Wrong sized space saver?

[bobfather]

My Edge ST-Line has 255/45-20 tyres giving a rolling diameter of 738mm.  My space saver is 155/70-18 which has a rolling diameter of 675mm.  That's 2 1/2 inches shorter.  I'm assuming they've put the wrong space saver in.  Can anyone with 20" rims tell me the size of their space saver tyre.

[Westville]

Mine has 255 45 20 road wheels/tyres

Space Saver is 155 70 17

[m50e30]

I wouldnt worry to much. It's a get you home wheel

[Tizer]

2 hours ago, bobfather said:

My Edge ST-Line has 255/45-20 tyres giving a rolling diameter of 738mm.  My space saver is 155/70-18 which has a rolling diameter of 675mm.  That's 2 1/2 inches shorter.  I'm assuming they've put the wrong space saver in.  Can anyone with 20" rims tell me the size of their space saver tyre.

It should tell you on the plate in the door pillar what size both the main tyres and the space saver should be.

[eDGeDout18]

Mine is also 155/70-18, I have at 210 Edge Sport. I've not had to use it yet, but not uncommon that spares are less diameter on cars with wheels over 19" . Like its been said it should only be used to get you home or nearest tyre seller / repairer in an emergency.

[m50e30]

First world problems lol

 

Worried about 63mm less rolling diameter, when you have starving kids in Africa going blind. 

[eddiek]

Mine has 255 45 20 road wheels/tyres

Space Saver is 155 70 17.     They must have upped to 18" on newer models .   The 17" space saver is way too small for this setup.  Used it once, it looked ridiculously small. 

[simonb65]

2 hours ago, eddiek said:

The 17" space saver is way too small for this setup.  Used it once, it looked ridiculously small. 

It's only function is to get you directly to a place where you can repair/replace your standard tyre ... space savers are not aesthetic fashion accessories or long term replacements but are a step up from a simple type repair kit! They also usually carry lower speed ratings too, so you need to watch your max speed when running on it.

 

For those commenting on the size ... The clue is in the name ... "Space Saver"!

[bobfather]

I'm thinking of getting a full size S-Max 17" 7.5J steel spare.  Swapping the S-Max tyre for a 195/70-17 would give a sensible rolling diameter spare.  This is an issue for Audi & BMW drivers on 20" rims too.  There is evidence that driving any distance on the standard spare risks damage to the differential gearing and the traction control system won't like it either as one reluctor ring will spinning too fast

[simonb65]

2 hours ago, bobfather said:

There is evidence that driving any distance on the standard spare risks damage to the differential gearing and the traction control system won't like it either as one reluctor ring will spinning too fast

I suspect that Ford have already thought about that and any potential damage that is caused by using the provided space saver is a clear cut case for Ford to repair as it can be proven that the factory supplied wheel was not fit for purpose.

On the other hand, if you use a non-approved wheel and any issues are caused because of it, you'll be picking up the repair bill yourself. Ford will wipe their hands of your very expensive problem!

Just something to think about before you go fixing/creating a problem that doesn't currently exist!

[m50e30]

I'd be more worried about coranovirus

[Hamster]

'I suspect that Ford have already thought about that and any potential damage that is caused by using the provided space saver is a clear cut case for Ford to repair as it can be proven that the factory supplied wheel was not fit for purpose'.

So many things wrong in such a short paragraph...........................

H

[simonb65]

14 hours ago, Hamster said:

So many things wrong in such a short paragraph...........................

...and they are? oh, please enlighten us.

[Hamster]

This is no time for an online disagreement so.........................

1. There is absolutely no chance of any damage occurring whilst using an OE, manufacturer provided, space saver spare wheel, used as described in the owners manual.

2. There is absolutely no way a manufacturer such as Ford would provide a space saving spare wheel which was 'not fit for purpose'. Where and what is the 'Proof'.

Considering the number of Ford vehicles out there, equipped with space saving spare wheels, since this type of spare was launched, Ford would be inundated with warranty claims arising from the space savers use. This has not, and does not happen. 

H

[bobfather]

57 minutes ago, Hamster said:

This is no time for an online disagreement so.........................

1. There is absolutely no chance of any damage occurring whilst using an OE, manufacturer provided, space saver spare wheel, used as described in the owners manual.

2. There is absolutely no way a manufacturer such as Ford would provide a space saving spare wheel which was 'not fit for purpose'. Where and what is the 'Proof'.

Considering the number of Ford vehicles out there, equipped with space saving spare wheels, since this type of spare was launched, Ford would be inundated with warranty claims arising from the space savers use. This has not, and does not happen. 

H

Can you please explain how you know with such certainty that no damage would occur or did you mean 'in your opinion'. 

Let me put this another way, as I suggest above, fitting a spare with the same rolling diameter as the standard road wheels can only be better.  Planet gears within the differential are not engineered to rotate constantly or at speed and this will occur if you fit a smaller diameter wheel.

