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If the rolling radius is not changed then the acceleration is not changed. But for Clio 172 drivers when changing to 17s there will be a increase in rolling radius because there isnt a tyre for 17 inch wheels to make the rolling radius the same as the 15s. Im getting 16s soon. With a smaller rolling radius I dont expect there would be much difference in acceleration tho.
Chun.
well, the main thing is the CM (centre of mass). On a 15" wheel weighing 8 KG (inc tyre) this CM is going to be much nearer the spindle since the heavy metal rim is closer to the hub. This means the car has to expend less energy to spin the wheel. A 18" wheel weighing the same (although it will be hard to find) will be harder to spin since most of its mass will be at least 1 1/2" futher away from the spindle. Alos, they tyre will weigh more etc, moving the CM even futher out.....Rolling raduis of 13mm really doesnt make any difference to speed or acceleration.
So, for a car producin 10 units of power, it will only use 3 units to spin the 15" wheels, leaving 7 to actuall move the mass of the car. An 18" wheel will use 6 units leaving 4 for moving the car.
The only reason Big GT cars and rally cars use 18" wheels is becasue they have tons of power andit allows for a much more rigid tyre, allowing the suspension to do the work and take tyre flex out of the handling equation.
Fair points Ben, but just one thing...I would have thought that on an 18" wheel the tyre would actually be lighter. Compare say a 215/35/18 with a 195/50/15. Hardly any difference in width but a big difference in profile. So the 18" tyre will be lighter. But as you say the weight of the wheel itself is a lot more and most of that weight is further out from the centre so would be harder to get moving and to slow down.
Could fit some monster brakes in there though.
hell yeah!!
HUge brakes!!! but that would only increase unsprung weight even more...have you held one of the 320mm ap racing discs? they weigh a ton!!
even the standard 16V discs weigh alot!
But its worth it if you got a 500BHP monster...or you could get a big disk kit from rally design with the 4 pot billet supelight calipers and 300mm discs!! would probably be a good investment in your car!!!
and only £450!
A question BenR. Im getting 16 inch SuperLs now. And its proberly lighter than the 15 inch Oz F1s. Now I thought there wouldnt be that much of a increase in energy used to spin the SuperLs compared to the F1s, or would there?. After all its only 0.5 inch increase either side on a lighter wheel. So theres less mass but its spinning further out from the centre of the wheel. So is there going to be that much more energy needed to spin the 16 inch SuperLs compared to the 15 inch F1s?. Not that it really matters just some interesting information I wanted to know
Chun.
I think I have followed the Science from the soon to be very rich and clever no doubt Ben R but I was wondering exactly how much this will have a noticable effect, I too have a 1.2 so speed is hardly the best feature of my car and I was hoping to get a definitive answer so I could buy some rims and feel good.
However I just seem to be confused and paranoid about making my slow car even slower!!!! NO!!!!!!!!!!
So what do you think, would I notice the difference between 15s and 16s??
haha guys!
to take the piss, i am studying Business Studies at UWE in Bristol. Its soooooooo boring and i hate it, i wanted to mechanical engineering but im not too good with the mass and i know that its a very popular deg with not much options for jobs....i need money to fund my racing!!
Anyway, the 16" Super leggerea wont need any exrta energy to spin them up. Since they weigh 6.2 kilos per rim (exc tyres).....Basically the super ls are their size in inches, minus 10 + 0.2-0.6.
well, the problem with super ls is that, although tey get up to speed quicker, they need more energy to keep them at the engines max speed! This is becasue their inertia is lower than the OZ F1 cups. This means that you might have a reduction in top speed. I have a RT with 15" Super Ls and its top speed takes ages to reach now, where before it did 100-110 (indicated) more than happily, with the super Ls its more happy at 80-90MPH. It still reaches 115 top (indicated and not true speed) it takes ages and a hill!!
So i have bought a set of 16V phase 1 wheels for day to day, and the super ls to fit with super sticky yokohama A032Rs (cut slicks!) for track days when i get my engine up to 140BHP.
When you drive it though, you can tell that the lighter wheels have moved the polar point of inertia more forward, and giving better initial turnin, but more likely to understeer.....how to fix it?.....raise the reas suspesion and use harder shocks and springs (torsion bars)....as this will force the rear axles to start doing some of the chassis work (more 3 wheel corner action!!!)
But with a 172 or 16V, i think that the increase in size (including the reduction i weight) will more than counteract the decrease in inertia. And with 172BHP on tap, the engine is more tha powerful enough to haul ass!!
In easier terms, your effectively lightning the flywheel.
Shiny red R32
Ben, I think you are wasting your time doing business studies. You should get a job as a technical adviser for some wheel companies so that you can tell car manufacturers and dealers about the type, style and size of wheels to put on their cars, you seem to know such a lot about them!
WOW, the 172 is yours!!!!
yeah i haveseen it, and i love it, i have spent 15 mins one time looking a it and reminising! cause my 172 is in HK and here i cant afford one, but hopefully when my dad retires i can get it shipped over. Anyway, my car is so slow i fall asleep, it takes ages to h=get to 100 and mostly just sits at 80....but my engine is completly, mind my language, f***ed! it stops and runs on 3 cylinders sometime, runs on 2 when cold....but i am waiting for a new engine soon, so i will just blow it up in a big way!!!
I bought some 16V phase 1 wheels for day to day, and to increase motorway speed....super ls will be for shows and track days with yokohama A032R cut slicks!!
oh, if you want, i can give you a few driving lessons in your clio if you want!!!!
well.. my number is 07779119745 if you ever want to call/meet whatever. i live in redland, you?
you at UWE too lofty?
Dont think i would of seen your car. To answer your ques. You want notice much of a difference apart from a harsh ride. The only real difference is that the side walls are more stiff, meaning that the tyre doesnt roll off the rim so much. The only problem is that the loose their progressiveness. On the track a stiff sidewall will make the car faster overall (ie reduce lap times) but it will break away more violently. On the road i dont think you would need 45 profile tyres as its too dangerous on the limit and the harsher ride doesnt make up for any handling benefits....i go for 50 profile. Besides their cheaper.
oh, and leaving my car parked in UWE when its busy resulted in my side strips being ripped off> and i know the boxing in thing, its a nightmare....i had a merc 3 ft infront of me one, took a million point turn to get out!!
