wheel size Vs mpg

[corkgsxr]

has anyone changed to 15" or 16" wheels and found it be be better on juice than on the std 14" wheels?

theory being that since there not short on torque, if the wheel covers more ground for the same revs will you mpg be higher?



other thing is mines the 75 hp version, whats the diff between the 75 and the higher power one (i think its round 100hp)

is it a computer controlled reduction or a combo of turbo, intercooler, injectors etc?

[pch]

I had 15 " winter tyres on my vw camper and 17" alloys for summer and you couldnt tell the differance.
the 17" just cost more to replace,,,,but they did look nice.
Pete

[3rensho]

Just curious, but doesn't changing wheel diameter affect the speedometer and odometer readings?

[andy-womble]

Just curious, but doesn't changing wheel diameter affect the speedometer and odometer readings?

Errrr yes.

Speedo/Odometer is calibrated on the following,
Final drive ratio and Rolling radius of the wheels.

In the good old days it used to be possible to swap the speedo drive gear at the gearbox end but don't know if people still do that

A lot of people do not seem to take this into consideration, also fitting different sized wheels could be viewed as "Modifications" by insurers and may invalidate your policy.

[pch]

yes def inform your insurer, some say as manufacturer fits say 15 inch on berlingo`s thats ok, but if alloys worth notifying them. Also speedo is affected, I could see difference cross relating to a gps fitted.
Aslo when I fitted my black alloys to my mk 3 I informed them and had to fit locking wheel nuts, McGuard. Sadly my local tyre dealer overtightened them and when I wanted to fit my winter tyres couldnt get em off. Had to pay local garage to crack them off. So I have decided not to refit mcguards again, got my money back on them as said they were no good to hALFORDS. It took my garage 4 mins with an oversize wheel nut remover....anyone could do it, even me...so whats the point in having them.....If anything happened I will just say locking nuts were fitted, I still have receipt.
Pete

[Chris]

For a 14" wheel (assuming you have 175/70 tyres) you get a tyre rolling circumference of 1832mm. If you were to swap to 15" with 185/65 tyres (which were standard fit on some mk.2 Multispaces) then you get a TRC of 1896mm, so 64mm extra distance travelled for each wheel rotation.

According to this TRC calculator (where I got the figures above) your speedo would be out by 3.5km/h at 100km/h which is within UK limits and probably not worth trying to correct.

[andy-womble]

Thanks Chris, I've never sat and worked the math out but I have just checked and it appears that under United Kingdom legislation a speedometer is permitted to have an error of up to +10%.
This means that as long as your speedo is either reading accurately bang on the nail or up to +10% faster than the speed you are actually travelling at then it is legal.

[Chris]

Mine over-reads by around 7-8% when checked with GPS which is fairly typical.

[corkgsxr]

mine reads almost bang on. which is weird

[andy-womble]

mine reads almost bang on. which is weird

You must have the one they made correctly