Measure your wheel / tyre for me please....
Turbo Mini Forums

I've just put together a spreadsheet for Carl so he could calculate his speed from his rolling radius, and it's giving me different answers than any gear calculators i've seen previously.
I've just measured the rolling radius of my mini (A048R 10") and it's coming out at 228.5mm - which equals a 1436mm circumfrence (Pi*2r).

Gear.exe and the Rugby mini club website calculator (looking at the source code) seem to be using 1523mm circumfrence for a 165/70x10" which equals a 242mm radius... ???

So - here's what i'm looking for:
Take a measurement from the floor to the bottom of your wheel rim (front wheels, vehicle on the ground, engine in,etc...).
Now take a measurement from the floor to the top of your wheel rim.
Take the average of the two measurements [ (a+b)/2 ] and post your answer - or just post the two measurements...
Also state the make and size of your tyre...


Cheers,

Edited by turbodave16v on 12th Mar, 2006.

dave ,hell just be using the overall stated hight ,not taking into account squashed tyre, surely.looks like 1/2" of squash .
carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

230.5 (from 62mm and 399mm)

165/60 12 on a 6x12 rim.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I believe that's all they were using Carl - very incorrect!

If others can follow Will's example please - then we can build a picture.
Wil - what was the make of you tyre?

I think i'll put together another gear calculator for the use of registered members on this site - based on ACTUAL tyre data.

Edited by turbodave16v on 21st Jan, 2006.

Just figured out what they've (very incorectly) done...

take a 165/70x10

so, 10" = 254mm
70% of 165 = 115.5
115.5+254+115.5 = 485
485*pi = 1523.6


oh wrong wrong wrong!!!

Why has it taken anyone this long to figure out these calculators are suspect? I'm pretty annoyed with myself as i started a speadsheet many years ago - but got sent gear.exe and forgot about it...

Putting a mark on the tyre and floor then rolling the car forward one complete tyre revolution and measuring the distance would give you a similar result correct ?

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Yokohamas.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

i have already worked mine out based on acctual speeds and revs collected on the strip with a 3.9 ,i just times it up. .well see if your match mine dave.but it wont quite hit 60 in first,lol.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Check your mail Carl...

if our answers don't match up - then your maths are wrong

Bridgestone Potenzas 175/50/13 = 152.4cm circumference measured by rolling the car one tyre revolution on garage floor. (Tyre Pressure 24psi)
1056.2 Revolutions per mile.

Does this sound about right ?

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Well, for that size tyre the 'other' calculators have been using 1587mm - 4% too much...
It seems the 10" stuff is worse.

Metro turbo weekend driver,Mini turbo in the making again!

theres more to this than meets the eye since people are running different weights and pressures and thats not including wear as stated above!

Maybe it would be better to do a gear calculator bassed on the measurements of your car, not a 'pre-profiled' wheel/tire?

Edited by andeh on 21st Jan, 2006.

I've seen the future and tbh its Pie

dave i dont have exel, i had my puter re-enstalled and office is not there anymore ,
help.

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

dave-is this why my car doesnt manage 115 at 7000rpm as the calculator states?

pm sent carl

Oh and what about centrafugal force on the tyre making it bigger the faster it goes round

Metro turbo weekend driver,Mini turbo in the making again!

Cetrifugal force is one thing - but we're talking about a mini here, not a top-fuel dragster.
Also - fact is most actually drop their pressures to 10psi or so when dragging - hence if they do grow (even slightly) then they'll still be significantly less than what the calculators say. Also remember that there is a significant weight over the tyres - which'll probably raise the 'top' of the tyre, but it'll soon flatten out under the centre-line of the axle...



Nic:
I assume from your comment that you're running 3.44 and 1:1 drops?

Well, the calculators say this (as you know) for 7k RPM.

1st.......2nd.......3rd........4th
45.46 _ 66.75 _ 91.65 _ 115.48

Below are my results:

42.83 _ 62.88 _ 86.33 _ 108.78




Tell you what - I'm glad I'm not running an LSD and hence restricted to a 3.44 which gives a max speed of 108.8 mph at 7K rpm

Edited by turbodave16v on 22nd Jan, 2006.

nic ,i tried the exel viewer but it tell me i need a nwer cersion of windows ,which is a bummer,
so i still cannot view your info dave ,
why dont you put it up here or just mail it in a doc.

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Dave how close is Gear.exe to Gearcal.exe then ?

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

ah good, because my speedo was only hitting 108 before i hit the limiter at 7000, i dont think its too far out, cheers for clearing that up dave

I've seen the future and tbh its Pie

Hi Dave,

I measured the rolling distance on the floor.. a lot more accurate than the diameter and calculation thing. My 10 inch Yokos A032R have exactly 1500mm. I also have done a Excel sheet where you can put in Transfer gear ratios, FDs, wheel circumference and gearbox ratios.
I also fitted a digital bike speedo calibrated with my 1500mm data. I proofed my calcs with the police speed guns. It is spot on! Interested in my Excel sheet?

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

i am :o

I've seen the future and tbh its Pie

Hi Harry,

I've already generated something just like that - I's my intention to suitably 'lock' it then have it on TurboMinis as a download.