Tyre & Rim Alternatives - questions from a newbie

[gavinpd4107]

Hi folks. 
After my Spicer 4 speed to Alison V730 transplant, I now have the potential to access a couple of oversize super single tyres for fitting to the rear wheels which would give me an ideal 7% increae in tyre circumference.  Two multiple questions arise.

1 (a) - Has anyone ever fitted super singles to their rear axle? (I'm a single/no tag fella)

1 (b) - What if any are the pro's & cons (apart from the wider single track being more likely to rip up ashphalt etc when turning!)? 

1 (c) - Are there any structural and/or stress issues to be concerned about?


2 (a) - The tyres I have access to are currently on steel spider rims, but I have a couple of spare 10 stud rims.  Has anyone converted spider rims to 10 stud or done the reverse? 

2 (b) - For example, could I laser cut the centres out of the spares and weld them onto the spider rims?

2 (c) - Alternatively, I wondered if anyone has seen or heard of a conversion plate to fit spider rims to 10 stud stub axles?

Cheers  Gavin pd4107-1023 West OZ

[Sunchaser Art]

Gavin-

By spider rims, I'm guessing you mean the five point star hubs that hold the split-rim assembly with the five wedges at the end of each star?  I've never done it on a bus, but I don't think you'd have much in the way of structural issues to worry about.  However, if you ever had a flat, you'd be pretty much dead in the water (I guess it's an argueable point whether they're good or bad in that respect).

If you have the type of wheel I described, I've converted a few trucks, but you need to buy new hubs (and usually brake drums).  The truck hubs and bearings are pretty standard; if you pull your bearings and get the numbers, that'll tell you what size hub you need to fit the axle.  You'll have to take some measurements to make sure the drum mount will correlate with the positioning of your brake shoes so the shoes will be positioned where they're supposed to be in the drums.

Good luck,

Art
www.webcove.com/eagle

[TomC]

The only true highway super singles that are made are the 445/50R-22.5 that is the same size as the 295/75R-22.5 or 275/86R-22.5.  The 455/55R-22.5 is the same size as the 11R-22.5. These super singles have a 75mph top speed.

The 385/65R-22.5, 425/65R-22.5, 445/65R-22.5 are large super singles for use in regional use only-like for concrete mixer, dump trucks, trash trucks, etc and have a 65 mph maximum speed.

Please stay with the normal 11R-22.5 or 12R-22.5 or 11R-24.5 tires.  They're duals for redundancy and can get tires most anywhere.  Those monster super singles are hard to find, plus with off set rims to bring the super singles to the edge of the bus, does impose undo bearing strain on the hubs, since the outer bearing is taking all the weight, compared to both bearings being balanced with duals.  Good Luck, TomC

[Sean]

1 (a) - Has anyone ever fitted super singles to their rear axle? (I'm a single/no tag fella)

Yes, it's been done.

1 (b) - What if any are the pro's & cons (apart from the wider single track being more likely to rip up ashphalt etc when turning!)?  

Pros:

• Slightly better fuel mileage (I doubt you could even measure it, though)
• Less unsprung weight on that axle
• Fewer wheels to buy, if you are changing wheels anyway
• Looks cool; all heads will turn at bus rallies

Cons:

• Can't rotate steers to drive to square them off and vice-versa
• Can't carry a single spare that fits all wheels
• Can't "limp home" if a drive tire goes, or swap drive to steer if a steer goes and no spare
• A blown drive will sideline you far longer than with normal duallys, as the supers are not widely stocked
• Supers are generally pricier than a pair of duals

FWIW, you don't see supers on owner-operator rigs or buses for all the "con" reasons above.  Generally, only large fleet operators benefit from the supers.  The get the benefit of volume pricing and having their nationwide maintenance outlets stock the tires and wheels for them, and their buying power means they can get the trucks equipped that way from the factory.  With hundreds of trucks on the road running millions of miles, the tiny bump in fuel economy adds up.  For most of us, the investment will never pay off, and one tire failure on the road can completely negate any benefit in a hurry.

