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 Post subject: Re: Welding wheels
PostPosted: Fri Feb 22, 2019 8:12 am 
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I"m waffling a little here....I'm pretty happy with the CF wheel design at this point but it is hard to make and know its right.......but I could fab the center in aluminum which would be pretty light and and weld it to the 550 rims or maybe hunt up a set with a more square edge profile....hmmmmmm


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 Post subject: Re: Welding wheels
PostPosted: Fri Feb 22, 2019 8:48 am 
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Here is a custom wheel made to look like the star wheel. It is 17 inch on a Boxer.


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 Post subject: Re: Welding wheels
PostPosted: Fri Feb 22, 2019 4:46 pm 
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mk e wrote:
...I noticed it just felt heavy....27lbs. Its 17×8. The 550 front is 18x8.5 and 22lbs. The 18x10.5 is 25lbs. Onshape says the rear 3 pc is 18lbs...
What is the impact of wheel weight on acceleration?

I have read many places were people attribute faster acceleration times to lighter wheels. This doesn't make sense to me since the amount of inertia (linear and angular) of even a heavy wheel are minor compared with the inertia of the weight of the car.

I totally "get" how lighter wheels improve suspension performance. I put lighter wheels on my track car and was amazed at how much I could feel a miniscule weight change in the unsprung weight. … but acceleration? … I felt nothing.

Is it a fallacy that lighter wheels accelerate faster or is it that I just don't understand the physics?


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 Post subject: Re: Welding wheels
PostPosted: Fri Feb 22, 2019 4:54 pm 
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Brian A wrote:
Is it a fallacy that lighter wheels accelerate faster or is it that I just don't understand the physics?

I thin you're right that its mostly in their heads but I did see a dyno test where they bough a really riced nissan or similar and started bolting stock parts back on. Removing the 19" wheels and big brakes was like...10hp? so double it for 4 wheels to 20hp on a dynojet type dyno. Nothing in my world but significant on a 120hp 4 banger I guess.

I was mostly just surprised the the BMW 17" wheel was heavier than the 18" ferrari....the rims seem to be very similar so I guess its mostly in the spokes for appearance.


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 Post subject: Re: Welding wheels
PostPosted: Sat Feb 23, 2019 10:14 am 
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mk e wrote:
... but I did see a dyno test where ... Removing the 19" wheels and big brakes was like...10hp...
Thinking about it, I can see the effect. On the dyno, the car is not really accelerating; just the wheels and power is inferred from that. Heavier wheels would hamper the car's ability to spin the dyno drum.


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 Post subject: Re: Welding wheels
PostPosted: Mon Feb 25, 2019 11:46 am 
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Brian A wrote:
mk e wrote:
... but I did see a dyno test where ... Removing the 19" wheels and big brakes was like...10hp...
Thinking about it, I can see the effect. On the dyno, the car is not really accelerating; just the wheels and power is inferred from that. Heavier wheels would hamper the car's ability to spin the dyno drum.


I think that's partly right. At the acceleration rate on the dyno, the hp change is real.....4th gear on the dyno might match 1st or 2nd in the real would for most cars...so in low gear when you're accelerating fast the hp is loss is hihger but in 5th where acceleration is slow the loss is less.


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 Post subject: Re: Welding wheels
PostPosted: Sun Mar 17, 2019 8:12 am 
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I got contact info for a chinese wheel company....looking at their forging sized now to see what could be done with them


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 Post subject: Re: Welding wheels
PostPosted: Mon Mar 18, 2019 3:03 pm 
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I'm actually curious about that - I'm stuck going Wide 5 on my tube chassis thing for cheap light wheels, another option would be nice.


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 Post subject: Re: Welding wheels
PostPosted: Mon Mar 18, 2019 3:52 pm 
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I'm still working on it but here it is and how it fits into the forging. Once I get the designs done I'll get a price.....I was told to expect around $500/wheel for monoblock but we'll see. Still kind of porky at 34lb but there is still some cutting I can do.

edit: oh and the centercap will need to be a press-in part, no way that will fit the forging I don't think


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 Post subject: Re: Welding wheels
PostPosted: Tue Mar 19, 2019 4:19 pm 
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Brian A wrote:
mk e wrote:
...I noticed it just felt heavy....27lbs. Its 17×8. The 550 front is 18x8.5 and 22lbs. The 18x10.5 is 25lbs. Onshape says the rear 3 pc is 18lbs...
What is the impact of wheel weight on acceleration?

I have read many places were people attribute faster acceleration times to lighter wheels. This doesn't make sense to me since the amount of inertia (linear and angular) of even a heavy wheel are minor compared with the inertia of the weight of the car.

I totally "get" how lighter wheels improve suspension performance. I put lighter wheels on my track car and was amazed at how much I could feel a miniscule weight change in the unsprung weight. … but acceleration? … I felt nothing.

Is it a fallacy that lighter wheels accelerate faster or is it that I just don't understand the physics?

What matters about the wheels (and the brake discs and the tyres), is that it's a rotational inertia. It's way more important to save 1 kg on a wheel than on any other part of the car that isn't in the drivetrain. AND you want your wheel to be as small as possible, or at least its weight to be the most centered, just like saving 1 kg on the roof is better for handling than saving the same 1 kg in the door sills.
Here's an intuitive demonstration: http://www.youtube.com/watch?v=CHQOctEvtTY


In some racing series (I think it's the case in formula Vee but I may be mistaken), competitors must use street tyres on their single seaters but have the right to remove thread material (sort of sanding the rubber). It matters because these few hundred grams (of a rotational part and the further appart from it center of rotation) saved are the most beneficial on the whole car.

In the present case, I'm not sure Mark is going to notice any difference. What will be important, though, is maintaining the integrity of the wheel (and thus Mark's integrity) would the car ride on a pothole or need to brake...



Mark, I cannot understand why you're so eager to cut your 550 wheels rather than buy 4 plain barrels (forgive me if that's not the right term) to add your own centers on?

Another idea that hasn't been suggested yet (I think): wire wheels
It's not period correct but I think the 308 could pull it off and they can be made compatible with modern tubeless tyres.
I've even found them in 18" for Ferrari : https://www.ruoteborrani.com/en/wire-wh ... wheel/79/#


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