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PaytonD21 Samba Member
Joined: August 11, 2015 Posts: 83 Location: Washington, USA
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Posted: Sun Aug 23, 2015 5:36 pm Post subject: Front end tire questions (speed/rpm's) |
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I just purchased a 1960 beetle and am looking to put different tires on it. I plan on lowering it and want to get the correct tires now for when that happens. In the front I'm looking at 145/65-15's or 155/65-15's and on the rear I heard 205/60-15's are a good choice. I want to get a narrowed beam and drop spindles.
My question is: with the smaller tires up front how much is your speed off? And how much are your rpm's effected? I've seen many people with small tires upfront, but I would like to know how much it effects the performance of the car. |
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Miklo ¡Chale!
Joined: August 27, 2008 Posts: 2058 Location: Antelope Valley, Ca
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Posted: Mon Aug 24, 2015 1:24 pm Post subject: |
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I am currently off by 5-7 mph with my 145/65's up front.
Rpm's are not affected by front tires. _________________ ✠Miklo✠
'55 Type1 "Ozma"
'66 Type1 "Charlotte" RIP
Antelope Valley's Mobile Air-Cooled Guru
Dr OnHolliday wrote: |
As I remember it, lowriding was not one of the criteria that Adolf gave to Dr. Porsche... |
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PaytonD21 Samba Member
Joined: August 11, 2015 Posts: 83 Location: Washington, USA
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Posted: Mon Aug 24, 2015 3:03 pm Post subject: |
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I was looking at 185/65-15's for the back. Would you know how much those effect the rpm's? Can I still cruise on the freeway at decent rpm's? |
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easy e Samba Member
Joined: May 28, 2008 Posts: 3930 Location: 1 hr north of Santa Barbara
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Posted: Tue Aug 25, 2015 9:22 am Post subject: |
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Need to know your:
4th gear
Ring gear
Desired speed
Tire diameter
Plug it into here:
http://www.crawlpedia.com/rpm_gear_calculator.htm
Maybe consider aiming for an RPM of 3,000.
I hear above 3,250 RPM = fan cavitation (fan just can't suck in air any faster, even if it spins faster) = engine gets hotter
I hear below 2,800 RPM fan isn't providing enough air for steady state freeway speed = engine getting hotter.
e _________________ aka: Evan
Spreadsheet for Bus RPM, based on gearing & tire size (Excel format)
Searchable, click-navigable 1958 Bus Parts List |
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911pickup Samba Member
Joined: March 06, 2004 Posts: 625 Location: Near Goats on the Roof
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Posted: Tue Aug 25, 2015 4:40 pm Post subject: |
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There isn't much of a diameter difference between a 165/80-15, which is roughly the stock tire size, and a 185/65-15.
At 60 mph your speedo will be off by just over 2 mph (60 mph compared to 57.81 mph).
As easy e mentioned, to be precise we will need the numbers for your 4th and R&P gears.
A rough guess......probably less than a 200 rpm difference. |
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PaytonD21 Samba Member
Joined: August 11, 2015 Posts: 83 Location: Washington, USA
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Posted: Tue Aug 25, 2015 4:54 pm Post subject: |
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Does anyone know an easier way to find the R&P? I found out my car has a non stock transmission. I don't want to assume stock R&P. |
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