Possible solution to the TC issues under slippery conditions

[spinkao]

Hi guys,
I've been reading about some Traction Control issues on the gen II Prii under particularly slippery conditions, such as cars refusing to climb a slope because of overly cautious TC, which does not allow for even the slightest wheelspin. We know that gen III's TC have been altered and allows for a little spin, making the things better. A very simple solution just occured to me and I would like to know your opinions.

I propose to fit a slightly larger diameter wheels on the front axis; say 16" to the front and 15" to the rear of the car. The TC works so that it computes the difference between RPM of the front (powered) and rear (unpowered) wheels, and when the powered wheels rev more than the unpowered ones it detects a spin and kicks in. With larger diameter wheels on the front, the rear wheels would rev a little faster under normal conditions, and therefore the TC would allow for a little wheelspin on the front, just as the gen III does now.

Unfortunatelly, I don't have 15" wheels at my disposal, as my Pri wears 16", and I don't have a chance to borrow them for the experiment either (not to mention that there is currently no snow around ). Would anybody be interested in doing a little evaluation and sharing the results with the rest of us? And what are your opinions in general?

BTW, you may argue that if the car refuses to move *at all*, the revs of the rear wheels would be zero, and therefore *anything* - 0 gives positive result (and therefore detection of a spin). But I don't believe that the TC really does not allow for *any* wheelspin at all, as the car would then barely move even under ideal grip conditions. Therefore, I believe that even in that case this solution would enable a *slightly* larger wheelspin than before.

[nerfer]

Interesting idea. Of course, your MPG and speedometer would be affected slightly.

My GII Prius does allow for some wheel slip, but there appears to be some differences from one car to the next that we haven't really resolved yet.

[David Beale]

Actually the mileage readout is from the front wheels, so if you increased the diameter of the rears it would have no effect.

It's an interesting idea, but I doubt it would have much effect. The 15" wheel/tire combo is the same overall diameter as the 16" wheel/tire. There isn't enough room in the rear wheelwells to increase the diameter much beyond about 10% circumference.
I would be interesting to see if 10% would have an effect, but I doubt it would. To do it you would have to buy two new -tires-, oversize. You -could- do it and stick to 16" for example. Or if you have 15" wheels you buy two new tires oversize for the rear. Either way would work the same.

I remember reading what the slip % was to trip the system, but I can't remember where.

[qbee42]

The Gen II allows wheel spin while you are still moving. Traction control only becomes a real problem when the car stops and you try to make it move again. At zero speed, the wheel diameters make no difference.

Later Gen IIs, like my 2006, allow some wheel spin even when stationary. I've been able to rock mine out of snow on many occasions, although the Gen III is much better.

Tom

[spinkao]

Originally Posted by nerfer

Interesting idea. Of course, your MPG and speedometer would be affected slightly.

My GII Prius does allow for some wheel slip, but there appears to be some differences from one car to the next that we haven't really resolved yet.

The speedo/MPG readings should be unaffected, as those are computed using the front wheels, which would be unchanged. What I proposed was to fit slightly smaller rear wheels.

Well, my good Pri is pretty cautious, as I saw today on some wet stone pavement trying to accelerate up the hill from a standstill... Made me a little worried about some winter mountain driving actually. And yes, I have bought good winter tires today .

EDITED: Sorry, I just re-read my original post and saw that I actually *did* write about fitting larger front wheels and not smaller rears - my mistake, I formulated it badly .

[spinkao]

Originally Posted by David Beale

Actually the mileage readout is from the front wheels, so if you increased the diameter of the rears it would have no effect.

It's an interesting idea, but I doubt it would have much effect. The 15" wheel/tire combo is the same overall diameter as the 16" wheel/tire. There isn't enough room in the rear wheelwells to increase the diameter much beyond about 10% circumference.
I would be interesting to see if 10% would have an effect, but I doubt it would. To do it you would have to buy two new -tires-, oversize. You -could- do it and stick to 16" for example. Or if you have 15" wheels you buy two new tires oversize for the rear. Either way would work the same.

I remember reading what the slip % was to trip the system, but I can't remember where.

Well, I didn't realize that the diameter of the wheel is not correlated to the rim size - you are right in that point, thanks for noting. Actually, I proposed to leave the front wheels alone (as I already have 16" as the car came from the factory), but to fit slightly *smaller* rears. The rears have to be smaller diameter than the front wheels, not the other way round, or it would actually make things worse .

[spinkao]

Originally Posted by qbee42

The Gen II allows wheel spin while you are still moving. Traction control only becomes a real problem when the car stops and you try to make it move again. At zero speed, the wheel diameters make no difference.

Later Gen IIs, like my 2006, allow some wheel spin even when stationary. I've been able to rock mine out of snow on many occasions, although the Gen III is much better.

Tom

Hi Tom,
you are right that my proposal would not make any difference at stillstand. I am aware that this is a major deficiency. Well, if you could fit slightly *larger* front wheels, than you would get slightly higher circumferential speed of the tire, which would make some difference. But larger front wheels probably won't fit in there and would affect speedo/mpg readigs, as Nefer stated...

OK, I think we may write my little proposal off as infeasible . Thanks for your answers!

[qbee42]

Some people have proposed injecting a synthesized ABS signal to the traction control ECU so that it wasn't aware of wheel spin. While you could do this, you risk damaging the HSD. An easier way to do this on a temporary basis is to use the traction control defeat dance to turn off traction control. Normally this is only used for testing, as you can damage the drive system if you aren't careful. Some users resort to this in emergencies.

Tom

[spinkao]

Originally Posted by qbee42

Some people have proposed injecting a synthesized ABS signal to the traction control ECU so that it wasn't aware of wheel spin. While you could do this, you risk damaging the HSD. An easier way to do this on a temporary basis is to use the traction control defeat dance to turn off traction control. Normally this is only used for testing, as you can damage the drive system if you aren't careful. Some users resort to this in emergencies.

Tom

Is it possible to turn the TC off? I didn't know that. How do you do it, would you explain the procedure please?

Yes, I was also thinking about messin' around the signals leading to the ECU, but this idea occured to me as a possible simple solution.

[qbee42]

It is called "Inspection Mode".

Here is a reprint from one of Patrick Wong's posts:

In case you do not know about Inspection Mode, here's how to enter that:

Make the car IG-ON (where all instrument panel warning lights are on)
Fully depress the accelerator pedal twice while the shift indicator is in P
Fully depress the accelerator pedal twice while the shift indicator is in N
Fully depress the accelerator pedal twice while the shift indicator is in P
You should now note the hybrid vehicle warning icon flashing in the MFD
Start the car by pressing the POWER button while depressing the brake pedal, as usual.

You can only rev up the engine to 2,500 rpm while in this mode. At idle the speed will be around 1,000 rpm and if you depress the pedal less than 60% then the speed will be 1,500 rpm.

When you are done and make the car IG-OFF, then Inspection Mode will automatically cancel. Do not drive the car when in this mode unless you want to run the risk of blowing the transaxle (this mode disables traction control which protects the transaxle from an overrev situation in the event of wheelspin.)

Tom