you know that highish pitched whine that builds and builds... of the transmision going faster... well it may be stupid question but why exactly is it... that you can hear that at all times in a race car... but you dont in a road car.. or not very loudly...

its just so different that im wondering there must be a certain thing... not just more power etc... that gives that sound...

thanks...

well besides the gearing im sure is different (has to be to be able to put up with load and whatnot) but i wonder if its also louder because they are made out of a lighter material and thus more sound resonates through them (well.. i dont know if they are made of something else to be lighter or not) but its interesting

Different gears, usually straight cut, sound different.

Yeah, a combination of the two posts above.

Generally race cars are stripped out completely, hence have no noise deadening materials and resonate alot.

Also, road cars gearboxes have helical cut gears, these are very quiet running, but tend to be much weaker than straight cut gears, but because road cars are generally not that powerfull, quietness is more of an issue than strengh, hence road cars having quiet gearboxes.

In a race car strengh is paramount, and noise is not a problem, so they have straight cut gearing to give much more strength.

Some fast road cars, my old Datsun 160J SSS was one, have a straight cut first gear, and the rest helical cut.

I'm not sure how much of a strength advantage straight cut gears give but my understanding was the main advantage was the efficiency of them.

Also cost is a big factor, straight cut are easier/cheaper to produce, but yes, they also offer more directional application of force allowing for less power loss. and higher acceptable loads until failure. Basically making the transmission stronger and more efficient. However though, like noted before, car manufacturers don't use straight cut due to the imense noise the transmission will produce.

i think that whatever resonates that much, in order to be heard thru all the casings and engine noise is under a lot of stress

Also note that in a road car, there is a fair bit of effort put into making the car quieter.

Quote from danowat :

Also cost is a big factor, straight cut are easier/cheaper to produce, but yes, they also offer more directional application of force allowing for less power loss. and higher acceptable loads until failure. Basically making the transmission stronger and more efficient. However though, like noted before, car manufacturers don't use straight cut due to the imense noise the transmission will produce.

That is how it is, there can rather easily be 100kg of sound dampening in a road car, when you remove it there is very lot of more noise, so much that one would not use such car as daily driver, you need to shout at highway speed to be heard.
Difference that makes is just something very few would believe before tested in real. Now add here exhaust that has practically no silencing and transmission that makes so much noise that without ear plugs your ears will hurt two days even you would do just one lap (trust me, you don't like to test it). Plain metal / plastic surfaces of race car interior are also working as inside of some instrument you play, sound vibrations bounce around hitting your ears much more than initial sound alone.

Even with earplugs it is damn loud, you can't yell enough loud when in race car accelerates at full throttle that you could actually communicate with driver/co-pilot, that is why they use helmet radios in rally.

Open wheelers are much more pleasant in this aspect as they are not as loud from driver's place.

so... hang on... the reverse gear in cars... it makes that kinda wine.... does that mean reverse gears and straight cut?

Yes

Always wondered why they whined in reverse!

Wikipedia for the win!

Quote from Wikipedia :

Reverse

The previous discussion applies to the forward gears. The implementation of the reverse gear is usually different, implemented in the following way to reduce the cost of the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the output shaft. However, whereas all the forward gears are always meshed together, there is a gap between the reverse gears. Moreover, they are both attached to their shafts: neither one rotates freely about the shaft. What happens when reverse is selected is that a small gear, called an idler gear or reverse idler, is slid between them. The idler has teeth which mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.

