Using smaller wheels when towing?

[anko]

More than once, it has been discussed here (mainly by me ;-) ) that the PHEV is not capable of maintain SOC when towing a decent size caravan. In short, it has to do with the long gear ratio when in parallel hybrid mode. The RPMs associated with caravan speeds are so low that the ICE simply cannot produce enough power to propel the car + caravan AND maintain battery SOC. In a 'normal' car we would down shift, but obviously, we can't.

What if we would install smaller wheels (smaller rims or lower tire side walls, resulting in lower overall circumference of the tires)? 5% less circumference would result in 5% more RPM and 5% more power at the same speed. My gut feeling says, this might already be just about enough to make a decisive difference: instead of the SOC dropping a little bit all of the time, it could be kept steady or even increased over time. Preventing SOC from hitting the low water mark eliminates the need for the car to switch to serial hybride mode at constant motorway speed.

Advantages of staying in parallel hybrid mode:
- Much more comfortable from a noise perspective, as RPM will stay linked directly to speed.
- Little bit more efficient as it eliminates two energy conversions.

Disadvantages of smaller wheels:
- Little bit less comfortable, due to smaller wheels and perhaps lower side walls.
- Little bit less ground clearance.
- Little bit less efficient when in parallel mode, as the ICE must turn over more often per same distance travelled.
- Odometer deviates.
- Speedometer deviates.
- Looks bitch ugly.

What do you guys think:
- Will this work?
- More advantages?
- More disadvantages?
- Legal apsects? Does the law allow it? Does Mitsubishi 'allow' it?
- ...

Let me hear what you think.

 

[HHL]

I seem to recall that there was a version of the PHEV supplied with 16" wheels.
The tyres were probably not low profile, so if you can get hold of these wheels and find some low profile rubber to suit, you can test your theory....

 

[greendwarf]

Don't really know much about this but with the speedo "error" effect, I am increasingly using the more accurate SatNav when motorway cruising - real 70mph comes up as 74mph on the car.

 

[elm70]

5% does no sound a lot of difference.
Having two set of tyres looks a waste of time and money

There is no way to force the PHEV to run in Serial mode ?

Maybe it is just enough to remove ECO mode for have a more aggressive "power mode" ... or maybe keep charge pressed all the time ?

I just know that when I floor on the gas pedal ... the parallel mode happen only at over 120km/h (or more)

PS: In some countries I know it is now allowed to mount tyres that have different size than what has been state in the car registration ... clearly police may never check it .. but in case of accident, if insurance notice it, this can be a big problem.

 

[anko]

5% does no sound a lot of difference.

I have been able (when the car was new) to tow my caravan over a distance of 250 km before the battery was empty. So, approx 8 or 9 kWh in 4 hours, meaning I was loosing charge at a rate of about 2 kW in average. 5% extra power is about 2 kW, at that speed.

Having two set of tyres looks a waste of time and money

Yep!

There is no way to force the PHEV to run in Serial mode ?

The idea is to prevent serial mode, rather than force it.

Maybe it is just enough to remove ECO mode for have a more aggressive "power mode"

Tried that. Doesn't help.

... or maybe keep charge pressed all the time ?

Of course. Without Charge mode, SOC is lost before you even leave town.

PS: In some countries I know it is now allowed to mount tyres that have different size than what has been state in the car registration ... clearly police may never check it .. but in case of accident, if insurance notice it, this can be a big problem.

Might be ...

 

[anko]

Don't really know much about this but with the speedo "error" effect, I am increasingly using the more accurate SatNav when motorway cruising - real 70mph comes up as 74mph on the car.

So do I

 

[anko]

I seem to recall that there was a version of the PHEV supplied with 16" wheels.
The tyres were probably not low profile, so if you can get hold of these wheels and find some low profile rubber to suit, you can test your theory....

My thought as well. But before making the effort ....

 

[Harald]

The 16" rims are the standard in Austria and Germany for the simple versions of the car.

I have my summer tyres on 18", the winter tyres on 16".
Enjoyed the higher tyres of the 16" version during actual holiday on bad rocky ground.

 

[elm70]

5% does no sound a lot of difference.

