Rolling circumference?

[thisAngelBites]

I trashed a tyre this week and had no spare, and I've learned my lesson and am now sorting out a full size spare and a space saver for when I need more boot space.

I'm trying to confirm that a 125/80 17 space saver will work with my other 225/45 17 tyres and won't trash my diff.

I calculate that the rolling circumference difference between the two is 8mm, which I think should be fine, because that's within normal parameters of wear. But the husband is not around and I want to order this wheel. Can anyone who knows how to do this double check and see if they get the same?

[lovbyts]

Is your car all wheel drive? That makes a difference.

Why can't you find the exact same one?

Yes that is a small difference and should be fine but still if you can get a exact replacement. Also having one different tire can cause other issues. You should have matching tires at the least side to side

[zempey]

Yo7 should be fine with a different size tirw as long as it is not a 4x4 or have a locking differential. If it came with a smaller donut style spare you are good to run a different size tire.

[lovbyts]

Yo7 should be fine with a different size tirw as long as it is not a 4x4 or have a locking differential. If it came with a smaller donut style spare you are good to run a different size tire.

Thats if she bought the car new. My daughter has a BMC X5 and had a blow out a few weeks ago. I went to change her tire since she was close and only after putting the spare on did I notice it was a different size. I assume the prvious owner for some reason changed it because the tires on the car were stock size. Never assume as they say it makes a ass out of u and me.

More than likely you are correct but always better to be safe than sorry.

Now is a good time to buy one of those emergency vehicle kits if you dont have one. Make sure it comes with jumper cables. Buy a can or two of tire inflate just in case you have no other choice but to use it and also a small $15 cigarette lighter powered tire pump. I have one in each vehicle. Just 2 nights ago my co worker had a flat tire and I used my air pump to her tire up since it was a slow leak so she could drive to a nearby tire store and have it fixed.

Also add some gloves in the kit to save the hands and a few hand wipes just in case. I also add hand warmers in mine and a few other things like duct tape and zip ties but that's just me.

[DCI]

Should be fine TAB, just don't drive on it too long imo. As it may increase wear unlikely but it may. Bmw wouldn't have fitted a space saver if it was going to cause them hassle in the long run.

You can only 50mph on them wheels too incase your where unaware.

And as the lads said if you have a 4wd car you will eat the transfer box out of it if you have odd size tyres on a car.

[Mr.BB]

^^^like DCI said, its fine as long its for short distance below 50mph

[lovbyts]

Yeah I finally calculated it also. Over all diamiter is 0.1 so you are fine for a short time. Still if it's AWD I would not want to drive on it to long.

[DCI]

Yeah I finally calculated it also. Over all diamiter is 0.1 so you are fine for a short time. Still if it's AWD I would not want to drive on it to long.

E90 330 so shes all good

[hawk14dl]

Space savers are only intended to get you to the repair shop. Most space savers are way smaller in diameter then factory.

Even in awd cars, or fwd/rwd for that matter (if you put it on the drive axle it doesn't matter if it's 2wd or awd, it's still a drive axle ), most cars are either open axles or limited slip. Open means only one side is doing the actual driving, limited slip means they're not locked in together, there are clutches inside and they're designed to turn different speeds (this happens every time you turn a corner).
solid axles, spools, those are in race cars where both axles are turning the same speed all the time. It's important for them to be exact. They also can't turn well lol

[lovbyts]

Space savers are only intended to get you to the repair shop. Most space savers are way smaller in diameter then factory.

Even in awd cars, or fwd/rwd for that matter (if you put it on the drive axle it doesn't matter if it's 2wd or awd, it's still a drive axle ), most cars are either open axles or limited slip. Open means only one side is doing the actual driving, limited slip means they're not locked in together, there are clutches inside and they're designed to turn different speeds (this happens every time you turn a corner).
solid axles, spools, those are in race cars where both axles are turning the same speed all the time. It's important for them to be exact. They also can't turn well lol

Yes and no. Not all are created equal, especially AWD, not the same as 4x4
Stealth 316 - Mitsubishi 3000GT AWD System

[DCI]

What lb said is on point. And with a e90 330 should have an open diff therefore should be fine to drive on for a few miles.