Ford sell very few cars with 20" wheels.  Most other Ford space savers are the same diameter as their road wheels.  Both of my Kugas had space savers and those were the same diameter as their road wheels.  Being narrower isn't a problem, being shorter is

[Hamster]

So I too, distinctly remember the lesson we had at college about how a traditional differential works. IE, one in a rear wheel drive Mk4 Cortina for instance. It was back in the late 70's. Things have progressed quite a long way since then. I can even remember how to explain its operation.

It is an opinion but it is a professional opinion based on 42 years of both dealer and manufacture experience.

If you have access to ETIS have a look on there using your own VIN. I doubt it is much different to mine. Transmission description & System Operation. I've not seen inside one of these transmissions as they are 'Black Box' but I can see no diagrammatic reference to a traditional differential. IE, same torque to both driven wheels but different rotating speeds.

So, if the space saver was used on the front, it would be OK for the 'Get you Home Distance'.

The AWD System is electronically controlled to continuously monitor the drive between the front and rear. In fact, a 'clonk' which is a 'characteristic' of the Edge's can be heard if there is a marked difference between tread depths of the front and rear tyres. This is the system re calibrating itself and is nothing to worry about. 

The PTU, Power Transfer Unit and rear axle is also similarly electronically controlled. The rear axle, as in the front transmission, does not appear to have traditional mechanical differential. 

So, if the space saver was used on the rear, it would be OK for the 'Get you Home Distance'.

The ABS Sensor Rings would maybe in this case help the electronic systems to determine that a slightly smaller rolling circumference had been detached on one of the wheels. I have never heard of a reluctor ring but I've never dealt with another brand apart from Ford and a bit of JLR.

It is all done with very complex actuators and electronics and I have every faith in the highly paid Power-train Engineers who wouldn't provide us, the end users, with a space saver spare wheel which wasn't suitable.

On all my cars which have had space saver spare wheels I've only had to use them a couple times and they have always been OK.

Please stop worrying about this and start worrying about how the Motor Industry as a whole is going to recover from the mess its in because of Corona Virus.

See, I've managed to get Corona Virus and Differential in the same post.

I've also sent you a PM.

H

[simonb65]

2 hours ago, Hamster said:

This is no time for an online disagreement so.........................

1. There is absolutely no chance of any damage occurring whilst using an OE, manufacturer provided, space saver spare wheel, used as described in the owners manual.

2. There is absolutely no way a manufacturer such as Ford would provide a space saving spare wheel which was 'not fit for purpose'. Where and what is the 'Proof'.

Considering the number of Ford vehicles out there, equipped with space saving spare wheels, since this type of spare was launched, Ford would be inundated with warranty claims arising from the space savers use. This has not, and does not happen. 

@HamsterThat's exactly what I was trying to say! So certainly no disagreement from here.

The Space saver has been chosen to suit the vehicle its installed in for the purpose of getting you home (with clear instructions in the manual to support it's use), so therefore the risk of damage to any other drive train components is not going to happen (by design). My point was, IF it did cause secondary damage, whilst being used in the recommended way, Ford would be liable as they are the ones who chose, did the analysis, provided it and instructed you how to use it! So if that was incorrect, then Ford are responsible.

As you say, these components are selected based on engineering calculations and suitability by the vehicle teams during the design/development process. (I used to work for a major UK construction equipment manufacturer and believe me, these things are all part of the design and validation process).

So, I'm not going to disagree with you, far from it ... but that was what my original comment meant (even if it didn't read that way!).

1 hour ago, Hamster said:

I have every faith in the highly paid Power-train Engineers who wouldn't provide us, the end users, with a space saver spare wheel which wasn't suitable.

Absolutely!

[bobfather]

Thank you for all these responses, I'll accept that it is possible to drive with the smaller rolling diameter wheel without causing damage though I won't ever do that.  I do not agree that it is safer to use a smaller rolling diameter spare than to use a spare that is the same diameter as the standard road wheels. 

[Hamster]

You accept that it won't cause any damage, yet you would not ever do it............................. Right!!

 

"I do not agree that it is safer to use a smaller rolling diameter spare than to use a spare that is the same diameter as the standard road wheels".

I don't recall a conversation about safety. Where did this come from? It is no less safe, or no more dangerous than a standard wheel.

Do you seriously think Ford would allow for a Space Saver Spare Wheel which was less safe than a conventional wheel. Do you think VOSA (or whatever they are called now), would allow that, or even the EU\USA Vehicle Certification agency.

Anyway, I've given up on this. Buy a full sized spare, with a full sized tyre and keep it in the boot. The wheel clamp wont fit properly and the boot floor won't sit properly but you'll just have to live with that.

I'm out.

[iantt]

Vosa is now dvsa. 

Space saver is really only to be fitted on the rear , and only limited milage to your nearest tyre fitting garage. Realistically that's normaly no more than 10 miles away . The rear diff will easily cope with the difference in wheel speeds . Also there are maximum Speeds that you should adhere to while a space saver is fitted. I'm sure it is 50mph/80kph. 

[Glenny]

Mine is also 18inches, it's there for a reason,to get you home,,,if  the car was fitted with a transfer box that would be a different matter,it is what it is.