GT3 gear ratios
Discussion
alexwagner said:
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
- will the car still be pleasant on motorways?
- will I actually FEEL the extra urge or does it only show up in laptimes?
- what BHP increase would give the same boost in perceived acceleration?
Cheers,
Alex
Can anyone answer this question please? I was about to ask the same My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
- will the car still be pleasant on motorways?
- will I actually FEEL the extra urge or does it only show up in laptimes?
- what BHP increase would give the same boost in perceived acceleration?
Cheers,
Alex
V8KSN said:
alexwagner said:
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
- will the car still be pleasant on motorways?
- will I actually FEEL the extra urge or does it only show up in laptimes?
- what BHP increase would give the same boost in perceived acceleration?
Cheers,
Alex
Can anyone answer this question please? I was about to ask the same My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
- will the car still be pleasant on motorways?
- will I actually FEEL the extra urge or does it only show up in laptimes?
- what BHP increase would give the same boost in perceived acceleration?
Cheers,
Alex
- 7.1 has 3.44 final drive, 8:32 is 4. With the 3.44 final drive a 7.1 will do 70mph in 2nd at 7k rpm. With a 4.0 final drive, a 7.1 will do 70x(3.44/4.0) = 60.2mph in 2nd at 7k rpm. A 7.2RS does 62mph in 2nd at 7k rpm based on the initial post in this thread, so yes, a 7.1 with 8:32 is geared ever so slightly shorter in 2nd (and assuming the ratios are spaced proportionally the same as an RS, for all the other gears as well)
- dunno, but you will be going about 15% more revs so 3.5k rpm would go to 4k rpm which is a not insignificant difference
- you'd feel the extra urge as you'd effectively have 15% more torque in each gear
- about 15% / 60-and-a-bit bhp
Yes I have this mod in my 7.1
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
Very similar in 1st, 2nd and 3rd but changes slightly after that. Send me an e mail address and I'll ping over the charts I have from Steve at JZM which shows comparisons.
- will the car still be pleasant on motorways?
No. Your shorting the ratios on all gears so motorway cruising is noisierand more rpm.
- will I actually FEEL the extra urge or does it only show up in laptimes?
Yes you will feel it, but this really is a TD mod only IMO.
- what BHP increase would give the same boost in perceived acceleration?
According to the JZM info 40 bhp, personally believe less but it does make a difference coming out of corners on track.
Personally if I did this again I wouldn't use a cup final drive, I'd go for the 3.8rs final drive as this will cause less wear issues due to gear ratios. Plus look at changing 6th gear.
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
Very similar in 1st, 2nd and 3rd but changes slightly after that. Send me an e mail address and I'll ping over the charts I have from Steve at JZM which shows comparisons.
- will the car still be pleasant on motorways?
No. Your shorting the ratios on all gears so motorway cruising is noisierand more rpm.
- will I actually FEEL the extra urge or does it only show up in laptimes?
Yes you will feel it, but this really is a TD mod only IMO.
- what BHP increase would give the same boost in perceived acceleration?
According to the JZM info 40 bhp, personally believe less but it does make a difference coming out of corners on track.
Personally if I did this again I wouldn't use a cup final drive, I'd go for the 3.8rs final drive as this will cause less wear issues due to gear ratios. Plus look at changing 6th gear.
Yes I have this mod in my 7.1
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
Very similar in 1st, 2nd and 3rd but changes slightly after that. Send me an e mail address and I'll ping over the charts I have from Steve at JZM which shows comparisons.
- will the car still be pleasant on motorways?
No. Your shorting the ratios on all gears so motorway cruising is noisierand more rpm.
- will I actually FEEL the extra urge or does it only show up in laptimes?
Yes you will feel it, but this really is a TD mod only IMO.
- what BHP increase would give the same boost in perceived acceleration?
According to the JZM info 40 bhp, personally believe less but it does make a difference coming out of corners on track.
Personally if I did this again I wouldn't use a cup final drive, I'd go for the 3.8rs final drive as this will cause less wear issues due to gear ratios. Plus look at changing 6th gear.
....
My questions:
- does an 8:32 pinion on a 97.1 give shorter gears than a 97.2 RS?
Very similar in 1st, 2nd and 3rd but changes slightly after that. Send me an e mail address and I'll ping over the charts I have from Steve at JZM which shows comparisons.
- will the car still be pleasant on motorways?
No. Your shorting the ratios on all gears so motorway cruising is noisierand more rpm.
- will I actually FEEL the extra urge or does it only show up in laptimes?
Yes you will feel it, but this really is a TD mod only IMO.
- what BHP increase would give the same boost in perceived acceleration?
According to the JZM info 40 bhp, personally believe less but it does make a difference coming out of corners on track.