I have been able (when the car was new) to tow my caravan over a distance of 250 km before the battery was empty. So, approx 8 or 9 kWh in 4 hours, meaning I was loosing charge at a rate of about 2 kW in average. 5% extra power is about 2 kW, at that speed.

There is no way to force the PHEV to run in Serial mode ?

The idea is to prevent serial mode, rather than force it.

5% ... the problem is also solved by driving slower .. under 70km/h the car does run in serial mode. .. at lower speed also required power is less .. still not sure this help in parallel mode.

I don't see why you are against the serial mode ... for me in your case .. once the battery is getting critical low ... running in serial mode is the best way .. only with serial it could be possible to have all 121hp available which should be able to move the car and as well recharge the battery ... in parallel mode is never possible to use the full power from ICE, unless you drive at 170km/h

So .. question is ... how can be possible to force serial mode when is needed to re-charge the battery ... I would expect in charge mode, the car should cancel parallel mode in case the battery get constantly consumed

 

[anko]

So .. question is ... how can be possible to force serial mode when is needed to re-charge the battery ... I would expect in charge mode, the car should cancel parallel mode in case the battery get constantly consumed

This is my topic. So no, this is not the question ;-)

Of course the car DOES go into serial mode when battery SOC is very low. No need to do anything to achieve this. But I would like to prevent this from happening, by keeping SOC a bit above the low water mark. Driving 90 km/h for a few hours where the cars switches between a 'near constant 2450 RPM' and 'somewhere between 3500 and 4100 RPM' every 2 or 3 km is no fun at all. Seriously, I have opened this topic to discuss ways to prevent serial mode from happening and you try to change it into discussing ways of forcing serial mode. I don't understand why.

Also, parallel mode starts at 60 - 65 km/h. I don't think driving 60 - 65 km/h to the south of France or Croatia is a practical solution. Plus, it totally defeats the purpose of what I am trying to achieve.

 

[anko]

The 16" rims are the standard in Austria and Germany for the simple versions of the car.

I have my summer tyres on 18", the winter tyres on 16".
Enjoyed the higher tyres of the 16" version during actual holiday on bad rocky ground.

Sure. But due to the higher tire walls, there is virtually no difference in circumference between these two standard sets (only 0.4%), so there is not much added value in the context of this topic. See:

https://www.tacomaworld.com/tirecalc?tires=225-55r18-215-70r16

 

[elm70]

Of course the car DOES go into serial mode when battery SOC is very low. No need to do anything to achieve this. But I would like to prevent this from happening, by keeping SOC a bit above the low water mark. Driving 90 km/h for a few hours where the cars switches between a 'near constant 2450 RPM' and 'somewhere between 3500 and 4100 RPM' every 2 or 3 km is no fun at all. Seriously, I have opened this topic to discuss ways to prevent serial mode from happening and you try to change it into discussing ways of forcing serial mode. I don't understand why.

Also, parallel mode starts at 60 - 65 km/h. I don't think driving 60 - 65 km/h to the south of France or Croatia is a practical solution. Plus, it totally defeats the purpose of what I am trying to achieve.

My aim would be to prevent to have SOC very low ... by forcing serial mode for recharge properly .. and then switch in parallel ... if 5% is what you believe can make the difference .. you may need to force serial mode only for 10% of travel time ... but mainly do this with decent SOC .. I don't think the battery is happy to cycle between around the 16% and 20% SOC

Anyhow ... it is your topic ... and your car too

PS: the missing 5% you can also achieve by making more aerodynamic your caravan :ugeek:

 

[elm70]

The 16" rims are the standard in Austria and Germany for the simple versions of the car.

I have my summer tyres on 18", the winter tyres on 16".
Enjoyed the higher tyres of the 16" version during actual holiday on bad rocky ground.

Sure. But due to the higher tire walls, there is virtually no difference in circumference between these two standard sets (only 0.4%), so there is not much added value in the context of this topic. See:

https://www.tacomaworld.com/tirecalc?tires=225-55r18-215-70r16

All you need is a 16" rim .. and a low/lower profile tyre ... still ... you need to check if NL car rules allow to mount whatever rim and tyre , or if these need to be in the the car homologation list

Anyhow .. possibly the PHEV with smaller tyres is all time more efficient (not only for towing) .... downsize is losing the top speed (and ground clearance) ... but the car should be more responsive and more fuel and battery efficient too ...

