Quote:
Originally Posted by shinytopman
Question for Slowone......
Any advice as to the timing sweet spot on the Hirosaka 13.5t?
Have just bought one and wanted a rough starting point
currently running 66t spur, 31 pinion, and new JFT in a zen sorry dont know the Diam. approx 48mm i think.
Thanks in advance.
Shiny.
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Shiney, try 38 degrees. I have run to 40 degrees, but prefer that smidge less. Rollout is 66 to 68 mmpr depending on track shape. Tighter track, lower number. If your tyres are 48mm dia then 68 is a 30T pinion and 66 is a 29 - roughly! Mine are 45 so its 31 for the lower number and 32 for the higher one.
Ratio depends mostly in how much speed you carry in the corners and your driving style. If you rarely let fully off the throttle and can carry a lot of speed, the higher numbers will work. If the track is tight, or you are an off/on to roll the turn/full on the way out sort of driver, the the lower ratio will help.
Car should be flat about half way down the straight depending on the exit speed from the last corner. I like the motor a lot as it doesn't fade much and has strong torque even at that level of timing. HTH
Quote:
Originally Posted by jimjav
Morning,
Yesterday I was preparing the body for my zen and when I was fitting the body post discover that for the rear I have 3 different options. I went for the rear one. but what are the difference between rear and mid position.
best regards
Javier
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I know what is said, but haven't yet found anyone who has tried both to give me a proper assessment.
On 12th cars we run off the mid position because the downforce them goes through the centre pivot and it wouldn't work as well as a mount from the pod. On a GT12 the chassis is solid between the alternative mounts so the rear one gives more leverage to centre pivot so more force into that part of the car. However, there is also a lever from the wing to the more forward mounts so in theory the effect should be the same.
The reality is that the wing mostly provides drag behind the centre of pressure so stabilising the car aerodynamically, and the open nature of the chassis with all that air trapped under the rear of the body provides lift. I have never been convinced that a wing provides downforce, but without that drag behind the CoP the car is less stable. Do we confuse one with the other?
[QUOTE=Martin.s;921448]
Quote:
Originally Posted by mark christopher
Pointless, use one or other, if you want stiffer damping use stiffer oil.[/Q
Ummm....and if you don't have stiffer oil available? Really just wondering why people don't try things that are a little more out of the box....if no one has EVER tried how does anyone know what effects it could have either positive or negative....
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O rings plus dampers equal so much damping the car hardly has enough force to overcome it and roll at all, thus reducing grip and making the rear tramp in the turns.
Not every possibility needs testing when experience and the application of simple theories can indicate what will work and what won't. It didn't need any testing to know that running friction bearings in the front axle of a GT12 (as they are run in Stock Cars) would not be as fast as running rolling element (ball) bearings as we do in GT12.
So it is that we know the combination of O rings and dampers all make the car too stiff and a stiff car will be liable to tramp in corners as it has no compliance to the effects of roll and tyre slip.
Keep up the good work one and all - GT12 is still the fun class!!
