Different size spare from the rest of the tyres?

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dpw

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Topic # 66736 22-Aug-2010 18:08

Hi folks,

My van seems to be revving quite high to achieve 100 km/h. I have found a set of 4 tyres as potential replacement - they are 205/65R16. The original tyres were 205/70R14, including the spare.

I'm not sure what is a car's tolerance to different sizes. If I replace the running tyres with the slightly larger can I still use my old spare? or do I need to replace the spare too?

Cheers,
D.

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Hammered
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Reply # 371155 22-Aug-2010 18:54

It's not a car 'tolerance' thing as such. Your speedo/odo are calibrated to the diameter of the tyres supplied when it was new. Any variance is going to affect your displayed speed and distance travelled. If the diameter is changed, you'll need to get your instruments recalibrated.

BlakJak

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Reply # 371161 22-Aug-2010 19:04

What he said, and for clarity, I would not recommend running a different sized wheel (where the diameter of the wheel is different, this being rims + tyres considered) for any length of time at all, emergencies only at least. I don't see how it could be a good thing...

Google for 'different sized spare' would seem to be a better place than a geek forum for straight answers :P

http://ca.answers.yahoo.com/question/index?qid=20100427082035AAr7HNl

http://www.jeepforum.com/forum/f13/spare-tire-different-size-bad-946581/

A couple I found after a very quick search.

Hoards of car forums in NZ as well...

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Batman

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Reply # 371165 22-Aug-2010 19:12

with larger tyres your acceleration is slower but you'd be revving lower for a similar speed. your speedo will underestimate your speed (ie cops will have a field day)

rscole86

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Reply # 371166 22-Aug-2010 19:15

Also, it is an offence to drive with different wheels on the same axle. So I would make sure you change the spare. Obviously there is an allowance for a 'space saver'.

dpw

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Reply # 371202 22-Aug-2010 20:45

Thanks everyone. Yes, I was fully aware the speedo will underestimate my speed. Yes, I am also aware acceleration will be slower. My aim is to rev lower at higher speeds. I had a thought that, since space savers are of different size from the rest, it may be okay to use.

However, thanks to rscole86 for pointing out it is illegal to do so. I won't be mixing sizes then :o)

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BlakJak

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Reply # 371205 22-Aug-2010 20:57

what rscole86 means is that you need to have matching pairs on a by-axle basis. You can change the diameter of the wheels as long as they match by-axle.

If you're running a space saver spare the reason is pretty obvious and i've never heard of anyone being ticketed for running a space saver as a spare.

Whilst a similar argument could be made for a non-space-saver spare it's not as obvious that you're doing it for emergency reasons....

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rscole86

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Reply # 371213 22-Aug-2010 21:13

BlakJak: what rscole86 means is that you need to have matching pairs on a by-axle basis. You can change the diameter of the wheels as long as they match by-axle.

If you're running a space saver spare the reason is pretty obvious and i've never heard of anyone being ticketed for running a space saver as a spare.

Whilst a similar argument could be made for a non-space-saver spare it's not as obvious that you're doing it for emergency reasons....

Thanks BlakJak, that was the point I was making, you should change your spare to match the rest of your new tyres.

dpw

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Reply # 371218 22-Aug-2010 21:25

rscole86:
BlakJak: what rscole86 means is that you need to have matching pairs on a by-axle basis. You can change the diameter of the wheels as long as they match by-axle.

If you're running a space saver spare the reason is pretty obvious and i've never heard of anyone being ticketed for running a space saver as a spare.

Whilst a similar argument could be made for a non-space-saver spare it's not as obvious that you're doing it for emergency reasons....

Thanks BlakJak, that was the point I was making, you should change your spare to match the rest of your new tyres.

Yup - I got the original point, just didn't do a good job at acknowledging it I guess! Anyway, it's all in the too hard basket for now, I haven't bought the new wheels and tyres yet and I don't think I will. One day maybe, when I can be bothered sorting out the full set of 5 identical sized ones.

Thanks again.

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marmel

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Reply # 371352 23-Aug-2010 09:36

This is one of the most common mods done to 4wd's that actually do go off road. Putting on a larger tyre gives more ground clearance.

It's not such a big deal as you may think. In fact I went from a 30.9" tyre to a 33" and my speedo was then more accurate than before (tested) due to the fact the vehicle is 20 years old and factory speedo's, especially in older vehicles can vary a lot anyway.

You need to work out how much bigger the replacement tyres will be though. If they are more than 5% bigger than the original factory items technically you will need a low level cert.

kiwitrc

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Reply # 371355 23-Aug-2010 09:47

You can calculate the change in your speedo due to different sized tyres using this http://www.club80-90syncro.co.uk/Syncro_website/TechnicalPages/TRC%20calculator.htm

As far as I am aware you are not allowed to change wheels/tyres if it changes the rolling radius.

