Hi all,

Can anyone point me in the direction of a site that has a spreadsheet for working out different nominal tyre circumferances based on imputting the tyse size, eg 205/55/15

Col

Go to the Toyo website, there is a tyre calculator there.

If you want a spreadsheat for working out gearing once you have your tyres let me know.

Gordon

Gordon,

Cheers for the link,

I have the tyres and everything, i have had my car on the road for the last 3 yrs and am considering a BEC conversion and need to fiddle with diff ratios and gearing etc to make sure i am not going to red line it at 50mph in top or anything stupid, can you mail me the spreadsheet?
have U2U'd my email.

I'm sure soemone will ridicule my maths but and I dunno 'bout a spreadsheet but isn't it as follows:-

If total diameter of wheel is A + 2B

Where A = rim size and B = profile

For a 205/55 X 15 boot

A= 15 x 25.1 in mm

B= Profile ie height of tyre above rim is 55% of 205mm = 112.75

Therefore total D in mm = (15 X 25.1) + ( 2X 112.75 ) = 602

Using C = 3.141 x D

Ergo C = 602 x 3.141 = 1.890mm

Substitute other sizes in the equation to suite

I THINK !


Or you could use the spreadsheet suggested by Ninja !!!


[Edited on 6/10/03 by jonti]

I measured tyres using string and tape method then used a formula I found to work out the speed at different revs in all 5 gears.
Circumference in feet x 60 xRPM divided by 5280 x gear ratio x diff ratio.
I used it to calibrate the speedo for sva and it worked for that.

yours, Pete.

Cheers pete,

i dont know what engine i want t go with yet so i dont know the output ratio for each gear yet, i have a 4 speed g box on my pinto at present, anyone got a clue what ratio these will be so i can run the exercise on the current set up i have?

Quaife have a nice calculator program you can download from their site, it even has a drop down for common tyres sizes. Simply pop in your ratios and rev limit and click the button and it tells you top speed in each gear and rpms at various speeds in top.

http://www.quaife.co.uk/downloads/QSpeedCalc.exe

For tyre size calculations:

http://www.miata.net/garage/tirecalc.html

[Edited on 6/10/03 by mackie]

try these, (If I can make the attachments)

Michelin provided a table of tyre sizes, I added a column of circumference. I then used this information in my own excel spreadsheet to calculate speed in different gears at a set RPM and RPM's at a given speed and gear

Here is one I made earlier that does everything

Mine's more colourful!