63 replies to this topic

[CHILL Gone DUTCH]

been doing some thinking (dangerous i know) and normally ends up costing me money 

 

with a overall reduction in tire and wheel size i am assuming overall weight is also reduced (may not always be the case) 

 

so that is first advantage [color=#0000cd;]unsprung weight [/color]

no real debate there 

 

i accept top speed will be reduced at a given rpm and gear 

 

but now im getting on to acceleration 

a smaller wheel in theory reduces the final ratio of the drive chain but does the increase the acceleration or just increases the rate of gear changes 

my thinking is the car will cover more ground per gear change at same rpm, but does the weight saving and smaller circumference make up for the bigger wheel 

 

lets assume traction is not a issue 

 

thoughts and opinions on a vx220 setup 

 

[CHILL Gone DUTCH]

its also worth mentioning i rarely get out of 4th gear on track (which is quite fast in the rev limiter )

 

there must be some clever maths around this somewhere 

Edited by CHILL Gone DUTCH, 20 May 2017 - 01:19 PM.

[Exmantaa]

??

[Exmantaa]

What are you trying to do? Smaller wheels is just like reducing the final drive ratio... (rpm's vs mile/hr)

[CHILL Gone DUTCH]

would it theoretically increase acceleration

 

[CHILL Gone DUTCH]

the more i thought about it the less straight forward it is 

[Exmantaa]

Off course; like accelerating in 3rd instead of 4th gear. (Until the rev limiter kicks in...)

[Danny Scarbro]

Smaller wheel + Tyre = more acceleration and reduced top speed.

 

On top of that you get better un-sprung weight which will make the car feel more nimble and change direction quickly better.

 

 

On track with the Mx5's the car is totally transformed with going from 15" wheels to 13"'s.

 

Giving better acceleration and the car feels alive.

 

 

I will at some point go down to a 15/16 or 15/15 combo on mine.

 

My aim is to get to just under the rev limiter in 5th on the back straight at Cadwell which in turn will be geared about right for most circuits.

 

Dan

[Danny Scarbro]

Here are my workings out Chris;

Stock Na gearbox, FD and 225/45/17 tyres;



With the 4.4 FD that I'm putting in mine;



Then with 16" wheels/tyres;



Then with 15" wheels/tyres;



You'll notice the difference between 15/16 wheels is very little as it's difficult to find a decent 45 aspect tyre.

Because of this I'll probable go 15/16.

Dan

[CHILL Gone DUTCH]

can you link me that web site 

 

very intrested in standard 3.95 gearbox with 16" rears 7500 rpm if you wouldent mind 

 

[Danny Scarbro]

www.cargister.com/calculator-gear-ratio

 

Top speed with that in 5th would be 167.2mph.

 

What was your terminal speed at Cadwell on GPS Chris? for both straights out of interest?

 

 

Edited by Danny Scarbro, 20 May 2017 - 02:46 PM.

[CHILL Gone DUTCH]

130 on the start finish straight 

and 138 on the dipped straight both 4th gear 

 

[CHILL Gone DUTCH]

so 16" rears would give me a few advantages 

 

lower sprung weight and still nver going to dare to do 167 in the vx if the power would push me that fast and straight was long enough 

and slightly better acceleration and am i right in thinking a smaller tire would heat up quicker than a bigger one 

 

as my eye is now on sprints 

 

[Danny Scarbro]

Christ!

 

Mine was 120 on start finish and 123 on back straight!

 

Yeah, I would be interested in seeing if we can get some 16x8 wheels at a good price, possible group buy?

 

 

I think the 16's will make a good compromise of aesthetics (15"s tend to look abit silly IMO) and just sharpening the feel of the cars up too.

 

Dan

[CHILL Gone DUTCH]

I will still be wanting to split size i.e. 15" front 16" rear

[CHILL Gone DUTCH]

We should check tire size to Would like to get a 235 on the rear and 205 on the front This will be a better option for me rather than 1.47 gearbox as I think I would be running out of gear at around 145-150 in 5th

[CHILL Gone DUTCH]

And the car wil sit lower

[Nev]

Dont forget your ground clearance will diminish if your rolling circumferance diminishes, hence possible ground clearance issues.

[Danny Scarbro]

I like the idea of 15/16 but limited wheels available and front brake clearance is a factor? I don't think I'll ever see anything over 135 on track with my power levels so should be fine! Your car however is silly fast!

[CHILL Gone DUTCH]

Dont forget your ground clearance will diminish if your rolling circumferance diminishes, hence possible ground clearance issues.

I have no addition low points on the car it's completely oem indertrays and no skirts or splitter so should be ok