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The same thing applies to the flywheel, and anything else that spins / rotates.
Never thought of it quite that way until a buddy of mine told me about a student replacing his factory steel wheels with lightweight Weld wheels. He said the kid could 'light them up' after the wheel change but couldn't before. Same tires, just lighter wheels.

Harold
 

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Pedal Smasher
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If you rebuilt a vehicle, and the only thing you did differently was to reduce all rotating weight from the pistons to the rims on the driven wheels, you'd wind up with a completely different vehicle. Realistically, it can be kinda hard to reduce some of this weight without having custom parts made out of stupid expensive materials like titanium. Granted, you'd see a larger increase in performance than replacing large parts of the body with carbon fiber.
 

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Are you shittin me ? Ounces of wheel weights and duct taped over
430556
. I raced for 12 years with these 7 x 13'' 3 piece RONEL Turbo wheels that weighed 8.5 pounds each. The centers drew air though the finned wheel area for brake cooling. In 1985 it was $1200.00 for four of them. The Goodyear 21-9.00-13 gumball tire weighed 15 pounds alone. At over 8000 RPM in top gear, 160 mph plus, your wheels better be balanced !
 

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Reducing rotating mass does indeed make a big difference!

I experienced this on my Yamaha 700 Grizzly Atv. I switched my Pitbull Growler tires from a traditional staggered set up of 26x9" fronts and 26x11 rears to my current 26x9 Growlers at all four corners . Well that shed 18 lbs of rotation mass of the rear axle. This made a HUGE difference in acceleration and overall fun factor on my quad!!! I can easily drift the rear end around up to 40 mph now.
 
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Reducing rotating mass does indeed make a big difference!

I experienced this on my Yamaha 700 Grizzly Atv. I switched my Pitbull Growler tires from a traditional staggered set up of 26x9" fronts and 26x11 rears to my current 26x9 Growlers at all four corners . Well that shed 18 lbs of rotation mass of the rear axle. This made a HUGE difference in acceleration and overall fun factor on my quad!!! I can easily drift the rear end around up to 40 mph now.
The 7075 T6 Aluminum flywheel with steel ring gear, 8 inch disc, floater plate and pressure plate in my racecar weighed 11.6 pounds total.
 

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Opel Rallier since 1977
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When it comes to HP/torque loss, such articles are pretty useless as they never quantify the losses. Example: In computing up the HP loss for reducing a small block V8's internal rotating mass by around 5 lbs (easy to do with modern parts), the result varied between <1 and 2 HP. That's all it is ... out of 400-500 HP.

I've never worked up computation on wheel/tire masses to see what the effect is. Keep in mind that it is all related to gearing too..... the higher the gear, the less the acceleration rate of the cars and the wheels/tires, and so the less this particular effect becomes.
 

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When it comes to HP/torque loss, such articles are pretty useless as they never quantify the losses. Example: In computing up the HP loss for reducing a small block V8's internal rotating mass by around 5 lbs (easy to do with modern parts), the result varied between <1 and 2 HP. That's all it is ... out of 400-500 HP.

I've never worked up computation on wheel/tire masses to see what the effect is. Keep in mind that it is all related to gearing too..... the higher the gear, the less the acceleration rate of the cars and the wheels/tires, and so the less this particular effect becomes.
Heavier wheel and tires will always need lower gearing to compensate... That's a Fact... Less rotation mass, means less need for more torque multiplication

This is well known in the atv world and owners (me including) modify our atv cvt systems to start at lower initial ratios to compensate for our heavier aftermarket tires witch typically adds anywhere from 30 to 75 lbs of rotating mass and can really bog down performance.

For snowmobiles, lighter tracks are known to spool up faster, accelerading harder and give better top speeds.


In all these cases dyno numbers never reflect this, or very little if at all , but in the real world applications the gains are undeniable
 
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Lighter wheels make a huge difference IMO.

Lighter engine parts...definitely, but you get more from large diameter things than small things. 5 lbs off a flywheel is far more noticeable than 5 lbs from a crank.

Similarly, lighter pistons and pins are more noticeable than lighter rods.

But I’ll take all lightweight parts over heavy parts any day. I suspect at sustained high rpms you’d want a heavier crank at least.
 
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Lighter wheels make a huge difference IMO.

Lighter engine parts...definitely, but you get more from large diameter things than small things. 5 lbs off a flywheel is far more noticeable than 5 lbs from a crank.

Similarly, lighter pistons and pins are more noticeable than lighter rods.

But I’ll take all lightweight parts over heavy parts any day. I suspect at sustained high rpms you’d want a heavier crank at least.
I agree with RallyBob, less rotational weight is better for accelerating and braking too. The powerband of your engine and drivetrain plays a big part. Racing with a stock geared transmission, build a high torque engine.
 

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On my 3 piece Ronel 7 x 13'' wheels I replaced all the 6mm bolts and nuts with Titanium 1/4 NF aircraft bolts, washers and mini steel locknuts. I lost half the total bolt & nut weight. Extreme maybe, but those served the purpose of weight reduction.
 

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The point is that how much you gain is not quantified in these articles. The potential gains are indeed there but the cost/benefit ratio can't be answered without knowing what you really gain, and how it can be used. That is why I mentioned the '5 lbs off the rotating assembly example'; if it costs $1000-1500, and you don't really use it, then it is a waste of $$ expended, as far as net torque/power to the wheels. These are the things that never get discussed in such articles and threads.

If you are road racing and can gain 1/2 car length on a straight, then the rewards may be there. But on the street, who are you racing? LOL And in rallying, the savings in unspring weight are of far more value than the acceleration gains; you very often can't put the extra HP to the ground in wet or loose gravel situations anyway; the traction is often simply not there to do so. I never felt/saw any acceleration advantge in my rally cars with alloy vs steel wheels for this reason. Part of this is that rally tires weigh a ton!

So to figure this gain out, you have to compute the energy absorbed in spooling up a particular part, Then figure/assume a rate of RPM and and translate that to HP/torque, and compare to what is going linearly into the total car's weight. Some pretty straightforward spreadsheet work will do that. (The hard part is figuring up the moment of inertia of the parts.)

BTW, how about a discussion of how the top end speed can be effected? Lighter wheels/tracks does not increase the ultimate energy that can be put into the car/snowmobile/atv's linear motion; only changes in drag (wind resistance, track drag, etc.) can do that. I think this notion needs to be examined a bit more.
 

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In Autocrossing and road racing the results show in lap times. For the street and highway driving a stronger wheel is needed for road roughness in the real world. I would never put my Ronel racing wheels on the street.
 

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Yes, and that is due to faster acceleration. But not top end speed, unless you happened to also change something else that lowers the drag forces. Like the snowmobile example.. any higher top speed would be due to less drag, like with a thinner track creating less drag around the rear suspension, or a different lug design/layout changing the drag in the snow. If the drag forces do not change, the top end speed does not change, regardless of weight change.

The cost-benefit example of not using wheel weights at 160 mph is a classic..... not much benefit and lot of problems!
 

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For my type of racing I’ve just decided to ignore weight reduction. Autocross is too short and quick for weight to play a huge factor. I take novices for ride alongs a lot to give pointers and the extra 150+lbs changes nothing on my average times. I’d rather just keep my AC and nice interior. Leave the race stuff outside the cockpit:)
I think 10% changes in HP/Weight would be about the limit to notice differences in autocross. So 200lbs added or removed or 10HP in my case.
 
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