Mixed size stock tires?

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SenorChispa

Well-known member
Joined
Sep 17, 2013
Messages
45
Does anyone know why chevy chose to put different width tires on the back vs the front? (195 vs 185)? Do they not believe in tire rotation?
 
SenorChispa said:
Does anyone know why chevy chose to put different width tires on the back vs the front? (195 vs 185)? Do they not believe in tire rotation?
Click to expand...
I believe they did it due to the fact that there is more weight in the rear of the car due to the placement of the battery pack.
 
markcmann said:
I believe they did it due to the fact that there is more weight in the rear of the car due to the placement of the battery pack.
Click to expand...

That would be a very reasonable explanation except that the weight distribution is nearly 50/50 according to the Car and Driver review. And the first time somebody rotates their tires then the size difference is backwards, which defeats the purpose of having different sizes.

Rotation is not optional if you want to get full life out of the tires. The fronts will wear out twice as fast as the back. Rotating left to right instead of front to back is a no-no.

I just can't imagine what Chevy was thinking with this.
 
Skinnier tires are more aerodynamic. The leading tires help cleave the wind for the trailing tires.
Maybe that was their reasoning?
 
I expect they wanted the rears wider for handling purposes. Your 50/50 comment makes sense in a static world, but the tires are sharing weight very disproportionately dynamically, especially with struts in front and a beam axle in the rear. The rear inner tire in hard cornering carries very little weight, usually.

Bryce
 
So would the smart thing be to change out the fronts with tires of the same size as the back so we could then rotate them as usual?
 
Is there anything wrong with just replacing the front tires twice as often as the rear? Unless you have very uneven wear across the tread, is there even any real use to rotating left-to-right?

I have never found any really convincing study that shows tire rotation helps in the long run. Although, it might be useful if you are just trying to make a single set stretch to the end of the lease.

-Nate
 
SenorChispa said:
markcmann said:
I believe they did it due to the fact that there is more weight in the rear of the car due to the placement of the battery pack.
Click to expand...

That would be a very reasonable explanation except that the weight distribution is nearly 50/50 according to the Car and Driver review. And the first time somebody rotates their tires then the size difference is backwards, which defeats the purpose of having different sizes.

Rotation is not optional if you want to get full life out of the tires. The fronts will wear out twice as fast as the back. Rotating left to right instead of front to back is a no-no.

I just can't imagine what Chevy was thinking with this.
Click to expand...

I can't either. If anything the front tires should be bigger given all the torque available.
 
Nashco said:
I expect they wanted the rears wider for handling purposes. Your 50/50 comment makes sense in a static world, but the tires are sharing weight very disproportionately dynamically, especially with struts in front and a beam axle in the rear. The rear inner tire in hard cornering carries very little weight, usually.

Bryce
Click to expand...

Perhaps but the stock suspension is so poor for handling that I don't think such a subtle difference in tire size would make any difference in the handling.
 
Is there enough room on the front to mount 195mm tires up there? I prefer the same size all around for rotation. Plus we usually put new tires on the front and move the 1/2 worn out tires to the back.
Any different in the rim width and offset front vs. back ?
 
buickanddeere said:
Is there enough room on the front to mount 195mm tires up there? I prefer the same size all around for rotation. Plus we usually put new tires on the front and move the 1/2 worn out tires to the back.
Any different in the rim width and offset front vs. back ?
Click to expand...

As has been mentioned many times on this forum, the front and rear wheels are different sizes and can't be rotated front to rear!

http://mychevysparkev.com/forum/viewtopic.php?f=10&t=3496

Nashco said:
For future reference, this is the stock Spark EV wheel specs.

Front
15x6.0
ET45
Part number 95024486

Rear
15x6.5
ET54
Part number 95024487
Click to expand...

I have put a LOT of work into getting the same size wheels and tires front to rear (for autocrossing purposes), and I intend to document how this can be done soon. However, I can tell you now that it is neither cheap nor easy to accomplish. By far, the path of least resistance is rotating side to side instead of front to rear and using the stock wheels with stock sized tires.

Bryce
 
Nashco said:
buickanddeere said:
Is there enough room on the front to mount 195mm tires up there? I prefer the same size all around for rotation. Plus we usually put new tires on the front and move the 1/2 worn out tires to the back.
Any different in the rim width and offset front vs. back ?
Click to expand...

As has been mentioned many times on this forum, the front and rear wheels are different sizes and can't be rotated front to rear!

http://mychevysparkev.com/forum/viewtopic.php?f=10&t=3496

Nashco said:
For future reference, this is the stock Spark EV wheel specs.

Front
15x6.0
ET45
Part number 95024486

Rear
15x6.5
ET54
Part number 95024487
Click to expand...

