifter has me confused as the flat shifting I am familiar with in a turbo car is more of an anti-lag thing and is engaged when I push in my clutch. A quick explanation of how to optimally use the clutch with the sequential gearbox in the video would clear things up for me.Amazing channel by the way! I just found it yesterday and I must have watched about 3-4 hours of video already. Learning a ton of info for Autocross and who knows, I might venture into Rally one day!
Hey thanks for the kind words! So with a sequential, you'd take off in 1st gear using the clutch just like normal. To shift into 2nd, you can use the clutch if you want, but you can also just lift off the gas and pull the shifter, and it'll go into 2nd pretty smoothly. Same all the way up and down through the gears, just lift and shift whenever you want and as long as you're not going way too fast or slow for the gear you want it'll go right in. The "flat shift" feature on some of them is just a momentary throttle-cut switch hooked to the shifter... So when you pull the shifter to upshift it basically lifts for you so you can shift up without ever letting off the gas pedal.
Is it possible to swap the gearing from the race one to the non race one? I prefer shifting vs the sequential. More for the feel vs the time per shift.
You can usually find a beefy race transmission with a normal H pattern shifter. It depends on the car... If it's something commonly raced like a Miata or a Subaru there will be options.
I've seen options on a website for straight gears for a standard Subaru 5 speed transmission that will fit inside and replace factory helical cut gears without modifications to the gearbox , so if you wanted 1st , 2nd , 3rd 4th gear straight cut . But 5th helical cut for long distance driving you can do that , or for any gears you want really. So many options out there
Nope these do not, they will just cut throttle momentarily during a shift but that's it. Some of them might, these ones that we use are fairly simple compared to some of the space-age stuff that's out there.
please tell me you can get strong helical transmissions. Would love to build a decently powerful car (500 - 800) at some point but it would be a daily driver ideally and i couldn't stand the wine of straight cut
There are definitely some pretty strong helical transmissions, but only for pretty specific applications... If you're using an LS motor for example you'll probably have more choices than if you're using something more unusual.
(I'm no expert, so take what I'm saying with a grain of salt but) to expand on Team O'Neil's answer, you may be able to find adapters for different transmissions for your engine as well. For instance, in Nissan-land, if you were, say, running an RB engine out of a Nissan Skyline, there are resources out there to purchase an adapter for it that would allow you to mount a 350Z transmission behind it, which would ideally be capable of holding more power than the stock transmission, while still being a helical box. I also believe adapters exist for mating an LS transmission behind it as well. Google is your friend - try " transmission adapter". You might find something cool out there.
Datamancer sounds good, thx for the added info. I'm gonna be completely honest, all these plans right now are just distant dreams. I don't even own a car yet. Trying to get a better job over summer, then maybe buy a car late fall or next year. Then the upgrades will begin
the zf-6 is a verry strong helical cut transmission. i think its exclusively used in trucks, but i dont see why you couldnt use it in a car if the size / weight works. lots of adapters for these for various engines.
DutchedUp It depends on if you're talking about the input or output shaft. High gears will be small on the output shaft and large on the input shaft (few engine rotations translate to many wheel rotations aka high speed) while lower gears will have larger output shaft gears and smaller input shaft gears (many engine turns to few wheel turns aka low speed and high mechanical advantage).
Can you explain how Andy Forrest's Subaru with a Nissan GTR transmission can engage the clutch for one gear while the previous gear's clutch is still engaged? Why doesn't the whole thing bind up when that happens?
I'm still so confused...this is what I'm referring to here. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9oBfj_D9DGE.html I mean I think I get how it works. One or both of the clutches have to be slipping during the shift, because obviously a wheel can't be turning at two speeds at once. I wonder how the engine matches the speed of the gears, since there's no off power moment. All of it seems very wear-and-tear-heavy, and maybe I'm being too mechanically sympathetic to understand.
We're not super familiar with these because they're not legal to use in rally, but it's super interesting... Not sure how they are swapping clutches with that overlap he's describing, engaging one gear before the previous gear is fully disengaged. Sounds like a recipe for disaster but it must work, wonder how many races they get between rebuilds...
Typical transmissions utilize two shafts (maybe three/four for reverse) - the input and output shaft. These include all of your possible gear combinations constantly meshing, but only one gear is ever tied directly to the input shaft (the gear you are in) through the use of dogs or synchros. DCTs utilize five shafts normally. Two input shafts, two "gearing" shafts and a fifth output shaft. The input shafts and the two gearing shafts act exactly like a normal transmission in that they are in constant mesh with varying sized gears. The difference is that one shaft will have all of the odd gears and the other will have all of the even gears. Which input shaft is connected to the output of the motor is where the dual clutches come in to play. When first gear is engaged, the input shaft in mesh with first gear has its clutch completely closed while the second clutch is open so that the even gear shaft is not being driven by the motor. This allows the transmission to preemptively "shift into second gear" by engaging the dogs. This shift does not affect the output speed of the transmission since the input shaft driving the even gears has the clutch open. Now you want to shift into second gear. Normally one must depress the clutch and shift from first to second, but we've already done so. Instead, we can open the clutch for the odd gear input shaft and close the clutch on the even gear input shaft. Now the engine is driving the input shaft connected to second gear and in turn drives the output of the transmission. During this time, the transmission can guess at which gear you might want next (based on how you're driving) and engage either first or third gear on the odd shaft. The next shift is then simply a matter of swapping which clutch is engaged. This process then repeats defending on whether you are accelerating (continue using higher gears) or decelerating (desire to use lower gears). Hopefully that explanation clears things up a bit!
"Instead, we can open the clutch for the odd gear input shaft and close the clutch on the even gear input shaft." The point I was making was that in this specific time attack car, these two operations happen in the opposite order. The next clutch comes in BEFORE the previous clutch is released. See how that changes things?
Holy shit, Dan, man, you're cute. Also, thanks to both you guys for being informative. Why are straight-cut gears so much stronger than helical ones? Is it a matter of all the forces on a tooth being aligned along a single axis, or something else?
aquaticko the straight cut gears themselves are not stronger, helical cut gears are because they have more mesh surface. the problem is helical cut gears create linnear force on the shaft when engaged, and this stresses bearings and other components more. thats why racing transmissions are generally straight cut, the bearings dont have to deal with linnear force.
