Cayman GT4 Track Blog
12-07-2015, 09:37 AM
#31
quote BGB
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
12-07-2015, 10:23 AM
#32
12-07-2015, 11:53 AM
#33
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quote BGB
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
The only additional things i have to note are:
- on the drive home i could tell the front had more potential to scrape when entering/exiting driveways.
- I want to know why it took me all weekend to realize i could put a curved Go Pro adhesive mount on the bar that sits behind the driver/passenger seat for perfect camera placement. This would have saved me from my super shaky video that i recorded via the iPhone 6 + which is too heavy for my windshield suction cup mount when being thrown around on track. The Harry's Lap Timer with the OBD WIFI feed (see screen shot below) worked great. I have yet to post video given that it included some language not suitable for some viewers that came as a result of the camera moving position constantly.
- While I originally suggested that the OBD port's being moved was a huge plus someone else posted that it still wasn't in a good place and I would have to agree. While I never hit it with my clutch foot, i could see it happening over time.
- Just as you guys warned me, the wider wheel spacers definitely make the car even more dirty on the street when they sling stuff back towards the door and intake. In fact, the outter most edges of the rear wing element had more dirt/grime because of the way the aero comes off the door and up and over the quarter panels. The wing just before the end plates was almost black when all else was just dirty.
- I was a bit shocked at how many people refused to run the car without the whole clear-bra thing but you guys are also right about that as well; the car takes such abuse on track and i wasn't even behind that many cars in the banking but i have enough chips and rubber marble marks that it looks like I've been on track multiple times already.
- I entered all of the data into Harry's and i was impressed to see how the horsepower was exactly what we all have expected it to be and what we have seen first hand on the Maha dyno in Germany...390 hp. In the screen shot you can see that i am 200 RPM below the rev limiter which measures 390hp at 7800 on the app.
- I am glad i didn't soften the front bar because by the afternoon i would have wanted to stiffen it back up to the middle setting once the balance at corner exit shifted from understeer to oversteer.
- The brakes never showed signs of fade and when you bury the pedal, the propensity towards getting ice mode or glide mode is not near what it was on the older cars.
- If i could have raised the rear 3 turns i would but i didn't want to lose camber and toe and didn't feel like re-doing the alignment at the track. I plan to put the car on the scale pad and just log the settings so i can know how much toe and camber i have front and rear. The added benefit of lowering the front ride height on a Cayman or a 911 is that you gain camber and toe out which will help the front work better on corner entry. The inverse is true when you raise the rear and I didn't want to reduce rear grip when i was after more front grip.
- These Michelin Pilot Sport Cup 2 tires are super sticky and I was very impressed with the grip level for a street car in stock trim.
- I think that 251F on the oil temp is a bit high for a stock car with no power mods on a day that was not hotter than 80F at a track with big long straights like Daytona.
Last edited by BGB Motorsports; 12-07-2015 at 03:08 PM.
12-07-2015, 12:17 PM
#34
- Just as you guys warned me, the wider wheel spacers definitely make the car even more dirty on the street when they sling stuff back towards the door and intake. In fact, the outter most edges of the rear wing element had more dirt/grime because of the way the aero comes off the door and up and over the quarter panels. The wing just before the end plates were almost black when all else was just dirty.
here is an approximation of what John is talking about with a compare to OEM thrown in to boot.Link
12-07-2015, 01:21 PM
#35
John, thanks for the data! Would be interesting to see if adjusting rake would have helped, all other things being the same (i.e. no camber change). For me, I didn't have turn-in understeer, I had mid corner as the car took a set - which seems like a roll/camber curve issue.
12-07-2015, 01:59 PM
#36
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I saw ~250 on TWS this weekend, ambient was 60F. This is with 0-40 M1 oil.
John, thanks for the data! Would be interesting to see if adjusting rake would have helped, all other things being the same (i.e. no camber change). For me, I didn't have turn-in understeer, I had mid corner as the car took a set - which seems like a roll/camber curve issue.
John, thanks for the data! Would be interesting to see if adjusting rake would have helped, all other things being the same (i.e. no camber change). For me, I didn't have turn-in understeer, I had mid corner as the car took a set - which seems like a roll/camber curve issue.
As for the rake question, i would think so. the car is very well balanced and stiff from the factory and responds well to rake and ride height changes. It does not squat like a 911 does but lowering the front has more of an effect given that the motor isn't as far back as it is on the 911.
