18" wheels and using 16" as a spare

[johnsh123]

The long awaited end of contract drive (six months in Papua Indonesia) is drawing close, I'm driving from Scotland to Bordeaux via the Hull-Zeebrugge ferry in early May, and really looking forward to it, its my first long drive with this car, though I've done it a few times in other cars and on the bike.

The car will by then have 18" non RFT's on it and I am toying with the Idea of taking one of my old 16" wheels as a spare, travelling solo and light so space isn't a problem.

If the worst happened and I had to use it on the rear, other than looking rather stupid, would it give me any other problems, I'm thinking about the diff and electricary here.

Any ideas anybody, mild piss taking tolerated!.

 

[Siener2]

My comments relate to my MC which has 18" wheels and 255/40 tyres on the back. Not sure if the 16" rims will fit, as the 17" (from my E46) only just clear the brake calipers - in fact the small balancing weights were rubbing against the caliper. The diameter of the 17" wheel and 225/45 tyre combination is roughly 3cm smaller than the abovementioned 18", so the diff will be "working" when driving in a straight line. For a short distance this should not be a problem IMHO.

 

[cj_eds]

Of top of my head, wheel circumference will be different by a few mm's (you can calculate it with the tire sizes etc or even easier search google for a website that does it for you). Would wonder if that would cause trouble with the TC etc because one wheel will effectively be turning at a different speed? It must be dealt with in software somehow though because otherwise ever car running on their space saver tyre would have a dashboard of warning lights lit up like a Christmas tree.

 

[a11y]

Should be fine if you're using old 16" alloys that were previously fitted to the car.

I've used this in the past: http://www.miata.net/garage/tirecalcold.html. Assuming comparing 255/35/18 with 225/50/16, the 16" are only 0.7% different in overall size, so won't knacker speedo readings, etc.

 

[AlanJ]

Would only do this in an real emergency and as a 'get me to the nearest garage' solution. Mixing wheels sizes on the same axle can never be a good idea and will always compromise the handling and performance (not speed) of the vehicle. Put yourself in the situation of an accident and how you would respond in court if it go that far, SMART LITIGATION LAWYER - 'So ABC you are telling the court that prior to the accident you had a 16" wheel on one side and an 18" wheel on the other etc etc....... .' Far better in my opinion to get membership of decent European roadside recovery service - may take a bit longer to sort out but a safer solution.

 

[a11y]

Would only do this in an real emergency and as a 'get me to the nearest garage' solution. Mixing wheels sizes on the same axle can never be a good idea and will always compromise the handling and performance (not speed) of the vehicle. Put yourself in the situation of an accident and how you would respond in court if it go that far, SMART LITIGATION LAWYER - 'So ABC you are telling the court that prior to the accident you had a 16" wheel on one side and an 18" wheel on the other etc etc....... .' Far better in my opinion to get membership of decent European roadside recovery service - may take a bit longer to sort out but a safer solution.

That's one reason I chose to invest in a proper space-saver wheel instead of buying a cheaper single 16" alloy to carry as a spare on long journeys. Although still a different size to the other wheels, manufacturers routinely specify space-saver wheels that are different diameter (wheel and actual overall diameter). In the case of mine, I've got a 17" space-saver and I've just realised that's handily-sized being sized between the two sets of alloys I have: my 16" winter ones and my 18" ellipsoids

 

[johnsh123]

Thanks for your thoughts guys.

Think I will take it for emergency use only of course. I did have a puncture in France a few years ago on a bike and it turned into a day and a half drama.

I'm not a big worrier and have no particular schedules to keep, so getting pissed on wine is ok at any location!.

I'm in a hotel in Jakarta after spending the day flying from Papua, pop into HQ tomorrow, and that's it contract finished and dosh in the bank, I love this bit!.

 

[IK.]

Can anyone recommend a good space saver?

 

[a11y]

Can anyone recommend a good space saver?

Mine was from an E46 330i/330d (apparently), completely unused. Not you on the model you have, but if it's a prefacelift then a 16" will clear your calipers, but post-facelift 3.0Si's need a 17".

 

[johnsh123]

The space saver is a good idea IK./ a11y, I've got an '07 2.5i SE, have you any idea if the one E46 330i/330d would fit mine?. I normally drive around with the boot empty, even on my planed big trip will only travel with one medium sized soft bag and laptop case.

 

[a11y]

johnsh123, it all depends on the brake caliper size. I'm not sure on what brakes are fitted to post-facelift 2.5's like yours. I only know that they changed the caliper/brake set up from the 3.0i to the 3.0Si: 16" wheels will fit my pre-facelift 3.0i, but won't fit a post-facelift 3.0Si.

Hopefully someone else will know about the 2.5's???

I guess it might be OK (in that I guess the brakes on any 2.5 won't be any bigger than on even the old 3.0 - not meaning that to be disrespectful of 2.5's!)

 

[PawnSacrifice]

johnsh123, a11y is right, you're fine. You're fronts are 286mm - they're 300mm on the standard 3.0. If there wasn't much difference in price I'd try and get a 17" wheel in case you want to do the 330 / 3.0si brake upgrade.

Actually, I think there are a couple 3.0 guys on here upgrading their's, may be worth given them a shout and then changing next time you need new disks and pads... I think it's a worth while upgrade, braking was the thing I felt most lacking in North Wales last weekend

If you did get a good deal on 3.0 brakes you would be fine with a 16" space saver.

 

[johnsh123]

Thanks again guys, very helpful!.

I'll start hunting local breakers etc for a E46 330i/330d space saver, I'm not too keen on the elec pump and goo idea though can't really base that on anything rational or scientific, horses for courses I guess!.

Cheers
John