Changing gear ratios

[stu112]

Hi guys. I've been watching the FP sessions for the Spanish GP and there has been quite a bit of talk about gear ratios (i guess there's always talk about how long to make 7th gear in relation to DRS) and it made me wonder how do they "lengthen" or "shorten" gears? Is it a case of swapping cogs or are there settings that can be changed without touching the gearbox or is it something else in the drive-train that gets adjusted? I guess this question doesn't just apply to F1, but all formulas of motor sport.

Stu

[Jersey Tom]

Pretty straight forward... the gears themselves are replaced - either internally or the final reduction.

[matt21]

They are changing the gear-pairs. Otherwise you would need a CVT, which is forbidden.

[Agerasia]

The gear pairs can be changed easily.
One thing to note is that altering the final drive alters all gears up or down.

[autogyro]

The gear pairs can be changed easily.
One thing to note is that altering the final drive alters all gears up or down.

It also widens or narrows the rev drop between shifts.

[riff_raff]

They are changing the gear-pairs. Otherwise you would need a CVT, which is forbidden.

Just a minor point, but it is possible that only one gear in the mesh must be changed. It is possible to design two interchangeable involute spur gears which have slightly different numbers of teeth (for example 30T and 31T) that will both mesh with a common mating gear mounted on the same shafts. Changing one gear by a single tooth count gives a much finer selection of ratios than changing both gears.

http://www.hewland.com/svga/ratio_list.htm

riff_raff

[xxChrisxx]

They are changing the gear-pairs. Otherwise you would need a CVT, which is forbidden.

Just a minor point, but it is possible that only one gear in the mesh must be changed. It is possible to design two interchangeable involute spur gears which have slightly different numbers of teeth (for example 30T and 31T) that will both mesh with a common mating gear mounted on the same shafts. Changing one gear by a single tooth count gives a much finer selection of ratios than changing both gears.

http://www.hewland.com/svga/ratio_list.htm

riff_raff

Gears need to be mated with the same tooth module. (tooth size basically)
http://www.tech.plymouth.ac.uk/sme/desn ... nomen1.htm

module = reference diameter / number of teeth

As you need to keep the same module for a gear mesh, if you increase the number of teeth, you increase the physical size of the gear and thus the distance between shaft centers.

As the distance between shafts are fixed you must change gears in pairs. As one gear increases a tooth (gains diameter), you have to lose a tooth on the other (lose diameter) to maintain the shaft centers.

[munks]

One might also note some related rules for F1 gear ratios, since you can't just choose any ratio at any time:

From the Technical Regulations:

9.6.2 The maximum number of numerical change gear ratio pairs a competitor has available to him during a Championship season is 30. All such gear ratio pairs must be declared to the FIA technical delegate at or before the first Event of the Championship.

And from the Sporting Regulations:

28.6.d) At each Event seals may be broken once, under supervision and at any time prior to the second day
of practice, for the sole purpose of changing gear ratios and dog rings (excluding final drives or reduction gears). Competitors must inform the FIA technical delegate which ratios they intend to fit no later than two hours after the end of P2. However, one additional change of ratios and dog rings will be permitted if a gearbox change is necessary on the first day of practice before the end of P2. Gear ratios and dog rings (excluding final drives or reduction gears) may also be changed under supervision for others of identical specification at any time during an Event provided the FIA technical delegate is satisfied there is evident physical damage to the parts in question and that such changes are not being carried out on a systematic basis.