My 1991 M5 has a double-row chain. It has 262,000 miles on it. I didn't replace it at the time of my rebuild. The tensioner and the guide rails have been replaced.

 

Did it still meet specs? All the bike manufacturers provide a stretch specification for replacing their cam chains.

 

I didn't have it checked but those in the know on these cars told me there is no need. The tensioner likely takes up most of the slack. 100,000 miles later it appears to be fine. Then again, I am sure it will seem that way until it goes boom.

 

I learned a very important lesson racing motorcycles: Chains wear out. Sprockets do not if if you replace the chain before it damages the sprockets. The same is true for the current crop of high performance bicycles (those 9 and 10 speed gear clusters make for a narrow, high wear chain). The mitigating factor for chains inside an engine is they are in the ideal environment for long life - constant oil mist.

So the thrust of the issue is, replace chain frequently and never replace sprockets, or replace chain AND sprockets when the chain starts skipping. Of course if you have zytel sprockets you figure this out when the teeth start breaking off and you get stranded wherever you happen to be. AMHIK.

I just wouldn't want to have to replace the sprockets on that BMW engine since they are machined from the crank's base material.

 

very nice curves indeed. Lets wait and see what is-f has to offer.

 

BMW just makes fantastic engines. Period. I know some mechanics that insist they make the best engines of anyone.
Lighter than the I-6 is a big plus.

420hp from 4 liters. Wow

 

How do smaller rims help performance/handling?

The point I'm trying to make is that it's silly to say "18" tires are ideal, 19" are too big". Such a thought or statement is too vague, and it obviously depends on the car, and many other factors.

 

I gotta say, when you're looking at cars in this segment (high performance sport luxury cars) then ride comfort should not be a big priority. With that said, Lexus did mention the IS-F would maintain Lexus traits of luxury, and comfort.

 

Considering the I6 engine is around the same size as a V10, and the fact that it was iron block, I really don't see how. The I6 was an older design. This V8 is state of the art, with composite and alloy construction.

 

It's a nice flat torque curve, but again ... low overall torque. The IS350's 2GR-FSE torque curve isn't too far from this one actually.

An interesting point actually. The 2GR-FSE makes about 250 lb-ft torque at 2000 RPM, virtually the same as this engine. Then at the other end of the spectrum. the 2GR-FSE makes about 250 lb-ft at 6500 RPM as well. The torque curves of both engines are very comparable in fact, although the BMW obviously makes a lot more HP, which makes sense since it revs much higher than the 2GR-FSE.

 

I was serious. How do larger rims help? I'm looking for an answer in return, not a snide question.

 

Don't jump to conclusions, I wasn't making a snide response.

As for tires, think of it this way ... larger tires tend to be wider, on average, than smaller tires. More tread means more grip. It depends of course on the car you're talking about, and all cars have an optimal tire size. FWD cars optimally should have smaller tires than RWD cars.

There is obviously a point when too much tread is bad, and the tire size becomes detrimental, but it all goes back to optimal tire size for each car.

 

Regardless of diameter both cars will probably come with 275+ tires in the rear, which should be more than enough to launch them effectively.

 

As for tire size, I let it up to the engineers to figure out the optimal size. Clearly what they think the car comes with is appropriate for the vehicle.

I honestly think 19s and 20s don't help much with handling or response. In reading reviews for years over hundreds of cars, it seems 18s is what most experts like.

The funny thing is you really learn how to drive with SKINNY tires and small diameter rims. The car is much more tossable and you "learn" how to drive.

When you have fat patches, it takes more power to have this same "fun" and you are just more planted. You also have a higher chance of hydorplaning and you feel more grooves and distrubances in the road.

Its about aestethics now. Cars are so much taller and wider, they would look ridiculous on small wheels. Thus 19s, 20s, 22s, it makes all these tall, slabsided, small window cars look better.

my 2 cents.

 

What do you mean by 'larger tires'? This is too general a statement. Larger tires doesn't necessarily tend to be wider, but again, what's your definition of "larger"? And why should FWD cars optimally should have smaller tires than RWD cars? Should a Cadillac Seville, DTS or an Acura TL have smaller tires than an MR2 or Smart ForTwo?

Smaller rims, or should I say, smaller overall diameter rims and tires package, will improve performance because of lower weight/inertia, but at the cost of stability and gas mileage (more revs to cover the same distance).

I hope you are not making personal attack and saying that I am silly just because I personally think that 19" is too big for cars in the size of the M3 and the IS-F.