Safe Speed Forums

In the case of high performance cars, it's largely true. Space-savers originated on such cars and they made a fair amount of sense - a Ferrari (or similar) rear wheel being a good foot deep and a couple of feet across. Clearly space (and weight) saving was much more of a concern than CO2 emissions or fuel consumption. Increasingly though (and for the reasons stated by lots of people elsewhere in the thread), you can only have a full-sized spare wheel by loosing most / all of your boot space. One could argue, in any case, that this happens as soon as you have a puncture because you then have to find a home for your damaged (full size) wheel somewhere in the car anyway! What really gets me is that some cars seem to give you the worst of BOTH worlds. A few years ago my wife had a Citroen Xantia that had a temporary spare. It was still limited to 50 and was no use as a "real" spare, yet it was only 10mm narrower than the full-sized tyres! To my mind, that's just plain stupid!

It makes sure you have similar grip and handling performance at each corner, the restriction on spacesaver speeds are, I assume, partially a result of an extreme example of this. Different tread depth will also lead to different rotational speeds as mentioned above, this may have an effect on the cars electronics and is not good for a car with a limited slip differential. On AWD cars this applies more so as the centre differential will be affected by front/rear size differences. It certainly makes having a puncture on an AWD with half+ worn tyres rather expensive. I have never been totally sure how marginal the safety gains are, my attitude is that the tyres are what keep you on the road so you spend as much as you can justify to keep them in top condition.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

[quoteIt makes sure you have similar grip and handling performance at each corner][/quote]

But only for a limited period until the uneven front/rear wear unbalances them. My preffered system (on a FWD 120hp hatch) is to replace tyres in pairs as they wear but if replacing rears shift front to rear and new on the front.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

most modern systems would make short work of detecting a mismatched tyre and compensating appropriately, on a platform where a space saver is standard i'd expect it to be a direct requirement from the manufacturer.

You might think the esp sensor could detect and inform on an under inflated tyre?

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Speed limit sign radio interview. TV Snap Unhappy
“It has never been the rule in this country – I hope it never will be - that suspected criminal offences must automatically be the subject of prosecution” He added that there should be a prosecution: “wherever it appears that the offence or the circumstances of its commission is or are of such a character that a prosecution in respect thereof is required in the public interest”
This approach has been endorsed by Attorney General ever since 1951. CPS Code

some indirect tyre pressure monitoring systems (TPMS) do just that.
although US legislation on TPMS requires (if i recall directly) direct measurement, and stipulates certain detection times.

That is not necessarily the case, yet.

Many vehicles still monitor tire pressures by measuring wheel rollout when the steering angle sensor reports 'zero'. If a wheel is rolling too fast - or too slow - compared to the others, it will report that you need to check your tires. It will NOT tell which one[s] are over- or under-inflated; you still have to determine which one[s].

Of course, if all four tires are under- or over-inflated, you are still in the dark.

More worrisome is that the indirect comparison systems usually cannot detect a difference less than 15%.

I prefer my direct tire monitoring system. I check my tire pressures every day. It may not be as good as having tire pressure monitors in the tires themselves, but we've done without such gadgetry for the better part of a century.

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The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

ah ok.... i'd missed the various appeals & changes:

http://www.nhtsa.dot.gov/cars/rules/rul ... mmary.html

Assuming you have the same weight and road surface on each corner, which in the real world you won't.

Something not mentioned is that a traditional spare is, for most people a waste. It sits under the car and never gets used. So by not providing a spare the manufacturers are catering to the majority of customers. When it does get used (generally somewhere down the 3rd hand market) it's probably past the manufacturers recommended replacement date.

On the two occasions that I have bought new cars, when the front tyres needed replacing I have bought a single new tyre and fitted this along with the spare, consigning the best of the worn tyres to the boot. I think that that must be a common practice because I have never bought a used car with a spare that is substantially above the legal limit.

If that assumption is correct the lack of a full size spare is effectively adding 50 or so pounds to the running cost of the car.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

I recall Porsche having a tyre check device many years ago.

On my way south I got a puncture on the M6 while towing my big trailer too. I stopped, and 15 mins later had it replaced. I took extra precaution of ensuring that the spare was all ready before removing the final bolt and the car fully jacked to take the spare as the lorries were wobbling the car and the supplied jack looks flimsy - but never had any probs with them though!
I do have LSD and so would hate a space saver. Plus if I had had to use one here (about 2:30 am) it would have been mad to only go 50 m as I had about 400 mile to go still !
I will say though that at the next services where I double checked the bolts etc, the cops that were checking cars and had stopped to glance over mine just as I was returning to it were amazed and impressed that I had changed it (all by myself). This seems really sad, surely we can change a wheel ! I was annoyed that it hadn't taken me 10 minutes but with a fair chunk of paperwork in the boot I was delayed in accessing the spare ! I would dream of calling the AA for such a simple task, unless I had had a problem like a double puncture etc.
The copper was off to check out this site by the time we finished chatting ! (Hi if you are here )
However the fuel pump fault did cause me to call the AA about a week later ! Still the AA chap was very impressed that I had a source for another pump at 7pm at night and only 5 miles up the road !
Then another copper stopped me as they were debating if I was actually wearing a seat belt, and thanked me for stopping which made me wonder if no one stopped for them ! (I was wearing it - just that the adjuster makes it stay at a more vertical angle for rear obs. - Mind they couldn't understand their PNC check just knew I was a long way from home!) Mind I don't think that they had allowed for me to have already long ago figured out that they were cops taking an interest in me, as they were in a 'plain wrapper' and I had already got a stop point planned when they lit up ! I miss very little (I like to think !)

