North American Turbocoupe Organization



Consider the weight of the shrader valve cap?
Bret B Offline
Junior Member
#1
Hi Forum !

I have a question about a tire issue on my other car (a Mazda). I know it's not a TC, but tire valves are pretty universal. Hope yo don't mind me posting this here. Btw, my '86 TC is still fat and happy in the garage. It's Florida winter (hot as H___ )and it's gonna stay there until the temps come back down in November. Here goes . . .

Last fall I had new P190-60R15 Dunlops put on my 15x7 rims (2002 Mazda Protege DX 5speed manual tranny). I told the tire people that I do turnpike driving and wanted them to be smooth at 70-80mph. I also wanted the chrome-over-rubber valve stems instead of the plain black ones. They said they put their best guy on it for me.

The car felt smooth around town but I didn't drive the pike for a month past the install. Then I had a turnpike trip to take. At 68mph I started to feel the shake that wasn't there before. at 72mph it was very noticeable. For the next six or so months I just kept it down to 68 figuring I'd take it back for a re-balance, but never had time for it.

About a month ago, before the same turnpike trip, I checked the pressure and they needed a couple pounds of air. This time I went around and took off all the valve caps before bringing out the portable air tank. I then noticed that although all the caps looked like chrome metal, two were actually plastic, and were almost weightless when compared to the other two that were metal. So I 'm thinking, "I bet they don't have these valve caps on when they spin balance the tires." So I left all the valve caps off the tires for the turnpike run. Guess what? No shaking anymore above 68mph. So I bought 4 plain black plastic caps, put them on, and have had joy ever since.

Today while waiting for some computer stuff to fully bake, I have time to to make this post. I made a simple balance beam from a wood ruler on top of a horizontal pencil. I put the valve cap on one end of the ruler and found that a new penny (ie. 2.5 grams) balances with the metal cap on the other end of the ruler.

So the question is: Am I having some delusional observation about the metal caps throwing my tire balance job off? Seems to me that 2.5 grams out there near the O.D. of the tire, at 70mph, would be enough to induce a vibration.

Also seems to me that if one were really picky, and absolutely had to have metal valve caps for some reason, that they'd want the tires balanced with those caps screwed down on the valves.

I look forward to your comments (and ribbing :-)

Regards . . .
1986 Ford TurboCoupe 5spd.
2000 Ford Taurus SES 24V Auto.
2000 Lexus RX300 2WD Auto.
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vinnietbird Offline
Senior Member
#2
The dirt on my tires probably weighs a lot more, and no balance issues.
1988 Thunderbird. No details will be given or spoken of.
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Bret B Offline
Junior Member
#3
I was prepared for the ribbing. But all jokes aside, consider this: we don't have dirt here. It's all sand. So the tires are usually perfectly free of debris.

I don't have a computer balancing machine, but here's a test someone could do: Balance a tire without a valve cap on it. Stop the tire and tape a new 2.5 gram penny on the inside of the wheel (that's about where the valve stem is anyway). Run the tire back up to speed on the balancer and see if the penny throws it off.

Any takers?
1986 Ford TurboCoupe 5spd.
2000 Ford Taurus SES 24V Auto.
2000 Lexus RX300 2WD Auto.
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zbird Offline
Posting Freak
#4
I know from experience that my Mazda 3s was very sensitive to any kind of unbalance. Especially with the stock tires. I got Michelin exahlto sports and it was a much better driving car. The original tires would flat spot after sitting overnight and you could feel it for a little bit. I recommend just doing what works for you.
Dom Z
88 T/C med grey. 140 MPH Speedo, Kirban FPR, Gillis valve,Tripminder, K&N.
87 T/C Silver, Auto (project Daily driver)
99 F150 4x4
14 Ford Escape 2.0L Turbo
IF YOU DRIVE A FORD YOU DON'T NEED A GOODWRENCH!!
88 T/C http://www.youtube.com/watch?v=ZihO_D1FLCE
87 Silver http://www.youtube.com/watch?v=_dVU5axnb...ature=plcp
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Bret B Offline
Junior Member
#5
Thanks for that comment zbird. The Dunlops weren't the least expensive, but more like a mid-grade tire. When I had a Triumph Spitfire (back in the day), the local Triumph GT6/TR4A guys and myself only ever used Michelin's on them. Maybe it's time to get back to basics again.
1986 Ford TurboCoupe 5spd.
2000 Ford Taurus SES 24V Auto.
2000 Lexus RX300 2WD Auto.
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5.0TurboCoupe1988 Offline
Posting Freak
#6
no way you're going to feel 2.5 grams out of balance. if that was the case, you could feel a nail in the tire(without hearing it). a tire balancer is a lot more sensitive than your butt-o-meter, plus it doesn't have pavement or 3 other tires figured in to the equation.

all tires will flat spot after sitting. i can feel it in my truck every morning for a few miles until the tires heat up a little. that's way different than feeling a 2.5 gram out of balance tire.
1988 TC 2.3/5-Speed, 148K
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Bret B Offline
Junior Member
#7
Hi 5.0TurboCoupe1988,

I just eBayed those stick on weights and they seem to come in packs with 1/4 ounce (7grams) and 1/2 ounce (14 grams) weights. So in retrospect, it seems that a single 2 1/2 gram weight would not be enough to fix, or create, a noticeable imbalance.

I'm going to go with the the general consensus that my "butt-o-meter" needs calibrated. That said, I'm also going to take them somewhere else and have them rebalanced, because they're not in balance now.

Thanks to everyone for their comments!

Brcobrem
1986 Ford TurboCoupe 5spd.
2000 Ford Taurus SES 24V Auto.
2000 Lexus RX300 2WD Auto.
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gtrag94 Offline
Member
#8
while I agre with Bret B on this one (I worked at a tire shop for 4 years... our weights were either hammer on (preferred) or stick on). The weights were .25 ounces at the smalles (and the hammer on ones were very tiny). My way overarching thought would be that there's no way you'd feel .25 oz much less 0.09 oz (2.5 grams).

That being said, you fixed your own problem and verified that we're all unknowledgeable outsiders. You removed the "heavy" caps and the problem went away. Problem solved.

The balancers we used (computerized) would only read down to 0.25 oz so I doubt rebalancing them with the metal caps would even show up on the machine.
1986 TC 5-spd (Red/Red cloth)
K&N Cone on VAM; front suspension by KYB, Moog, Energy Suspension.
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Not B Anymore Offline
Posting Freak
#9
When I lived in MD, I used to go to a shop that balanced the wheels/tires while they were on the car. My old pos '85 Daytona probably had a smoother ride than a lot of new cars at the time! I've not been able to find a shop down here that can do that.
Brian Leavitt
'86 TC 5-Speed -- MS2x w/COP | 83 lb. injectors | T3/T4 50 Trim Stage 3 .63AR | Full 3" Exhaust - No Cat | Motorsport FMIC | Ranger Roller | Ported E6 | Walbro 255HP | Kirban | 20psi | 120-amp 3G | 8.8" 3.55 rear | '03 Cobra Wheels
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