Whats the benefits 16" to 15"

[Ph1 Tom]

ive just seen a thread, my 16s are 8.9k a corner and o.z f1s are 9k a corner i thought they would have been lighter?

OZ F1s are 7.7kg.

Improved gearing and acceleration??? Educate me...

It effectively gives a shorter final drive of 0.10. E.G the Ph2 final is 4.07 and the Ph1 is 3.89. You fit 16s rather than 15s to a Ph2 and it effectively makes it 3.97 rather than 4.07. But if you put a Ph2 final drive on a Ph1 it would be 4.07. Similarly if you put 16s on a Ph1 you would effectively make the final drive 3.79 rather than 3.89.

?? Please explain

Also to those who say the cars loads better on 15's etc etc.

If that is the case then why did renault not fit that size to the mk2 ph2 then? Surely the cars was setup suspension wise and so on for 16's. And if the benefit was that good on 15's they would have fitted them as standard?

See my answer above, they put a shorter final drive in the Ph2 and bigger wheels to compensate for it (bring the gearing for cruising down etc.)

There is no one line generic answer to this.
The key issues are wheel weight (apparently every kilo saved on a wheel can be multiplied by 4 as it's both unsprung weight and rotated mass) and cheaper/greater variety of tyres.
If you go for one of the superlight type wheels (OZ Superleggera (5.2kg), OZ Ultraleggera (5.6kg), TD Pro Race (6.2kg)) the "real" weight saving can be around 50 kilos.
Bear in mind that those wheels are spinning on the end of the hubs, you are going to notice that weight saving under braking, turn in etc.
I still maintain it's the single most effective change you can make to a car with heavy wheels. The standard 182 wheels are over 10kgs each!

You won't get those wheel weights in Clio fitment Definitely add 0.5kg for the Pro Race, even Steve head of TD themselves in Brum said the lightest they have is 6.4kg.

Yes you save unsprung weight and there's less inertia but you don't really get much real world benefit from the weight. Besides, track tyres are heavier than road tyres.




Other benefits of 15s include a lower CofG, there's 14mm less diameter, so you can get the car lower.
Tyres are cheaper.
The wheels themselves are usually cheaper.

There will be more I can't think of off the top of my head.

 

[imprezaworks]

You have way too much time on your hands, lol.

 

[Ph1 Tom]

You have way too much time on your hands, lol.

Doing some MSc work at the moment so it gives me a 5 minute break from that

I forgot to say with the above a shorter final drive gives more torque at the wheels.

 

[imprezaworks]

Take me all day to even google half that, lol

 

[underdog]

i have a st170 track car and i run 16s on track instead of factory 17s. the diameter is 30mm less for me on 16s and as ph1 tom says its like changing the final drive in the box. i can notice the difference a lot on track swapping between wheels. the points you need to change gear will change on track and for my car with tall gearing it helps a lot. on the road i wouldnt care or bother though.

 

[Steven103]

I'd of thought 16's would be better due to lower profile.

All racing cars where regulations permit (F1 to Formula Ford, GT1 to GT4 cars, touring cars, rally cars) - relatively high profile tyres. Sporty road cars - low profile tyres. As far as choosing a tyre profile for minimum laptime goes - who do you think is doing it right?

I am just playing devil's advocate here because it's interesting IMO. Although high (or should I say normal?) profile is ultimately a better route to take you need suspension and sidewall stiffnesses that you'll never find in a road car to make it work. Going out on a limb my personal suspicion is that the whole "15 inch handle better" hype is probably more to do with fitting a "more correct" profile of tyre than the reduction in (albeit unsprung) mass.




EDIT: Well turns out I'm late to the party.

Yes IF you were using the same section tyre on each wheel size... 45/16 and 50/15 differ by less than 1% on the speedo, as stated above, so surely the acceleration/ gearing argument is moot.

Inertia. Like a lightweight racing flywheel. Lower value of inertia = less resistance to making the wheel rotate faster.

=1/2*mass*radius^2

So even if the radius hence gearing is the same, by saving 4kg per corner you still reduce inertia. And furthermore because you're replacing heavy "wheel" with light "tyre" you're actually changing the distribution of the mass more towards the centre of rotation. Think of swinging a 5kg pendulum around your head. You'd need to put more effort in to sustain the "swinging" action if it was on a 2m piece of string than a 1m piece of string.

<3 science.

 

[MartinR]

Great bit of info going on now

 

[is1]

You won't get those wheel weights in Clio fitment Definitely add 0.5kg for the Pro Race, even Steve head of TD themselves in Brum said the lightest they have is 6.4kg.

Yes you save unsprung weight and there's less inertia but you don't really get much real world benefit from the weight. Besides, track tyres are heavier than road tyres.

Well Team Dynamics quote 6.2kg for a 7 x 15 Pro Race 1.2. I accept there may be slight variations due to offset but it is still around 4kg lighter than an OEM 182 wheel.
The OZ Superleggeras I had in 7 x 15, ET37mm with a 67.1mm centre bore were just over 5kg and the Ultras half a kilo more.
As for track tyres being heavier, I accept that but that's not the fault of the wheel i.e. if you fitted a track tyre to a heavier wheel, you'd get a heavier combined weight, the weight saving from the lighter wheel still applies on a like for like case.
As for "real world benefit" it's subjective until someone provides some science behind it. However, if I had to have a component spinning at the end of a driveshaft/hub, I'd rather it was lighter provided it wasn't weaker.

 

[Alex_X93]

?? Please explain

Also to those who say the cars loads better on 15's etc etc.

If that is the case then why did renault not fit that size to the mk2 ph2 then? Surely the cars was setup suspension wise and so on for 16's. And if the benefit was that good on 15's they would have fitted them as standard?

Note as the diameter or width of wheel increases, the weight of the overall wheel and tyre package increases, thereby increasing unsprung weight. Reducing unsprung weight is key to handling the lower the unsprung weight, the less work springs and shocks have to do to maintain contact with the road. The inertia of higher mass also accelerates and decelerates slower. From experience larger wheels give higher top speed and vice versa smaller better acceleration e.g renault 5 gt turbos on 13" wheels always had faster acceleration and lower top speed compared to 15" or 16" wheels respectivley, this is noticed in gear changes also hope this helps.8)