4x4 is more simple that awd some awd cars like the gallardo etc are more rear bias than front bias due to the electronics and speed sensors etc

[hawk14dl]

If you'll read, third paragraph (inside the vcu) or describes exactly like i mentioned. When it determines a slip (different wheel speeds) the oil hearts up, expands, engages the clutches and removes torque from the wheel that's slipping.

That would be the effect of a smaller tire as well.

Thanks for the confirmation LB

[kelkel]

This is like another language....

[lovbyts]

This is like another language....

Now you know how some of us feel when you start talking gibberish medical stuff.

[kelkel]

Now you know how some of us feel when you start talking gibberish medical stuff.

That hurt.

[thisAngelBites]

Yes, open diff, and the car comes with runflats, which I ditched for proper rubber after I trashed the first one. But with runflats (or at least BMW Rrfs) there is no spare fitted to the car, period. And my BMW roadside would only recover/tow the vehicle to a dealership, which is silly. So my husband came with a floor jack, jacked it up, I took off the wheel (thank goodness already had gloves - I don't mind changing tyres, but I do not like with dirty hands) and he popped it over to the tyre shop, which fitted a new tyre, and he brought it back and we put it on. But having a space saver would have saved me waiting for him.

My old e39 came with a full size spare, but since this car has no spare whatsoever, I need a donut to carry around (that's why it's smaller - it's a space saver - intended to be smaller than a full size spare), and I'm currently looking for a full size matching rim so I can keep a full size spare at home (for my husband to bring if something happens locally).

I do know not to drive too long and not over 50 mph (and I cannot tell you how much that hurts my heart, to drive 50). I was on the autobahn last weekend, doing 240 kmh in my skyline and was much more at home.

[lovbyts]

Craigslist for the full size spare. My daughters BMW tires were discontinued so it would have cost $$$$ for one tire and I found 4 like new better quality (BF Goodrich) on nicer BMW rims for less than what it would have cost for 1 tire after mounting and balancing.

[lovbyts]

If you'll read, third paragraph (inside the vcu) or describes exactly like i mentioned. When it determines a slip (different wheel speeds) the oil hearts up, expands, engages the clutches and removes torque from the wheel that's slipping.

That would be the effect of a smaller tire as well.

Thanks for the confirmation LB

Yes but what happens in our cars is the fluid inside the VCU will overheat from the difference in rotational speed between the front and the rear, rendering it useless. Trust me, I have read numerous post where people had this happen and it's expensive. $$$$

In summary, the claimed 45/55 front rear torque split for the AWD 3000GT/Stealth only applies when the VCU is not limiting differential rotation rates and 1) the transfer case is removed so that center output shaft can rotate at a different rate than the front output shaft, 2) the front wheels are slipping and so rotate slightly faster than the rear axles, or 3) the car is just beginning to move (analogous to either the carrier or sun gear being locked). Once the car is moving and there is the same traction at all wheels, torque is split evenly (50/50) between transfer case and front differential.

[thisAngelBites]

Craigslist for the full size spare. My daughters BMW tires were discontinued so it would have cost $$$$ for one tire and I found 4 like new better quality (BF Goodrich) on nicer BMW rims for less than what it would have cost for 1 tire after mounting and balancing.

Craigslist is not big here, but yes, I'm watching the secondhand sites and eBay. Much cheaper.

[GirlyGymRat]

That hurt.

I get the slip differential. My eyes roll back into my head with medical journals. Some are better then others with conclusion....others I just wait for Kelkel to interrupt.

[DCI]

If I was you TAB just get a 17inch any style wheel as if you get a matching wheel to your own alloys you'll never fix the puncture because you will forget about it lol.

I know cos I did this with a 166 I owned 5 full size alloys and punctured one and fitted the spare then forgot to replace the spare tyre and had to use the wheel sealer foam on the punctured tyre lol.

