Go Back   The 75 and ZT Owners Club Forums > The 75 and ZT Owners Club Forums > Technical Help Forum
Register FAQ Image Gallery Members List Calendar Mark Forums Read
Notices

Reply
 
Thread Tools Display Modes
Old 12th February 2019, 23:51   #1
Goldrover
Loves to post
 
Goldrover's Avatar
 
Rover 75 Saloon

Join Date: Apr 2017
Location: Lincoln
Posts: 280
Thanks: 242
Thanked 231 Times in 93 Posts
Default changing wheel/tyre size?

If you change your wheel size from 15" to 16" then the rolling circumference changes. This then alters the speedometer and odometer reading, will a T4 session re-adjust this anomaly if it is input into the ecu?

I only ask as there seems to be a variety of size wheels fitted to our cars and they cannot be all reading the same mph and miles travelled.

Any info would be interesting.

regards Dave,
Goldrover is offline   Reply With Quote
Old 13th February 2019, 08:01   #2
ratchet
Posted a thing or two
 
ZT-T + CTDI

Join Date: Oct 2014
Location: Gone walkabout
Posts: 1,185
Thanks: 179
Thanked 361 Times in 289 Posts
Default

If you increase the size of the alloy, you decrease the profile of the tyre to keep the rolling circumference the same.

There are a number of calculators on the www where you can enter your existing wheel and tyre sizes, and they will calculate the size of tyre required if moving from say 16 inch wheels to 18 inch wheels.

https://www.willtheyfit.com/

There is also a table on the forum, and probably in the handbook where they give you the tyre sizes required for the different sized wheels offered on the 75
ratchet is offline   Reply With Quote
Old 13th February 2019, 08:33   #3
BigRuss
Premium Trader
 
BigRuss's Avatar
 
75 CDT Tourer,2.5 Launch Saloon, Omipro MG/Rover (T4)

Join Date: Jul 2007
Location: Liversedge, West Yorkshire
Posts: 5,405
Thanks: 1,105
Thanked 1,340 Times in 661 Posts
Default

If you change wheel sizes and keep the standard tyre profiles for our cars then there isn't any change in the rolling diameter so the Speedo reading is unchanged.

The only wheel size that changes the Speedo reading is the 18 wheels this can be changed by altering the ZCS coding but it's not really necessary as it's within the 10% of the normal over reading of the speedometer

Russ
__________________


Replacement Key Service
http://https://the75andztclub.co.uk/...d.php?t=244732
Full T4 Testbook diagnostics available.
Diesel ECU repair and replacement.
Options enabled or disabled as required.
Diesel X-Power 135 and 160bhp, Rover 1.8T 150 to 160
MG 160 V6 to 177 upgrades available
P.M. for details.
BigRuss is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 21:25.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © 2006-2023, The Rover 75 & MG ZT Owners Club Ltd