Thus, in other words, when reverse gear is selected, in fact it is actual gear teeth that are being meshed, with no aid from a synchronization mechanism. For this reason, the output shaft must not be rotating when reverse is selected: the car must be stopped. In order that reverse can be selected without grinding even if the input shaft is spinning inertially, there may be a mechanism to stop the input shaft from spinning. The driver brings the vehicle to a stop, and selects reverse. As that selection is made, some mechanism in the transmission stops the input shaft. Both gears are stopped and the idler can be inserted between them. There is a clear description of such a mechanism in the Honda Civic 1996-1998 Service Manual, which refers to it as a "noise reduction system":

Whenever the clutch pedal is depressed to shift into reverse, the mainshaft continues to rotate because of its inertia. The resulting speed difference between mainshaft and reverse idler gear produces gear noise [grinding]. The reverse gear noise reduction system employs a cam plate which was added to the reverse shift holder. When shifting into reverse, the 5th/reverse shift piece, connected to the shift lever, rotates the cam plate. This causes the 5th synchro set to stop the rotating mainshaft. (13-4)

A reverse gear implemented this way makes a loud whining sound, which is not heard in the forward gears. The teeth on the forward gears of consumer automobiles are helically cut. When helical gears rotate, their teeth slide together, which results in quiet operation. In spite of all forward gears being always meshed, they do not make a sound that can be easily heard above the engine noise. By contrast, reverse gears are spur gears, meaning that they have straight teeth, in order to allow for the sliding engagement of the idler, which would not be possible with helical gears. The teeth of spur gears clatter together when the gears spin, generating a characteristic whine.

It is clear that the spur gear design of reverse gear represents some compromises—less robust, unsynchronized engagement and loud noise—which are acceptable due to the relatively small amount of driving that takes place in reverse.

Is it true that the alleged "straight cut gears" are not in the literal sense straight, but of so little degrees of mesh as to justify generalization of the term?

Quote from jayhawk :

Is it true that the alleged "straight cut gears" are not in the literal sense straight, but of so little degrees of mesh as to justify generalization of the term?

At least these look rather straight to me, but I don't have seen very much of race gearboxes disassembled, only few and all those have had similar gears in.

My truck has a gear whine. It doesn't build up like a race car, just through the gear. Dunno if it has straight cut gears though. Its a 92 Ranger.

http://media.putfile.com/exhaust2-9

Quote from ajp71 :

I'm not sure how much of a strength advantage straight cut gears give but my understanding was the main advantage was the efficiency of them.

That's right - straight cut gears are far weeker then helical cut gears but you lose less power in transmission loses. The reason is that helical cut gears are pushing away from each other and this creates the loses. Straight cut gears are not pushing away from each other so all the force is transferred from one cog to the next. The disadvantage is that you are more likely to snap a tooth.

Quote from Gentlefoot :

That's right - straight cut gears are far weaker then helical cut gears

Quote from Gentlefoot :

That's right - straight cut gears are far weeker then helical cut gears

Yeah I always thought the "gear" itSELF was weaker when straight cut, but they're stronger in the way that they don't destroy bearings, or smash gearbox casings by putting load on the shafts. They also can transmit more power because of this, as it's not being wasted loading the shafts.

So they make a stronger gearbox, but more prone to shredding teeth.

Pretty sure the ONLY reason straight cut gears are not used in most non-racing applications is because they're noisy as hell. All other aspects of them are far superior (strength, losses, etc.). Most motorcycles have straight cut gears (not sure but Harley might use helical).

Well over the width of the gear, helical gears area of contact is around 1.5 times more.
I'm pretty sure helical are less prone to shedding teeth, but they do ruin bearings and cases with big throughput, along with robbing power of course, which makes them worse for motorsport. Motorsport drivers are also MUCH more caring of a transmission than the average road user too. Rev matching and all that.

No one abuses the transmission quite like a kid on a sportbike.

afaik its true that straight cuts are weaker
think about what causes the noise in the first place ... its cogs clashing against each other repeatedly which will eventually lead to faliure

Aren't all gearbox gears involute teeth, so there isn't any 'clashing', as each tooth rolls on the next one, reducing wear and peak loads...

I always believed that straight cut gears were stronger and more efficient than helical gears.

As for sideways loads damaging bearings, this won't happen if you stay in the torque range of the 'box, as the bearings will be designed to cope with those side loads. Obviously if you use a 200lbft 'box with a 300lbft engine then you have to expect failures, and only a dunce would do that.