News

Modern(348) Wheels on Mondial

Discussion in 'Technical Q&A' started by mickarrows, Sep 22, 2004.

  1. mickarrows

    mickarrows Rookie

    Sep 22, 2004
    7
    UK
    Full Name:
    Mick Arrowsmith
    I've got 348 Wheels on my 3.2 Mondial cab and although it certainly looks the biz the steering is heavy (v heavy). Offsets/insets seem to be the same although I may have mis measured but I was wondering if anyone out there could help as I have had shims/castor angle alteration suggested but am not too sure it would work (front tyres also are not as wide as original fit(I think!)........I desperately do not want to go back to the option of slippy & expensive TRXs.
     
  2. To remove this ad click here.

  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Mick
    Just saw this thread and got your email. While I'm not the expert, here's my experience:
    All Mondials have about the same offset, and indeed by parts book comparison, use all the same suspension parts. This is why the later 16" convex wheels bolt right up to the earlier 390 rims. Some more Mondial history - initially Mondials came with 240/55-390s at all 4 corners. Well, that didn't last long as the steering was quite ponderous even with the lower geared Mondial rack. They went to 220/55-390s through the early Mondial 3.2s. When they switched to 16" wheels later in the 3.2 run, they lowered the front section even further to 205/55-16. This was such a change from the original 240 section they brought the rear section down to 225/55-16 I would imagine to avoid understeer and keep ride height and suspension. Of course tire technology and politics had changed, and they went to the (POS) Goodyear Gatorbacks, which carried on through the later 3.2s to the t. Heck, they put power steering on the t even with 205 section tires!
    The steering effort is dependent on a couple of things. The type of tire and inflation pressures makes a big difference. When I went from the original 205 gatorbacks to 215/55 section Pirelli P-6000s, the steering got much lighter and response improved at the same time. When I put on 17" wheels, the first tire I tried was the Bridgestone 215/50 RE-71s (same as original 348s) at again 215 section as the Pirellis and the steering became quite heavy again. More grip probably, but not as much fun as the safe and easy to throw about quiet P-6000s. So, if you're running a max performance earlier technology tire - that will contribute to your steering heaviness.
    The other interesting thing about Mondials that affects the steering is the suspension geometry. One of those things is scrub radius - this is how far the steering pivot axis intersects the ground away from the centerline of the tire. Smaller scrub radii reduce the effort needed to turn the tire and reduce steering kickback. This is why small scrub radii are needed on ABS cars to prevent having the steering wheel ripped from your hands if the ABS kicks in with differential front braking. Don't know if they were planning for ABS or just wanted to reduce the steering effort and kickback, but all Mondials have always had scrub radii close to zero. For comparison, the 308GT/4 has a scrub radius of about 3" and a 246 (a lighter steering car) has a scrub radius of about 2".
    So, if you put 308 qv 16” wheels on a 308 (they will fit - I have photos) with their smaller offsets, they will push the wheel out away from the original wheel centerline increasing track and scrub radius. This will increase both steering effort and steering kickback. I know what’s been said about spacers required in this thread, and I would imagine them to be minimal (if at all) to duplicate the original near zero offset. I’ve seen factory photos of the original 348 prototype and it was wearing Mondial convex wheels! When I went to 17” Speedline wheels, I shod the car with Bridgestone RE-71 (OE on 348s) at the same section as the 215 P-6000s I had, but steering effort went way up. I finally just got so tired of it I took them off with only a few K miles on them (they’re for sale) and replaced after much research with Michelin Pilot Sport A/S – and what do you know – the wider section Michelins (225/50) actually are lighter to steer than the RE-71s!
    Have rabbited on long enough, and none of this may be right due to my current Actifed dosage. Summary:
    1.Look at tire type, section (tread width) and inflation pressures. Higher pressure in the front will reduce contact patch, but lighten steering.
    2. Get the new total offset (wheels and spacers, if any) close to the original to have a near zero scrub radius, which will lighten steering. Be sure to use the correct bolts for the correct wheel and insure clearence from the suspension. If you have spacers already on the front, may want to try without. I do not have the offset #'s handy unfortunately.
    All this said I'm betting the steering heaviness is probably going to be mostly a function of the normal Mondial and the type of tires/pressures you have if no steering rack binding.
    Hope this gets you started – always looking to learn something new if anybody knows a bit more.
    Back to bed
    best to all
    rt
     
  4. mickarrows

    mickarrows Rookie

    Sep 22, 2004
    7
    UK
    Full Name:
    Mick Arrowsmith
    Russ,
    Thanks very much for your reply. As a rookie I certainly wasn't expecting such a quick response, especially from a thread from a couple of months back.
    It has definitely given me a bit of hope as I really want to keep the wheels.
    I've been putting 33psi in the front p-zeros but will try slightly higher (although I wouldnt know how far...36ish??). I will need new tyres on the front soon anyway and will certainly take your recommendations, as well as trying to get the offset back to zero (although the wheels did not need any spacers at the front and were bolted using 348 bolts).
    Thanks again and I'll post another thread when I get a bit further forward with this problem.
    Get well soon!
     
  5. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Mick -
    See how you like it with 36 - 38 pounds for the street; Optimizing for the track is a different story.
    thanks
    rt
     

Share This Page