Seamless Gearboxes (aka blowing in the shifts)

[machin]

Using a higher first gear will result in higher engine rpm than is ideal to achieve maximum tyre grip from that ratio without engine stall. The higher gear will therefore practicaly assure wheel spin in a powerful light F1 car, which will be less controllable than for a lower ratio.

I'm sorry, I can't avoid it again....

Watch an onboard start from an F1 car and you'll see that they all use a long (low ratio) 1st gear:-
[youtube]http://www.youtube.com/watch?v=6EEkMBROgCY[/youtube]

->Notice how the car uses 1st gear up to 100km/hr, and then shifts up rapidly through the remaining gears (Kimi is shifting up to 4th at 175km/hr). The reason is that a shorter gear is harder to control and doesn't confer any improvement to acceleration (since the performance is traction limited and not power limited); i.e. it would be pointless.

The beauty with Physics, as I say, is its simplicity; and simple physics tells us that it is the relative quantities which matter, not the absolutes... therefore trying to use 750bhp on a high grip tarmac surface is exactly the same problem aas using 140bhp on a damp or icy surface. Next time it is damp (or icy) try using 1st gear to pull away, and then try using 2nd or 3rd.... There is a reason that motoring groups advise using 2nd or 3rd in icy conditions, and it is easily described using simple physics.

[bhall]

[...]

->Notice how the car uses 1st gear up to 100km/hr, and then shifts up rapidly through the remaining gears (Kimi is shifting up to 4th at 175km/hr). The reason is that a shorter gear is harder to control and doesn't confer any improvement to acceleration (since the performance is traction limited and not power limited); i.e. it would be pointless.

[...]

This isn't to challenge the veracity of your statement, but it should be said that such shifting is pretty much required by the regulations either way.

9.8.2 Gear changing is restricted during the following periods:

- Race start: one gear change is permitted after the race has started and before the car speed has reached 100kph, provided every gear fitted to the car is capable of achieving at least 100km/h at 18,000rpm.

- Pit stops: No gear change is permitted after a pit stop and until the car speed gets within 10km/h of the pit lane speed limit when leaving the pits.

[timbo]

If you stack them up with say 300ms between each, then changing from 7 to say 3 = 4*(300+300) = 1.8 sec. If the driver can sync that with late braking then that'd give more downforce on the corner entry?

I guess it would, although the primary effect that driver would feel is more stable rear end.

It'd only help on tight corners, they'd not get any benefit on fast bends or a sequence like Eau Rouge or the Susuka S

As Eau Rouge is taken flat out I don't think they have much problem with exhaust flow anyway. Not sure about partial throttle corners, but I guess the most problems they have is on long braking events.

[Richard]

the rules say one gear change is permitted, but Kim made zero gear changes before 100kph.

[autogyro]

The video shows the engine 'bogging' for at least a second as the driver feathers the throttle to prevent excess wheel spin.
The amount of traction at that point was limited by the low revs of the engine.
A lower ratio 1st gear would have resulted in a faster increase in engine rpm and faster acceleration.

Kimi made no gearchanges from start to 100kmh, which shows his gearing was higher than usual for 1st gear.

[bhall]

the rules say one gear change is permitted, but Kim made zero gear changes before 100kph.

As it's been explained to me, "...provided every gear fitted to the car is capable of achieving at least 100km/h at 18,000rpm," limits that allowable shift to short tracks like Monaco and Hungary, otherwise you're stuck in first until 100km/h. The rule was instituted during the crackdown on launch control.

[timbo]

the rules say one gear change is permitted, but Kim made zero gear changes before 100kph.

As it's been explained to me, "...provided every gear fitted to the car is capable of achieving at least 100km/h at 18,000rpm," limits that allowable shift to short tracks like Monaco and Hungary, otherwise you're stuck in first until 100km/h. The rule was instituted during the crackdown on launch control.

I wonder whether it was used to prevent shortshifting and using allowed gearshift gaps to control torque.

[bhall]

If memory serves me correctly - big if - I think the rule was put in place back when teams could change engine maps at-will, and there were concerns that teams were using specific engine maps as launch control. McLaren drivers, for one, used map paddles that were effectively connected to the gearbox paddles to change maps with every shift. So, the idea with the rule was to prevent gear shifts (EDIT: thus map changes) until after the car was more or less up to speed.

(Before that, there was a rule that required the engine map used at the start of the race to be used for a full 90 seconds, the thought being that teams wouldn't sacrifice power for 85 seconds after the benefit of a controlled launch. To get around that rule, however, teams simply selected a start map while on the formation lap about 60 seconds prior to the start of the race. Lesson: the FIA is always a step or two behind.)

