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Impact of bigger alloys?


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#16 JAR897

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Posted 30 May 2009 - 10:33 PM

Yes, more friction = more thrust required to move, but when regarding rotation of a cylnider at 0 velocity and 0 speed there is no difference in friction between a very grippy pair of tyres and a flat pair apart from gravitational weight.

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#17 mintalkin

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Posted 30 May 2009 - 10:35 PM

tyre grip increases the amount of resistance that the engine must first overcome before it can accelerate the vehicle. so in actual fact an overall bigger wheel will actually slow the car down.

#18 JAR897

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Posted 30 May 2009 - 10:36 PM

yes but the point which im obviously not getting accross is that the size of a tyre has no relationship to the amount of grip!

#19 Nipz

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Posted 30 May 2009 - 10:36 PM

Yes, more friction = more thrust required to move, but when regarding rotation of a cylnider at 0 velocity and 0 speed there is no difference in friction between a very grippy pair of tyres and a flat pair apart from gravitational weight.


But when you start to move there is :D

I tell you what ill agree to disagree as im nakered and need to go bed, got wake boarding early :D

Hope your foots ok!

#20 Fraser.

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Posted 30 May 2009 - 11:12 PM

When talking about wheel sizes effecting accelleration etc. If the larger alloy weighed roughly the same as the smaller one, then the alloy size shouldn't really have that much of an impact should it? Rolling radius will be roughly the same for both alloys as the larger wheel will have a smaller profile tyre.

#21 Burton

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Posted 31 May 2009 - 11:48 AM

yes but the point which im obviously not getting accross is that the size of a tyre has no relationship to the amount of grip!


thats right in practice, but if u look at it form a therotical point of view, the rolling friction of a wheel is less, the bigger its radius is...
but thats just totally theoretical.
but what my point is: the bigger the radius of the wheel the smaller the force u get on the road at a given torque of the wheel.
its this formula: force = torque/radius
thats also the fundamental fact why we use transmissions - its very important cause otherwise we would need BIG engines.
and to come to ur point about more grip is more acceleration:
from the physics point of view this is totally wrong. but what is right is that with more grip u can transfer more force to the road, so the wheel wont slip so easily, thats why u can accelerate faster with more grip. thats of course only the case with a strong engine that u operate on its limits. (of course u can slip ur wheels with a smaller engine too, but u will feel a slight decrease of acceleration with more grip)

#22 BenW

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Posted 31 May 2009 - 12:19 PM

LMAO.... what a thread.... :lol:

Love the physics bits (Physics A-level myself). From my understanding more grip/opposing force from the road/tyre's = more work/engine power required therefore less output/acceleration under the same enviroments (road, engine, forces & weight).

lol...... ;)

#23 JAR897

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Posted 31 May 2009 - 01:35 PM

From stand still (i.e. no velocity) there is no opposing force exerted onto the road. Acceleration tkaes more into account than simple physics which is what is being used here as argument.

Slip Differential and pwoer output as well as weight and even the type of grip all have effect. More grip may cause more opposing force and consuquently slow the car when stopping, however during positive velocity the grip will create a more adhesive base to propell the car.

When the car is at a nutural velocity (i.e. constant speed) the grip will come into effect as described above, slowing the car at a faster rate than an under-gripped tyre.

Furthermore, Less grip will have negligible effects regarding motionless kinetics, creating opposite momentum which would actually reduce velocity.

There is, however, an equlibrium to be met here; too less grip will return the effects mentioned above, where as too much grip will simply bring the velocity(vs)friction equlibrium too low so that the negative effects of grip come into play before the car has accelerated to the desired speed.

Hope this makes some sence... Iv'e been talking to my housemate who works for a racing team and he tends to agree.

#24 Burton

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Posted 31 May 2009 - 05:19 PM

From stand still (i.e. no velocity) there is no opposing force exerted onto the road. Acceleration tkaes more into account than simple physics which is what is being used here as argument.

Slip Differential and pwoer output as well as weight and even the type of grip all have effect. More grip may cause more opposing force and consuquently slow the car when stopping, however during positive velocity the grip will create a more adhesive base to propell the car.

When the car is at a nutural velocity (i.e. constant speed) the grip will come into effect as described above, slowing the car at a faster rate than an under-gripped tyre.

Furthermore, Less grip will have negligible effects regarding motionless kinetics, creating opposite momentum which would actually reduce velocity.

There is, however, an equlibrium to be met here; too less grip will return the effects mentioned above, where as too much grip will simply bring the velocity(vs)friction equlibrium too low so that the negative effects of grip come into play before the car has accelerated to the desired speed.

Hope this makes some sence... Iv'e been talking to my housemate who works for a racing team and he tends to agree.


i know what u mean but since english is not my mothertongue its pretty difficult for me to explain what i mean...

the wheel will slip (and thus reduce the acceleration) as soon as the force applied on the ground (by the torque of the wheel) is greater than the maximum force of static friction available (between the tyre and the ground)

and in theory this maximum static friction is detemined only by 2 factors: the weight of the car and by the coefficient of friction, which is determined by the two surfaces that have contact (the rubber and the road) - thats what u mean with type of grip i guess cause this coefficient is smaller when its more slippy and higher in good roadconditions and has many other influences like temperature etc. and of course also the wideness of the tyre.

the conclusion: the higher the static friction between the wheel and the road (thats the more adhesive base to propell the car) the more force u can apply without the wheels to slip and thus have a better acceleration. but since u dont drive like a racer on ur way to work u wont need such a high grip since the force u apply never reaches the limit of the static friction, but u will definatly feel a slightly slowlier acceleration (except if u re a boyracer, we all know those i guess :D)

#25 JAR897

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Posted 31 May 2009 - 05:25 PM

the higher the static friction between the wheel and the road (thats the more adhesive base to propell the car) the more force u can apply without the wheels to slip and thus have a better acceleration


I.e More force without wheel spin <-- my point exactly.


but u will definatly feel a slightly slowlier acceleration (except if u re a boyracer, we all know those i guess :D)


Boy = true.
Racer = true.

BoyRacer = True.

#26 RIIIDAA

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Posted 31 May 2009 - 05:32 PM

guys you are quibbling over a 3% difference in rolling radius, get outside and enjoy the weather :lol:

Sussex put some more mileage on the car to wear the tyre tread down a bit ;)

#27 jkc89

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Posted 31 May 2009 - 07:03 PM

Gotta love the debates LMAO

#28 paulworthing

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Posted 31 May 2009 - 07:19 PM

Good debate but aren't we missing the bigger picture - 17" alloys look so much better than the 15" ones??

#29 sussex

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Posted 31 May 2009 - 09:06 PM

Thanks for all your help (interspersed with debate on physics!!)

MPG definately about 5-7mpg lower than I got on my 15"s and acceleration is not quite as good. But will give it a bit of time. Its not just a case of the MPG reader being out as I am checking the miles to empty gauge and the fuel dial as well as well as the miles covered since I pressed the trip.

As for looks? The 17" titanium X alloys are gorgeous!

#30 JAR897

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Posted 31 May 2009 - 10:39 PM

Lol thanks guys.. I'm pretty adament that the reduced acceleration will be due to the rolling radius, NOT any difference in tyre profiele or wideness though.

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