Compact Space Saver Tire/Wheel Solution

[TsRocket]

Very very interested in this subject matter, not a tire person, but everyone wants to be safe, not sorry on the side of the road.

 

[jerry33]

Still working on this. The only place I've found so far that will order me a 155 80 18 tire (0.3 percent bigger than stock) is Pep Boys, and they want $314 for it.

Tire Rack has the 145 80 18 tire (2 percent smaller than stock) for $203 prior to shipping.

Just be sure that the percent-bigger/smaller-than stock is based on the tire RPM, not the overall diameter.

 

[TsRocket]

You might mention to Tire Rack what you are attempting here. It would be to their benefit for you to find a tire/wheel that works out. They then could put together a suggested package for Model S owners. With this in mind, maybe they would loan you or sell you one discount.

Too bad Tesla, with all their engineers, couldn't figure this out for us, for our safety. The fact there is nothing, and we have to research it ourselves (read yourselves) is a little backwards thinking for so forward thinking of a company.

 

[JST]

Just be sure that the percent-bigger/smaller-than stock is based on the tire RPM, not the overall diameter.

RPM is also off by 2 percent

Revolutions per mile (km)	728.59 (452.72)	743.28 (461.85)	14.69 (9.13) 2%

But I have no idea whether the car could cope with that, or whether it would just shut everything down the way it does with the really small tire mentioned above.

 

[linkster]

JST,

Here is the info you requested from the thread: Got a Flat, Here's a - Page 2

It is a Bentley wheel with a 145/80-19. An X5 '02-'06 should work as well. I really like your idea of using the lighter 18". I would definitely go with the larger 155/80-18 over your the smaller 145/80-18 since these narrow donuts get compressed further (even at the recommended 60psi) than our full size tires. I don't think anyone outside of Tesla knows the true acceptable tire rev/mile variance before the "S" gets upset.

 

[William13]

When my car had a flat with only 30 PSI there was no problem with the traction control at 30 mph. This flat of a tire with 19 inch wheel looked to be at least 2 inches flatter than standard. I think your solution will work. Please let us know all sizes in one post if it works. Thanks

 

[Cal1]

Ok, so I drove around a bit on the compact wheel and existing, smaller diameter tire.

As expected, it freaked the car out, and the car disabled a whole list of features, including ABS, traction control, stability control, and regen. Power assistance to the steering seemed gone, as well, or at least greatly reduced.

The good news is a) the car was still driveable, though you obviously had to be careful, and b) when I put the stock 19" wheel back on, it cleared all those errors within a few feet.

So, I would definitely suggest a bigger tire. The 155/80 I mentioned above is probably the right choice, assuming I can find one with sufficient load rating. Will work on that after the holiday.

It remains to be seen whether using that size (which is still not exactly the same as the others) will cause the same problems.

So I wonder what told the vehicle you had a smaller tire? Obviously it would notice the missing air pressure sending unit but I wonder if there is any other indicator/sensor. Perhaps it (the car) thinks you are driving on a flat and it's trying to save you?

 

[Thumper]

The ABS sensors would tell the computer that the wheels are going different RPM. That is how ABS knows to kick in. With a different wheel diameter, the difference would be great and continuous.

 

[jerry33]

When my car had a flat with only 30 PSI there was no problem with the traction control at 30 mph. This flat of a tire with 19 inch wheel looked to be at least 2 inches flatter than standard. I think your solution will work. Please let us know all sizes in one post if it works. Thanks

The RPM of your OE tire was dictated by the circumference of the steel belts, not the radius when it lost air. It would still have virtually the same RPM at 15 psi. The doughnut spare is another matter--especially if it's a bias-ply doughnut spare (where tire pressure makes a very big difference to the RPM of the tire).

 

[JST]

I am sure it's the wheel speed sensor-- it's not that the car knew I had a smaller wheel, it's that it thought one of my wheels was spinning much faster than the other three for some reason.

The computer undoubtedly has expected ranges of variability for the wheel speeds; that's how it knows how to apply traction control, stability control, and ABS. I suppose it makes sense that regen would work the same way, since the car is working to keep regen at a certain limit.

Linkster, thanks for the info. Have you test driven the car with your spare fitted? Looks like that's about a half an inch deviation in diameter.

 

[linkster]

The RPM of your OE tire was dictated by the circumference of the steel belts, not the radius when it lost air. It would still have virtually the same RPM at 15 psi.