PS: Losing on top speed is not a big minus .. our PHEV it is already slow .. 170km/h or 160 or 150km/h makes no much difference .. both are relevant only in german motorway , but enter german motorway without a over 200km/h car is already a limitation ...

 

[anko]

My aim would be to prevent to have SOC very low ... by forcing serial mode for recharge properly .. and then switch in parallel ... if 5% is what you believe can make the difference .. you may need to force serial mode only for 10% of travel time ...l but mainly do this with decent SOC .. I don't think the battery is happy to cycle between around the 16% and 20% SOC

Anyhow ... it is your topic ... and your car too

PS: the missing 5% you can also achieve by making more aerodynamic your caravan :ugeek:

I take it you do not tow with the PHEV (over long distances) and you do not have a caravan either? :roll:

 

[anko]

Anyhow .. possibly the PHEV with smaller tyres is all time more efficient (not only for towing) .... downsize is losing the top speed (and ground clearance) ... but the car should be more responsive and more fuel and battery efficient too ....

I agree with the advantage of less ground clearance, although when towing a caravan this only exposes the caravan more than before. Advantage of lower top speed totally depends on driver right foot and again does not apply when towing. Using smaller tires effectively shortens the gear. Don't think this is likely to increase fuel efficiency.

 

[elm70]

I take it you do not tow with the PHEV (over long distances) and you do not have a caravan either? :roll:

Good guess

I have the hook in my PHEV

But I just stick on it the bike carrier .. and this did not cause any problem up to 150km/h speed

Camping and Caravans .. are not in my life style :?

 

[elm70]

Anyhow .. possibly the PHEV with smaller tyres is all time more efficient (not only for towing) .... downsize is losing the top speed (and ground clearance) ... but the car should be more responsive and more fuel and battery efficient too ....

I agree with the advantage of less ground clearance, although when towing a caravan this only exposes the caravan more than before. Advantage of lower top speed totally depends on driver right foot and again does not apply when towing. Using smaller tires effectively shortens the gear. Don't think this is likely to increase fuel efficiency.

I bet the parallel mode is more efficient on lower gear ... as well ... it reduce the minimum speed of having parallel mode ...

In my experience in ICE mode and low speed with serial mode ... my PHEV was consuming way more then at higher speed in parallel mode

Electric motor with lower gears are more efficient ...at least this is from my memory of gearing eMotor when I was doing RC model car racing ...

 

[anko]

I bet the parallel mode is more efficient on lower gear ... as well ... it reduce the minimum speed of having parallel mode ...

Hang on, making the gear ratio lower does not make parallel mode more efficient. It makes the car more efficient, as parallel mode can be used more often. But parallel mode itself will be less efficient. And here, I am talking about towing long distances, at speeds at which parallel mode is available anyway (provided you have sufficient SOC).

In my experience in ICE mode and low speed with serial mode ... my PHEV was consuming way more then at higher speed in parallel mode

Half of the reason I want to prevent serial mode from happening.

 

[elm70]

About efficiency ... I'm speaking efficiency in normal generic usage ... nor specifically to towing only

In EV mode, lower gear means higher efficiency, and faster acceleration ...

Parallel mode kick in faster .. which is an advantage if driving in some sub-urban streets ...

At constant speed and towing .... I'm not sure ... yes your engine will need to rev higher, in both cases the end will be at 100% load .. but in higher gear there is a need to a help from battery (which will cause inefficient serial mode) ... in the other one the battery get even charged .. so .. towing an lower gear in the PHEV will be more fuel efficient

Different story maybe happen at some high speed without towing ... up to speed X ... the lower gear has an advantage .. above some speed ... the higher gear may have an advantage ... it will be needed to know ICE efficiency at each rev and load level ...

For generic usage in traffic and sub-urban both EV and ICE ... smaller gear I see an advantage

 

[elm70]

Anyhow ... thinking of fuel efficiency for the towing on motorway ... is a bit odd ...

I would be more concern on having to cycle the battery at low SOC with potential limited power available (which maybe is the reason why your PHEV battery has degradated so fast)

For me ... the ideal solution would be to force serial mode before SOC go to critical level ... charge up to 50% SOC ... and then back in parallel mode till 30% SOC