Speedo Gear Changes

[sankyp]

Hello guys. I own a Maruti 800 and an Indica Zeta. Recently changed wheels to 13inches for M800 and 14 inchers for the Indica. The problem is that it has induced speedo errors and the speedo now shows lower speeds . I would like to know if I can change the speedo gears or recalibrate the speedo without changing the gears so that I can get the speedo readings as before. Any parts number? I know that it is probably close to accurate speeds than before but I need the readings as before.

Thank you.

 

[Umang]

Well...Speedo Error has to happen after wheel upgrades. I'm not sure about solution, let experts shed the light.

 

[RSM]

The problem is that it has induced speedo errors and the speedo now shows lower speeds.

How did you measure, if this is speedo is not showing the correct speed?

 

[Neil.Bhujbal]

I font think there is much you can do.

Even the original speedo meters in vehicles/bikes aren't 100% accurate.

 

[Zinam]

Its really hard to acheive 100% speedo accuracy!

Most OEM has 3-4% err on their readings.

Upsizing wheels will always cause speedo errors & you have to adjust that

 

[cooldhaya]

Probably he has learnt it and that is why he has not updated here again!

 

[Aditya]

The best way to avoid speedo error while upsizing your tyre is to maintain the same DRR (Dynamic Rolling Radius) of the tyre by going for a lower profile tyre with higher wheel size.

 

[RSM]

What is DRR (Dynamic Rolling Radius)? Can you please explain for us.

 

[Aditya]

Tyres are not perfect doughnut shaped in running conditions. There is always a little bit of flattening out at the bottom of the tyre due to the weight of the vehicle.
When the vehicle is moving, the height from the flattened out portion to the center of the tyre will be the DRR (dynamic rolling radius).
All standard tyres will have a specified DRR, which can be got from any tyre manual.
That means that, for example, all 145/70 R13 tyres, irrespective of the manufacturer should have the same DRR, within standard tolerances.
The above is the reason why your speedometer and odometer readings remain unaffected if you change your tyres (same size) from say MRF to JK.
As I said earlier, if you are changing your wheel size, then you should opt for a tyre, which, with a suitable combination of the width and aspect ratio has a DRR as close to the original specification as possible to eliminate speedo and odo error.

 

[Aditya]

The following link will explain what I tried earlier to put into words ...

http://www.raceandroad.com/acatalog/Rolling_Radius.html

And further sankyp, the enclosed link is very useful ifor bigger wheels, and you don't want to have any adverse effect on your speedo readings, or, in your case, to get a grip on the actual speeds!!

http://www.club80-90syncro.co.uk/Syncro_website/TechnicalPages/TRC calculator.htm

In the first column, fill in the stock tyre details, and in the second, put in your desired wheel size, and the options available in terms of tread width and aspect ratio, and voilà!! You have your options available, and the likely speedo error!!

 

[Landrover]

this is a handy calculator. download it and enjoy.

Its a swf file. meaning you need to have flash installed or flash plugins for IE or mozilla.

Usage is pretty self-explanatory.

http://rapidshare.com/files/358919448/tyre_size_calculator.swf.html

PS to Mod: Please allow pdf, rar, zip and some flash files as attachment too. limit the size though.

 

[sankyp]

Hi guys. Sorry for not updating anything here. The car in question M800 was not being used since a long time now. Also I noticed that I mentioned that I owned a Xeta. Not sure why I said it as I have a DLS and it has a diff fuel type altogether. Sorry again.

I guess the thread can be closed if there is nothing more that anyone wants to add here.