1 (c) - Are there any structural and/or stress issues to be concerned about?

To change standard dual drop-center offset rims to a super-single?  No.  To increase wheel circumference by 7%? Maybe.  You'd need to measure clearance in the wheel well and to the other running gear, and you'd need to calculate the increase in torque required to turn the bigger wheel, and make sure your powertrain is up to the task.

2 (a) - The tyres I have access to are currently on steel spider rims, but I have a couple of spare 10 stud rims.  Has anyone converted spider rims to 10 stud or done the reverse?  

I am assuming you are talking about mountable rims or what many would call "Dayton" rims here.  Dayton wheels use a completely different hub than disc wheels; you'd need to change out the hubs.  By contrast, there are "adapters" to mount Dayton-style wheels onto stud-pilot hubs.

If you are going to change hubs anyway, I would recommend changing to the more modern hub-pilot design rather than stud-piloted (also called Budd wheels).

I think I mis-read this the first time through.  If I understand correctly, your bus has 10-bolt hubs, which I assume are stud-pilot.  You have some tires available that are mounted to split rims or Dayton rims.  Apparently, you also have some stud-pilot rims (which I assume fit your hubs).  I can only guess this question has to do with the tires you have on the other rims being the wrong size for the correct wheels.

The simple answer to this is to ditch the incorrect tires and get the proper size ones for your wheels.

2 (b) - For example, could I laser cut the centres out of the spares and weld them onto the spider rims?

Not sure why you would want to do this.  You'd have a major challenge aligning things before welding, and it will never be as strong as a forged wheel.  Welding on the forged rims will likely weaken them.  Steel wheels are cheap, and take-offs are even cheaper from folks upgrading to aluminum.  Buy the drop-center wheels if you fit that type of hub.

2 (c) - Alternatively, I wondered if anyone has seen or heard of a conversion plate to fit spider rims to 10 stud stub axles?

Yes, but they are rare.

Again, not sure why you'd want to save the rims.  If you change to 10-bolt hubs, just buy the wheels and be done with it.  If you really want to get use from those rims, keep the clamp-style hubs you have now.

If you do go to the supers, the clamp-on rims are of no use anyway, and you need to go to the 10-bolt hub.

-Sean
http://OurOdyssey.BlogSpot.com

[RJ]

Gavin -

OK, my take on this is a little different, but still food for thought:

GM designed the OEM drivetrain around tires that turned 495 revs per mile.  With the original 8V71/Spicer 4-spd and 4.125:1 rear axle, that resulted in 60 mph @ 1650 rpm.

Buying tires that turn MORE than 495 rpm will increase your fuel consumption and lower your top speed.

Tires that turn LESS than 495 will have the opposite effect.

EXCEPT

You've installed a V-730.  That changes the equation somewhat, because the automatic uses a lower bevel gear ratio compared to the 4-spd (0.875:1 vs 0.808:1), which changes the effective rear axle ratio from 3.333  (0.808 x 4.125) to 3.589 (0.87 x 4.125).  (Note - both gearboxes are 1:1 in high gear.)

So, in order to maintain performance similar to the original, you must use TALLER tires, ones that turn LESS than 495 rpm, in order to bring it back.  The closest I've been able to find, IIRC, is a Bridgestone 11R24.5 drive tire that turns 470 rpm, which results in just about a perfect match to the stick shift setup.

If you go to Daris Boutillier's site and click on the "MPH Calculator" link in the LH column, you can play with all kinds of tire (oops, tyre) sizes to see what the effect is by changing the rolling diameter.  Here's the URL:  http://www.thebouthilliers.com/4106/

For the original manual drive train, use 3.333 for the final drive ratio and 40.725 for the tire diameter.  Without changing the tire size, change the rear axle ratio to the automatic's effective ratio (3.589) and you can see the difference.

IMHO, I'd keep the duals, for the reasons stated above (plus it's a LONG way between civilizations in some parts of Australia should you have a flat), and go with a tire that keeps the coach close to the original performance criteria, with the same-sized tyre as a spare, too.

FWIW & HTH. . .