Change tyre size

[Bert Turnbull]

As 185x80x14 are becoming difficult to buy here in New Zealand, will it effect handling etc if change to 185x75x14, thanks, Bert Turnbull.

 

[GRTV8]

I'm running 195 70 14 on my P6b here in NZ
Handling is still understated

 

[Bert Turnbull]

Thanks, you still keep to recommend pressures?

 

[PeterZRH]

Not in the slightest a lower profile tyre won't deflect laterally as much, if anything improving the handling. In the case of a 175, I doubt you'll notice it. Your only issue is the speedo calibration.

 

[PeterZRH]

I run 185/70s BTW because this size is available in a top-tier quality tyre - Continental PremiumContact 5s in my case.

These reduce the gearing slightly and improve the performance of the V8 as the gears are nearer to where they should be. I have the ZF box so I still have the overdrive/lockup and electronic calibration means my speedo is OK.

 

[Bert Turnbull]

Thanks, FYI, my Rover is 3500S being manual, cheers, Bert.

 

[quattro]

As 185x80x14 are becoming difficult to buy here in New Zealand, will it effect handling etc if change to 185x75x14, thanks, Bert Turnbull.

185/75 14 will be around 3% smaller by circumference so will drop the gearing by 3%, meaning you use a little more petrol, have a slightly better 'pick up' and your speedo will be out by 3%

196/75 14 will only be 0.8% different.

 

[Penguin]

185/75 14 will be around 3% smaller by circumference so will drop the gearing by 3%, meaning you use a little more petrol, have a slightly better 'pick up' and your speedo will be out by 3%

196/75 14 will only be 0.8% different.

Confused here! i have only been selling and fitting tyres for 30 years but to my knowledge with the exception of a few transit sized commercial tyres, theres no such thing as a 75 profile!

 

[quattro]

Confused here! i have only been selling and fitting tyres for 30 years but to my knowledge with the exception of a few transit sized commercial tyres, theres no such thing as a 75 profile!

I was just answering Bert's original posting where he asks if changing to a 185/75 14 would affect handling.

I don't know much about tyre fitments apart from how to work out differences in gearing, what is available in New Zealand, who these guys are, but it does look like they are available.

 

[Bert Turnbull]

185/75 14 will be around 3% smaller by circumference so will drop the gearing by 3%, meaning you use a little more petrol, have a slightly better 'pick up' and your speedo will be out by 3%

196/75 14 will only be 0.8% different.

I was just answering Bert's original posting where he asks if changing to a 185/75 14 would affect handling.

I don't know much about tyre fitments apart from how to work out differences in gearing, what is available in New Zealand, who these guys are, but it does look like they are available.

View attachment 23108

sorry I should have written 70 instead of 75, my mistake, thanks, Bert.

 

[quattro]

sorry I should have written 70 instead of 75, my mistake, thanks, Bert.

That will be 5.8% difference, meaning when your speedo is reading 70, you'll be doing 66, bearing in mind that speedos aren't that accurate anyway.

 

[PeterZRH]

Confused here! i have only been selling and fitting tyres for 30 years but to my knowledge with the exception of a few transit sized commercial tyres, theres no such thing as a 75 profile!

US cars used this profile a lot so I'm guessing imports to AUS/NZ or perhaps native models.

 

[ghce]

Here in New Zealand I am running 205/75/14's on my P6B with of course SD1 mags, very much improved handling and braking.
Rolling circumference is identical to the OEM 185's so no difference in speedo reading.



Graeme

 

[PeterZRH]

Here in New Zealand I am running 205/75/14's on my P6B with of course SD1 mags, very much improved handling and braking.
Rolling circumference is identical to the OEM 185's so no difference in speedo reading.



Graeme


View attachment 23115

You really need that 6" rim here. You shouldn't do that on the standard P6 wheel.