spare wheel query

Tyres, exhausts, suspension, strut braces, air filters, brake pads/rotors and anything else for 'dawn raiders'.
Post Reply
walter05
Joined: Wed 25 Aug, 2010 19:12
Posts: 39

  Z3 roadster 2.8
Location: belper,near Derby

spare wheel query

Post by walter05 »

Hi all, after viewing comments and pics of neglected space saver wheels I decided to check mine, looks ok. Then I noticed tyre size T125/90/R15. My wheels/tyre are 17inch. Local tyre place say it should be ok to use in case of puncture.Is he correct? Seems iffy to me. I would welcome your thoughts/comments. The wheels were on the zed when i bought it so previous owner ought to have known. Thanks.
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: spare wheel query

Post by Southernboy »

It should be fine for 10-15 miles at low speed (35kph)...Question you must ask, are your tyres good enough to withstand everything short of a large nail or spike...most punctures are caused by large items if the tyre and tread are in better than 50% wear condition...the risk obviously increasing with wear. Also, when last did you have a puncture? I have been driving for 45 years, and I have yet to suffer the indignity. I do however maintain tyres at above 50% wear and change for new at that stage...I get a fair "trade-in" on my used tyres which offsets the new costs. There is a market for "used" tyres, so it's worth considering...even if it only ammounts to 20% - 25% of the cost of new rubber. Like buy 4 and get one free... :D
"Normal is overrated"
Image

Z3 Upgrades and Additions
walter05
Joined: Wed 25 Aug, 2010 19:12
Posts: 39

  Z3 roadster 2.8
Location: belper,near Derby

Re: spare wheel query

Post by walter05 »

Hi
, I keep my tyres till around 50% worn.I have a trade account so its not so hard pricewise to renew them. I always buy top class branded tyres.I was just wondering about the space saver as a spare. Thanks for your input.
User avatar
mwpe
Joined: Wed 05 May, 2010 17:55
Posts: 183

  Z3 roadster 3.0i
Location: Camberley

Re: spare wheel query

Post by mwpe »

According to my handbook, the spare should be T115/90 R 16 92 M so it looks as though yours is an inch too small. It woud still get you out of trouble though in an emergency though.
I have had at least two occasions when a can of goo would not help, once a metal bar penetrated the tyre and on another occaasion I pcked up a nail or something which suddenly deflated on the motorway at ***Mph and by the time I managed to stop the tyre was shredded. :)
User avatar
Robert T
Site Admin
Joined: Mon 12 Jun, 2006 10:35
Posts: 10170

  Z3 roadster 1.9
Location: Cheshire

Re: spare wheel query

Post by Robert T »

Regarding the size - all wheels should have the same overall dimensions regardless of the rim size, as the profile of the tyre is adjusted to keep the rolling radius the same.

These are some common tyres sizes for the Z3:

125/90R15 = 2*(125 * 90%) + 15*25.4 = 606mm
225/50R16 = 2*(225 * 50%) + 16*25.4 = 631mm
225/45R17 = 2*(225 * 45%) + 17*25.4 = 634mm
255/40R17 = 2*(255 * 40%) + 17*25.4 = 636mm
225/40R18 = 2*(225 * 40%) + 18*25.4 = 637mm

From that, you can see that the spare is around 25mm smaller than the normal wheels, but as new tyres normally have around 7mm of tread (14mm if you count both sides) then the spare is not that much smaller than running one new and one bald tyre, and as it's only supposed to be used at no more than 50mph, it should not be a big problem.

Cheers R.

Edit: Just seen the post above - 115/90R16 would be 613mm. I have 125/90R15 on mine - it seems that manual for the later cars lists both 15 and 16 inch spares, but with different width tyres. You do have the correct size spare.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
Image
Post Reply