Results 1 to 10 of 10

Thread: determining tyre pressures

  1. #1
    Jedi Warrior
    Join Date
    Dec 2008
    Location
    Calgary, Alberta, Canada
    Posts
    721
    Chats
    0

    determining tyre pressures

    The manuals specify tyre pressures for radial and for bias ply tyres, but does anyone have wisdom regards the optimum pressures for the wider rims and tyres that are commonly used today?
    As a bit of an extreme example: we have a Meyers Manx clone dune buggy (take a 1962 VW chassis (in our case) and shorten it and then put the fibreglas buggy body on; drop about a thousand pounds and slap 15x7 or 8 rims and associated tyres on it) and I've been playing around trying to figure out what would be optimum pressures for that beastie, which lead me to thinking about our BJ7 with it's 72 spoke (vs stock 48) wider rims etc.
    On the dune buggy, I've tried going down the highway and taking temperature readings across the tread width at 2 psi increments (nothing consistent enough to be useful), plus most recently painted white stripes across the tyres plus a band of duct tape and masking tape and electrical tape, trying to look at wear patterns. Again, nothing to really hang my hat on - and it's about six months now until I get to try again.
    Any suggestions for figuring out what pressures should be using today's rims and tyres on the 3000? any suggestions for trying to figure this all out?
    I'd hoped to find some sort of Internet programme where you could enter weight and tyre size etc. etc., but no luck thus far.
    Wisdom? Thanks, Doug
    1959 pristine 948 cc Bug-Eye; DCOE, 5 speed; bought 1971
    1960 BE bought 1971 & stored since; body tub restored and reassembling (1275; etc.)
    1962 AH 3000 BJ7; 3rd owner (1982?); in shop Oct. 2015 for paint job - home soon!
    1962 VW Meyers Manx clone dune buggy; stripped last winter and being reassembled
    1969 Kawasaki 500 H1 Triple, orig. owner; stored since 1973, but runs again! 1999 Buell S3

  2. #2
    Senior Member
    Join Date
    Aug 2016
    Location
    Greensburg, PA
    Posts
    73
    Chats
    0

    Re: determining tyre pressures

    Since you're not measuring the volume of air but rather the pressure, I wouldn't think there would be a significant difference between say a 165 tire on a 4" wide rim and a 205 on a 6". For the Healey, I would probably put a few extra psi in the wider tire to reduce steering effort and then adjust to your taste.

  3. #3
    Jedi Warrior
    Join Date
    Dec 2008
    Location
    Calgary, Alberta, Canada
    Posts
    721
    Chats
    0

    Re: determining tyre pressures

    I was wondering about going lower than the originally recommended pressures. My thinking is that the wider tyre would tend to be - effectively - over-inflated as there would be less weight per unit of tyre width to keep the rubber flat on the pavement (start looking like a bicycle tyre in profile). How do the racers out there optimize their tyre pressures?

  4. #4
    Yoda Randy Forbes's Avatar
    Join Date
    Feb 2003
    Location
    SW Florida (Sarasota/Bradenton area)
    Posts
    4,182
    Chats
    0

    Re: determining tyre pressures

    Unless you like the sound of squealing tires, you don't want to go to lower pressures. My thought align with Jack T's completely.

    When I autocrossed the Healey on a regular basis, I think I was using about 40-42 psi front & 38-40 psi rear, depending on surface, temperatures, etc. (interestingly enough, my M Rdstr with 225 & 255 tires were pretty close to the same, except with a 3 psi bias towards the fronts).

    I don't drive the Healey quite as much during the summer, and we all know that tires tend to read lower in the fall, but I took the thing out a couple weeks ago anyway, and was amused at how much the tires were squealing during a routine turn (at first I was thinking it was because I'd made the light, for a change) but when I had them squawking through another corner, I knew right away what was up. Sure enough, when I pulled up the shop to check them, all four (4) were reading 20 psi instead of 30.

    For the sake of handling, economy and reduced steering effort, run the tires as hard as you can stand them__up to their designed limit on the sidewall (typically around 50 psi)__only run them softer if you're worried about losing a filling.
    http://www.britishcarforum.com/bcf/image.php
    57 Healey BN6L-942 Wine Red/Honey Tan
    99 BMW M Rdstr Cosmos Black Eurosport Twinscrew Supercharger
    01 BMW M Rdstr Steel Gray Performance Center (factory) Delivery
    11 X5 35i Sport Deep Sea Blue Metallic Wife's Turbo Hauler

  5. #5
    Jedi Warrior CLEAH's Avatar
    Join Date
    Feb 2012
    Location
    Cleveland, OH
    Posts
    461
    Chats
    0

