Any one got 16 inches ???
Discussion
Last part of the Growlers facelift and I need a pair of 16 inch wheels - don't mind the cosmetic state as want to get them and the fronts refurbed anyhow but would prefer them to be straight and fairly well balanced
If someone also wants a pair then we could maybe find four and split the cost
Any thoughts appreciated
Ty
If someone also wants a pair then we could maybe find four and split the cost
Any thoughts appreciated
Ty
I already have 16's on the back and they are a useful upgrade - they make the car slower (top end wise) but with more grip (so acceleration is better from a standstill - maybe).
Mine are OK straight and true but cosmetically a little ratty. I could do with a spare pair "just in case" and so I can put nicer ones on. So I am interested in splitting a set if you find 4 or even 3.
BTW you may have to pay attention to the wheelarch clearance - I packed out my body/chassis rubbers slightly on the passenger side to eliminate some rubbing under bottoming out.
Mine are OK straight and true but cosmetically a little ratty. I could do with a spare pair "just in case" and so I can put nicer ones on. So I am interested in splitting a set if you find 4 or even 3.
BTW you may have to pay attention to the wheelarch clearance - I packed out my body/chassis rubbers slightly on the passenger side to eliminate some rubbing under bottoming out.
Excuse my possible ignorance and intrusion gents! but if I am right in presuming that you are talking of increasing wheel size to 16" from 15", wouldn't this mean increasing diameter and thus the top end speed would be increased not reduced and acceleration - possibly slightly slower.
If you talking going down to 16" from bigger, ignore my comments or ignorance
If you talking going down to 16" from bigger, ignore my comments or ignorance
Top end speed is not a function of wheel size, but of overall drag (rolling, aero) and horsepower.
Otherwise I could put tractor wheels on the back and go at 250mph....
The extra width (I take it we are talking 9J) of tyre means the rolling resistance goes up.
Yes the diameter goes up very slightly (for 45 profile tyres) but on mine that has the beneficial effect of correcting a 4% underread to spot-on for the speedo.
Otherwise I could put tractor wheels on the back and go at 250mph....
The extra width (I take it we are talking 9J) of tyre means the rolling resistance goes up.
Yes the diameter goes up very slightly (for 45 profile tyres) but on mine that has the beneficial effect of correcting a 4% underread to spot-on for the speedo.
Time for a physics lesson.
The car will stop accelerating when the torque curve of the engine intersects the force needed to overcome drag.
Working back from the rear wheel the first conversion is force to torque around the rear axle, then this goes through the diff, propshaft and gearbox to the flywheel.
I think we are all in agreement that the engine, gearbox, diff etc are being kept constant throughout this comparison?
If the rolling radius at the rear wheel increases, then for the same drag force, the torque to be overcome at the rear axle increases too.
Going from 15" with 225/50/15's to 16" with 245/45/16's results in a rolling radius increase of 3.45%.
So we'll get in torque balance with the engine earlier, I'd guess maybe 1.7% lower speed. Don't forget that aero drag increases with V squared - the 2 * power effect means you can halve a small percentage in a calculation. I am assuming that aero drag is dominant at around 160mph....
One effect I didn't mention is that as the rear of the car is raised by 10.5mm (which looks cool BTW), the drag coefficient might be affected (possibly go up a bit?) but I don't know how easy it will be to measure this part of it. Also as the tyres are wider there will be a little more aero drag under the car, and a bit more rolling resistance. So all in all maybe 2% off the top speed?
The car will stop accelerating when the torque curve of the engine intersects the force needed to overcome drag.
Working back from the rear wheel the first conversion is force to torque around the rear axle, then this goes through the diff, propshaft and gearbox to the flywheel.
I think we are all in agreement that the engine, gearbox, diff etc are being kept constant throughout this comparison?
If the rolling radius at the rear wheel increases, then for the same drag force, the torque to be overcome at the rear axle increases too.
Going from 15" with 225/50/15's to 16" with 245/45/16's results in a rolling radius increase of 3.45%.
So we'll get in torque balance with the engine earlier, I'd guess maybe 1.7% lower speed. Don't forget that aero drag increases with V squared - the 2 * power effect means you can halve a small percentage in a calculation. I am assuming that aero drag is dominant at around 160mph....
One effect I didn't mention is that as the rear of the car is raised by 10.5mm (which looks cool BTW), the drag coefficient might be affected (possibly go up a bit?) but I don't know how easy it will be to measure this part of it. Also as the tyres are wider there will be a little more aero drag under the car, and a bit more rolling resistance. So all in all maybe 2% off the top speed?
Don't believe a word of it
I was coming from more theoretical perspective of fixed revs/min though fixed ratio's of box and axle all leading to diameter of wheel: The wheel will turn faster at the perimeter, if diameter of wheel is increased, which is why as Zig says, the speedo calibration changes.
But get your theory.
Steve
I was coming from more theoretical perspective of fixed revs/min though fixed ratio's of box and axle all leading to diameter of wheel: The wheel will turn faster at the perimeter, if diameter of wheel is increased, which is why as Zig says, the speedo calibration changes.
But get your theory.
Steve
Well if you follow your perpsective through, for a certain rpm of the engine/speedo:
Energy = Force * Distance
so
Power needed = Force * Distance / Time
= Drag * Circumference * 60(seconds) / rpm
let's say drag and rpm is constant for now.
So: Power needed is proportional to Circumference
If the circumference of the tyre goes up, so must the engine power IN PROPORTION.
Obviously my tractor wheel idea is now ridiculous, because you'll need twice as much power to turn the wheel. (or else Bugatti Veyrons would all have tractor wheels and hit 500mph...)
Energy = Force * Distance
so
Power needed = Force * Distance / Time
= Drag * Circumference * 60(seconds) / rpm
let's say drag and rpm is constant for now.
So: Power needed is proportional to Circumference
If the circumference of the tyre goes up, so must the engine power IN PROPORTION.
Obviously my tractor wheel idea is now ridiculous, because you'll need twice as much power to turn the wheel. (or else Bugatti Veyrons would all have tractor wheels and hit 500mph...)
adam quantrill said:
Well if you follow your perpsective through, for a certain rpm of the engine/speedo:
Energy = Force * Distance
so
Power needed = Force * Distance / Time
= Drag * Circumference * 60(seconds) / rpm
let's say drag and rpm is constant for now.
So: Power needed is proportional to Circumference
If the circumference of the tyre goes up, so must the engine power IN PROPORTION.
Obviously my tractor wheel idea is now ridiculous, because you'll need twice as much power to turn the wheel. (or else Bugatti Veyrons would all have tractor wheels and hit 500mph...)
Might work if you live on top of big hill Adam Energy = Force * Distance
so
Power needed = Force * Distance / Time
= Drag * Circumference * 60(seconds) / rpm
let's say drag and rpm is constant for now.
So: Power needed is proportional to Circumference
If the circumference of the tyre goes up, so must the engine power IN PROPORTION.
Obviously my tractor wheel idea is now ridiculous, because you'll need twice as much power to turn the wheel. (or else Bugatti Veyrons would all have tractor wheels and hit 500mph...)
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