Actually, thats not true. Some auto manufactures are going to an "indirect" tire pressure monitoring system where there is no TPMS mounted inside the rim. The car uses an ABS type sensor to monitor the relative speed of the wheels and can determine when a tire is low by the reduced rev/mile of a lower pressure tire. I hope Tesla adopts this system (maybe via an update) so we can eliminate the in-wheel sensors.

 

[JST]

Great idea. JST, nice work. I suggest PMing doc@tirerack here -- he is a sponsor of TMC.
The Tire Rack is proud to be a part of teslamotorsclub.com!

I sent him a message, but he has not gotten back to me.

I'm still hunting around. The Mercury Marauder from 2003 and 2004 is the only car I've been able to confirm uses the 155/80 18 size. The local Ford dealer has the same Bridgestone Tempa Spare as Pep Boys, and also wants north of $300 for it. I found a reference to a Uniroyal tire in that size, but I don't know what car it was used on and haven't been able to find a dealer willing to order me one.

 

[Musterion]

I sent him a message, but he has not gotten back to me.

I'm still hunting around. The Mercury Marauder from 2003 and 2004 is the only car I've been able to confirm uses the 155/80 18 size. The local Ford dealer has the same Bridgestone Tempa Spare as Pep Boys, and also wants north of $300 for it. I found a reference to a Uniroyal tire in that size, but I don't know what car it was used on and haven't been able to find a dealer willing to order me one.

Just noticed you had already posted in the other thread so I deleted my post here in the interests of tidyness -- but you were too fast and had already responded! Thanks for the ongoing updates.

 

[wycolo]

> The Mercury Marauder from 2003 and 2004 is the only car I've been able to confirm uses the 155/80 18 size. [JST]

One could keep an eye on <www.car-part.com> for this exact spare tire. List the junkyards by distance.

This is turning into a real $$$ fest, but MS owners might be strongly motivated by having enough space available in Frunk for a briefcase or travel bag on top of the space saver spare. If you have 2 full sets of wheels already and can afford that space loss plus the extra weight of the full size tire then why bother. Plus the stock wheels will fit in the back; space saver might get interference from parking caliper(?).
--

 

[JST]

> The Mercury Marauder from 2003 and 2004 is the only car I've been able to confirm uses the 155/80 18 size. [JST]

One could keep an eye on <www.car-part.com> for this exact spare tire. List the junkyards by distance.

This is turning into a real $$$ fest, but MS owners might be strongly motivated by having enough space available in Frunk for a briefcase or travel bag on top of the space saver spare. If you have 2 full sets of wheels already and can afford that space loss plus the extra weight of the full size tire then why bother. Plus the stock wheels will fit in the back; space saver might get interference from parking caliper(?).
--

Now I am just being obstinate because I refuse to believe that there isn't a solution out there. And the extra space on top of the spare (and behind it) is nice to have.

Latest possibility is 155/85 18, which is 2.5 percent bigger than stock, but which Tire Rack sells for $99. I think the 145/80 might be better, but it's twice as much money.

 

[L@urens]

Found a tool for those 175Nm lug nuts yet?

 

[JST]

Found a tool for those 175Nm lug nuts yet?

To break them loose, a 12" breaker bar works no problem; so does a regular T-handle lug wrench. 129 lbs-ft is high, but it's not as bad as most tire shops do when they use air wrenches to put tires back on.

As far as re-mounting, I'm not carrying a torque wrench around, but for temporary purposes you can put enough force on the nuts with a T-handle to get close enough.

 

[wycolo]

JST - I was like you obsessed with carrying some sort of spare across my 'empty quarter' locale. Then I discovered that my blizzak snow on 19 in stock rim would fit in frunk quite nicely, contrary to all reports. Everyone just repeating what the first poster said, I guess. So that was enough for me, having grabbed 4 extra 19in rims at Service Center for $1000-US.

Roadster still is without a spare with very little hope of being able to carry one aboard. Actually might need two different sized spares.
--

 

[Musterion]

Found a tool for those 175Nm lug nuts yet?

I use a standard-size 4-way cross wheel brace. Torqued to spec, it is only 50-60 lbs (<25 kg) per hand -- no problem.

 

[jerry33]

Actually, thats not true. Some auto manufactures are going to an "indirect" tire pressure monitoring system where there is no TPMS mounted inside the rim.

Actually it is true. Toyota did the indirect bit for a while, but they went back to pressure sensors presumably because the rotational method was too inaccurate. Yes, there will be a very slight difference, but it's tiny. The steel belts dictate the tire's RPM. In bias-ply tires a 30%+ difference in tire RPM with pressure change is not uncommon.