An expensive but worth while mod
Discussion
In my eyes anyway.
I have a 996 Getrag box and one of the things I disliked about it was the gearing, far too short, 3000rpm equated to 70mph, tiring on long trips not to mention a tad more fuel. I was thinking about swaping it for a G96 from a turbo but when I got into the costings proper it was a lot cheaper to keep the box and sort the gearing.
I found on Californian MotorSports website a crown wheel and pinion set, see my previous thread http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Well finally I've had the car on the road for a few weeks now and the drive is much more relaxed, in 6th 70mph comes up at 21-2200rpm, it may only be 8-900rpm less but it does make a difference to the driving experience, not sure how that compares with a G96 but I'm happy.
I did make another change and that was the rear wheels are now 19" x 11" with 305/30/19 PS2s and tram lining has disappeared and front end has calmed down.
Graham
I have a 996 Getrag box and one of the things I disliked about it was the gearing, far too short, 3000rpm equated to 70mph, tiring on long trips not to mention a tad more fuel. I was thinking about swaping it for a G96 from a turbo but when I got into the costings proper it was a lot cheaper to keep the box and sort the gearing.
I found on Californian MotorSports website a crown wheel and pinion set, see my previous thread http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Well finally I've had the car on the road for a few weeks now and the drive is much more relaxed, in 6th 70mph comes up at 21-2200rpm, it may only be 8-900rpm less but it does make a difference to the driving experience, not sure how that compares with a G96 but I'm happy.
I did make another change and that was the rear wheels are now 19" x 11" with 305/30/19 PS2s and tram lining has disappeared and front end has calmed down.
Graham
I have the same issue with my 5 speed G50/01. Having a SBC which is an engine that needs to rev I would dearly like to swap my box out for a G50/50 or G50/52 but unfortunately these are as rare as you know what these days!
However if anyone has one to sell or swap do let me know 😀
However if anyone has one to sell or swap do let me know 😀
Hi Graham
The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
Yes CMS makes a longer 4th and 5th for the g50 box. I have the mod and it takes 4th to 1 to 1 and 5th is .66. this brings you 83 mph at 3000 RPM. The only thing that could be improved would be a slightly longer 1st gear, but its not something that is bad enough to get to excited about. Lee
Storer said:
Hi Graham
The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
Total Contact patch will be very little different, what will make much more difference is the weight of the wheel and tyre... If you run the stock wheels and tyres then they are not light and you can increase traction quite a bit by dropping weigh even at the expense of contact patch.The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
Remember as you reduce the width of the tyre the depth of the contact patch increases (if all things remain equal), so any reduction/increase in tyre width isn't directly proportional to total contact patch change.
My 265,s have immense traction!
andygtt said:
Storer said:
Hi Graham
The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
Total Contact patch will be very little different, what will make much more difference is the weight of the wheel and tyre... If you run the stock wheels and tyres then they are not light and you can increase traction quite a bit by dropping weigh even at the expense of contact patch.The wheel change is an interesting one for me (got a G50/52).
Has anyone worked out the contact area difference between 335/30x18 versus the 305/25x19?
I had a 'moment' over a bump on a piece of motorway in Europe when travelling at 100mph and accelerating hard. Wheel spin at that speed is not 'ideal' even if it was not a real issue.
I have softened the dampers since then but reducing the 'grip' of my rear tyres is not what I want to do.
Tramlining is only a slight issue for me at present but if the smaller width/larger diameter helps then I may opt for a change over the winter.
Paul
Remember as you reduce the width of the tyre the depth of the contact patch increases (if all things remain equal), so any reduction/increase in tyre width isn't directly proportional to total contact patch change.
My 265,s have immense traction!
Reducing tyre width (but maintaining the same diameter) will only see the contact patch grow if the same pressure is maintained (tyre slightly 'flatter').
Wheel/tyre weight make little difference to centripetal traction but obviously aids sideways grip. If the wheel/tyre change reduces the total weight of the car then there will the benefit of a lighter weight to propel (obviously) needing less rubber for the same traction.
Only by increasing the wheel/tyre diameter can you achieve the same contact patch area when you reduce the width.
The danger of reducing the tyre profile is the need to maintain the wall height. This tends to see tyre pressures rise. This has the effect of reducing tyre 'footprint'.
If I seem to know a bit about the subject of traction and wheel diameter it comes from one of my day jobs. Tractor tyres have evolved massively over the years. Attempts have been made to reduce the profile of tractor tyres but increase traction therefore keeping the overall height of the tyre down. These have not worked. Tyre manufacturers have gone back to a deep tyre wall for high hp machines. 900mm is now about the maximum tyre width and has been for a while but diameters have risen to see the largest (400+hp) wheeled tractors using wheel and tyre combinations of well over 2.2m. With the weight (15 to 18 tonnes +) of these high hp wheeled tractors and the inflation pressures used (15 to 25psi) you end up with a very 'long footprint' to transmit the power.
