205 50 15 tires on an 01?

Please check the archives of the YahooGroup "Prius Technical Stuff" but I believe one owner tried some 205 and 195 Yokahamas on his NHW11 and had interference on the rear wheel well.

I've been running Sumitomo T4s:

• 175P65R14 - 5.4" tread width, replacement from Toyota
• 175P70R14 - 5.2" tread width, current tires, to reduce tire rpm
• 195P70R14 - 5.8" tread width, 0.8" wider section width, an experiment pending delivery

I suspect tread width is the major challenge but increasing the section is also a risk. So I've ordered one tire to mount on a full-size, spare rim. I'll then rotate it between rear and front wheels to check the clearance. If it works, I'll get a second one and do my next set of tests.

I'm interested in changing the tire diameter to measure the impact on mileage and operation. We know the NHW11 control laws allow hybrid operation below 42 mph. I want to change the tire rotations per mile so I can achieve hybrid operation at higher, true speeds. For example, today I use 38 mph indicated with a true speed of 39 mph. If the new tires work, 38 mph should give 41 mph.

Now you mentioned handling. Do you have a read-out of your current alignment? It is possible to use shims on the rear wheels and camber bolts on the front to achieve perfect, 4-wheel alignment. This helps most if your current alignment is off but it does no harm to start out with perfect alignment.

Bob Wilson

 

Ok, I mounted the 195/70R14 this morning on the right rear wheel and neither speed bumps nor speed dips caused an interference hit. I'll do some more testing but right now, I can't find a problem. However, it is as large of a tire as I ever want to test.

There is only 1" clearance to rear; 1.5" clearance to front and; about 4" clearance in the vertical, top center. To really test, I'll have to put a maximum load and then do the speed bump tests.

I'll post photos and more dimension information as a formal report. In the meanwhile, I just ordered a second one that I'll use for front and rear wheel testing. The front has a lot more room so I don't see a problem there.

Bob Wilson

 

I'm following this specification for tires:
Tire Tech Information - Calculating Approximate Tire Dimensions

Handling is often a subjective term because of the absence of hard numbers. You might check for car reviews that use a skid-pan to measure maximum G force during a turn. But things like body roll and under and over steer remain subjective qualities along with 'road feel.' So take these as my impressions:

• neutral stability - the car has almost no lane stability even after perfect alignment. Poor alignment and it is not fun.
• little road feedback - the electronic steering assist pretty much isolates the car from the road feel. You have to steer the car all the time, more than others. There is a hack that desensitizes the electronic steering assist so more road feel comes
• low center of gravity, takes turns like nobody's business - I almost rolled an Echo because I took a turn at Prius speeds. The car doesn't 'power' turn as much as 'sticks like spiderman' through a turn. It is my favorite way to get rid of a tailgater.

 

I upgraded to bfgoodrich touring t/a pro on the stock rim and stock size, the difference in handling and steering feel is great. It sticks to the road unlike the potenza RE92s and the goodyear allegras.