×
Grey Pictures! (19 Mar 2017)

Pictures from IPHONES in PORTRAIT mode are coming out grey. Either take the picture in landscape mode or upload to a sharing site such as Photobucket or use a picture editor to remove the EXIF data.

× A place for more technical discussions. Please make sure you post in the correct section on the site, this way it keeps the site tidy AND ensures you get a more relevant answer.

JImny - correct gear ratios

More
10 Jan 2018 04:21 #188209 by florinelu07
florinelu07 created the topic: JImny - correct gear ratios
Hi all

I have a Dec-2005 Jimny (with electrical controlled transfer box) and recently after driving a same technical generation Jimny (2012), I discovered that at 3000rpm, tacho indicated ~90kmh while in the tested car it was only 80kmh (10kmh less).

Just to make sure, I've asked a friend to check the rpm at his 2010 Jimny (same tech spec) and he confirms that his is cruising with 80kmh at 3000rpm in 4th gear.

All three cars are VVT (M13A engine with that big bulge on the front of the engine), with standard rims and 205/70 r15 tyres with H/T 7 A/T threads.

My question is what are the specific gear ratios for the Jimnys and if I should be concerned for the configuration that I've got (no need for the moment to fit bigger tyres).

I do have reasons to belive that at least the gear box was removed from the car at a moment in time (maybe for a clutch service). Currently the car has a 134kkm.

Thanks

Please Log in or Create an account to join the conversation.

  • 11/60
  • 11/60's Avatar
  • Offline
  • Moderator
  • Moderator
  • The quickest Jimny in Harrogate...(that I own)
More
10 Jan 2018 05:41 #188213 by 11/60
11/60 replied the topic: JImny - correct gear ratios
Don't worry too much and also remember that just because a tyre has the same size on the sidewall doesn't mean that it is actually exactly the same size as another different one. My 205 bfgs were visibly taller than the old unused Bridgestone spare from the factory.

Mooo said Ermintrude (black)
Boing said Zebedee (blue)

Please Log in or Create an account to join the conversation.

More
10 Jan 2018 05:57 #188214 by florinelu07
florinelu07 replied the topic: JImny - correct gear ratios
True, but 10-12kmh is quite a variance.

Looking at the gear ratios specs, it looks right what I'm having on the car:

205/70/r15 = 2.09 meters circumference
3000rpm
4th gear ratio - 1/1190
transfer case High ratio - 1/1
~88kmh at 3000rpm

Please Log in or Create an account to join the conversation.

  • 11/60
  • 11/60's Avatar
  • Offline
  • Moderator
  • Moderator
  • The quickest Jimny in Harrogate...(that I own)
More
10 Jan 2018 06:37 #188217 by 11/60
11/60 replied the topic: JImny - correct gear ratios
Which is about 10 percent which is easily accountable for in the manufacture of different brands of tyres, and that's before you factor in tread wear and the vagueness of remoulded tyre sizings.

Mooo said Ermintrude (black)
Boing said Zebedee (blue)

Please Log in or Create an account to join the conversation.

  • 11/60
  • 11/60's Avatar
  • Offline
  • Moderator
  • Moderator
  • The quickest Jimny in Harrogate...(that I own)
More
10 Jan 2018 06:46 #188218 by 11/60
11/60 replied the topic: JImny - correct gear ratios
Other contributions are also made by tyre pressures, ambient temperature, speedometer calibration and vehicle loading. Tyre sizings are not mathematically pure there have to be tolerances built in.

Mooo said Ermintrude (black)
Boing said Zebedee (blue)

Please Log in or Create an account to join the conversation.

More
10 Jan 2018 07:03 #188219 by florinelu07
florinelu07 replied the topic: JImny - correct gear ratios
I'll have a validation of the tacho readings vs. GPS.

Please Log in or Create an account to join the conversation.

  • 11/60
  • 11/60's Avatar
  • Offline
  • Moderator
  • Moderator
  • The quickest Jimny in Harrogate...(that I own)
More
10 Jan 2018 07:18 #188221 by 11/60
11/60 replied the topic: JImny - correct gear ratios
Yeah I do that with all my vehicles, better than finding out the hard way with a speeding ticket.