I have put a LOT of work into getting the same size wheels and tires front to rear (for autocrossing purposes), and I intend to document how this can be done soon. However, I can tell you now that it is neither cheap nor easy to accomplish. By far, the path of least resistance is rotating side to side instead of front to rear and using the stock wheels with stock sized tires.

Bryce
Click to expand...

There would have to be some awful close clearances if a 1/4" more tire rubs on something. There must be some difference in the rim offset front to rear ? Can't be a whole lot if the front and rears follow the same track?
 
buickanddeere said:
There would have to be some awful close clearances if a 1/4" more tire rubs on something. There must be some difference in the rim offset front to rear ? Can't be a whole lot if the front and rears follow the same track?
Click to expand...

Did you read my post? The offset IS different, as I showed above. The front wheels have 45mm offset, the rears have 54mm offset. If the rears are installed in the front, the spokes hit the calipers.

The clearances are extremely tight, the tightest of any factory car I've ever worked with. They're so tight that the car has rolled fender lips in the rear and almost no fender lips in the front from the factory. Don't take my word for it, go look at your own car. When in jounce (like hitting a bump) the stock tires are extremely close. Again, don't take my word for it, remove your springs and try it, or load a bunch of weight in the back until the suspension sags.

You CAN bolt the front tires on to the rear without any drama. So, if you really want the same size wheels and tires all around, it's easy as long as you use four of the smaller front wheel and tire combinations (185 on a 15x6 et45). I didn't see any rubbing when I tested it on my car, but proceed with caution as I didn't drive it this way. This isn't cheap, of course, because you would have to buy two new wheels...and it's not really any advantage.

Bryce
 
Nashco said:
buickanddeere said:
There would have to be some awful close clearances if a 1/4" more tire rubs on something. There must be some difference in the rim offset front to rear ? Can't be a whole lot if the front and rears follow the same track?
Click to expand...

Did you read my post? The offset IS different, as I showed above. The front wheels have 45mm offset, the rears have 54mm offset. If the rears are installed in the front, the spokes hit the calipers.

The clearances are extremely tight, the tightest of any factory car I've ever worked with. They're so tight that the car has rolled fender lips in the rear and almost no fender lips in the front from the factory. Don't take my word for it, go look at your own car. When in jounce (like hitting a bump) the stock tires are extremely close. Again, don't take my word for it, remove your springs and try it, or load a bunch of weight in the back until the suspension sags.

You CAN bolt the front tires on to the rear without any drama. So, if you really want the same size wheels and tires all around, it's easy as long as you use four of the smaller front wheel and tire combinations (185 on a 15x6 et45). I didn't see any rubbing when I tested it on my car, but proceed with caution as I didn't drive it this way. This isn't cheap, of course, because you would have to buy two new wheels...and it's not really any advantage.

Bryce
Click to expand...


Sorry, never seen that format used before to state the offset at ET and being measured in mm.
What is going to happen if a Spark EV is driven in freezing slush and snow? Or on a muddy rural road? Those wheel wells are going to load up and drag on the tires.
 
gmarcucio said:
Actually the suspension along with unibody reinforcement is upgraded on the Spark EV from the ICE version because of the torque involved.
Click to expand...

Doesn't feel like it :(
 
Hi Bryce,

Is there any chance you would have weighed the wheels by themselves? I've read that they are 36.6 lb with the tire on this forum, but have not seen any measurements for the wheels themselves.

Thanks!
 
I haven't weighed the wheels only personally, but the internet says the stock tires are about 18-19 pounds (fronts slightly lighter than rears), leaving the stock wheels at approximately 18-19 pounds. My stock wheel and tire assemblies were in the 36-38 pound range when I weighed them myself, IIRC. Keep in mind the front and rear wheels and tires are different sizes, so they don't weigh the exact same front to rear.

Bryce
 
I learned a couple of things regarding rotation. 1) The front and back stock tires are different widths and 2) the tires are unidirectional. This means you cannot go either front to back because of #1 or left to right because of #2. Each tire is assigned to stay on the car in a specific position only. Chevy and their dealers (once they figure it out themselves) will tell you this is by design. I called my "spark advisor" who works for chevy. The suspicious might say it is by design that they are willing to live with your tires wearing out quickly. They will say these tires are designed to wear evenly without rotation. Well, if that last sentence is true why isn't everybody making tire rotations a thing of the past ?

I see no indication on the tires themselves that they are unidirectional (like "this side out" or an arrow indicating direction of travel) but the spark advisor says they are in fact unidirectional tires. Maybe I'm missing the indication on the tires somehow, I'll look again.
 

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