Cast to forged wheels

[dave5240]

Can anyone tell me what?s involved in upgrading from cast to forged wheels.

 

[needsmust]

I don't really know, but I'd say quite a lot of cash and thicker brake discs. Racers don't like carbon wheels so you might actually find it cheaper to go carbon rather than forged, on the second-hand market.

 

[bananaman]

Sprocket carrier and spacers I think

 

[tordep]

Can anyone tell me what?s involved in upgrading from cast to forged wheels.

If you check realoem it will tell the different parts between cast and forged/carbon wheels including think it?s under upgraded parts. Wheels, carriers, discs and few other bits and bobs.


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[steve929rry]

In my opinion it's a massive waste of money in changing from standard to forged as there is very little weight saving - carbon is another matter.

I've weighed all three rear wheels on my Gen 3 including discs, sprockets, carrier and spacers and all bolts fitted ready to go on the bike whith new V02 slicks on each. The forged wheels are OZ wheels that I bought from Smiths racing that had been further lightened for BSB by turning as much material off as they dared without significantly weakening (which shows that race teams take rotating mass seriously). I use BST on track with the OZ rear as a spare.

The main reason that carbon is not used for racing is due to the difficulty in assessing if they have been damaged in a crash. The only negative is that carbon don't hold and transfer heat from the tyre warmers to keep the tyres from cooling if you're not that fast on track as well as aluminium and if you're very fast carbon won't help to conduct heat away from the discs quite as well as aluminium although all carbon wheels have aluminium hubs and carriers.

See weights below:

BMW standard rear = 14.09 kg
OZ forged BST rear = 13.29 kg (5.7% saving but remember these were lightened by machining as well)
BST carbon rear = 11.81 kg (16% saving but all in the spokes and rim which is a much larger percentage of rotating inertia)

BMW standard front = 11.36 kg
BST carbon front = 9.88 kg (13% saving; again more in rotating inertia)

Obviously this is for Gen 3 but percentage weight savings would be the same for Gen 4. PS I went for M Sport on the Gen 4 for the carbon wheels.

Steve

 

[dave5240]

Thanks for the post Steve , makes for interesting reading.

 

[alex]

It's not just the total weight but where the weight is that matters. MOI - Moment of Inertia. That defines how easy it is to change direction.

 

[Cupracing]

A dealer said the cast are actually lighter than the forged ones due to smaller brake discs. I only went for the forged because I think they look better and should be more desirable come resale time

 

[steve929rry]

Exactly, as I said in my post the main mass saving in a carbon wheel is in the rim and the spokes as the hub and other parts at the centre of the wheel (i.e. nearer to the axle) are aluminium.

As many of the parts around the hub such as discs, carriers and the hub itself are still alumimium then it follows that there is a much greater weight saving in the rim and the spokes which are further from the axle (or radius of gyration).

Carbon fibre is 7 times stronger than aluminium and weighs 50% less (1,800 kg/cubic metre compared to 2,700 kg/cubic metre)

As moment of inertia = mass x radius of gyration squared (or the square of the distance from the axle) then for a 50% weight saving on the rim you are looking at a 225% saving in moment of inertia - less than half the inertia making it easier to accelerate, brake or change direction of the wheels.

 

[bmwbadboy]

A dealer said the cast are actually lighter than the forged ones due to smaller brake discs. I only went for the forged because I think they look better and should be more desirable come resale time

he lied to you

 

[bmwbadboy]

Exactly, as I said in my post the main mass saving in a carbon wheel is in the rim and the spokes as the hub and other parts at the centre of the wheel (i.e. nearer to the axle) are aluminium.

As many of the parts around the hub such as discs, carriers and the hub itself are still alumimium then it follows that there is a much greater weight saving in the rim and the spokes which are further from the axle (or radius of gyration).

Carbon fibre is 7 times stronger than aluminium and weighs 50% less (1,800 kg/cubic metre compared to 2,700 kg/cubic metre)

As moment of inertia = mass x radius of gyration squared (or the square of the distance from the axle) then for a 50% weight saving on the rim you are looking at a 225% saving in moment of inertia - less than half the inertia making it easier to accelerate, brake or change direction of the wheels.

CF delaminates same second it touches the tarmac.

Unless you have $$$ to replace them just avoid them

 

[stuartb]

Here's a question.. Cast Aluminium v Std Cast Alloy wheels

I have it in my mind from previous chats that HP4 forged rims were more susceptible to road damage than std BMW cast rims.. what's the Gen on that ?

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[alex]

Trying to solve this convo?
https://www.s1000rrforum.com/index.php?posts/2415939

I don't know the answer or I would dive in and confirm.

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[stuartb]

Yea.. guys a prat..typical yank (nearly a typo there) emphasising his words.. grrrrr..

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