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Old December 27th, 2018, 02:37 PM   #1
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Wheels worth it for 748?

Hi All,
I'm contemplating upgrading my stock Brembo 3 spoke wheels on my 748. Looking for a little more performance out of this bike for the track instead of bumping up to an 848, 899, 959, etc. Being that my current wheels are so heavy, do you think it would be worth paying roughly 1/3 or more of what the bike is worth to upgrade the wheels or bite the bullet and upgrade to a different bike? The 5 spoke aren't much lighter but 10 spoke or something newer is quite a bit lighter.

Thanks, Matt
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Old December 27th, 2018, 06:36 PM   #2
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I've done it on a 916 — and there are benefits. But, the same money spent on Superbike School will make you faster.
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Old December 27th, 2018, 08:45 PM   #3
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Thanks Shazaam for the input. Yes, I went to school and it has made a huge difference. I try to go at least once a year. The 748 definitely has more ability than I do. Like anything else, always looking to feed the addiction with new parts.
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Old December 28th, 2018, 07:37 AM   #4
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Gearing

Have you experimented with rear sprocket sizes?

Most 748 owners change from the stock 38-tooth (94 link chain) rear sprocket to a 40-tooth (96 link) for the street. All stock 748s have a 14-tooth front sprocket, which is the smallest practical size. In the US, a stock 748 comes stock with 38-tooth rear sprocket that is too high, most will agree.

Of course, the track gearing selection criteria is different. You should expect to need different gearing for different tracks. The problem is that people will suggest sprocket sizes to you that can only be used as a starting point.

Gear selection is very dependent upon your style of riding.

In general, you would like to have a final drive gearing that allows you to hit the peak horsepower rpm at least one place on a given track. Otherwise, you’re not using all the gears in your transmission and aren’t taking advantage of the closer-spacing between the higher gears. (Daytona is an obvious exception because gearing for the high speed oval section will result in over-gearing for the infield sections. This also illustrates the need to select a compromise gearing that doesn’t permit the maximum top speed but gives better drive out of the corners.)

So, you also need to find a final drive gear ratio that will minimize your number of gear changes and still place you at engine speeds that give you the best drive out of the corners. You need to build power quickly, sometimes at the slight expense of outright top speed in the straights. The fastest lap times are not so much controlled by top speed as they are by getting from one corner to the next as quickly as possible.

Lower gearing usually means more gear changes that lower your lap times. Sometimes you just can’t shift mid-corner, so you go in slower in a lower gear which allows you to come out harder. It is always a trade-off between gear selection and riding technique.

PS. Ducati uses an eccentric to adjust the chain tension so remember to measure your rear ride height BEFORE you change your rear sprocket so you can later raise your rear ride height back to where it was after the change.

Lightweight Wheels

The whole idea behind using aftermarket alloy wheels is to reduce rotational inertia and unsprung weight so a magnesium wheel at 2/3 the weight of aluminum offers better handling. If you forge (rather than cast) the metal you get more strength from the same amount of material so you can create designs having even less weight. If the design preferentially reduces metal thickness at the rim you get a much larger reduction in rotational inertia (gyroscopic loads) than if you removed a similar amount of material from the hub.

Both magnesium and aluminum wheels are able to absorb a fairly high level of impact type loads without damage when used on the street. But if you hit a deep pothole hard enough you'll damage any wheel.

The two carbon fiber wheel manufacturers, Dymag and BST, certify their wheel designs for street use by performing dynamic fatigue testing to BS, TÜV and impact testing to JWL standards. The USDOT requires that each wheel manufacturer conform to the Tire & Rim Association standards to be DOT compliant.

Other manufacturers duck the issue by claiming that their wheels are designed to be only used on a race track where there are no road imperfections. This allows the wheel designer to minimize the thickness of the rim portion which has the greatest effect on reducing the wheel's rotational inertia, but as a result, it will also be less resistant to pothole damage.

That's why Marchesini magnesium wheels have machined rims to reduce rotational inertia and also why they caution that:

Although magnesium wheels are stronger then most aluminum wheels, Marchesini wheels, like other magnesium wheels, are for racing applications ONLY and are not intended for street use.

