How fast am i going?

[DR SCHNITZEL]

FD standard manual Diff 7800 rpm, 17 inch wheels with 50 profile tyres.
 
also whats the formula to work it out?
 
Hypothetical obviously:Ladys-man

[raceralexuk]

FD3s standard manual diff ratio:
 
4.1:1
 
FD3s standard gearbox ratios:
 
1st 3.483:1
2nd 2.015:1
3rd 1.391:1
4th 1.000:1
5th 0.719:1
 
17 inch wheels with 50 profile tyres:
 
Width is important here as the 50 profile refers to the sidewall height relative to the tread width. For now I\'ll presume a width of 265, giving a rolling diameter of 695.8mm and a circumference of 2.18m (0.00218km).
 
----------------------------
Ok, now we have all the numbers we need. The maths goes as follows:

(((Engine RPM/Gearbox Ratio)/Final drive ratio)*60)*Driven tyre circumference=Ground speed in KPH.

Multiply by 0.62137 to show the KPH value in MPH.
 
----------------------------

Using the numbers you provided:

(((7800/0.719)/4.1)*60)*0.00218
 
 
=346.090kph
 
*0.62137
 
=215.04mph

[ENVYD]

that seems far to fast for stock fd box dont it :|

[DR SCHNITZEL]

Yeah way too fast, i thought it would be 170ish

[ENVYD]

nah i think it will be a bit faster, i member going 165 at 6800, clocks and power fc might be out though!

[DR SCHNITZEL]

i dont see how tread width is important, i think the circumference of the tyre is wrong

[ENVYD]

what am i saying its only 1k more lol!

[DR SCHNITZEL]

From the 200mph build thread they guy has to do 9020 rpm to hit 200 dead, on a auto diff

[JBerg]

tread width is important because the aspect ratio eg, 50 like in your case, is 50% of the height of the width...
 
so a 265/50, is taller than a 255/50.

[DR SCHNITZEL]

oh right, hmmmm thats interesting, so im looking at 165mph at 6800?

[ENVYD]

i am 90% sure thats what mine was around!

[raceralexuk]

The single biggest factor in producing that huge calculated speed value is the huge height (or radius - I use the term height because that\'s how race car tyres are numbered) those 50 profile tyres have.
 
A 50 profile 265 equates to a height of 695mm(!) As a comparison on my race car I run 285/650 rears. 695 is as tall as a skyscraper, is it a drag tyre or maybe borrowed from a rear-engined Porsche..? On 650 rears at 7800 rpm an FD3s using a standard drivetrain would be travelling at 179 mph.
 
If this is a real car in question and not a hypothetical one, I seriously suggest running much lower profile rear tyres unless there\'s a darn good reason for those tractor boots!

[turbotoaster]

ok guys, ill help you out with this.

assuming 4.1 diff at 7800rpm

235/50/17 181mph
245/50/17 184mph
255/50/17 187mph
265/50/17 189mph
275/50/17 192mph

this makes the assumption that the tyres are new and havent been worn down, the more used(less tread) the slower you are going at a set rpm

most people run 255/40/17 ont he back of there rx7, with a stock diff you need to hit 9020rpm to do 200mph, with an auto diff you need 8580rpm

If you want to know exactly ill need either the diameter or the circumference of your current tyres

[DR SCHNITZEL]

I have just measured the diameter its 626mm (oh and they are 255/40/R17) oooops.
Can you do a little list of speeds for that matey

[Timmy]

172 mph i think.