11 replies to this topic

[josh austin mini city e 82]

Hi all, just wondering (roughly) how much out my speedo is likely to be reading ? The mini was originally a City E with the lower ratio final drive. It's now got a 1275 from a Mayfair (which I think are about 3.4??) and 13x7 wheels fitted. Does anyone know how much this will have affected the accuracy of my speedo reading ? And if so in what way
Thanks
Josh.

[ado15]

The ratio in the 'new' gearbox is unlikely to be 3.44:1 if it's a 1275 Mayfair. To be this model, it would have to be a '90's Mini and they will have had 3.1:1 mainly. But I believe other ratios were also used at this time, including the 2.95:1 which is likely to have been the same in your City E.

 

The wheels/tyres make no difference. Well, not a difference that is worth worrying about. The rolling radius on all Mini tyres is pretty much the same. Although it's for a different reason, there are some diameters in our article here to demonstrate just how little difference there is:

http://www.dsnclassi...and-clearances/

 

The speed percentage difference is directly proportional to the diff ratio difference. However, it is also possible that the speedo drive gear ratio might be different.

 

Given Mini speedo's are not exactly accurate at the best of times, I'd check it against a GPS to get the most accurate idea of the error.

[Gerbil367]

I downloaded a speedometer app on my i-phone as my speedo is out by miles - says Im doing 50 when Im actually doing 70.  Phone app is pretty acurate tho which surprised me.  One day I  might sort it out if I can be ar*ed.  Rev counter seems all to ******* as well!

[ado15]

I downloaded a speedometer app on my i-phone as my speedo is out by miles - says Im doing 50 when Im actually doing 70.  Phone app is pretty acurate tho which surprised me.  One day I  might sort it out if I can be ar*ed.  Rev counter seems all to ******* as well!

 

Interesting. Is this just a GPS speedo?

[Gerbil367]

I think it must be - not seen any results of going through bad reception areas. 

[ado15]

I think it must be - not seen any results of going through bad reception areas. 

 

Yes, that's the biggest issue with relying on GPS. But the OP could use it to check speedo inaccuracy assuming there's an app for his phone!

[Gerbil367]

Just looked - his age is down as 19 - BOUND to have an new type phone if he's anything like my 19 yr old son!!!  As you rightly say Ado15, it could give him a fair idea of his speedo variation.

[tiger99]

Yes, and if it reads 50 when doing 70, it is seriously illegal and needs the correct drive gears fitted to sort it out. But first the diff ratio needs to be established.

 

It is worth reminding people, just in case anyone reading this misunderstands, that using GPS as your speedo is not legal, and no-one here is saying that it is. Your speedo is legally required to operate at all times, GPS does not (tunnels, among tall buildings, when deliberately and illegally jammed, which I have actually found on occasion, when Obama turns it off for military operations, etc.) however it is an excellent way of checking that the speedo is correct. I do that regularly in my daily driver. There have been tedious and somewhat acrimonious debates on this subject in the past, and it would be best to not go there again.

Edited by tiger99, 07 February 2014 - 04:02 PM.

[josh austin mini city e 82]

Thankyou for all the replys people. Think iv about got my answer on that ! I think most mini speedometers are out by a few MPH anyway aren't they ? I know mine bounces around when it's over 60 !

[ado15]

You can either play with the speedo drive gears as tiger99 says, or there are companies that will recalibrate your speedo.

[josh austin mini city e 82]

Well as long as the reading isn't too far out it won't really bother me so are we just talking a few MPH ? Like 2-4 ? Or a little more ? Just don't want any speeding fines !

[69k1100]

There is another way, to open the housing and calibrate the speedo by closing the distance between the magnet and the drag cup.

http://home.comcast....odes/speedo.pdf

It won't fix the odometer though.