[Tommy Cookers]

A vehicle's inertia is a measure of its mass, and, in the case of rotational inertia (applicable to the car's wheels, engine, brake discs, props shaft, etc) the placement of that mass about the component's centre of rotation. For a given gear ratio it is a fixed value whether the car is stationary, moving at a constant speed, or accelerating. Fundamentally the equation F=mA (or A=F/m) is what determines vehicle performance.
The fastest start is achieved when the motive force at the driven wheels exactly equals the tyre's traction capacity... try increasing the force any more than the tyre's limit (e.g. by opening the throttle more or using a shorter (higher ratio) gear) will simply result in wheel spin and a loss of acceleration. If you decrease the force below the tyre's traction limit (by using a longer (lower ratio) gear, or reducing the throttle opening a bit) you are simply giving yourself less force to accelerate the car, and remember A=F/m.

regarding the effect of rotational inertia the engine/clutch inertia has much the greatest effect when the car is in 1st gear
eg in Can-Am or 427 Cobra that inertia can be roughly equivalent to adding a mass doubling the weight of the car
this added mass effect (as described in the quote) is related to the square of the gear ratio
which means with such light, large-engined cars 'shortening' 1st gear below a certain ratio becomes self-defeating
because it gains no acceleration due to the very large added mass effect
(this effect is independent of whether we may have already reached the traction limit by then)
this is part of the reason why you don't have a 40mph 1st gear in such cars

all of this assumes road-style driving ie minimum engine revs as the clutch is engaged
the added mass problem disappears if we use eg max rpm and slip or drop the clutch

PS my source (a book) says the acceleration decreases, I think that it just doesn't increase

[machin]

The video shows the engine 'bogging' for at least a second as the driver feathers the throttle to prevent excess wheel spin.

This is not engine bogging, but simply the driver feathering the throttle to prevent the engine from attempting to develop a motive force above the tyre's traction limit, which would cause the wheels to spin. If the driver were given a shorter (higher ratio) first gear, the car would generate more motive force for a given throttle setting, and therefore the driver would have to feather the throttle even more to prevent wheelspin, there would be no increase in acceleration (in fact, as Tommy points out, it would be even worse due to the higher inertia caused by the increase in ratio between the road wheel rpm and the engine rpm). Added to that the team would be forced to provide a lower second gear to fill the "hole" left by the overly short first gear; widening the gaps between subsequent gear changes and therefore causing the engine to operate out of its ideal range.

The amount of traction at that point was limited by the low revs of the engine.

Traction ("the maximum frictional force that can be produced between surfaces without slipping"), is unaffected by gearing, engine revs, engine power, engine torque, driven wheel power or driven wheel torque. It is a function of the tyres, the road surface, and the "normal" (downward) force acting between the tyre and road surfaces.

Kimi made no gearchanges from start to 100kmh, which shows his gearing was higher than usual for 1st gear.

Whilst a 100km/hr up-shift from 1st would be considered high for a normal car, A long (low ratio) 1st gear is typical for any car which has a high power to weight ratio and therefore is traction limited at low speeds, and therefore would not benefit from a shorter (higher ratio) 1st gear. A typical modification to a hillclimb or sprint car (a discipline in which the start is much more important than a race due to the short run length) is to change the gear ratios for one with a long (low ratio) 1st gear. Alternatively many competitors simply start using 2nd gear, ignoring 1st gear for the reasons given. The following link shows the gear ratios offered by Quaife for their Ford Type E gearbox replacement as used in many Lotus 7 type cars used in competition which have high power:weight ratios (by virtue of their very low weight). The original gearboxes typically come from Ford with a short (3.5:1 or there abouts) 1st gear (with top gear remaining the same at 1:1). Quaife, and all the people buying and using these gearboxes in competition, didn't get their sums wrong.

http://www.quaife.co.uk/shop/products/qbe9z

******

I'm sorry if it feels like I'm picking on you Auto, but I find it hard to take in the rest of your posts when you get the fundamentals so wrong... sorry dude.

[machin]

To get around that rule, however, teams simply selected a start map while on the formation lap about 60 seconds prior to the start of the race. Lesson: the FIA is always a step or two behind.)

That is awesome! =D>

[autogyro]

Thats alright Machin.
I cant answer your post because it is so full of contradictions.

[machin]

Thats alright Machin.
I cant answer your post because it is so full of contradictions.

Please point out these contraditions so we can all learn something.

Cheers.

[andylaurence]

I used to find starting tricky, but switched to a shorter final drive (14 tooth front sprocket to replace a 15 tooth item) and found it much easier to get off the line. With the longer final drive (~70mph in 1st), the car would bog down if I got it wrong. Intriguingly though, the difference in time off the line wasn't much, whether it bogged down or not.

[machin]

Oh I agree Andy; there is definitely a sweet spot... I'm not suggesting everyone pulls away in 5th gear.... as you say that would result in bogging down... "just short enough to allow wheel spin to occur near full throttle with clutch fully engaged" would be my recommendation for first gear selection.... 70mph in first does seem a little high!

The gears represented by green curves in this image show what I would consider to be an "ideal" set of gear ratios for this particular application... The orange curve shows a "too short" (too high ratio) 1st gear alternative which would generate far more motive force than the tyres can handle (as shown by the red curve), and have extra inertia.; i.e. would actually be detrimental to performance.



In reality I'd say go for a slightly shorter 1st than the first green curve shown, this would ensure that on the hot days that you visit a track with a really high grip tarmac you can make full use of that grip by having a little bit of motive force in hand on the "normal" days.