Tag Archives: unsprung weight

Catching the Rolex 24 on Internet radio

I went to bed way early for me, shortly after 2400, then woke up way, way early at 0340 and couldn’t get back to sleep. I have the IMSA app on my phone so I plugged my earbuds in to catch the race while there is no TV coverage. The TV coverage doesn’t start back until 0700 and it’s only 0556 right now.

Clyde spent the night sleeping in my office on a pile of drawstring bags I got as promotional items, apparently quite comfortably. We have been trying to get Clyde to eat more by not letting him back out as often when we can get him to come in. He has lost a lot of weight during the cold weather we recently had, so we are trying to get his body fat % back up to a healthy range. One thing we have been doing to get him to eat more is to put treats on top of the food in his bowl when he gets treats.

After adding the vertical brace to the torque arm mount no more progress has been made in the design of the Sprint-T, but I found a potential rear axle in the 7.5″ Ford which was under several 1990s and early 2000s. It’s fairly lightweight, has mounting points for a torque arm and some were made with rear disk brakes with parking brakes, so it’s a strong contender to be the rear axle. Another strong contender is the 7.5″ Chevy which is within a few pounds +/- of the Ford depending on the model year of the axle. The Chevy also has provision for a torque arm which was standard on the Camaro for over a decade. Point being there are a few thousand of both in the Beautiful Suburbs of Hell so they’re pretty cheap, and they can handle about 300-350 HP on street tires or 250-300 on race slicks making standing starts. The weight of course is highly dependant on the width and brakes. Wider is heavier by a few pounds, and some brakes are very heavy. I’m not sure if the drums or the disks are heavier, but I’m going with the disks anyway. I prefer to keep the unsprung weight as low as possible but I have to take what I can get weight-wise.

Right now I’m surrounded by sleeping cats, which sounds like my cue to publish this post.

Can’t stop thinking

Yes, I’m still thinking about the rear suspension on the Mid-Bucket, mainly how to make it lighter. And simpler if I can. One way I can do both is to eliminate the adjustability and just weld the adaptor plate directly to the truss. I hate to do that, both because of all the time and brain processing cycles that went into the adjustable adaptor, and because throwing a little negative camber for racing is a great way to increase total grip and reduce oversteer a tad. I would probably do that for street, too. But I can do that in the jig while welding the truss, probably holding to a half degree precision if the jig is stout enough. That is a mighty big IF.

Which brings me to the other reason for adjustability, correcting for floppy welding jigs for the de Dion truss. And for weld joints that move from thermal stress during construction. I don’t know about how floppy the welding jig is going to be, I mean it’s not like I’m building this to make production runs. I just want the ability to make crash repairs when and if necessary.

And while I was on my walk I was thinking about upgrading to the Pentastar and the 62TE after I get a bit more bucks up. Again I forgot to save the engine and transmission mount picture and now I can’t find it again so I can’t show you how similar the mounting points are between the two generations of minivan. But without having one of each side by side to compare I can’t say for sure it’s a drop-in swap. It’s pretty damn close.

Moment of levity, Amazon apparently thinks I eat enough fancy Italian Provolone cheese to justify buying it in $1K chunks at a time. I have no idea how they got that idea since I get that kind of cheese in the $5 shaker bottle at the deli counter mixed with parmesan. Not that I don’t know what to do with a good Provolone, I do have a Sicilian grandmother and Mrs. the Poet is adopted Sicilian, and I did spend a couple of years working for pizza places helping make the pies.

I got to use the high-precision scale when we were shopping today and I was sure not to rest against the rail on the back that is part of the machine but not part of the scale. Anywho I came in under 210 even after a big breakfast, so progress is being made on destroying the heart-clogging fat monster. I don’t know that I will ever reach 160 while still alive and also still be able to get around on my own, unlike last time, but dangit I’m trying.

Billed @€0.02, Opus the fat but still Unkillable

Dying saved my life and other seemingly contradictory statements on a Wreck-Free Sunday

OK I dunno if I ever thought about this before so I don’t remember blogging about it if I did, but I was contemplating earlier this week about the wreck (that thing that’s never far from my mind no matter what I’m doing because it literally defines my life into 2 sections, before the wreck and after) and I was thinking about why I didn’t bleed out from the gaping hole in my left leg where it was blown apart while all those people were just standing around staring at my body in the street. And then it struck me that while I was “dead” I had no pulse, no pulse means no heartbeat, and no heartbeat means I wasn’t pumping my blood out in the street instead of keeping it in my body. So QED, dying saved my life. If I hadn’t been dead for those 2 minutes there might not have been enough blood in my body to save me when I got to the hospital. I was in bad enough condition when I got there as it was, can you imagine what it would have been like minus a few pints more? I barely pulled through as it was.

