Alloy wheel question

[core00]

Hi,

I found a set of alloy 15" 4x100 from Civis EJ9 that I'm planning to put on my 2003 Yaris, PCD and ETs are similar I believe except the centre bore size but can be corrected by hub centric/spigot ring. My concern is the speedo reading as the Civis set already have good tyres of (195/55/15) and wheel-size.com is only showing 185/55/15 size for my Yaris.

Also what's the legal requirement of speedo reading in the UK? 😕 Pretty sure not all cars have accurate speedo reading haha.

https://www.wheel-size.com/size/honda/civic/1999/

https://www.wheel-size.com/size/toyota/yaris/2003/

Did this earlier and I'm getting -2.08% speedo error, does it sound a lot? is there a way to correct it without throwing away the good set of tyres that's already on the Civic?

[FROSTYBALLS]

It is illegal for a speedometer to show less than the true speed - so speedometers are set to over read. Current UK legislation states that speedometers should read no more than 110% of the true speed, and for speeds between 25mph and 70mph no more than 110% plus 6.25mph.

It depends what percentage your current set up over reads by, as to whether the proposed wheel/tyre combination continues to over read or under read.

One could get an idea of how much the current wheel/tyre combination over reads by, by comparing the speedo readings with the GPS speed readings on a sat nav. If the current over read is, for example, over 3% then you may be OK. 

[core00]

2 minutes ago, FROSTYBALLS said:

It is illegal for a speedometer to show less than the true speed - so speedometers are set to over read. Current UK legislation states that speedometers should read no more than 110% of the true speed, and for speeds between 25mph and 70mph no more than 110% plus 6.25mph.

It depends what percentage your current set up over reads by, as to whether the proposed wheel/tyre combination continues to over read or under read.

One could get an idea of how much the current wheel/tyre combination over reads by, by comparing the speedo readings with the GPS speed readings on a sat nav. If the current over read is, for example, over 3% then you may be OK. 

So I will have to replace the tyres from the Civic to something like 185/55/15 to have a positive speedo reading instead of negative? 😮

[core00]

10 minutes ago, FROSTYBALLS said:

It is illegal for a speedometer to show less than the true speed - so speedometers are set to over read. Current UK legislation states that speedometers should read no more than 110% of the true speed, and for speeds between 25mph and 70mph no more than 110% plus 6.25mph.

It depends what percentage your current set up over reads by, as to whether the proposed wheel/tyre combination continues to over read or under read.

One could get an idea of how much the current wheel/tyre combination over reads by, by comparing the speedo readings with the GPS speed readings on a sat nav. If the current over read is, for example, over 3% then you may be OK. 

Unfortunately I can't do a GPS reading as the car is s till on SORN haha.

[FROSTYBALLS]

20 minutes ago, core00 said:

So I will have to replace the tyres from the Civic to something like 185/55/15 to have a positive speedo reading instead of negative? 😮

As I said it depends how much your current wheel/tyre combination over reads by.

The table you've quoted compares the speedo readings at 30 and 70 of your current wheels/tyres with the new wheels/tyres - but built into your current wheel/tyre combination there will already be a degree of over reading, which could be anywhere between 1 and 10%.

[martswain]

Don't forget to tell your insurance company, or you may end up without cover if you have any sort of incident.

[Mick F]

Sorry, but a bit off topic here.  My hobby-horse about percentages.

If your boss gave you a 100% pay rise, would your pay stay the same or would it double?

If your speedo read 110% of the true speed would it read 10% more or 110% more than the true speed?

True 30mph would read 33mph ................ or 63mph? 

Pedantic Mick.

[Bomber209]

Hi, try www.etyres.co.uk. Input your old tyre size, then input your new set up. It will give you mph differences as well as % profile change. Check the wheels fit properly before committing. I tried to fit 15" wheels from a Honda Jazz, but they fouled on the brake caliper, I tried fitting spacers but they looked S***.