Mooo said Ermintrude (black)
Boing said Zebedee (blue)

Please Log in or Create an account to join the conversation.

More
10 Jan 2018 10:19 #188229 by florinelu07
florinelu07 replied the topic: JImny - correct gear ratios
Tacho shows the correct speed - just validated it with Waze on a 10 km route.

So the question remains opened.... do I have the corect gear ratio?

Please Log in or Create an account to join the conversation.

  • 11/60
  • 11/60's Avatar
  • Offline
  • Moderator
  • Moderator
  • The quickest Jimny in Harrogate...(that I own)
More
10 Jan 2018 10:38 #188232 by 11/60
11/60 replied the topic: JImny - correct gear ratios
So at 80 kmh you actually have a lower engine speed. That's good as it will be using less fuel. All good.

Mooo said Ermintrude (black)
Boing said Zebedee (blue)

Please Log in or Create an account to join the conversation.

  • Busta
  • Busta's Avatar
  • Offline
  • Platinum Boarder
  • Platinum Boarder
  • Norfolk's official off-roading God.
More
10 Jan 2018 10:42 #188233 by Busta
Busta replied the topic: JImny - correct gear ratios
The car doesn't know what size wheels it has. Unless the speedo has been re-calibrated, indicated speed is simply a factor of the rpm of the transfer case output shaft. So we can rule variations in tyre size or the fitting of a diff with a different ratio out of the equation.

I'm fairly sure the early r72 gearbox ratios are close to or the same as the pre-vvt gearboxes, so even if they had fitted a completely different gearbox it would not be possible to make the gearing longer. However, I heard someone mention recently that 5th in the new Jimnys was like 4th on older ones, so there may have been some changes made more recently, perhaps driven by emissions requirements.

You must have the correct gear ratio as, apart from replacing your transfer box with a manual one, there is no way of making it longer. And it seems the newer Jimnys may well have shorter gearing. Now we need other owners of VVT Jimnys to confirm their model year and speed at 3000rpm in 4th and we can work out when it changed. And maybe somebody can dig up some gearbox and diff specs to see where in the drivetrain the change has been made.
The following user(s) said Thank You: 11/60

Please Log in or Create an account to join the conversation.

More
10 Jan 2018 11:08 - 10 Jan 2018 11:44 #188237 by mlines
mlines replied the topic: JImny - correct gear ratios
As stated, the speed DISPLAYED is derived from a measurement of the rotation of the transfer box output shaft.

The speed ACHIEVED is a function of the differential ratio and tyre diameter.

RPM of engine for a given speed is the combination of gearbox, transfer box and differential ratios

You can see the information I have so far here:

www.bigjimny.com/mediawiki/index.php?tit...erential_information

(updated with gearing)

Martin

2003 M13 early KAP build.
3" Trailmaster lift with 1.5 Spacers on front
Customised winch bumper and roll cage
235/85R16 Maxxis Bighorns on 16" Rims, 4:1 Rocklobster, Rear ARB locker and on-board air
Corrected arms all-round, rear disks, Recaro seats and harnesses
Last Edit: 10 Jan 2018 11:44 by mlines.

Please Log in or Create an account to join the conversation.

More
10 Jan 2018 11:47 #188240 by yakuza
yakuza replied the topic: JImny - correct gear ratios
The analogue speedometer is a friction based device so there will be variations from car to car in addition to the obvious tire difference.

2005 Jimny MT M16A VVT, 2" Trailmaster, 235/75-15 MT
1987 SJ413 lwb, G16BB, 4" trailmaster, 2xARB, 4.16:1 transfer, 325/75-15 MT -project in pieces..

Please Log in or Create an account to join the conversation.

Moderators: funkyjimnyooky_123
Time to create page: 0.214 seconds
Powered by Kunena Forum

I hope you enjoy using this forum. Please consider making a donation towards the upkeep of this forum website.