Just got new wheels put on my focus. The originals were 205 50 17, and the new ones are 205 40 17

prob is, i didnt think at the time about the effect it might have on the speedo, which is quite significant (speedo reads 79 and sat nav reads 70)

is it possible to recalibrate the speedo?

Just got new wheels put on my focus. The originals were 205 50 17, and the new ones are 205 40 17

prob is, i didnt think at the time about the effect it might have on the speedo, which is quite significant (speedo reads 79 and sat nav reads 70)

is it possible to recalibrate the speedo?

to be honest the wheels shouldnt really make any difference to the speed as you havent went up that much if you had put 19s on maybe but not as much of a drop as that have you thought maybe the sat nav is wrong? last time i trusted one i almost ended up into a brick wall

when your speedo reads 70, your actual speed will be 68 so nothing to worry about.

A modern sat nav (tom tom etc) will show a more accurate speed than the car speedo does, as all car manufactures ‘under’ set the speedometer. Ford always seem to be more so at around 4 - 6 mph below your actual speed and I'm sorry to say the answer is No you can't adjust your speedometer :)

your still running 17s so there should not be any difference.

Many years ago i modified an old Triumph Spitfire....i changed the final drive ratios and gearbox ratios and went up to 14 inch rims...i got the recalibration of the speedo done by a firm in kingston (Surrey).... it was a case of re facing the dial when on a rolling road. It was expensive to have done about £100 but that was back in 84ish ?

Many years ago i modified an old Triumph Spitfire....i changed the final drive ratios and gearbox ratios and went up to 14 inch rims...i got the recalibration of the speedo done by a firm in kingston (Surrey).... it was a case of re facing the dial when on a rolling road. It was expensive to have done about £100 but that was back in 84ish ?

either youre speedo is wrong shouldnt be showing 9mph of a difference a few mph yes but not that much or the sat nav is wrong with those wheels on you should have 0 difference at all so i suggest use the dash trick and use the speedo on there as its more accurate

the wheel size is the same, but the tyres have gone down from 50 profile to 40, making the rolling radius different.

To be honest since it already had 17's on there i thought they would be fine, but with the lower profile im wishing id gone for 18's instead :(

just hoping it looks ok when i lower it, cause at the minute it looks odd...

A modern sat nav (tom tom etc) will show a more accurate speed than the car speedo does, as all car manufactures ‘under’ set the speedometer. Ford always seem to be more so at around 4 - 6 mph below your actual speed and I'm sorry to say the answer is No you can't adjust your speedometer :)

so if it could be up to 6mph standard then it hasnt actually made that much difference!

I know that its against the law if you actual speed is faster than the indicated speed, hence why manufacturers usually set them a little less

the wheel size is the same, but the tyres have gone down from 50 profile to 40, making the rolling radius different.

To be honest since it already had 17's on there i thought they would be fine, but with the lower profile im wishing id gone for 18's instead :(

just hoping it looks ok when i lower it, cause at the minute it looks odd...

If the wheel size has stayed the same but the tyre profile is smaller then your speedo should be reading slower, not faster.

Only if you increase the circumference of the wheel will it read higher. And even then it wont change much. Would make the speedo more accurate if anything

If the wheel size has stayed the same but the tyre profile is smaller then your speedo should be reading slower, not faster.

Only if you increase the circumference of the wheel will it read higher. And even then it wont change much. Would make the speedo more accurate if anything

thats basically what i was trying to get at in a round about way it should be more accurate technically

thats basically what i was trying to get at in a round about way it should be more accurate technically

Yeah but this guys basically saying that he now has smaller tyres. So really the speedo should be even more out then it was before. But the other way round to what he's saying. His satnav should say that he is going faster than his speedo.

does anyone wana buy a set of nearly new 205 40 17 yokohama tyres? lol

Speedo's always under-read. A Sat-Nav will always read different to a speedo!

Going from 205/50/17 to 205/40/17 will knock your speedo out by +6.9% as your original circumference was 78.8inches, and your new circumference is 73.7inches. Not great, but not bad enough to warrant re-calibration!

You can take your car to your local Ford garage where they will be able to re calibrate your speedo on ids to the new wheel and tyre size, but to be fair the difference between the two isn't massive I'd only bother if you actully changed the size of the wheel. they will charge you for this of course!!! :)

The profile is in relation to the width of the tyre so having a lower profile tyre doesn't neccesarily mean you have a smaller circumference because usually the width of the tyre has increased. A 40 profile equates to 40% of the width of the tyre so it all depends on the width of the tyre and in this case as the tyre is the same width, you've made a big boo boo.

You should have done your homework before getting the different tyres, usual 3% difference in rolling circumference is the maximum advised.