Wheel/tyre size and speedo reading. - Page 2

Duotone · 13th April 2012, 17:33

Quote:

Originally Posted by CMWI

Does the different final drive ratio on the ZT explain why their 18 inch rims also have 45 profile tyres?

From the Price list and Options guide for the Rover 75 [July2004] you could choose as an option the 18" Hairpins alloy with the 225/45/R18 tyres.

The change to 18" alloys and 225/45/R18 tyres woud not have required a change of the final drive ratio as they could have been fitted as a dealer option.

Dave T

MrDoodles · 13th April 2012, 19:46

Quote:

Originally Posted by R D 1057

From the Price list and Options guide for the Rover 75 [July2004] you could choose as an option the 18" Hairpins alloy with the 225/45/R18 tyres.

The change to 18" alloys and 225/45/R18 tyres woud not have required a change of the final drive ratio as they could have been fitted as a dealer option.

Dave T

Interestingly enough, the correct size tyre to maintain the correct rolling radius on a 75 when fitting 18" wheels is actually a 225/40X18, rather than the 225/45X18 as fitted to a ZT!

Oh and referring back to a previous question, the correct size tyre for a 75 on 17" wheels is a 205/50X17, which again is different a ZT which has a 225/45X17!

Duotone · 13th April 2012, 20:21

Quote:

Originally Posted by MrDoodles

Interestingly enough, the correct size tyre to maintain the correct rolling radius on a 75 when fitting 18" wheels is actually a 225/40X18, rather than the 225/45X18 as fitted to a ZT!

Oh and referring back to a previous question, the correct size tyre for a 75 on 17" wheels is a 205/50X17, which again is different a ZT which has a 225/45X17!

Re. the 18" tyre size. MG Rover never fitted 225/40/R18 tyre to any of their models, Rover 75 or MG ZT.

Re. the Serpents. Rover and MG Rover fitted 225/45/R17 tyres to the Serpents when chosen as a option on the pre facelift 75.

From a 2003 brochure.

When the facelift was introduced the 17" tyres fitted to the Serpents and all 17" alloys were changed to 215/50/R17

Dave T

Phil63 · 13th April 2012, 21:23

Quote:

Originally Posted by R D 1057

Re. the 18" tyre size. MG Rover never fitted 225/40/R18 tyre to any of their models, Rover 75 or MG ZT.

Re. the Serpents. Rover and MG Rover fitted 225/45/R17 tyres to the Serpents when chosen as a option on the pre facelift 75.

From a 2003 brochure.

When the facelift was introduced the 17" tyres fitted to the Serpents and all 17" alloys were changed to 215/50/R17

Dave T

I beg to differ.....

http://www.the75andztclub.co.uk/foru...306#post943306

MrDoodles · 13th April 2012, 21:54

Quote:

Originally Posted by R D 1057

Re. the 18" tyre size. MG Rover never fitted 225/40/R18 tyre to any of their models, Rover 75 or MG ZT.

Never said that they did, just that it was the correct size to maintian speedo accuracy on a 75, when fitted with 18" wheels!

Duotone · 14th April 2012, 06:05

Quote:

Originally Posted by Phil63

I beg to differ.....

http://www.the75andztclub.co.uk/foru...306#post943306

I'm not sure what Rover/MG Rover publication recomends 225/40/R18 for the 75 but I would be most interested in having the publication no. for my records..

The only 18" alloys recomended for the Rover 75 are Hairpins [pub.6264]and Vortex with 225/45/R18 tyres [V8 only][pub.6304]

I think we must be right on this matter because new and old members should buy 18" tyres that are of the correct recomended size. Very few [non V8]Rover 75's left the factory with 18" wheels but members are now retro-fitting them because of looks/price and they should have the correct tyre size fitted because of insurance, safety and ride quality.

Dave T

Phil63 · 14th April 2012, 08:40

Quote:

Originally Posted by R D 1057

I'm not sure what Rover/MG Rover publication recomends 225/40/R18 for the 75 but I would be most interested in having the publication no. for my records..

Dave T

Hi Dave, I can't for the life of me remember where I read it. Nor can I find it in a search. Probably wasn't a Rover/MG publication.

Cheers, Phil

wutang · 14th April 2012, 08:50

also remeber that on a tyre size the profile measurment is a percentage figure. i use the following web site to work out the various details

http://www.club80-90syncro.co.uk/Syn...calculator.htm

Richard

MangoMan · 14th April 2012, 08:58

Quote:

Originally Posted by Unclefista

Check the difference in the rolling circumference here http://www.miata.net/garage/tirecalc.html you might find there's not much difference.

Yep, this is the site I've been using over the years to get the right sizes!

Singvogel · 14th April 2012, 09:32

I've found this site to be more 'user-friendly' but maybe that's just me.

http://www.tyrestore.in/upsizing.htm

It's very, very handy for comparing alternatives side by side.

Singvogel.

14th April 2012, 08:50	#18
wutang Posted a thing or two Rover 75 2.5 auto (LPG) & mg tf 160 Join Date: Nov 2006 Location: Dartford Posts: 1,124 Thanks: 5 Thanked 39 Times in 36 Posts	also remeber that on a tyre size the profile measurment is a percentage figure. i use the following web site to work out the various details http://www.club80-90syncro.co.uk/Syn...calculator.htm Richard

14th April 2012, 09:32	#20
Singvogel Gets stuck in 75 CDT, 1966 2000TC P6, TD4-M47 Join Date: Oct 2011 Location: Deepest darkest Aberdeenshire Posts: 626 Thanks: 0 Thanked 3 Times in 3 Posts	I've found this site to be more 'user-friendly' but maybe that's just me. http://www.tyrestore.in/upsizing.htm It's very, very handy for comparing alternatives side by side. Singvogel.