Gearbox build

K30DPC · Post by **K30DPC** » Sun Sep 01, 2013 3:19 am

and change it after about 600 miles and very carefully check whats come out. If You will see any shining bits of metal it will be a sign that something could go wrong.

eDaniel · Post by **eDaniel** » Sun Sep 01, 2013 11:18 am

Nice advice, thank you!

Froidas · Post by **Froidas** » Wed Jan 15, 2014 8:47 pm

Could anyone remind me how to calculate that "rolling radius"? I need it for 205/60 R16 tyre.

I tried many tyre size calculators online, but not at least one gave the result of 184,2 cm for 215/40 R17 or 185 for 205/45 R17. Until I won't get the same number for these tyres, I can't trust I have the correct radius for my needed tyre.

And I didn't have any problems with this radius in page 5, but I can't remember, how I got it

Post by **Donald** » Wed Jan 15, 2014 9:04 pm

That original figure isn't correct is it?

Radius of a 17" rim alone is ~216mm. RR of 205/60 R16 is around 265mm.

Or am I misunderstanding?

[(16*25.4)+(205*0.6)]/2

Froidas · Post by **Froidas** » Wed Jan 15, 2014 9:09 pm

I assume, that original one is correct, because several people used it and somehow I got 184,2 cm
But all calculators give around 189,6 for 215/40 R17.

So I want to find out, was everybody calculating wrong 2 years ago or what

[(17*25.4)+(215*0.6)]/2 = 280,4

Post by **Donald** » Wed Jan 15, 2014 9:16 pm

More than likely I'm not accounting for something, not accounting for the tyre being squished a bit or something, I assume the actual rolling radius is from the wheel centre to the furthest point of contact with the road?

Froidas you forgot to change the sidewall part to 0.4 (40%) instead of 0.6 (60%). This gave figures closer the one you had before: http://www.kouki.co.uk/utilities/visual ... calculator

Froidas · Post by **Froidas** » Wed Jan 15, 2014 9:25 pm

Hey !!!! That is my old tyre size calculator I used for several years, but couldn't find now

I found this and calculated 1896.89 mm too :
http://www.clarks-garage.com/shop-manual/trans-02.htm

So to sum it up, I don't know how everybody got those numbers 2 years ago, but I will use your given calculator for what I need now. I will sleep better now, thank you Donald

Post by **Donald** » Wed Jan 15, 2014 9:32 pm

That makes sense now. I assumed rolling radius was something to do with how the radius changed as the wheel turned, e.g. tyre compression at point of road contact. So rolling radius is circumference

why don't people just say circumference? Simple case of pi * wheel+tyre diameter.

So for future reference: