Omega Owners Forum

Chat Area => General Car Chat => Topic started by: Shackeng on 05 November 2011, 11:38:59

Title: Tyre size calculator
Post by: Shackeng on 05 November 2011, 11:38:59
This seems to be a useful calculator: http://www.boosttown.com/wheels_tyres/tyre_size_calculator.php :y
Title: Re: Tyre size calculator
Post by: MV6Matt on 05 November 2011, 20:35:43
That looks like a good one! :y

I use this one as it has a great visual guide too

http://www.miata.net/garage/tirecalc.html

Matthew
Title: Re: Tyre size calculator
Post by: Martian on 06 November 2011, 11:33:40
Also available on the market, and I expect there is also something similar for those taking it up the backside from crapple.
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 09:32:29
This seems to be a useful calculator: http://www.boosttown.com/wheels_tyres/tyre_size_calculator.php :y

just tried that one out - it's over an inch out in tyre diameter
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 09:53:01
from last week's thread.... (adjusted to suit)

the maths on all of these websites and in the hand calcs is worng, sorry.

the tyre business and the auto business doesn't use them because they're wildly inaccurate. The problem stems from the static figures vs. what actually happens on the road. It's for that reason that every profile is tested and the measured figures are what's used. There are two important figures, the wheel revs per mile ( which gives you the gearing ) and the hub height, around which the suspension geometry is designed. Using measured figures takes out the installed sag and the effects of slip.

Omega B is designed around 817 wheel revs per mile. Anything between 807 and 827 will be acceptable ( i.e. 5 either way )

some comparisons :-

205/55 x 16     811 wrpm     594mm diameter on the car     654mm diameter calculated
245/50 x 16     811 wrpm     594mm diameter on the car     651mm diameter calculated
235/45 x 17     820 wrpm     595mm diameter on the car     643mm diameter calculated

tell you what - I'll write a sticky on the subject......
Title: Re: Tyre size calculator
Post by: Kevin Wood on 08 November 2011, 10:03:37
It would be great if someone could write an accurate calculator, actually.

Oh, 5h1t! that's as good as volunteering. :-X
Title: Re: Tyre size calculator
Post by: aaronjb on 08 November 2011, 10:08:22
It would be great if someone could write an accurate calculator, actually.

Oh, 5h1t! that's as good as volunteering. :-X

Yeah.. Hop to, Kevin! ;D
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 10:15:28
that's just the point - every size, profile and tread combination has a different figure, so they are measured, rather than calculated.
Title: Re: Tyre size calculator
Post by: Kevin Wood on 08 November 2011, 10:16:35
that's just the point - every size, profile and tread combination has a different figure, so they are measured, rather than calculated.

I was thinking of something that works on a table of known values, perhaps?
Title: Re: Tyre size calculator
Post by: Shackeng on 08 November 2011, 11:02:14
This seems to be a useful calculator: http://www.boosttown.com/wheels_tyres/tyre_size_calculator.php :y

just tried that one out - it's over an inch out in tyre diameter

Is that for every alternative Stewart? I was looking at going from 225/55 R16 to 205/60 R16 for winter tyres, which it claims is only 2mm difference. :-\
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 11:25:28
unfortunately, it's not a "blanket" error - it's a different error for every combination.

why 205/60 x 16 ? why not the size from the owner's manual ?
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 11:26:05
I was thinking of something that works on a table of known values, perhaps?

I have the known values.......
Title: Re: Tyre size calculator
Post by: Shackeng on 08 November 2011, 11:53:38
This seems to be a useful calculator: http://www.boosttown.com/wheels_tyres/tyre_size_calculator.php :y

just tried that one out - it's over an inch out in tyre diameter

Is that for every alternative Stewart? I was looking at going from 225/55 R16 to 205/60 R16 for winter tyres, which it claims is only 2mm difference. :-\

As recommended to use narrower tyres for winter, this looked closest on that table. How far out is it?
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 16:00:39
that's a very good question, as my figures only go down to 55 profile - I need to do a search and get back to you.
Title: Re: Tyre size calculator
Post by: Shackeng on 08 November 2011, 16:03:45
 :y :y :y
Title: Re: Tyre size calculator
Post by: 2woody on 08 November 2011, 16:08:29
195/65 x 15 would be your best choice
Title: Re: Tyre size calculator
Post by: Shackeng on 08 November 2011, 17:09:07
I agree, but this entails buying, and storing, yet another set of wheels, I have one set of 16" alloys already in the garage, hence consideration of 205's. :y
Title: Re: Tyre size calculator
Post by: cem_devecioglu on 08 November 2011, 18:23:37
It would be great if someone could write an accurate calculator, actually.

Oh, 5h1t! that's as good as volunteering. :-X
;D :y
Title: Re: Tyre size calculator
Post by: cem_devecioglu on 08 November 2011, 18:26:08
from last week's thread.... (adjusted to suit)

the maths on all of these websites and in the hand calcs is worng, sorry.

the tyre business and the auto business doesn't use them because they're wildly inaccurate. The problem stems from the static figures vs. what actually happens on the road. It's for that reason that every profile is tested and the measured figures are what's used. There are two important figures, the wheel revs per mile ( which gives you the gearing ) and the hub height, around which the suspension geometry is designed. Using measured figures takes out the installed sag and the effects of slip.

Omega B is designed around 817 wheel revs per mile. Anything between 807 and 827 will be acceptable ( i.e. 5 either way )

some comparisons :-

205/55 x 16     811 wrpm     594mm diameter on the car     654mm diameter calculated
245/50 x 16     811 wrpm     594mm diameter on the car     651mm diameter calculated
235/45 x 17     820 wrpm     595mm diameter on the car     643mm diameter calculated

tell you what - I'll write a sticky on the subject......

honestly, rare drivers keeps the tire pressures upto spec (and I'm not one of them ;D ) .. so most of the tires are more flat compared to the original calculations.. :-\
Title: Re: Tyre size calculator
Post by: Kevin Wood on 08 November 2011, 20:11:06
honestly, rare drivers keeps the tire pressures upto spec (and I'm not one of them ;D ) .. so most of the tires are more flat compared to the original calculations.. :-\

I over-inflate the ones that lose pressure to compensate for the fact that I can't be @rsed to check them very often, so on average, they are perfect. :y

 ;)
Title: Re: Tyre size calculator
Post by: cem_devecioglu on 08 November 2011, 22:02:31
honestly, rare drivers keeps the tire pressures upto spec (and I'm not one of them ;D ) .. so most of the tires are more flat compared to the original calculations.. :-\

I over-inflate the ones that lose pressure to compensate for the fact that I can't be @rsed to check them very often, so on average, they are perfect. :y

 ;)

so you are one of those drivers ;D :y

seriously , roads are so bad that I always use 2-3 psi lower than the normal spec.. :-\