    Re: determining tyre pressures

    Doug,

    The Hendrix supplied Vredesteins mounted on 72 spoke wheels on my BJ8 run at 30psi. That is as specified by my restorer (and presumably by Hendrix). For your dune buggy, I would draw a chalk line across the tread and drive it. In short order the chalk will reveal whether the tire sits flat on the road--adjust accordingly, and adjust for increased weight if you significantly load the vehicle. Speaking of loads, my RAM 2500 rolls on E-Rated tires pumped to 80PSI, maximum pressure. Letting air out of the tires to improve comfort causes the TPMS to go bonkers--so, the manufacturer has programmed the system to require maximum pressure, whether the truck is empty or fully loaded.
    Hugh
    1965 BJ8
    1958 AN5


  6. #6
    Darth Vader Michael Oritt's Avatar
    Join Date
    Jun 2001
    Location
    Lusby, MD, USA
    Posts
    2,647
    Chats
    0

    Re: determining tyre pressures

    The general rule in racing is that tires should increase 4-5 psi over the course of an event--if more occurs decrease pressures and visa versa. That being said, consistent temperatures and wear across the face of the tire are probably a better indicator with ride and road feel being most important of all. If I anticipate a wet track I increase pressures by a few psi to hopefully maximize the tires' ability to shed water.

    On my street Healey I like a firm, responsive ride and run 30 psi all around on Michelin 180-15 XAS's. don't forget to over-inflate your spare by a few psi to allow for periodic loss, etc.

    Best--Michael Oritt
    1954 Austin-Healey 100 Lemans
    1958 Elva Courier
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

  7. #7
    Jedi Warrior
    Join Date
    Dec 2008
    Location
    Calgary, Alberta, Canada
    Posts
    721
    Chats
    0

    Re: determining tyre pressures

    With the dune buggy, I ran with 18, 20, (front) and 22 and 24 (rear) in the rear tyres when we took it out to storage Monday. I had painted white lines across the tread plus a band of electrical tape, masking tape, and duct tape. Temp was -2 or 3 C (28 or 27 F), and took pictures before and after - gosh danged electrical and duct tape was still pretty much good after 30 or so km (20 miles).
    I've heard a recommendation to chalk the tyres and then roll them over construction paper at different pressures as well; figure I'll try all the options again in the Spring when we fish it out of storage. We've got a 1995 Ford F350 crew cab long box dually; I run those at about 50 psi and jack them up when hauling a load - no real science behind the 50 psi. And - until I can get a tyre pressure gauge that has a guaranteed level of precision, I'm probably just fooling my self by running anything other than the recommendations for the 3000 and for our bugeyes, irrespective of tire size. We've also got an old BMW 2002 whose 15 inch rims are a lot wider than the original 13s, and the same concern.
    I'd like to be able to optimize tyre wear, as that also implies that I've got the optimum tyre patch planted on the pavement.
    1959 pristine 948 cc Bug-Eye; DCOE, 5 speed; bought 1971
    1960 BE bought 1971 & stored since; body tub restored and reassembling (1275; etc.)
    1962 AH 3000 BJ7; 3rd owner (1982?); in shop Oct. 2015 for paint job - home soon!
    1962 VW Meyers Manx clone dune buggy; stripped last winter and being reassembled
    1969 Kawasaki 500 H1 Triple, orig. owner; stored since 1973, but runs again! 1999 Buell S3

  8. #8
    Darth Vader John Turney's Avatar
    Join Date
    May 2002
    Location
    Concord, CA
    Posts
    2,633
    Chats
    0

    Re: determining tyre pressures

    Quote Originally Posted by twas_brillig View Post
    ... We've got a 1995 Ford F350 crew cab long box dually; I run those at about 50 psi and jack them up when hauling a load - no real science behind the 50 psi. ...
    If your F350 is like my E450, the tire pressures listed by Ford are based on the maximum weight rating for the axles. For truck tires, the weight capacity is related to tire pressure.

    I run my 195/65R-15s on my 100-6 at 35 psig. That's what my tripmeter is calibrated at, and gets me out of the driveway without scraping if I'm careful.
    John, BN4

  9. #9
    Jedi Knight RAC68's Avatar
    Join Date
    May 2010
    Location
    NJ Shore
    Posts
    1,442
    Chats
    0

    Re: determining tyre pressures

    Hi All,

    The original equipment Dunlop Road Speeds were "Cross Ply" construction on 60 spoke wires with a recommended Healey pressure profile of 24lbs front/26lbs rear. Although I did initially maintain the same pressure profile for their 165R15 Pirelli Cinturato Radial replacements, I eventually increased the fronts to 26lbs and the rears to 30lbs. Today, I still maintain this same profile on my 65R15 Vredesteins radials on 72 spoke wires but do not push the car as hard.

    Ray(64BJ8P1)

  10. #10
    Luke Skywalker
    Join Date
    Mar 2003
    Location
    Hampshire in the UK
    Posts
    1,518
    Chats
    0

    Re: determining tyre pressures

    I'm running Vredestein classics 185s at 30lbs all round

    Very good



    Bob

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •