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Author Topic: Optimum Size Wheel/Tyre for performance/handling etc?...  (Read 6760 times)

Offline J5BWS

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #15 on: July 22, 2009, 10:23:45 pm »
I really like my Monza's if I'm honest, much more than the 18" version (can't remember their name?), but I am concerned that the OZ or whatever I decide to go with will look a little small...

Offline tony_danza

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #16 on: July 23, 2009, 07:32:49 am »
Get 18s then - they're a very, very light wheel anyway, so you're still going to get some benefit. I did with mine.

If these are going to be your 365 wheels, then you've got to be 100% happy with them. You've just got to choose where you compromise, size or weight?
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Offline RedRobin

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #17 on: July 23, 2009, 09:46:37 am »

The difference between a lightweight 17" wheel with grippy tyres and a 19" bling wheel is amazing.

You will be able to get an alloy at 17" weighing 7kg (OZ Alleggerita for example)
a typical aftermarket 19" bling alloy can weigh 14kg (Helios)

The tyres weigh about 0.5kg extra in the 17" size, so you have 6.5kg extra at each wheel = 26kg on the unsprung rotational weight.

To get the equivalent effect of this as deadweight in the car you need to multiply by 5, so......

26kg x 5 = 130kg

This affects accelleration, decelleration, fuel consumption, handling and ride quality.


....To put this very helpful info into perspective, does anyone know what the stock Monza 17s and 18s weigh each, please?

And are those weights given without tyres?

:happy2:


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Offline tony_danza

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #18 on: July 23, 2009, 10:44:57 am »
Nips out to the garage....

A BBS Monza II 18" weighs 12.06 kilos, The Ronal version weighs more - rougly 1.5kilos iirc.

Also, Hurdy has been a bit over enthusiastic with the x5 calculation, whilst it is near impossible to give a 'rule' due to the differences in weights of barrels and the more of an effect rotating mass has dependant on how far it is from centre.. It is generally considered to be somewhere between a x3 and x4 effect, the latter being the more commonly used, depending on the wheel's size and weight, tyres obviously have weight differences and an effect too.

I'll ask my father in law (Prof. of engineering) to explain it a bit better than I remember from Physics and get a better idea of a more accurate x? effect for us.
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Offline RedRobin

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #19 on: July 23, 2009, 11:18:59 am »

A BBS Monza II 18" weighs 12.06 kilos, The Ronal version weighs more - rougly 1.5kilos iirc.
 

....Probably because the BBS Monza has their Hollow Wheel Technology (their patents, I expect).

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Offline tony_danza

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #20 on: July 23, 2009, 02:58:49 pm »
Right,

I've spoken to Prof Yaffle and my brain now aches. Basically what I put earlier in the thread is sound, there is no easy way of calculating an effective loss/gain as there's too many variables in wheels, you just have to understand the principles of polar moment of inertia and the gyroscopic effect.

The bigger a wheel is, i.e. the further the bulk of its mass is from centre, the bigger its resistance is to rotational acceleration/deceleration, also once spinning the gyroscopic effect is what makes something harder to turn the bigger it is. So, larger wheels have a direct impact on performance in terms of acceleration, deceleration and steering response... steering is slower to react, it saps more power from the engine and the brakes have to work harder. This where the similarities are drawn in terms of it being equivalent of adding/removing xxkilos.

Even if a 17" wheel is the same weight as an 18", it will still respond better to turn and accelerate/decelerate quicker. That's why they're deemed to be the best for pure performance.

Unsprung mass is pretty much as I described. The lower the mass, the less effect it has on the car's suspension making the ride smoother.

Hope that helps.
« Last Edit: July 23, 2009, 03:56:04 pm by tony_danza »
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Offline Hurdy

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #21 on: July 23, 2009, 04:17:39 pm »
Good  info  :happy2:

Did you get to speak to Bagpuss as well :laugh:
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Offline RedRobin

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #22 on: July 23, 2009, 06:04:15 pm »

Even if a 17" wheel is the same weight as an 18", it will still respond better to turn and accelerate/decelerate quicker. That's why they're deemed to be the best for pure performance.


....I've still got my Monza 17s - What colour should I powdercoat them, guys?

Stick some track rubber on them, put the back seats down, bung 'em in the back, and off to The Ring! :wink:


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Offline tony_danza

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #23 on: July 23, 2009, 07:04:52 pm »
Satin black.
Sideways yo!

Offline RedRobin

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Re: Optimum Size Wheel/Tyre for performance/handling etc?...
« Reply #24 on: July 23, 2009, 08:02:15 pm »

Satin black.


....My thoughts exactly! Keeps it looking oem (sort of!) :drinking:


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