GT3 gear ratios

Ken.
Thanks for the info and further posts. Great stuff.
What data can you read from your system. It sounds very interesting indeed.

That 6RS trace was good to see too. The new 7.2 RS is the first car imho that's equal too or better than the 6GT3 in terms of lap times/pace assuming all are stock and even still it needs really worked to achieve. That it needs better gearing and 3.8 to do it speaks volumes. Especially when you factor on its improved aero aswell.
As Steve mentions in detail, Its a ball dropped rather than the power of the 6 (which I love).
The paradox is that in cup form where it's just the raw cars the 7 obliterates the 6. the 7 platform is so much better but you can't tell due to PASM.
Now with a suspension change on a street 7 everything changes.

Standard

It's telling when effectively taking grip away from the rear is the only way to get some balance into a 911 chasis. The rule of thumb is always to maximise rear and front grip on the geo and the driver creates the balance himself by using weight transfer. I believe that the gen 2 car had an even stiffer rear end and a wider front track to try to get round the understeer created by the PASM.

Just for anyone interested in the graphs and gear ratios and CW&P changes - they should be aware that once you have drawn the graph showing the internal gear ratios and gearchange points - IF you change the revs you change gear at or the CW&P ratio - or the wheel or tire sizes and diameters etc - you can use exactly the same graph shape but just simply change the scale at the vertical or horizontal axis (the shape stays the same.

So if for example you altered the CW&P to raise or lower the top speed in 6th at say 7K (or whatever) you only need to alter the horizontal scale so at 7K the speed is the new top speed and pro-rata down the scale to see the new speeds in each gear.

Similarly if you rev more or less when changing gear - just alter the vertical axis scale to suit.

Acceleration is mainly proportional to rear wheel torque and so the most useful graph is a rear wheel torque graph in each gear. To get this first write down (or put on a spread sheet preferably) the revs in each gear and the corresponding road speed from the graph already posted or in the manual - say every 500 revs. Then write down (or spreadsheet) the torque from the engine at those revs. Then multiply the internal and CW&P ratios and multiply by the torque to create the rear wheel torque at different road speeds in each gear.

Then plot a graph of rear wheel torque in each gear (vertical) and road speed (horizontal). Where the lines cross shows the best road speed in each gear to change gear at and then you can work back to the ideal revs accordingly (more detail in our buyers guide www.hartech.org).

From this you will see that the biggest influence on acceleration is the gear ratio and therefore if a close ratio gearbox simply crowds together the ratios at a higher speed range than you can use on a track - the car will be slower.

Similarly you can see that even revving an engine over the best torque range before changing gear can still be beneficial if the result of the drop in torque from changing up is greater than the drop in torque at high revs.

Most road gearboxes are too high for track work and most low gears are too low - resulting in drivers often using 2 or 3 gears only with wide rev drops and low rear wheel torque.

If a C/R gearbox changed the car to be able to use all 5 or 6 gears where previously 2 or 3 could be used - it would almost certainly be faster that using less gearchanges - despite the time lost changing gear - because you don't have to change so often is you don't want to (as there is now w more usable range available to you to suit corners etc).

It is usually when the ratios combined with the CW&P ratio move the cluster of close ratios away from the usable range for a circuit that the extra gearchanges in a C/R box can become counterproductive.

Generally the more usable gear changes available the faster the car should accelerate since the biggest loss of acceleration occurs when you change up (more than the drop off in torque as the engine runs over its peak
torque range).

You can only understand this if you create the rear wheel torque against road speed graph and study it.

If anyone reading this is clever enough to create a spreadsheet graph that automatically can create this road speed to rear wheel torque graph - from the data available - I would really appreciate it if they could show me how to do it - as I cannot manage to make the automatic graph systems do this and have to resort to manual scaling etc - which is time consuming and the resulting hand drawn graph looks amateur. Worse of all it handicaps trying different settings on paper to assess the results.

Fortunately we don't have to worry about this for this season as we are racing our Boxsters in a series that does not allow such changes - but for others (and perhaps ourselves one day in the future if we upgrade our events and cars) we may find it useful.

Baz

Good stuff guys, keep it coming...

I thought we were just saying some cars go faster in 3rd than others no

996. Nice platform unhindered through having normal suspension
997. Even nicer platform hindered by active suspension
996 Cup. Quick
997 Cup. Quicker

I'll be there on the RS day, grey RS with Fearnsport sticker on the back, it would be good to catch up, what are you driving ?

The developer of the system looked at taking data from the ECU but there was some issue about refresh rate and it's getting a bit ott. You would need extra sensors for brakes, steering etc.

I had a race car built last year and had the brake sensor, steering sensor, engine temperature sensor with the intention of putting the data into a DL1, it all got a bit hard to do without specialist help and for club racing again going a bit ott.

Thread resurrection!

Having picked up my new to me 7.1 GT3 the other day, I've noticed that the ratios are quite long (84mph in 2nd, 116mph in 3rd etc) and IMO too long for the road. People in this thread and others have suggested fitting a Cup final drive which, by my calcs shortens the gearing by about 10%, as good option. Can anyone give me an indication of parts cost and labour cost to have this done?

Many thanks

Sorry, couple more questions!

1) does the gear it replaces have any real second hand value?
2) presumably the speedo etc won't have to be adjusted to show correct speed?