Back to cars
Spinning the wheels also reduces the footprint via centripetal forces stretching the tyre. Another reason racers try to avoid wheel spin at the start.
Paul
Good explanation though 
True I wasn't exactly clear what I was trying to say.
If the cars weight, wheel diam and air pressure in the tyre remain constant, then as the tyre width is reduced thus the psi on the contact width increases and thus the contact patch with deepen.... It's not massive, but it's there. I guess it does depend on what tyre pressures you run.
Reducing wheel weight will have a bigger effect on traction for a different reason, especially if it's actually the tyre that the weight is shed from due to centrifugal forces.... I'm not suggesting any change in wheel diameter at all or it's because the tyre is narrower... It's simply that reducing your tyre weight.
Going over a bump at speed and loosing traction resulting in a scary moment itsnt a contact patch size issue, it's the car not being able to control the weight of the wheel.
0-150mph in around 9 seconds shows my car doesn't lack power to spin my 265 tyres (same diam as ultima), and I have been able to use full throttle in 1st with no driver aids, so there is a lot more to traction than simply width of contact patch which is what I was trying to say :-)
If the cars weight, wheel diam and air pressure in the tyre remain constant, then as the tyre width is reduced thus the psi on the contact width increases and thus the contact patch with deepen.... It's not massive, but it's there. I guess it does depend on what tyre pressures you run.
Reducing wheel weight will have a bigger effect on traction for a different reason, especially if it's actually the tyre that the weight is shed from due to centrifugal forces.... I'm not suggesting any change in wheel diameter at all or it's because the tyre is narrower... It's simply that reducing your tyre weight.
Going over a bump at speed and loosing traction resulting in a scary moment itsnt a contact patch size issue, it's the car not being able to control the weight of the wheel.
0-150mph in around 9 seconds shows my car doesn't lack power to spin my 265 tyres (same diam as ultima), and I have been able to use full throttle in 1st with no driver aids, so there is a lot more to traction than simply width of contact patch which is what I was trying to say :-)
Deadscoob. I am limited by the top gear of my box for top speed, but I also feel I am not getting enough length out of my gears for my SBC engine as it's an engine that needs to rev especially to the top of its rev range to get its full power and my thoughts are that a G50.52 will be better for this reason. Not easy to find at all. California Motorsport just quoted me $13000. Boom!
Not really, it will accelerate faster as its lighter, but also it will decelerate faster and thus be easier to control wheelspin.
once a heavy wheel starts to spin it will want to continue more than a lighter one that will more quickly be controlled by the traction available.
It's a complex area and I am by no means a total expert, I have researched it quite a bit however.... What I was trying to point out is that reducing the tyre width won't mean the car is less controlled under power and there are a load of other factors that will mean it might actually be better.
What I do know is that I ran smaller tyres on my canam and then for the next owner fitted the stock wheels and larger tyres that were a whole load heavier (30 plus kgs heavier from memory)... And the car had loads less traction afterwards and tram lined terribly.... The car had stock shocks and wishbones etc.
I've driven Graham's car the other day, and it is drives every bit as well as it looks.... I envy him a lot. Awesome.
once a heavy wheel starts to spin it will want to continue more than a lighter one that will more quickly be controlled by the traction available.
It's a complex area and I am by no means a total expert, I have researched it quite a bit however.... What I was trying to point out is that reducing the tyre width won't mean the car is less controlled under power and there are a load of other factors that will mean it might actually be better.
What I do know is that I ran smaller tyres on my canam and then for the next owner fitted the stock wheels and larger tyres that were a whole load heavier (30 plus kgs heavier from memory)... And the car had loads less traction afterwards and tram lined terribly.... The car had stock shocks and wishbones etc.
I've driven Graham's car the other day, and it is drives every bit as well as it looks.... I envy him a lot. Awesome.
im not sure about the reduction to 305
my engine is very cammy and power comes in very agressively when on cam and i struggle not to break tracktion, but when it does i feel it before hand and can predict it...so when it does its controllable.
see there is another side to the coin... on a corner when you tail slide its controllable... teh rule of thumb is you loose a slide big time if you snap the throttle shut... if the wheel and tyre has no momentum, it will be easy to back off and snap out of control,
where as a heavier wheel and tyre will continue with momentum and backing off less severe and not visiting the hedge?
my engine is very cammy and power comes in very agressively when on cam and i struggle not to break tracktion, but when it does i feel it before hand and can predict it...so when it does its controllable.
see there is another side to the coin... on a corner when you tail slide its controllable... teh rule of thumb is you loose a slide big time if you snap the throttle shut... if the wheel and tyre has no momentum, it will be easy to back off and snap out of control,
where as a heavier wheel and tyre will continue with momentum and backing off less severe and not visiting the hedge?
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