12-07-2015, 02:38 PM
#37
Rennlist Member
Thanks John, for all your help this weekend. I love that pic showing the car going 164 mph! Awesome!!!
Perhaps it might be interesting to some to learn how forgiving the car is to novice/intermediate driver mistakes on the track - as I made my share and was still able to stay out of trouble.
Perhaps it might be interesting to some to learn how forgiving the car is to novice/intermediate driver mistakes on the track - as I made my share and was still able to stay out of trouble.
12-07-2015, 03:35 PM
#38
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Mid-corner grip, just as you suspected, is tuned mostly via camber and the LSD but the bars help. The rake is going to help you on entry and by raising the rear it will reduce rear grip. I agree that the car points very well on entry and that it's really that it's somewhat tight at the apex when you want to pick up the throttle and have to wait a second or two. At the end of the day we are looking for more camber when on track and we want to hustle through the corner and can't because we don't have enough camber.
12-07-2015, 03:45 PM
#40
Nordschleife Master
Originally Posted by Yargk
Do we need to be worried about cooling? I thought I remember reading the gt4 did well on 100+ F days when 991 gt3s needed to cool.
12-07-2015, 04:59 PM
#41
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Caymans run hotter than 911s so it's more of a mid-engine thing. I have that covered too though for the race car folks given that I have one of the best Motorsport radiator companies in the world with new aluminum 981 and 991 radiators on the shelf. I think 251F is okay but it was cool out and Daytona isn't known for causing a car to run hot so it's just an indication of a potential hurdle for cars that get raced.
12-07-2015, 05:02 PM
#42
12-07-2015, 06:43 PM
#43
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quote BGB
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
" trust me! Big spacer got rid of half the understeering by adding front grip without cheating and defeating rear grip! "
more grip !, how can a front spacer give more front grip ?
I thought spacers don't give you more grip, which is what you were after, they give you better turn in because of the wider front track which can be nice !
But add load to the rear tyre reducing grip at the rear ! hence the balanced feel, not more front grip, you are now making less rear grip. (More load on a tyre generates a higher slip angle)
so your neutral balance was due to more load on the rear increasing the slip angle. Not added front end grip imo.
only imho mind you, I am only playing at it, but have put my rear bar to full stiff and will add front shims which will give me 3 upfront changes, more track, more camber and lower front ride height.
one can then play with spacers to fine tune the car as we don't have adjustable shocks and not much else available to fine tune balance.
I do find it VERY odd Porsche GT cars have never had adjustable shocks, it's a far nicer way to dial in the balance of the car imo.
as for more grip up front that = wider tyres ;-)
I might be 100% wrong though, just thinking out loud and want to get the best from my GT4.
It's fine, as we are just tossing around ideas and theory at this point. It could be the way i word my statements but it has been my experience that adding front track relative to doing nothing in the rear will improve the responsiveness on corner entry of the front end because you have an increase of front track relative to no change in rear track. I was solely looking to improve the performance of the front end because i felt that the car had adequate rear grip for a street car but i wanted the front end to work better. By day 3 the balance went from being pushy or having understeer from entry to exit to neutral and then to being way more free at the exit. NOW...i think 4 things contributed to this: 1.) adding over 1" of total front track to the car by adding two 15mm spacers up front 2.) the track gaining grip throughout the weekend 3.) driver pushing harder from getting used to car 4.) tire wear of rear tires relative to fronts. Caymans and 911s always burn off rear tires faster than they do the fronts because of the weight on the rear. I think that as the rears wore away faster than the fronts, the balance shifted contributing to the aggregate effect of all changes made.
According to Paul Haney, author of the book, The Racing and High Performance Tire:
Tires are load sensitive, less incremental grip with more load.
and:
...weight transfer is proportional to lateral acceleration and the ratio of center-of-gravity to track width.
Said another way. If track width is increased weight transfer (load) to the outside tire in a turn is decreased. Which results in increased grip on the axle with the increased track. Thus, less understeer.
and:
...weight transfer is proportional to lateral acceleration and the ratio of center-of-gravity to track width.
12-07-2015, 07:03 PM
#45
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Caymans run hotter than 911s so it's more of a mid-engine thing. I have that covered too though for the race car folks given that I have one of the best Motorsport radiator companies in the world with new aluminum 981 and 991 radiators on the shelf. I think 251F is okay but it was cool out and Daytona isn't known for causing a car to run hot so it's just an indication of a potential hurdle for cars that get raced.