Personally if I did this again I wouldn't use a cup final drive, I'd go for the 3.8rs final drive as this will cause less wear issues due to gear ratios. Plus look at changing 6th gear.
majordad said:
Could anyone update this with GT3 and RS 991 info please ? What effect has the 7th gear made and or PDK?
This is one of my favourite threads on PH, I keep coming back to it again and again, thanks to all who posted ( and hope to see you at the RS Day Oulton 11 th March )
I posted this answering another thread earlier, I'll do the same for the 991 when I get a moment!This is one of my favourite threads on PH, I keep coming back to it again and again, thanks to all who posted ( and hope to see you at the RS Day Oulton 11 th March )
Thanks. That's brilliant.
So the numbers in the beginning of this thread were at 7000 rpm, whilst your calculations are at max revs right?
Interesting to see how similar the 996 gt3 and gt4 max speeds are. I have never had an issue with 996 gt3 gearing and therefore wonder whether (regardless of press reports) one gets equally used to the gt4 gearing.
Having said that, I recall in the Nurburgring gt4 in car video the driver was definitely using lower gears than I would in a 996 on many corners....
So the numbers in the beginning of this thread were at 7000 rpm, whilst your calculations are at max revs right?
Interesting to see how similar the 996 gt3 and gt4 max speeds are. I have never had an issue with 996 gt3 gearing and therefore wonder whether (regardless of press reports) one gets equally used to the gt4 gearing.
Having said that, I recall in the Nurburgring gt4 in car video the driver was definitely using lower gears than I would in a 996 on many corners....
Edited by LaSource on Friday 15th January 07:28
If you don't normalise the RPM to something common when doing the above sort of analysis, you can't really gain much of an insight into relative gearing.
You only see maximum (theoretical) in gear speeds. This can be useful but it isn't the whole story. How the gearing of one car relates to a second car is lost as a result of the difference in applied RPMs
The GT4 has shorter gear ratios in every gear but 1st when compared to a 996.2 GT3 ( assuming GT3 is running stock 3.44 final drive) but when combined to its huge bling wheels ends up losing out.
For the same RPM in each of the 6 gears, the GT4 ends up pulling higher kph than the GT3. The gap is pretty small in 5th and 6th but fairly significant in the other gears.
Those with a GT4 need to get them onto smaller wheels.
You only see maximum (theoretical) in gear speeds. This can be useful but it isn't the whole story. How the gearing of one car relates to a second car is lost as a result of the difference in applied RPMs
The GT4 has shorter gear ratios in every gear but 1st when compared to a 996.2 GT3 ( assuming GT3 is running stock 3.44 final drive) but when combined to its huge bling wheels ends up losing out.
For the same RPM in each of the 6 gears, the GT4 ends up pulling higher kph than the GT3. The gap is pretty small in 5th and 6th but fairly significant in the other gears.
Those with a GT4 need to get them onto smaller wheels.
Number31 said:
Here is the GT4 compared to the 991 GT3. If someone can get me confirmation the RS ratios I'll do that too! Rev drops to follow!!!
Why does anyone need to be able to do 53 mph in reverse? Edited by Number31 on Thursday 14th January 23:18
I feel as if reverse is way over-geared in my GT3 but I know nothing about how a reverse gear ratio is determined.
In a short answer - yes. With a bigger rim and tire radius you suffer in two areas; acceleration is reduced due to the larger diameter and road speed for a given RPM increases.
I can only assume market reasons are behind the bigger rear tire on the 991 RS though I will be kind and say perhaps the aero needs it.
I haven't got the ratios for the RS, and despite a quite google didn't come up with any. Ive limited options for finding out at 11.30pm on a Friday night
Interestingly, the spread of the individual gear ratios on the 991 GT3 are pretty much identical to the 996 GT3 gear ratios. The PDK obviously has 7 gears so benefits from a reduced drop between each gear. The different spacing makes direct comparisons trickier, however the upper and lower limits are 3.75 - 0.84 on the 991 versus 3.82 - 0.85 on the 996.
The 991 however benefits from a shorter final drive at 3.97 versus the 3.44 used OEM in the 996 so total gear ratio is shorter as a result.
For a 996 GT3 with a 4.00 R&P though things change - a touch of advantage to the 996 in overall ratios, and an advantage back to the PDK for having 1 extra cog in between to help drops.
The tire diameter difference is pretty remarkable though. 27.2" diameter tire on the 991, 25" on the 996, and a massive 28.7" on the 991 RS
As a result, 7000RPM in 3rd gear in the 991 GT3 is ~ 133.4 km/h, the 996.2 GT3 it is ~ 155.80 km/h, and a 996.2 GT3 with a 4.0 R&P is ~ 122.5 km/h. The GT4 is ~164.8km/h
The tire diameter increase of around 5.5% on the 991 RS (versus the 991 GT3) would hurt gearing by the same 5.5% though. The question for the RS is whether the ratios have been dropped by an equivalent (or greater) amount.
