Gearing for top speed on the straights

[hispanicpanic]

So in f1, and really any open wheel series, there is a certain amount of aero you need for an optimal lap time in a track. The amount of aero you run should theoretically determine your top speed on the track's straights. Typically, how do f1 cars choose their gearing for the straights? I had heard once that they choose gearing to achieve top speed in top gear 3/4 of the way through the straight because it provides a higher average speed, but i don't know if this is true.


I ask because i'm getting really heavy in iRacing and am racing in the star mazda series. I am running out of my top gear just past the halfway mark on the longest straight on bathurst, but i'm not sure if it would provide any benefit to extend 6th and tweak aero to allow me to get a higher speed on the straight. I'm not the most consistent driver, so doing a few laps to compare times won't help.

[toraabe]

So in f1, and really any open wheel series, there is a certain amount of aero you need for an optimal lap time in a track. The amount of aero you run should theoretically determine your top speed on the track's straights. Typically, how do f1 cars choose their gearing for the straights? I had heard once that they choose gearing to achieve top speed in top gear 3/4 of the way through the straight because it provides a higher average speed, but i don't know if this is true.


I ask because i'm getting really heavy in iRacing and am racing in the star mazda series. I am running out of my top gear just past the halfway mark on the longest straight on bathurst, but i'm not sure if it would provide any benefit to extend 6th and tweak aero to allow me to get a higher speed on the straight. I'm not the most consistent driver, so doing a few laps to compare times won't help.

I think no, because if you are reaching top speed as soon as possible that is the best solution, but you need to have enough revs left before rev limiter when it comes to slip streaming. So if max rpm is 9000 and max hp at 8500 you should reach 8600-8700 without slip streaming and 8900+ when slip streaming. Just an example. So what you need is to get around the track as quick as possible hence short as possible gears just without hitting rev limiter is the best solution.

[hispanicpanic]

Good point, with a draft i would hit rev limiter just before 1/2 way down the long straight on bathurst. I don't know where peak hp is at on a star mazda rotary, but i would assume 8500, and the limiter is at about 9k i think. The next gearing option i have on my 6th gear gives me about 5 mph more.

As far as 5th gear is concerned, i hit the limiter barely before my braking point on turn 2 without a draft. If i was in a draft coming into turn 2, having a slightly taller 6th might not be a benefit?

I also hit the limiter in 5th a bit before turn 11. In the star mazda with my current aero (low-ish downforce trim), i'm hitting the brakes just at the crest of the hill entering 11. A shift into 6th might be futile here due to the area between 10 and 11 being a solid grade uphill.

I'd like to get everone's thoughts on this. I could probably reduce aero more to take advantage of a 6th gear in the spots mentioned above. My 5th gear also has an option to increase gearing for an additional 3mph, but i haven't had the time to see if my 4-5 shift would put me at a disadvantage in some spots. The constant uphills and downhills make gearing a very tricky animal on bathurst. You don't want to be caught at the bottom of a tall gear going uphill!

[hollus]

Typically, how do f1 cars choose their gearing for the straights? I had heard once that they choose gearing to achieve top speed in top gear 3/4 of the way through the straight because it provides a higher average speed, but i don't know if this is true.

OK, this was true in F1 up to 2013, when they could optimize gearing for every track. They did trade the top speed in a bit of the fastest straight for better gearing everywhere else, which indeed optimized lap time.
This is off topic but in 2015 when gearing is fixed for the whole year, all cars can reach 370 or thereabouts by 13000 rpm in 8th. They lose power by approaching 13000rpm, but never truly become "gearing limited" (they would around 430km/h).

[Phil]

I'd say determing your gearing is very tricky. The optimum would be different on every single track, because each track is different. The one constant that is important is the engine characteristic of your engine. Depending on where maximum power is, you'd want to spend the maximum amount of time where the engine produces the highest power output for the rev-range. Then you also have the drop-off in revs after a gear-change to consider.

As an example; In my car, my revs will drop by 2000-2500rpm per gear-change. So, if I redline in 1st gear at 8500rpm, the engine will drop to 6000rpm as I go into 2nd. If you don't chose your gearing wisely and you drop lower, you will drop out of the "power-range" and it will take longer to accelerate.

Now in a F1 car with 8 gears, obviously you have many gears to spread over the speed range. On a track like Monza, you will want to be able to reach a very high top-speed, so you can't afford to 'red-line' at lower, or you'll be losing out. But you also have to consider that drag and wind resistance quadruples. So you may want your gearing to accomondate that - by using a lower ratio (more torque at the wheel = higher acceleration) to actually get to a slightly lower top-speed quicker than the theoretical max slower. So coming back to Monza - red-lining before the theoretical VMAX on that circuit might still yield a faster track-time in the end if you are shaving off time while accelerating.

Ideally, you want to have good drivability at all times - regardless which corner you are in, or which part of the track, you want to be within a rev-range that produces as much power as possible.

Anyway, F1 is a tricky one to answer because they are limited to I think two sets of gear ratios for the entire season (meaning they can only change it once). So what they choose at the beginning of a season must yield a good trade-off for pretty much the entire season on all tracks.

[Juzh]

Ratios are locked as of melbourne. no change is allowed this year.

[toraabe]

Seems that you only need a slightly longer 6th gear. Your 5th seems to be slightly short, but should be not longer than necessary. You will loose more time when shifting into 6th . And you need to lengthen the 6th to avoid the rev limiter when drafting, but should be as close as possible. Just 50-100 revs left. Then it is perfect. You need to calculate for fastest way around the track.