Go to a scrappy and see if they have any pranged beemers with 3 wheels you might be lucky and get a spare wheel with tyre also

[thisAngelBites]

I thought about that, but if I can leave the spare on, and then fix the flat (I am generally pretty good at that - bc it just involves dropping the tyre at the guys behind the tesco - but it'll be sod's law now that I said that), then I can keep that one in the barn, and don't need to change it back again. That was the thinking anyway.

I think the trick is to leave the flat one in the boot (which will drive me nuts bc the boot is relatively small and the proper spare is big), so I will be sure to drop it off.

But you're right that just grabbing the first good deal makes sense - it takes less than 5 mins to swap a wheel and I will definitely do it if it doesn't match. :-) Maybe I'll ring around the local places. x

[hawk14dl]

Oh man. . I'm sorry to say, but your lingo has me cracking up. The boot, the proper, sods law. . I love the diversity of this place

[hawk14dl]

Yes but what happens in our cars is the fluid inside the VCU will overheat from the difference in rotational speed between the front and the rear, rendering it useless. Trust me, I have read numerous post where people had this happen and it's expensive. $$$$

In summary, the claimed 45/55 front rear torque split for the AWD 3000GT/Stealth only applies when the VCU is not limiting differential rotation rates and 1) the transfer case is removed so that center output shaft can rotate at a different rate than the front output shaft, 2) the front wheels are slipping and so rotate slightly faster than the rear axles, or 3) the car is just beginning to move (analogous to either the carrier or sun gear being locked). Once the car is moving and there is the same traction at all wheels, torque is split evenly (50/50) between transfer case and front differential.

Lb, i suppose that sounds rational. I don't understand the front/rear split being affected by one carrier or the other. But by the sounds of it, you've got one and you're quite familiar with it.

But being as the 3kgt and stealth are essentially one off (i don't know of any other cars using this particular drive setup), I'd say the basic principle is applicable in most scenarios.

Thanks for the education on the 3kgt though, I've always loved those cars. Wanted to get one years ago but couldn't find a vr4

[lovbyts]

Lb, i suppose that sounds rational. I don't understand the front/rear split being affected by one carrier or the other. But by the sounds of it, you've got one and you're quite familiar with it.

But being as the 3kgt and stealth are essentially one off (i don't know of any other cars using this particular drive setup), I'd say the basic principle is applicable in most scenarios.

Thanks for the education on the 3kgt though, I've always loved those cars. Wanted to get one years ago but couldn't find a vr4

Not much I have not done myself including transmission and transfer case, engine and suspension and much more.

[hawk14dl]

Very nice ride. Looks like a stealth though? Did they share engines?

[lovbyts]

Very nice ride. Looks like a stealth though? Did they share engines?

Only difference is the Dodge emblem and a couple trim pieces. Dodge knows nothing about these cars. It's 100% Mitsubishi.
Yeah Dodge stealth RT TT 13g turbos, 550 injectors, custom pistons I had wisco design, air feul controller and dyno 400 up at the wheels.

[hawk14dl]

That's what i was thinking. Very cool.

[DCI]

I thought about that, but if I can leave the spare on, and then fix the flat (I am generally pretty good at that - bc it just involves dropping the tyre at the guys behind the tesco - but it'll be sod's law now that I said that), then I can keep that one in the barn, and don't need to change it back again. That was the thinking anyway.

I think the trick is to leave the flat one in the boot (which will drive me nuts bc the boot is relatively small and the proper spare is big), so I will be sure to drop it off.

But you're right that just grabbing the first good deal makes sense - it takes less than 5 mins to swap a wheel and I will definitely do it if it doesn't match. :-) Maybe I'll ring around the local places. x

Good job let us know how you get on

[DCI]

Lb, i suppose that sounds rational. I don't understand the front/rear split being affected by one carrier or the other. But by the sounds of it, you've got one and you're quite familiar with it.

But being as the 3kgt and stealth are essentially one off (i don't know of any other cars using this particular drive setup), I'd say the basic principle is applicable in most scenarios.

Thanks for the education on the 3kgt though, I've always loved those cars. Wanted to get one years ago but couldn't find a vr4

AWD Audis have a similar set up and evos are pretty technical too along with the new gtrs and late model imprezas too