If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed, registering will remove the in post advertisements. To start viewing messages,
select the forum that you want to visit from the selection below.
This means you should apply for your renewal now to avoid any disruptions to your membership whilst the renewal process is taking place! NOTE: If you have an auto renewing subscription this will happen automatically.
I think you will find the variance in speed is not completely related to the wheels but just the way they calibrate the computer.
Out of the 3 combos of wheels offered standard, doing 100km/h on the GPS I would be getting this on the speedo:
195/55r15 (596mm Radius) (108km/h)
215/40r17 (604mm Radius) (106km/h)
So for the 1% difference in side wall height I have about 1% difference in speed.
At the end of the day though the speedo is out on average 5km/h, (disregarding the variance from the wheels) which I would say is good because it allows for variance in tyre pressure and the height of the remaining tread and also if you are speeding a bit you don't get snapped by the camera
So hearing that the speedo is linked to the size of the wheels, if I was to get bigger wheels, that would stuff the speedo up would it not? Or is there a setting somewhere to specify your wheels size?
Current Ride: Golf GTI Mk7 MY2014|DSG|Carbon Steel
Previous Ride: Polo GTI MY2012|DSG|RNS510|Shadow Blue|Lenso GF7 18” rims Instagram: @lemonskin
So hearing that the speedo is linked to the size of the wheels, if I was to get bigger wheels, that would stuff the speedo up would it not?
Not strictly.
The bigger the rolling circumference of the tyre, the less the speedometer will underestimate the vehicle's speed.
Think of the tyre as just another gear - the bigger it is, the more "slowly" the needle in the speedo will rise.
Fitting bigger tyres (for example 205/50 R17 or 215/50 R17) will reduce the discrepancy, but will also affect the vehicle's dynamics, which you may or may not approve of.
No the speedo is not linked to the size of the wheels it's a mathematical calculation on how speed is determined. The speedo is configured to accommodate for all situations so the speedo is always faster through all models, specs, options and ranges.
You have to do that math on it. If you wanted to go to 18" you would need a 35 (will display 103 when doing GPS 100) or 30 (will display 107 when doing GPS 100) tyre profile (so 225/35r18 or 225/30r18 ) wether it will even fit on the car or not is another story
The bigger the rolling circumference of the tyre, the less the speedometer will underestimate the vehicle's speed.
Think of the tyre as just another gear - the bigger it is, the more "slowly" the needle in the speedo will rise.
Fitting bigger tyres (for example 205/50 R17 or 215/50 R17) will reduce the discrepancy, but will also affect the vehicle's dynamics, which you may or may not approve of.
As I already posted, the answer for which I asked a tyre company in USA
mine give an incorrect speedo reading of 7kph over.
They are 195/ 55/ 15
To correct it I would have to go to 195/65/15 which are 6.7% taller or 40mm
Would fit but unfortunately are illegal
Will also affect take off as it will up the gearing somewhat and put some extra strain on drive components
2021 Kamiq LE 110 , Moon White, BV cameras F & B
Mamba Ebike to replace Tiguan
Just wondering why would you bother going to such effort to correct it. If you know it's out, go 7km/h faster or just do the limit and never ever get busted by the police...it's what i do.
I definitely wouldn't bother spending the money to get the speedo 100% correct (which you never will anyway, due to 100 factors including the fact that a speedos accuracy varies from 0-240km/h) and especially wouldnt do it at the cost of fatter worse performing tires.
Hi, my Polo has the standard Lakeside 15" wheels with 195x55 R15 rubber and when my Garmin GPS reads 100 km/h the speedo reads ~107 km/h. When the GPS reads 110 km/h, the speedo reads ~118 km/h. When the GPS reads 120 km/h, the speedo reads ~122 km/h. It seems then that the rate at which the speedo overestimates the car's true speed is inconsistent and so I think that changing wheels/tyres to make the speedo accurate will actually do the opposite, and make it much less accurate. Just my opinion.
Hi, my Polo has the standard Lakeside 15" wheels with 195x55 R15 rubber and when my Garmin GPS reads 100 km/h the speedo reads ~107 km/h. When the GPS reads 110 km/h, the speedo reads ~118 km/h. When the GPS reads 120 km/h, the speedo reads ~122 km/h. It seems then that the rate at which the speedo overestimates the car's true speed is inconsistent and so I think that changing wheels/tyres to make the speedo accurate will actually do the opposite, and make it much less accurate. Just my opinion.
If you dont speed you will be ok cos its ok up to 110 same as mine LOL They are usually linear that is the difference gets larger the faster you go. Havent checked mine at 120 as I cant afford the fine ROFL
2021 Kamiq LE 110 , Moon White, BV cameras F & B
Mamba Ebike to replace Tiguan
If you dont speed you will be ok cos its ok up to 110 same as mine LOL They are usually linear that is the difference gets larger the faster you go. Havent checked mine at 120 as I cant afford the fine ROFL
Haha I wasn't the one driving, backseat passenger I was! Mum was driving and inadvertently sped while I was looking at the GPS so I quickly glanced to the speedo to check the difference. When I get my licence I won't speed. Promise
Haha I wasn't the one driving, backseat passenger I was! Mum was driving and inadvertently sped while I was looking at the GPS so I quickly glanced to the speedo to check the difference. When I get my licence I won't speed. Promise
I think you misread it at 120k It was more likely to read 132 not 122
EG 80 = +5 or 6 100 = +7or 8 110 = +9 or10 120 = +11 or 12
2021 Kamiq LE 110 , Moon White, BV cameras F & B
Mamba Ebike to replace Tiguan
I think you misread it at 120k It was more likely to read 132 not 122
EG 80 = +5 or 6 100 = +7or 8 110 = +9 or10 120 = +11 or 12
That's perfectly possible, I'm well known in my family to be slightly dyslexic when it comes to remembering numbers. Your formula seems right to me so we'll run with that.
As I already posted, the answer for which I asked a tyre company in USA
mine give an incorrect speedo reading of 7kph over.
They are 195/ 55/ 15
To correct it I would have to go to 195/65/15 which are 6.7% taller or 40mm
Although my reply was more aimed at Lemonskin and his car (Polo GTI with 215/40 R17 tyres), you are correct in regards to the 15 mm limit for allowable increases in the overall tyre diameter (at least for QLD, NSW & VIC).
Just wondering why would you bother going to such effort to correct it. If you know it's out, go 7km/h faster or just do the limit and never ever get busted by the police...it's what i do.
I definitely wouldn't bother spending the money to get the speedo 100% correct (which you never will anyway, due to 100 factors including the fact that a speedos accuracy varies from 0-240km/h) and especially wouldn't do it at the cost of fatter worse performing tires.
Just my two cents.
I agree.
To depart significantly from the manufacturer's recommended tyre fitment for the sole and only purpose of altering the speedometer's readout, is perhaps a bit short-sighted.
Tweet
Comment