stupid gearing question

ishmael · Feb 23, 2006

hiya, another stupid question... my landy (series 3, 109, ex military) has bridgestone 235/85R16 tyres fitted, which look a fair bit bigger than others i have seen. i *think* that 205/75R16 is standard, which i think means my gearing is increased by 14%. now i understand this to mean that i should go faster for a given number of revs, but with less "power". also, my speedo will be wrong, surely? and by how much? 14% i can manage, but is it likely to be more than that?

there'll be another stupid question along in a bit.

Gareth Coe · Feb 23, 2006

Standard military 109 tyres are 7.50 x 16. That's the old way of describing it - I'm not sure how this translates into the new speak.
You're right in principle, though: bigger (diameter) than standard tyres will give you more speed and less power. Haven't a clue about that percentage thingy. Bigger front tyres could also foul the bodywork when steering.

ishmael · Feb 23, 2006

found a site that reckoned that older spec tyres couldn't manage profiles less than 1, so a 7.50R16 has a width and a depth of 7.5 inches. this would give a total diameter of 31 inches. my bridgestones have a diameter of just under 32 i reckon, so there should be very little difference. i can stop worrying about that now and start finding something else. like why have i got an 88" brake system on my 109"?

cool site, btw gareth.

Ashoofack · Feb 23, 2006

Ishmael, where was the site that you got the tyre info from? sound interesting. Although not as interesting as your brakes! What year is your 109?

ishmael · Feb 24, 2006

Ashoofack said:
Ishmael, where was the site that you got the tyre info from? sound interesting. Although not as interesting as your brakes! What year is your 109?

i'll have to have a look on monday when i'm in work (in work looking at landrover websites, that is...

) my 109 is 73, but it wasn't released from the MoD until 86(?) - M Reg. hence all sorts of "interesting" features - like the 88" braking system...

Gareth Coe · Feb 24, 2006

ishmael said:
cool site, btw gareth.

Heidi says "Thank you" Now, why didn't you leave a message in the guestbook?

ishmael · Mar 2, 2006

Ashoofack said:
Ishmael, where was the site that you got the tyre info from? sound interesting. Although not as interesting as your brakes! What year is your 109?

i know i said monday, but anyway:

http://www.4wdonline.com/Wheels/Tyres.html

stupid gearing question

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