Good point, with a draft i would hit rev limiter just before 1/2 way down the long straight on bathurst. I don't know where peak hp is at on a star mazda rotary, but i would assume 8500, and the limiter is at about 9k i think. The next gearing option i have on my 6th gear gives me about 5 mph more.

As far as 5th gear is concerned, i hit the limiter barely before my braking point on turn 2 without a draft. If i was in a draft coming into turn 2, having a slightly taller 6th might not be a benefit?

I also hit the limiter in 5th a bit before turn 11. In the star mazda with my current aero (low-ish downforce trim), i'm hitting the brakes just at the crest of the hill entering 11. A shift into 6th might be futile here due to the area between 10 and 11 being a solid grade uphill.

I'd like to get everone's thoughts on this. I could probably reduce aero more to take advantage of a 6th gear in the spots mentioned above. My 5th gear also has an option to increase gearing for an additional 3mph, but i haven't had the time to see if my 4-5 shift would put me at a disadvantage in some spots. The constant uphills and downhills make gearing a very tricky animal on bathurst. You don't want to be caught at the bottom of a tall gear going uphill!

[machin]

Typically, how do f1 cars choose their gearing for the straights?

As has been previously said gear ratios are now fixed in F1, but for pretty much any other championship:

The first step is to create or buy a laptime calculator which takes as its input as much data about the car and track as possible... at some point adding more data only adds a very small % to the accuracy and you can stop refining.

You then need to figure out an aeromap for your car which gives Cd.A vs Cd.L for different aero kits that you have developed using CFD/windtunnel testing.

Then write a really simple bit of code which inputs into the laptime calculator the data for each different aero configuration of your car and then incrementally adjusts each gear ratio and determines what lap time you will get for each adjustment. You can include in your code any gearing restrictions and/or driver preferences...

You then get a huge table of results with one aero configuration/gear set-up which gives the lowest lap time, and the corresponding gear ratios to use to achieve that time.

So not particularly difficult... just time consuming to begin with, but once you have the lap time calculator and the aeromaps its a 2 minute job...

[Jersey Tom]

I ask because i'm getting really heavy in iRacing and am racing in the star mazda series. I am running out of my top gear just past the halfway mark on the longest straight on bathurst, but i'm not sure if it would provide any benefit to extend 6th and tweak aero to allow me to get a higher speed on the straight. I'm not the most consistent driver, so doing a few laps to compare times won't help.

Might want to work on being more consistent before worrying about trimming out

For a good test you don't necessarily need to be driving at 10/10th's. I feel like you're better off backing off just a bit, drive easier, be more consistent, be able to focus on what you're feeling.

Could also say - if you back-to-back two options and you can't tell a difference in lap time, i.e. if it's within the noise - then I wouldn't worry about it just yet.

[Charlatan]

I think it's pretty simple actually, as Power is basically Air-resistance times Speed at velocities above 200 km/h,
you select the gearing that gives you terminal speed when the engine is at it's peak-power in the highest gear?

[Tim.Wright]

Its not that trivial. You need to verify that if you even have a straight long enough to exploit that top speed. If not, then its better to shorten the gearing to improve the straight line acceleration which in the end will give you a faster velocity down the straight.

This will depend on the exit speed and gear of the corners preceding the straights.

[toraabe]

You have to reach the target speed as soon as possible, and have enough revs left for DRS and slip streaming.
Normally the target top speed is 5-1000 rpm above peak power.

[Speed_Demon]

So in f1, and really any open wheel series, there is a certain amount of aero you need for an optimal lap time in a track. The amount of aero you run should theoretically determine your top speed on the track's straights. Typically, how do f1 cars choose their gearing for the straights? I had heard once that they choose gearing to achieve top speed in top gear 3/4 of the way through the straight because it provides a higher average speed, but i don't know if this is true.


I ask because i'm getting really heavy in iRacing and am racing in the star mazda series. I am running out of my top gear just past the halfway mark on the longest straight on bathurst, but i'm not sure if it would provide any benefit to extend 6th and tweak aero to allow me to get a higher speed on the straight. I'm not the most consistent driver, so doing a few laps to compare times won't help.

It would really depend on the track, you have to balance the downforce to be quick in the slow turns and have as little wing to keep the speed up on the straights. In recent years Mercedes have been luck and can run as much downforce as they want as they had the HP advantage to overcome the drag. I don't know what tires you are running or the # of laps but..is you take of too much downforce the tire wear might be too much.

As for gearing, they know the drag coeff. of the setups and just need to punch it into calculators to spit out what gearing they need. If the track doesn't have many very low turns you can lower the numerical final drive gear allowing you to be quicker down the straight without losing the acceleration of the turns. If you had a customizable transmission, that would give you even more options.

Richmond gear has calculators that can give RPM drop and rpm/mph with different gear/transmission/tire combinations.

http://www.richmondgear.com/index.php/g ... alculators

[bigpat]

The golden rule is to reduce the rev drop between ratios as you change up through the gears. you want the engine at max power, not torque in the top 2 gears at least. Some cars only drop 1000-1500 rpm between the top 2 ratios.

The track map is your friend here, looking at approach speeds and corner radii, to determine corner speeds, and choosing ratios to suit the power curve of the engine.

Depending on the car & engine, it may be easier to leave the gear ratios alone, and just change the differential ratio to suit the fastest part of the track. Then you may tweaks the ratios as needed. Makes life a lot easier!

A few major series do used fixed ratios /changeable diffs this like V8 Supercars in Australia, and Nascar. It is generally easier with classes that have powerful engines with good torque.l