Cruiter

Thanks. I haven't looked yet, but don't think I'll see it on mine. But nice to look for in the future. I do know from one minute timing and the mileage markers on the highway, we're recording slightly more speed and miles than we actually do. Try that on yours after calibrating and see if you drive exactely one mile in 60 sec. I'd be interested in what you get.

1NEAT_SC

Just put 4 new tires on the RX450h yesterday using Michelin's Latitude Tour HP -P235/55R19 101V. I had 40K on the Dunlops with probably 5-8k left on them, but made the executive decision to go ahead and replace them now (while the sale was on) rather than chance a sudden tire replacement. I definitely notice a ride difference with the Michelins. (To the better)

Lar

Dolphin

I have the 19" rims on my 13.... I prefer more cushion between the rim and the tread, as it really does act as a great shock absorber for the smaller bumps.... I realize I can't really go wider, without wider rims, but how much taller can I go? I assume very little, as the wheel wells are designed for a specific size tire, right? By taller, I mean, 1" diameter added? 2" ? Just curious what's possible?

Also, anyone know why the RX tires are so thin? Very little tread contact on the road surface vs. other rigs this size?

vlad_a

There's plenty of space to go tall, if that's what you want. However, the speedo will be too far off. Here's the list of tires I posted previously that I think will fit on the stock 19":
I think the width of stock tire may have something to do with the fuel economy. I haven't noticed a big change when I switched to 255mm snow tires. Also, bad tires do better in snow and water if they're narrower, as there is more pressure on the surface and less snow/water to displace upon contact. I always try go to wider for new tires and have been happy with the results.

Dolphin

Thanks Vlad... can you clarify this....

>Also, bad tires do better in snow and water if they're narrower,

bad = typo? bad = bald? If so, that is very interesting....

About how much greater diameter will the tires you mention above be, vs. my factory 19" rims and tires? The only diameter label on tires, seems to be the diam of the rim, not the diameter of the tire. My LC had 17" rims and very tall sidewalls, and the ride was so much more enjoyable than my new RX, which transfers every tiny road imperfection. taller sidewalls are the ultimate dampener of small road imperfections, you agree?

dEV80

I found that 17's from 2011 Sienna will fit with no clearance issues. This would allow for a much larger tires. If I had the additional funds to explore I would try 17's with 255/70/17. The 70 series tire should provide an even smoother ride over rough roads and parking lot speed bumps.

Thanks,
dEV

vlad_a

Got to be careful with 17s. They may not clear the calipers with big glued weights. That's why TireRack stopped selling them for the RX. When I was running 16" rims on my IS, and had them balanced off the car, I had to move the big weights closer to the edge so they would not hit calipers. Of course, lip-mounted weights would not be an issue.

vlad_a

No typo, bad both in terms of design and/or bald. That's my theory and I'm sticking to it.

The 1st number on the tire is it width in mm. The 2nd number is the relation in percent of the sidewall relative to the width. If you multiply the 1st and 2nd numbers and divide by 100 you will get the sidewall height in mm.

From above, if either width or the profile increases, so will the sidewall. Divide it by 25.4 and you will get the result in inches. Multiply by 2 to account for top and bottom and add the wheel diameter to get the total diameter of the tire.

Therefore, the stock diameter for 19" wheels will be:
235*55 / 100 / 25.4 * 2 + 19 = 29.177
Simplify:
235*55 / 1270 + 19 = 29.177

Here's the breakdown for sidewall increase (both top and bottom w/o rim) and then the overall diameter, same as above:

Dolphin

Thx Vlad, understood.... it appears the most you can increase tire sidewall is 2" using 19" rims, vs. factory tires, right? And these will fit in the wheel well? Not sure how significant that would be to the ride.

If you wanted a bit plusher ride, I guess one would move to 18" rims?

vlad_a

No prob.
Actually, the sidewall height number I have in there is multiplied by 2 to get the tire diameter by adding 19". Max I have estimated is 1". One might be able to get away with more, depending on how much clearance there is.
I would say the wider tires will also make a plushier ride, as there is more air inside to compress and play.
Also, the tires themselves play a huge role. Some have softer sidewall, resulting in a softer ride.
If you wanted to go even "softer", then you would have to get 18" or even 17" rims.

Dolphin

Agreed...when I mentioned 2", I meant in diameter, but what really matters is the radius, so only 1 added inch between road and rim. So your max. increase, is marginal, unless your tires are worn and ready to replace. Anyway, I see this as a mixed bag.... I fear the 17" rims would give me the nice soft ride, but make the ride to sloppy. I am enjoying the relatively tight ride for Crossover right now. Just hate all the tiny road imperfections coming through. Will take more air out of tires....

good point about wider tires having more air cushion, and also, sidewall design. More flexible sidewalls prob. plusher ride, but surely will create some sloppy handling. I might hold off, I think this $ upgrade might be too high, and the gains too marginal (and risky) to justify. but good education for when these tires need replacing, I will take the added inch :-)

mkeeney

Vlad, your formula is correct, and in a perfect world that would be all you need. Unfortunately, the Tire and Rim Association specifies a range that tires must fall within in order to be labeled as a particular size. That means that tires of the same size from different manufacturers are not necessarily the same size, in both width and sidewall height. The best method is to check the specs of the tire and get the actual diameter of the finished tire there. If you look at the two stock sizes for the 3rd gen RX, the tires I checked on TireRack range between 29.1” and 29.3” overall diameter.

Another example I can share comes from when I worked for a tire manufacturer. We were producing both a 305/35-24 and a 315/35-24 – in the same mold. By using the formula, the 315’s should have been 0.28” taller than the 305’s. The tires were exactly the same though - same carcass, same tread - we just swapped out the sidewalls with 305 or 315 depending on which size we were producing at the time. We also charged about $120 more per tire at the time for the 315’s, even though there was only a one-digit difference in the sidewall lettering.

vlad_a

Thanks, that's good to know! I will use that in the future when comparing individual tires.

dEV80

I neglected to mention the total weight of my tire and wheel combination. This also plays a big part not only in stop and go straight line performance but also how well the package behaves in corning and over bumps on the road. The RX suspension seems to have been tuned for a lighter wheel and tire combination giving an overall sporty feel.

I'm almost certain with lighter wheels (17's) and a slightly smaller tire (235/60-17), you would get a much better ride quality in all road conditions versus just having larger tires with less tire pressure on stock 18's. I have to admit by putting on the larger tires on my stock 18's, the car suffers in corning at 35mph+ and over large dips 65mph+ the car gets upset very easily. The car feel a bit more bouncy and wants to hop or skip over large humps in the road.

But in a straight line over rough roads the car feels so much more comfortable, like it could roll over anything in its path