Tire Pressures

[Arm]

Hey Folks:

Can anyone verify that the 2018 i3s BEV and 2019 i3s BEV have the same tire pressures of 33/41?

I have a 2019 i3s REX and the tire pressures are quite a bit higher...particularly on the front. For this car it's 39/44.

I'm curious why such a large difference?

Thanks

 

[eNate]

Those are all 175 & 195/20 on the S models, right? No 19s?

 

[Arm]

Correct.

 

[Arm]

So does anyone have an idea why??

 

[Joff]

I think they all need higher pressures, but especially the 20 inch rims, as they have less distance to go before the rim bottoms out on a pot hole.

 

[eNate]

Huh, I'm confused. I expected to find a chart of 19 vs. 20, i3 vs i3S, REX vs. BEV, but instead I'm just finding one combo for the i3, another for the i3S, and they seem to change from user report to user report, but nowhere am I finding a comprehensive breakdown for what and why.

 

[Arm]

Huh, I'm confused. I expected to find a chart of 19 vs. 20, i3 vs i3S, REX vs. BEV, but instead I'm just finding one combo for the i3, another for the i3S, and they seem to change from user report to user report, but nowhere am I finding a comprehensive breakdown for what and why.

Yet it's confusing or illogical. Clearly BMW increased the tire pressures for 2019 and on. Not sure why and begs the question if I should be running my 2018 i3s at the new tire pressure levels.

 

[alohart]

I think they all need higher pressures, but especially the 20 inch rims, as they have less distance to go before the rim bottoms out on a pot hole.

I agree. Since buying our i3 in 2014, I have increased the inflation pressures of our 19" tires by 10 psi over the recommended pressures of 33F/41R. The inflation pressure of the rear tires then matches the maximum inflation pressure embossed on the sidewall of 51 psi. Another advantage is a slightly lower rolling resistance and thus slightly greater range. Disadvantages include a slightly rougher ride and a smaller contact patch which reduces traction a bit. I regularly measure tread depth across the tread's width and haven't measured any unusual tire wear.

Many of us in the 1st generation Honda Insight community increased the inflation pressures of the Bridgestone low rolling resistance tires installed by Honda on our Insights without any negative consequences that I'm aware of. That experience makes me confident in doing so on our i3.

 

[Arm]

I think they all need higher pressures, but especially the 20 inch rims, as they have less distance to go before the rim bottoms out on a pot hole.

So you're suggesting that BMW has under-estimated the i3 tire pressures up through 2018?

 

[Joff]

I think they all need higher pressures, but especially the 20 inch rims, as they have less distance to go before the rim bottoms out on a pot hole.

So you're suggesting that BMW has under-estimated the i3 tire pressures up through 2018?

Rather than say they made a "mistake" I would prefer to say the made a "decision" based on their priorities. They want the car to feel nice (not harsh) to people test driving the I3 for the first time, so that they buy the thing. MY priority is to have less tire and rim damage, more range, and cooler tires that last longer.

 

[Arm]

I think they all need higher pressures, but especially the 20 inch rims, as they have less distance to go before the rim bottoms out on a pot hole.

So you're suggesting that BMW has under-estimated the i3 tire pressures up through 2018?

Rather than say they made a "mistake" I would prefer to say the made a "decision" based on their priorities. They want the car to feel nice (not harsh) to people test driving the I3 for the first time, so that they buy the thing. MY priority is to have less tire and rim damage, more range, and cooler tires that last longer.

Well I prefer the handling feel at higher tire pressures but the ride is considerably harsher. Plus, I can honestly say my 2019 i3S tires didn't last very long at 39/44. Barely got 15k out of them which I don't think is very good.

 

[diamondroad]

There may be a difference between the Rex and BEV models due to the extra weight of the engine in the Rex. But that difference hasn't changed across model years. What has changed is the battery capacity/density as the range increased. I know that spec increased for the 2017 and 2019 model years, but I don't know if there were increases from 2014 - 2016. These non-S models all had the 19" wheels/tires. Starting in 2018, they introduced the S model, which used 20" wheels so again, you would expect slightly different pressure recommendations. So, I'd say the main driver of pressure variations is tire size and/or changes in load, which was material when BMW upped battery range.

 

[diamondroad]

There may be a difference between the Rex and BEV models due to the extra weight of the engine in the Rex. But that difference hasn't changed across model years. What has changed is the battery capacity/density as the range increased. I know that spec increased for the 2017 and 2019 model years, but I don't know if there were increases from 2014 - 2016. These non-S models all had the 19" wheels/tires. Starting in 2018, they introduced the S model, which used 20" wheels so again, you would expect slightly different pressure recommendations. So, I'd say the main driver of pressure variations is tire size and/or changes in vehicle weight, which was material when BMW upped battery range.

 

[tob1as]

There may be a difference between the Rex and BEV models due to the extra weight of the engine in the Rex. But that difference hasn't changed across model years. What has changed is the battery capacity/density as the range increased. I know that spec increased for the 2017 and 2019 model years, but I don't know if there were increases from 2014 - 2016. These non-S models all had the 19" wheels/tires. Starting in 2018, they introduced the S model, which used 20" wheels so again, you would expect slightly different pressure recommendations. So, I'd say the main driver of pressure variations is tire size and/or changes in vehicle weight, which was material when BMW upped battery range.

My 2017 non-s has 20 inch wheels. The s models have wider tires (175/195) vs non-s (155/175). I wouldn’t think the weight differences between different model years and Rex/non-rex would matter enough when you consider payload variation possibilities - just a single driver vs 4 passengers and luggage. A much bigger variable for tire pressure is ambient temperature. I inflate my winter tires to about 40psi at maybe 60 degrees and they will range all the way down to 32 psi on a cold morning (20 degrees), and slowly increase as the tires warm up driving and/or the ambient temperature increases.

 

[alohart]

There may be a difference between the Rex and BEV models due to the extra weight of the engine in the Rex.

Recommended tire inflation pressures are the same for REx and BEV models.

But that difference hasn't changed across model years.

The recommended inflation pressures increased from 33 psi F/41 psi R for the 2013-2017 model years to 39 psi F/46 psi R for the 2018-2022 model years.

I know that spec increased for the 2017 and 2019 model years, but I don't know if there were increases from 2014 - 2016.

All 2013-2016 i3's had 60 Ah battery packs.

These non-S models all had the 19" wheels/tires.

20" wheels/tires were an option on non-S models.

Starting in 2018, they introduced the S model, which used 20" wheels so again, you would expect slightly different pressure recommendations.

However, BMW didn't recommend different inflation pressures for S models despite their wider wheels and tires.

So, I'd say the main driver of pressure variations is tire size and/or changes in vehicle weight, which was material when BMW upped battery range.

BMW changed its recommended tire inflation pressures only once with no explanation that I know. I think this occurred with the LCI (mid model run refresh). If so, the battery pack capacity remained 94 Ah, so the recommended inflation pressures had nothing to do with an increase in battery pack capacity. A 120 Ah battery pack weighs only 40 kg/88 lb more than the 60 Ah battery pack and only 17 kg/37 lb more than the 94 Ah battery pack, so increasing battery pack weights don't seem sufficient to justify an increase in the recommended inflation pressures. Total i3 weights as published by BMW increased by less than 15% from 2013 to 2022.

Maybe the gross weight was nearing the load capacity of the tires for the heaviest REx models. If so, BMW could increase the tires' load capacity without specifying larger tires by merely recommending higher inflation pressures.