Someone else might be able to confirm this as I have heard there is an allowance of a few percent, but not sure that is gospel.

Edit: As above 5%

dpw

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Reply # 371371 23-Aug-2010 10:09

kiwitrc: You can calculate the change in your speedo due to different sized tyres using this http://www.club80-90syncro.co.uk/Syncro_website/TechnicalPages/TRC%20calculator.htm

As far as I am aware you are not allowed to change wheels/tyres if it changes the rolling radius.

Someone else might be able to confirm this as I have heard there is an allowance of a few percent, but not sure that is gospel.

Edit: As above 5%

Well that changes things somewhat. I obviously made a mistake rough mental calculations - according to that online calculator the change of size I proposed falls within the 5% allowance.

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jjnz1

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Reply # 371376 23-Aug-2010 10:14

Who polices this? Certainly not the WOF people and I have been pulled over many a time by the police.. I have a 2.4l Hiace that had r15's on it, and I 'upgraded' to r18's. The diameter of the wheel/tyre is now definitely bigger than 5%, and yes my speedo is now more close to accurate, low revs at higher k's, but the engine struggles more, less power, and less fuel efficient. But the van now handles impeccably.

My spare is still the old r15, and I would not hesitate to use it in a emergency, ie, not travelling more than 80kmh, and going straight to the tyre dealer.

Are you sure this is not one of those laws that exist but not enforced for certain reasons?

Although I think that if you do get bigger wheels, end up using your smaller spare and drive around for weeks on it, then you deserve to get ticketed! Its just common sense.

marmel

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Reply # 371377 23-Aug-2010 10:15

The only other thing to consider is that fitting larger tyres without changing the diff ratios will suck power.

My Nissan Safari was slow at the best of times but now it struggles a bit with really long hills and you can forget about trying to overtake anything that isn't stationary.

I'm about to fit a turbo though so this should sought that out nicely.

I see you have a van which aren't reknown for great power either or great aerodynamics. If you stay within the 5% it may not make much difference but if you fit them and it feels like you are towing a boat all the time you know why :-)

marmel

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Reply # 371378 23-Aug-2010 10:19

jjnz1: Who polices this? Certainly not the WOF people and I have been pulled over many a time by the police.. I have a 2.4l Hiace that had r15's on it, and I 'upgraded' to r18's. The diameter of the wheel/tyre is now definitely bigger than 5%, and yes my speedo is now more close to accurate, low revs at higher k's, but the engine struggles more, less power, and less fuel efficient. But the van now handles impeccably.

My spare is still the old r15, and I would not hesitate to use it in a emergency, ie, not travelling more than 80kmh, and going straight to the tyre dealer.

Are you sure this is not one of those laws that exist but not enforced for certain reasons?

Although I think that if you do get bigger wheels, end up using your smaller spare and drive around for weeks on it, then you deserve to get ticketed! Its just common sense.

Have a look here:

http://www.lvvta.org.nz/stdWheels&Tyres.pdf

You are correct though that 99.9% of the time you won't get ticketed, in fact most people won't even be able to tell the difference.

If you happened to find yourself in the middle of a boy racer convoy that gets stopped and they have a ltnz compliance officer you could be in trouble though.

jjnz1

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Reply # 371383 23-Aug-2010 10:25

marmel:
jjnz1: Who polices this? Certainly not the WOF people and I have been pulled over many a time by the police.. I have a 2.4l Hiace that had r15's on it, and I 'upgraded' to r18's. The diameter of the wheel/tyre is now definitely bigger than 5%, and yes my speedo is now more close to accurate, low revs at higher k's, but the engine struggles more, less power, and less fuel efficient. But the van now handles impeccably.

My spare is still the old r15, and I would not hesitate to use it in a emergency, ie, not travelling more than 80kmh, and going straight to the tyre dealer.

Are you sure this is not one of those laws that exist but not enforced for certain reasons?

Although I think that if you do get bigger wheels, end up using your smaller spare and drive around for weeks on it, then you deserve to get ticketed! Its just common sense.

Have a look here:

http://www.lvvta.org.nz/stdWheels&Tyres.pdf

You are correct though that 99.9% of the time you won't get ticketed, in fact most people won't even be able to tell the difference.

If you happened to find yourself in the middle of a boy racer convoy that gets stopped and they have a ltnz compliance officer you could be in trouble though.

Yes your right. My van, even though it has very sexy wheels, looks very much like a commercial vehicle, ladders, roof racks etc, and gets treated like one.

I wonder how I would get a turbo on my 50Kw engine?

Might then be able to make it up the gorge (wellington) doing 80.

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