Wheel Diameter Questions

[GK]

My standard AU 1 Futura wheels are 15 inch. What changes to speedo would occur by fitting 16 inch wheels? The speedo would read slower than it actually is right?

Secondly, If I bought a set of 16 inch wheels (4) for my Futura and I kept an original one as a spare, what would happen to the car if I needed to fit the spare? In other words, if I had to drive a few hundred kays with 3x 16 inch and 1x 15 wheel, what would this do to handling? Would I notice much? Would it do any damage?

Cheers,

GK

[rag top]

It depends on what tyre you fit. If you keep the rolling diameter the same, the speedo will remain accurate. Look at the tyre placard on the inside of the driver's door area. It will give you the correct size tyre in 16" to suit the AU1's.

Same with the spare 15" wheel. The difference will be in the handling, with the different profile tyres.

[The Monty]

I have 17's on mine with the 15 s a spare. Rolling difference is 4.4% (not sure if its + or -) but I had to use the 15 for 2 days while I got my tyre fixed. The only handling worries were from accelerating hard (in the dry) because the 15 was 215 and the 17 235, the side with the 15 would just lay rubber. And if I went around a corner that took the load off the 15, its hold on time, itd just start spinning as soon as I hit the go pedal. Was pretty fun though.

[Casper]

GK,
So long as the 16" tyres are rhe correct size to suit the 16" rim for an AU your speedo will not change more than 1 or 2kph + or -.
I have 17" rims and a 16" spare, overall rolling diameter on both is basically identical though as the tyre on the 16" is a higher profile. I could even run 18, 19 or 20" rims and, so long as the type profile reduced accordingly, none would have any major impact on my speedo.

[GK]

Originally Posted by '67

The difference will be in the handling, with the different profile tyres.

No worries.

Originally Posted by The Monty

The only handling worries were from accelerating hard (in the dry) because the 15 was 215 and the 17 235, the side with the 15 would just lay rubber. And if I went around a corner that took the load off the 15, its hold on time, itd just start spinning as soon as I hit the go pedal. Was pretty fun though.

Sounds like quite a lot of fun. I can hear your conversation with the Police now! "Sorry officer it's the difference in the wheel diameter!" :

Originally Posted by Casper

GK, So long as the 16" tyres are rhe correct size to suit the 16" rim for an AU your speedo will not change more than 1 or 2kph + or -.
I have 17" rims and a 16" spare, overall rolling diameter on both is basically identical though as the tyre on the 16" is a higher profile. I could even run 18, 19 or 20" rims and, so long as the type profile reduced accordingly, none would have any major impact on my speedo.

All sounds good then! In any case, I wouldn't have as pronounced a difference having 16's and a 15 spare I guess as those with 17's + and a 15 spare.

Thanks guys.

GK

[JC]

I have 18s and a 15" spare on the XR8, and 18s and a 16" spare on the wagon.

[GK]

Originally Posted by JC

I have 18s and a 15" spare on the XR8, and 18s and a 16" spare on the wagon.

Alrighty then!!

GK

[Sleeperau]

:Reverend:

Originally Posted by GK

My standard AU 1 Futura wheels are 15 inch. What changes to speedo would occur by fitting 16 inch wheels? The speedo would read slower than it actually is right?



Cheers,

GK

An interesting thread for the speedo correction when you change your wheels or tyre profile is:

www.fordmods.com
Go to the top right of the page & click on Technical Documents
Scroll down to "Speedo Calc".
This calculation document automatically works out the % difference & tells you what colour/type speedo drive to buy.

[BPXR6T]

When going through the speed trap at the start of the hume highway running 245x35x19 instead of the standard 245x45x17 on my AU series 1 XR8 it said I was doing 96 when the speedo read 100.

[Whoosha]

Originally Posted by FourBarrel

When going through the speed trap at the start of the hume highway running 245x35x19 instead of the standard 245x45x17 on my AU series 1 XR8 it said I was doing 96 when the speedo read 100.

hey matey. most cars show up to 5ks quicker than actual I guess they figure its better that way than to show slower also cheaper the old "my speedo said I was only goin xxxx" doesn"t seem tocut it any more I use the hume 5 nights a week with gps speed + tracking fitted that speed trap is 2ks fast as per gps reading guess they figure that excuse wont work either..
cheers

[Mechan1k]

I have found since changing to 17" rims and 235/45R17 rubberr that my speed is 2-3km/h out (ie: shows 102km/h on the speed when GPS indicates I am doing 100.3km/h (or thereabouts).

I had a slightly higher profile 16" tyre on the older 5-spoke wheels and it was dead on accurate (I think I was running 215/65R16s at the time ... will have to check my spare though).

Rececntly change my spare though in the ute to a fullsize 17" rims with 235/45R17 rubber too.

[JC]

Try this link. It will show you the differences in diameters etc.
http://www.miata.net/garage/tirecalc.html

[GK]

Originally Posted by JC

Try this link. It will show you the differences in diameters etc.
http://www.miata.net/garage/tirecalc.html

Thanks for the link JC.

GK