I can only assume market reasons are behind the bigger rear tire on the 991 RS though I will be kind and say perhaps the aero needs it.
I haven't got the ratios for the RS, and despite a quite google didn't come up with any. Ive limited options for finding out at 11.30pm on a Friday night
Interestingly, the spread of the individual gear ratios on the 991 GT3 are pretty much identical to the 996 GT3 gear ratios. The PDK obviously has 7 gears so benefits from a reduced drop between each gear. The different spacing makes direct comparisons trickier, however the upper and lower limits are 3.75 - 0.84 on the 991 versus 3.82 - 0.85 on the 996.
The 991 however benefits from a shorter final drive at 3.97 versus the 3.44 used OEM in the 996 so total gear ratio is shorter as a result.
For a 996 GT3 with a 4.00 R&P though things change - a touch of advantage to the 996 in overall ratios, and an advantage back to the PDK for having 1 extra cog in between to help drops.
The tire diameter difference is pretty remarkable though. 27.2" diameter tire on the 991, 25" on the 996, and a massive 28.7" on the 991 RS
As a result, 7000RPM in 3rd gear in the 991 GT3 is ~ 133.4 km/h, the 996.2 GT3 it is ~ 155.80 km/h, and a 996.2 GT3 with a 4.0 R&P is ~ 122.5 km/h. The GT4 is ~164.8km/h
The tire diameter increase of around 5.5% on the 991 RS (versus the 991 GT3) would hurt gearing by the same 5.5% though. The question for the RS is whether the ratios have been dropped by an equivalent (or greater) amount.
Edited by fioran0 on Saturday 16th January 00:14
fioran0 said:
In a short answer - yes. With a bigger rim and tire radius you suffer in two areas; acceleration is reduced due to the larger diameter and road speed for a given RPM increases.
I can only assume market reasons are behind the bigger rear tire on the 991 RS though I will be kind and say perhaps the aero needs it.
I haven't got the ratios for the RS, and despite a quite google didn't come up with any. Ive limited options for finding out at 11.30pm on a Friday night
The tire diameter increase of around 5.5% on the 991 RS (versus the 991 GT3) would hurt gearing by the same 5.5% though. The question for the RS is whether the ratios have been dropped by an equivalent (or greater) amount.
]
Yes I believe so. Per the product info pdf i have saved up, the 991RS has final drive of 4.188 vs 3.973 in the 991 gt3 which is ~5% over I think which corresponds to the tyre diameter difference.I can only assume market reasons are behind the bigger rear tire on the 991 RS though I will be kind and say perhaps the aero needs it.
I haven't got the ratios for the RS, and despite a quite google didn't come up with any. Ive limited options for finding out at 11.30pm on a Friday night
The tire diameter increase of around 5.5% on the 991 RS (versus the 991 GT3) would hurt gearing by the same 5.5% though. The question for the RS is whether the ratios have been dropped by an equivalent (or greater) amount.
]
fioran0 said:
I can only assume market reasons are behind the bigger rear tire on the 991 RS though I will be kind and say perhaps the aero needs it.
I had assumed that it was logistic reasons actually - to get the desired width of contact patch without having to have another bespoke sized (N rated obviously) tyre size created (as we all know: 991 RS matches 918 tyre sizes). Why the 918 wears Carlos Fandango sizes I suspect is aesthetic/marketing based, but I thought that the 991 RS was actually getting its wheel sizes so that its tyres could be sourced from the proverbial parts bin? Even if they were different compounds there would be construction/tooling savings for the boys at Michelin...?Just to follow this up. Here are the effective gear ratios for the 996 GT3, the 991 GT3 and the GT4 when normalised for rear tires.
Cay GT4 - 11.92, 7.03, 5.08, 4.07, 3.42, 2.92
996 GT3- 13.14, 7.40, 5.37, 4.16, 3.44, 2.92
991 GT3- 13.67, 8.68, 6.27, 4.89, 4.05, 3.50, 3.06
Interestingly, 2-6 on the 991 GT3 when looking at its normalised effective gearing is very close to the 2-6 on a 996 GT3 when fitted with a 4.0 R&P.
With the R&P on the 991 RS being adjusted to offset the increased tire size, its effective normalised gearing should be the same as for the regular 991 GT3.
Cay GT4 - 11.92, 7.03, 5.08, 4.07, 3.42, 2.92
996 GT3- 13.14, 7.40, 5.37, 4.16, 3.44, 2.92
991 GT3- 13.67, 8.68, 6.27, 4.89, 4.05, 3.50, 3.06
Interestingly, 2-6 on the 991 GT3 when looking at its normalised effective gearing is very close to the 2-6 on a 996 GT3 when fitted with a 4.0 R&P.
With the R&P on the 991 RS being adjusted to offset the increased tire size, its effective normalised gearing should be the same as for the regular 991 GT3.
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