I was also thinking about the Sprint T that I’m never going to get to build now, so I said to myself “If money was no object, how would you build this car?” meaning picking the “best” components for the build regardless of the cost. And I was really getting into what would be the “best” thing for a specific use, and if compromising in one direction or another would invalidate another use of the vehicle. So I went back to the premise of the build: “A car that’s fun to drive, that can be driven across the country on highways, then raced in SCCA Solo events or Goodguys autocrosses with minimal preparation and quick return to street configuration.” Then I listed what characteristics went with each parameter of “fun to drive”, “can be driven across the country”, and “raced in SCCA Solo events and Goodguys autocrosses with minimal preparation and quick return to street configuration” then see what characteristics were shared and what characteristics were contradictory.

So, “fun to drive” category is first and shortest.
power-to-weight
good brakes
good turn-in response
good grip overall with a controllable break when exceeding limits of grip
Comfortable seating and driver ergonomics
pleasant exhaust note (muted rumble at idle with definite rumble at full throttle)

“Can be driven across the country” is different.
fuel economy
reliability
weather protection
large fuel tank (range)
easy access to refuel
luggage space
tunes
comfortable seating and driver ergonomics
not-loud exhaust (not a cop magnet)
not harsh ride

“Raced in SCCA Solo and Goodguys autocrosses with minimal preparation and quick return to street configuration”
power to weight
good brakes, both at first and after several uses (no fade)
good initial turn-in and stable in the middle of the turn
good grip in all directions
comfortable driver’s seat and ergonomics
something to carry race tires and other parts
quick-change mounts for shocks and springs
roll cage that meets SCCA standards

Common requirements
comfortable driver’s seat and ergonomics
power-to-weight
good brakes, both at first and after several uses (no fade)
good initial turn-in and stable in the middle of the turn
good grip in all directions

And basic parts needed to make the car are the body that defines the car. The rear brakes needed for street legality. If I use the Wide 5 version of this rear axle with the aluminum axle tubes and the drilled drive axles I will combine light weight, both unsprung and total, with the ability to switch from a tall drive ratio for getting to the race to a short (high numerical) ratio for racing. It allows the use of these rear hubs for lower unsprung and rotating weight. A quick steering box will be needed no matter what else I use.

If I decide to go with an independent front suspension I’ll need to use this spindle so that I can mount the lighter Wide 5 hubs or this spindle for a tube front axle. The tube axle is lighter than the independant front suspension but has higher unsprung weight for the weight concerns, but has perfect camber control for the turning concerns. And both spindles are compatible with these front hubs for lower unsprung and rotating weight.

I’m sure that those who read my blog for the bicycle news have little or no knowledge of suspension dynamics are wondering why I am stressing so much about unsprung weight. That’s because unsprung weight has impacts on both grip and ride comfort. As the wheel goes up and down over imperfections in the road/track lower unsprung weight allows the wheel to move more quickly without transferring the motion to the rest of the car. Going up and down more quickly means the tire stays in better contact with the surface making for grip (no contact = no grip) and not transferring the motion to the rest of the car means better ride. Now rotating weight obviously affects any change in speed as rotating weight has to be changed first before the car can go faster or slower.

The engine is a big question, as this will need high horsepower reliable engine with a good low end torque band, which means cubic inches or supercharging or a hot cam and lots of work with the shifters.
I could “put a Hemi in it” or go with a modern legend or the successor to that legend or a hot cam in a slightly smaller, lighter, engine.

And the engine choice has a direct effect on the transmission choice. The GM engines will require either the 4L85E or the 4L70E transmission, while the Hemi will require a compatible donor vehicle to have the electronically controlled automatic transmission because the transmissions are not sold as a crate part.

Another question that needs answering is frame materials. Aluminum is lighter, but there are two flies in that equation. First is SCCA rules prohibit aluminum rollover structure. Second is the frame will have to be farmed out if made from aluminum because my aluminum welding skills are lousy. Even with money as no object I still want to build as much of this car as I can. Then there is the interface between the SCCA required Chrome-moly rollover structure and the aluminum frame, and preventing galvanic corrosion. I know what to do and how to do it, I’m just concerned about the failure modes and what they would do to the longevity of the car. Sticking with steel everywhere for the frame material eliminates all those problems at a slight weight penalty. Also staying with steel means I can do more of the fabrication myself if I want to and that in case of a wreck the structure is more repairable: bent steel can be straightened, bent aluminum has to be cut out and replaced.

Then there is the requirement to have some way of toting the tires and other parts needed for racing with the car while it isn’t racing. That implies a trailer (or the ridiculous notion of lashing the tires to the back of the car somehow for a thousand mile (+/-) road trip.

And this has made for a very long blog post for a Sunday and I’m not even halfway done, but I will end it now.

PSA, Opus the unkillable badass Poet