odometer to fast or to slow ???

[charlski]

Not a mathematics whizz ................ so if my speedo is reading 10% slower than the motors actually doing (which it is because of bigger wheels / tyres)

does that mean the odometer is also reading 10% slower i.e. if ive done 100 miles the odo will show 90 ........... thats how i see it, .......... what do the experts say ???????

thanks
KC

[Morr]

Go straight to the top of the class

You've got it 100% correct

[Blizzard]

Mmmm... I'm not sure...

My truck had 215R15 wheels from stock. Now I've BFG M/T's in 31x10.5x15.

My speedo works nearly perfect, 120km/h are 119.7 from the GPS, but my odometer seems to read quite less... So my truck seems to drink a lot of gas more and this is not real... How can be this? Tomorrow I'll test the odo with the GPS...

David

[charlski]

thats the reason i ask, because when i go past a sign lets say on the motorway that says the services are 10 miles away, i seem to get there in 9 miles time on my odometer, also, this means that the average of 260miles i get from filling my tank to the top to first sign of the fuel warning light would actually be 286........... i guess. ...................my tyres are 33,s would be interested in what your sat reader says

[Blizzard]

I tested it yesterday in a trip.

While my speedo it's near perfect (For ex. 120 sppedo 119.7 GPS) my odometer is between 10-20% less reading than the GPS.

I travelled 35km (Odo) and the GPS readed near 40km...

This explains why since I changed the tires I thought the 4Runner was drinking a lot more!

I've 31's that are 7.92% bigger than the stock 215R15...

David

[charlski]

I tested it yesterday in a trip.

While my speedo it's near perfect (For ex. 120 sppedo 119.7 GPS) my odometer is between 10-20% less reading than the GPS.

I travelled 35km (Odo) and the GPS readed near 40km...

This explains why since I changed the tires I thought the 4Runner was drinking a lot more!

I've 31's that are 7.92% bigger than the stock 215R15...

David

thought so, looks like my 33,s will have an even bigger difference, so my mpg is a lot better than i anticipated, cheers for checking

kc

[Morr]

Its been discussed here before how sometimes increasing the overall diameter of the tyres has actually increased the accuracy of the speedo. Many vehicles have speedo's which are not exactly accurate to start with, often reading too fast, which bigger tyres helps to correct.

Assuming that a speedo was reading too fast on the dial but recording on the odometer correctly (a common enough scenario), fitting bigger tyres affects the readings of both by the same percentage, in this case leading to the speedo reading slower and therefore more accurately, and the odometer recording less distance and therefore less accurately.

So in answer to the original question, they are both reading lower than they previously did by the same amount (in this case say 10%), the happy consequence of this change being a more accurate speed indication.

[Tallyman]

And when you come to sell on the vehicle, it will show about 10% less mileage than it's actually done since you changed the tyres. Legally "clocked" or what!!!

[Morr]

And when you come to sell on the vehicle, it will show about 10% less mileage than it's actually done since you changed the tyres. Legally "clocked" or what!!!

Don't forget to adjust your service schedule to ensure its done based on the actual mileage covered rather than that indicated

[exmee46]

Depends on the reason for the difference. A lot of speedo needles get put back wrongly after the dial face change for mph. The odometer is likely to be more accurate and will obviously not be affected by having the needle yanked off and put back. Changing the wheels/tyres will affect both, but could correct an error introduced into the speed reading.

Kev