They mean it. You get into trouble when the attempt to save weight results in thinner, and consequently weaker, cross sections.

So think twice about buying the lightest wheels available. For the street, the lightest wheels offer the greatest handling improvement but are not the best choice in terms of survivability.

Also, the price difference between magnesium and aluminum will get you a long way towards a much larger weight reduction from fitting lightweight front brake rotors.

Magnesium alloys also require more maintenance. Without a durable protective coating, they'll corrode in damp environments unlike aluminum which naturally forms a protective oxide coating. The thin protective layer applied to magnesium by Marchesini and Dymag, is a chromate coating which is then painted. Except for Dymags, the paint on all magnesium wheels are somewhat fragile. Dymags are powder coated and have a tough clear coat, but they still get stone chipped and need paint touch-ups regularly when used on the street.

Then there is a point that sometimes is overlooked when considering the switch to mag wheels, and that is – it's not just the total weight savings but how it's distributed that can make a difference.

In the case of tires, the seemingly small difference between the heaviest Dunlop 207RR's (10 lb. 7 oz.) and the lightest Pirelli Supercorsa (8 lb. 6 oz.) front tire recently tested by Sport Rider June 2002 is more important than an even larger weight savings at the wheel.

Simply stated, the rotational inertia of a wheel or tire is proportional to the square of the distance the weight is placed from the axle. Because of this square-effect, the tire weight has more effect on the rotational inertia of the wheel-tire combination mainly because of its somewhat greater distance from the axle.

In fact, a 1.5 lb. lighter front or rear tire will have the same order effect as switching from an aluminum to a magnesium wheel.

Looking at it another way, you can negate the handling benefits of expensive magnesium wheels by switching to a heavier tire. This is also the best argument for choosing aftermarket wheels such as Dymag that have carbon fiber rims and magnesium centers. When compared to all-magnesium wheels with the same weight, the Dymags will have significantly lower rotational inertia that most agree results in improved acceleration and handling.

Basically, the effect of changing to lightweight wheels on a bike's acceleration is identical to the result that you get when you increase your engine's torque output through performance modifications. Since they also improve a bike's handling as well, it is probably the best single modification you can make to a bike.

That said, here's some comments from an owner who's done the conversion.

"The wheels were initially the biggest disappointment, given how so many on this list had recommended this as the first mod they'd do. At first ride all I noticed was a modest improvement in flickability. After a bit more riding I noticed a similar improvement to acceleration. With a similarly modest improvement to how well the bike tracks over bumps, brakes, etc. The only major change was that the slight wobble I'd get at around 90 seemed to have completely vanished (I may take off the steering damper)

So at first I was disappointed. After all, I'd just had a walletectomy, so where was the huge difference?

Then, after a week with these wheels, I realize that this amounts to a modest improvement in *every* aspect of the way the bike feels. So while this was easily the priciest upgrade I've ever made to a bike, it's completely transformed everything! Here I was expecting a 'brick over the head' change in my bike, instead I just got a bike that works better in *every* way.

Verdict: If you can get over the sticker shock, this is a great mod that simply makes your whole bike work better. And think about how much you'd have to spend for a 10% improvement to every part of your bike".
– John Offenhartz
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Old December 31st, 2018, 04:24 PM   #5
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Wow! Thank you for so much information. Roger that on the rear sprocket size. Currently I am running a 40.

Are you in Marketing by any chance? Kidding, but you are helping me determine that I am going for new wheels. The bike has much more than I have and swapping out the wheels will provide a performance upgrade while helping me focus on getting into and off of the corners better and technique in general knowing that I don't have the horsepower to hide behind.

Thanks Again
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Old January 2nd, 2019, 09:32 PM   #6
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Old March 11th, 2019, 03:11 PM   #7
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Well I pulled the trigger and purchased the OZ Racing GASS wheels with Q3+s. The Placebo Effect is telling me that they were worth the money but living in NE Ohio it is still very cold.

I did weigh the wheel tire combo OEM/Shinko 005 to OZ/Q3+ and the delta was about 6-7lbs for the rear and 4-5 for the front.

Also, neither the front or rear needed wheel weights for balancing.

Excited to get on the track.

Thanks again for all the feedback and advice.
Matt
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