looking for a 4x4 tyre/gearbox/axle ratio engine rpm calculator..
Submitted: Sunday, Aug 28, 2005 at 09:46
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flyology
Hi folks, I used to have a link to a site that had a good engine rpm calculator, puting in all the relevant factors like gearbox final drive ratio, axle ratio, tyre diameter etc, but on going to use it, the page is unfortunately no longer available. Does anyone out there have a link they can post or send me to a similar calculator? I have a 87 HJ61 'cruiser with 31x10.5x15 all terain T/A's and I am thinking of putting 16"x8"
wheels on it, and want to work out how much difference it will make. I get pretty good fuel economy at the moment (9.8klms per L), driving the 50 klm round trip to
Cairns and back from
Gordonvale, part highway, part town driving, but if I sit on 100kpm on the highway engine rpm is around 2300, and fuel economy drops off.
thanks in advance....
Marty Bristow
Reply By: GaryInOz (Vic) - Sunday, Aug 28, 2005 at 11:10
Sunday, Aug 28, 2005 at 11:10
The rim size makes no difference
The tyre size on your new rims will be ??????
If the overall tyre size is the same, (265/70R16 = ~31"), then there will be no difference in overall speed per rpm
AnswerID:
127165
Follow Up By: GaryInOz (Vic) - Sunday, Aug 28, 2005 at 11:19
Sunday, Aug 28, 2005 at 11:19
Go for 33" tyres on your 15" rims would be the cheapest way for a proportionate reduction in revs
(old dia/new dia) x rpm,
ie. your case (31/33)x2300 = 2160 rpm
Remember though, you are driving a brick with zero aerodynamics so changing tyre dia may not actually fix youtr problem after allowing for speedo/odometer correction.
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Follow Up By: Utemad - Sunday, Aug 28, 2005 at 13:09
Sunday, Aug 28, 2005 at 13:09
Changing to a 32in tyre would make the fuel econonomy better I'd think as a 31in is probably smaller than the factory tyre whereas a 32in would be about right.
You might need to change rims anyway though because if you currently have 15x7 rims you will need to source 15x8.
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Reply By: Sarg - Sunday, Aug 28, 2005 at 13:33
Sunday, Aug 28, 2005 at 13:33
is this what you are looking for ?
http://www.osella.com.au/gear-ratios.htm
AnswerID:
127183
Follow Up By: flyology - Sunday, Aug 28, 2005 at 13:49
Sunday, Aug 28, 2005 at 13:49
thanks Sarg, exactly what I was looking for.
FollowupID:
381716
Reply By: flyology - Sunday, Aug 28, 2005 at 13:59
Sunday, Aug 28, 2005 at 13:59
Yes, I think it could end up being expensive which ever way I go, but I do like the idea of changing to 16" rims and tyres. Using 32's or 33's has crossed my mind, but I dont like the idea of having a bigger sidewall, which leads to more flex and also a larger area to get staked/damaged when off road.
I am also considering a couple of sets of 3.7 gears for the diffs, (I don't go rock crawling) also expensive, but when you add up the saving in fuel, less engine wear and less road rage from sitting on 90kph in a 100kph zone, it might end up saving me money....
I cant complaint to much though, nearly 10 klms a Litre 'aint bad for the old girl. standard 12HT with the exception of a 3" exhaust, not bad for a brick.
AnswerID:
127188
Follow Up By: Utemad - Sunday, Aug 28, 2005 at 14:11
Sunday, Aug 28, 2005 at 14:11
Lowering your RPM is not always the best way to conserve fuel. Your engine has a place in the rev band which it prefers to be in. If you normally cruise at say 2500rpm yet change your ratios to sit on 1800rpm at the same speed then your economy may not appreciate it.
To have better economy than you currently do I would just fit either the standard height tyre or the next size up perhaps.
Perhaps having less sidewall flex, hway tread pattern and a skinny tyre would help also.
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381717
Reply By: Beast Of Bodmin - Monday, Aug 29, 2005 at 13:46
Monday, Aug 29, 2005 at 13:46
G'day Fly,
I found this website:
www.1010tires.com/TireSizeCalculator.asp
Really good way to compare tyre sizes against the effect on the speedo. There are other too that will accept diff ratio changes etc, but l haven't got the link at the mo.
Cheers
Beast o' Bodmin
AnswerID:
127302
Reply By: craig - Wednesday, Aug 31, 2005 at 12:12