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Safe Speed for Intelligent Road Safety through proper research, experience & guidance.

Quite a few people seem to have mentioned the thing about LSDs. I think we ought to keep this in perspective! They are just that - "limited" slip, as opposed to "no" slip! If the difference in rolling circumference was something like a tractor wheel on one side and a skateboard wheel on the other, I might be able to see the point, but were not talking THAT much difference with space savers!

I completely agree on the wheel changing thing though - we're rapidly becoming a nation of useless "victims"! A generation ago, many (most?) motorists would have not only carried a jack and spare, but also tyre lever and a puncture repair kit! I realise that modern tyres (being wider, tubeless and low profile) can't be repaired like this but I think it shows just how self-reliant people used to be compared to how helpless they are now!

The debate about having the spare wheel in a well so that you have to empty the boot to get to it VS having it in a carrier under the car where it gets filthy and might get nicked, has existed for many years. I'm not sure I'd know which way to "vote" if I got the choice to be honest! A couple of years ago, I had (can't really call it a "blow-out", more of a "rapid deflation" - within a few hundred yards) on the motorway at night. Murphy's law being what it is, that mean it was an offside rear tyre and I have to admit, it wasn't nice changing it with trucks flyng past. I was grateful that it was in a cage under the car on that occasion as it took a lot less time to change. It would have taken even less if the car had been fitted with good, old-fashioned wheel studs and nuts rather than the more modern "wheel bolts"! Does anyone know why they do that? It's MUCH quicker working in the dark with the former setup!

Of course, in my time, I've had FOUR cars whose (full-sized!) spare has been under the bonnet!

My first wife had several 2CVs which had the spare on top of the engine. Wouldn't some of the more upmarket Citreons balance on three wheels?

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

My tyre completely blew out yesterday on the 6006. Front driver's side tyre was done for, but as it was on the inside of the tyre and completely out of side even if you got under there, I had no idea. Was driving along and in half a second it had no air in it. Asked a mechanic and he said there's something up with the steering because of the pattern of the wear and tear, which annoys me most because I sat in the workshop and watched them allegedly sort that out last time. I was on the M1 only half an hour before, so I was very lucky it blew while I was doing 30 after a corner on the empty 6006 rather than in Saturday evening traffic on the M1. Luckily I had a full-sized spare in the back, so I changed it at the side of the road. I've since checked the other front tyre and it shows similar, although not quite as bad, wear and tear. Blessing in disguise I think, could have been a lot worse.

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David

Big government/Big business likes helpless people.

They are much easier to manipulate, controll and exploit!

The last thing that multinationalists (in govmnt as well as business) want are people who can think for themselves!

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"The road to a police state is paved with public safety legislation"

How about 10pm on a Saturday night? In that case that'll be around the middle of last year for me (broken glass in the Tesco car park), and I had a long trip to make on the Sunday.

Fortunately one of the local mobile tyre fitters was prepared to come out in exchange for a cash tip on top of the payment for the tyres, but for most folk that would put the car off the road until Monday, 9AM. Hope you didn't need to get to work on time.

It doesn't really matter if it's 11.30 on a sunday night or 2pm on a tuesday afternoon though, like my last. Cost to my business was 30 mins + reasonable price on new tyre, not optimistically* half a day + butt d on the tyre.

*I say optimistically, cos despite giving my mechanic the exact specs and asking him to match as close as possible, the first tyre the supplier dropped off was some cruddy michelin commercial tyre, it took a second attempt to find a dunlop that reasonably matched the OE continentals (and was sufficiently speed rated)

The last memorable tyre change before that was on the way to a wedding and running late already. Changed on the side of the M3 in about 5 mins in whistle & flutes. Thank gawd for wet wipes. Full size spare meant I could happily bury the throttle in the berber and continue.

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Fear is a weapon of mass distraction

The other thing to remember is, depending on the car, your preferred tyre may not always be in stock, Particularly if you have a vaguely sporty car and/or want to replace both (or all 4, in the case of certain 4WD systems) at once.

Worst case scenario is that you have a puncture on a Saturday evening after all the tyre shops are closed, can't get anything done until Monday and no-one carries Eagle F1's in your size and has to order them in for tomorrow.

Now when I get punctures I keep the old tyres, I have ended up with a matched pair sat in the shed and can then get the fitter (and possibly even the RAC?) to put them onto my wheels and keep me going, this also means I can order my replacements online at a discount so it saves me money.

Getting rid of them wasn't a problem either, they had a good 3-4mm of tread left so I just put them up for free on the owners club forum and someone came and took them off me, his MOT ran out a couple of days before he got paid and he couldn't afford new ones until then.

I'm still stuffed if I get a puncture 200 miles from home though

I had a tyre start to lose pressure just before going on holiday, only a couple of psi a day - I took an old one with me just in case it got worse as I did not have time to get it checked/changed before going away.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Three of the four cars I was talking about WERE, in fact, big Citroens - 2 DS and a CX. And YES, they COULD stand on three wheels - but only two fronts and a rear, not the other way round. People used to say it was due to the tricky suspension, but in fact, it was just because the cars were so incredibly nose-heavy - something like 70/30% I think!! You had to put the suspension on its highest setting otherwise the trailing arm with no wheel on would scrape on the ground with (almost) no weight on it. If the car was at its highest setting, the wheel-less corner was held high enough for this not to happen. I've a feeling the old Austin "Land Crab" could do the same trick.