Print

[steddie eddie]

G'day there,
I've got a problem i have tried to work out myselve ,but i am not able to do so, maybe someone here in the room is more able to do than myselve.
The speedo in my Forfour is 3 to 4 km slow, I am on 195/50r15 tyres, on those tyres the circomference is new 1809.56mm and does 552.62 turns per 1km       My plan is to go to 195/55r15 tyres.on those tyres the circomferenceis is 1870.82mm and does 534.525 turns per i km.
What i've tried to work out is how much different the speed is on the speedo with the bigger tyres.
Can anybody help me please..
Greetings,
Eddie.

[CrazyG]

Using 195/55R15 tyres will give approximately a +3.47% difference
in the speedo reading over the original 195/50R15 tyres.

http://www.tyresizecalculator.com/tyre-wheel-calculators/tire-size-calculator-tire-dimensions

[steddie eddie]

G'day CrazyG,
Thank you for the very useful tyre guide, i found that if i go to a little bigger again it will be exactly right.
When i go through a speedtrap with my speedo on 50km/h i am doing 47km/h, so if i go to 195/60r15 i do exactly 50km/h.
Maybe the tire guide is something to put in the help guides for help to other members.
Thanx again and Greetings,
Eddie.

[mr singh]

Speedos deliberately over read for that very reason. Its to have a buffer so you dont get caught by a speed camera.
Why do you want to do EXACTLY the speed shown on the speedo anyway?

[CrazyG]

I tend to agree with mr singh there as it's best to have
a smallish buffer to be on 'the safe side' of things so to speak.
Consider that even a brief gust of wind from behind could 'push'
the car over the limit at an inoppurtune moment and land you
with a speeding ticket, eh ?
Also consider that the speed trap may be a little 'out' and affect
the reading given....it has been known.
And finally....in some countries it is illegal to fit tyres of a size
that is not approved/specified by the manufacturer. OK, so I
know that's going a bit far, but still worth considering as the
manufacturers know from extensive pre-production testing
which tyre size is best overall for the car...as in handling and
safety aspect etc.
So I'd suggest in your case not to go above 195/55R15.

[Alex]

I think 195/60R15 will rub anyway...

I have them on the rear but i have colt d-id springs.

On the front i have 175/65R15 and it's fine at full lock but only just.

[steddie eddie]

G'day there,
Thank you MrSingh, CrazyG and Alex for your input to my small delima.
As Mr sing says i do like to know how fast i realy go but its not that important, Mr Singh and CrazyG i think you  are right about the small buffer zone to the safe side of the speed limit.
Alex, thank you for the imput about rubbing of the tyres, i never thought of that.
I thought of a good thing about it as it will get my Forfour a couple inches higher of the ground to stop the annoying speedhumps rubbing on the rubber strip under the front bumper.
I think as you suggested when the time comes i will stick with 195/55r15, that will be the best ones for me.
Thanx again and,
Greetings,
Eddie.

[CrazyG]

Re speed bumps.....
This works for my daughter in her's....
decelerate as you come towards the hump...
then accelerate (not madly) just a fraction before you
meet the hump. The front of the car lifts a fraction as
suspension 'unloads' and it should just clear the hump...
that, or make/have less of an 'impact' than expected.
(obviously decelerate as you crest the hump)

But of course, this all depends on how high the speed hump
(or speed 'mountain') is, as they do vary considerably.