Question about a Gen II brace....

There is a 'U' channel that runs through the back floor of the Prius. This channel would allow the floor to flex, so it comes with an attached brace. The thinking is that the attached brace is too flimsy, so some owners replace it with a stiffer after-market brace. As an engineer, the argument doesn't make sense to me. The existing brace is loaded in tension, a task for which it should be plenty strong. Still, many swear by stiffer braces. It could be the placebo effect, but perhaps not. It's up to you to decide.

On the other hand, good tires do make a difference. I'd put my money there.

Tom

 

qbee42 is correct up to a point. the stock brace DOES help if the forces on the car put it in tension, however in those scenarios where it needs to resist compression it is almost useless.
The aluminum brace I used resisted compression as well. Before I bought it I felt insecure in side winds like when you passed a semi. After I bought it I never again felt that way. I cannot rule out co-incidence or the placebo effect.

prius g7 | eBay

 

I developed and made several examples of ny "box beam" brace based on the late 2012+ improved increased stiffness brace with reduced "torsional" resistance.

From my experience, the B T Tech and the G7 brace shown above has too much torsional resistance that may cause unwanted long term repeated stress loading on the rails and eventual metal fatigue.

I sold several of the GEN II braces, and everyone who got them installed them easily and reported positive results.

I've attached a photos of my brace with the OEM brace for everyone's reference.

 

I would also look to the most obvious, the tires and the alignment. Either can be a huge issue in terms of handling. If the tires are wearing evenly across the tread then it's unlikely to be the alignment. I would say the tires are then the most likely culprit. What are the tire brand, model, size, miles, and pressure? Are they all the same? What kind of mileage are you getting? Have any of these things changed? These answers may help.

BTW, when you say the high tire pressure makes all the difference, what do you see as the difference? And how does it behave with lower tire pressure?

 

AJP,

There does seem to be varying opinions on the Harmony but many are pleased with it. But I don't think it's a LRR tire and is reported to take a 4-5 MPG hit. That could account for your 45 MPG, which is not bad, just saying.

I have recently become aware that tire pressure gauges are notoriously inaccurate. A good digital gauge can be had for $15 or less and should probably be a standard tool in the Prius owner's glove box. But lets assume your pressure is correct. You state that when you increased the pressure the problem decreased. Possibly you could increase the pressure by 2lb increments from there and note the results.

You state that you recently changed to your wider 195 winter tire and that helped a bit more. My Assurance 185's also do a little "wandering" and I've wondered if a wider tire would improve that. I've read that others have seen no MPG hit with wider tires so I think it is worth considering. Your notice that the 195 improved the stability is encouraging. Some have gone to 205. I would like to hear from them about their thoughts on the resulting difference, especially concerning handling and MPG.

The other factor that comes to mind is this car is light. I would expect some wind buffeting in open areas. If the wandering is caused by the wind then weight and footing are definitely factors and a certain amount may just be unavoidable, except for heavier cars.

 

Yep, after looking at this again I find you are correct. They are LRR.

Personally I'm a little skeptical this chassis stiffening plate will help this particular issue but it's a relatively inexpensive try for a fix and likely wont hurt.

 

I've read many theories about why a brace shouldn't work, but in my experience, it does. When I first drove my new Prius, it felt like it was hinged in the middle. The front end would go around a corner, followed sometime later by the back end. It wandered on the highway, didn't feel like it went where it was pointed, and was easily blown sideways. I can't say a brace solved all of these problems immediately, but it made a significant difference that was well worth what I paid for it.

Later, when it was time for new tires, I bought much better ones, and was impressed by the big difference. In comparison, the original Integritys are so bad, I'd consider them unsafe.

 

Whatever problems the brace improves should improve immediately. And I assume that's what you're saying, that the issues improved moderately with the brace but weren't eliminated immediately. What size tire are you running? I have read several reviews recently that going to the wider sizes in a good tire improves the handling and stability significantly on the Prius.

 

If "it doesn't work?" Why did Toyota quietly introduce a new stiffer bend resistance but with lesser ttwist or torsional reistence brace in early 2012 on all their new Gen III and "v" Prii?

I've attached a few photos of the newer brace.

The BT Tech plate and the G7 was a good first try. Toyota saw the need for torsional flexibility. My designs incorporate that fexibility.

 

The brace eliminated the 'hinged in the middle' feeling immediately -on the first corner, and I wasn't even going fast.

It seemed to help somewhat with the wandering, but the large, immediate difference there was the tires. I switched to 195 Goodyear TripleTred. After that, the car felt like it was actually in contact with the road, instead of just rolling along the surface. Handling and safety are so vastly improved that the original tires, even when new, are a safety hazard.

 

I felt much more secure in wind buffeting after I installed the G7 plate.

 

I guess with so many claiming improvement and even Toyota adding it, there has to be something to it. Glad it has helped. I would still start with the tires.

 

IMO the 185/65/15 is too small for the Prius. When you need new tires, look into going a size or two wider (195-205). The mpg loss is made up for by the extra stability and safety.

 

Yeah, from what I've read it does seem going to a wider tire has benefits in stability. And I also see little support for decreased MPG due to tire wide. More from tire brand it seems. But I am really interested in the stability, straight tracking, and low wandering from side winds, especially if there is no hit in MPG.

 

I would expect a small hit from the wider tire if you do mostly high speed driving. At low speeds the hit should be very small. Choose a great LRR tire like the Energy Saver A/S and you shouldn't see any hit at all.

Wider tires and a chassis brace cures a lot of the wandering.

 

I would also expect to see a MPG hit with the wider tire having more rubber on the ground but I don't see that consensus reported by the majority. I see most saying there is little or no hit with this difference. If that is the case it is nearly a no-brainer to go with the wider tire.