BCM Community

Having read not just nearly every post on this site on this topic, but also a good portion of the ones elsewhere on the Internet, I'm still trying to figure out where to come down on this.  Getting to the right side of that magic 495 RPMs number is tough!

I'm currently running 11r24.5s that came with the bus and are junk.  Haven't driven it enough to really have a feel for startability, don't trust the tires enough to get a better feel or determine the top speed.  Options are:

Swap rims and go to 11r22.5s.  Unless I buy specific models new, putting retreads on the rear will likely put me over 500RPM, which is a hit to an already low top speed which I think I'd rather avoid.

Low profile 24.5s - these tend to hover pretty close to 495 RPM on average, which is nice, but it sounds like these are tougher to find in a pinch than the others.  Currently my favorite option.

11r24.5s - readily available, but inverse issue of the 11r22.5s - buying retreads could drop down into the low 470 RPMs or even high 460s, with troubling implications for startability.  I really don't want to get stuck on a hill.

With that said, what are you running, and are you happy with your current setup?

Different bus than yours but here's what we have... We have a 4108 with the 8V71 mated to a Spicer 4-speed manual.

Bus came to us with 315/80R22.5 all around on the original steel rims. Too much tire for the bus and really unnecessary. But, they do spin at 490 RPMs which is pretty darn close to the spec.

When we replace the tires in the spring we're going with 12R22.5, which will give us about 487 RPMs. Same basic diameter/circumference as the 315s, just a bit narrower. There is always going to be a slight difference of a few RPMs between different tire brands/models, even in the same size. I can currently cruise easily over 70 mph if I want, so I'm not worried about the slight drop in upper speed.

Goodyear has an 11R22.5 which is listed at 496 RPMs. We had these on our 4106 and thought they were good tires.

https://www.goodyeartrucktires.com/tires/product-details.html?prodline=160631&prodcode=13817967400000&lat=42.9480628&lng=-88.26558449999999

Seems like if you're trying to get close to the 495, you might consider going with 22.5 rims. But, if you gain low end performance you'll be giving up some on your top speed.

With the "little" six,, he needs lower gearing anyway, for climbing.>>>Dan

My brothers 4104 runs 3:55 rear with 11x22.5. With 2 valve head and 65 injectors. Starting out wasn't  too bad. Still had top speed of about 75-77. Actually higher because he has the governor set higher than normal.

It isn't about general tire sizes.

Every tire is a different diameter.

You have to spend some time on the different tire manufacturer sites and look up the specs for each desired tire.

The revolutions per mile are there for 'em all.

You can't decide 24 or 22 or 11 or 12 or 275 or 315...

They all overlap on revs.

Happy coaching!
Buswarrior

True, but the tire sizes do correspond to a range - there is no readily available 11r24.5 that runs 495 RPM, nor is there an 11r22.5 which runs 480.  I've done a lot of research on new tires, but the trouble is that no place I've spoken to has a record of RPMs for their retreads - I could buy new on all six wheels, but that's a thousand dollars that could be better used elsewhere if I can help it.

Here's my current working doc of research:
https://docs.google.com/spreadsheets/d/1PR2JrD2XIyEDo1kFxOK6MpmSBnQqRL3I3KrmFrKyy2s/edit?usp=sharing (https://docs.google.com/spreadsheets/d/1PR2JrD2XIyEDo1kFxOK6MpmSBnQqRL3I3KrmFrKyy2s/edit?usp=sharing)

11r22.5 is currently winning the poll, and when it comes down to it I think I would prefer the gains in starting and climbing over top speed - no one's ever gotten stuck because their bus couldn't go fast enough on the highway.  Low profile 24.5s are tempting because they tend to hover a bit closer to the ideal RPM range on average and it would mean keeping the same rims, but I'd be concerned about finding one in a hurry out in the wild.

Quote from: Nova Eona on November 08, 2019, 01:03:04 PM
...but I'd be concerned about finding one in a hurry out in the wild.

Carry a spare - mounted or unmounted. Then you're covered in case you have need.

Nova-285/75R-24.5 low profile runs about 495rpm. 295/75R-22.5 runs about 517rpm. Good Luck, TomC

We've always carried a spare this way we're at no one's mercy if a tire does go out. Yes we have changed several tires on the go over 4 decade of bus ownership but never on the front. The newest tires run the front with rotation putting the oldest to the rear duals. Has worked for us...

Alright, it figures that the option I'm most drawn to is the one nobody has voted for!  Getting ready to bite the bullet on this soon and really thinking of going with the 285/75r24.5 low-profiles.  Anyone have any words of caution or encouragement when it comes to these?  I know low-profile car tires are a magnet for damage and poor ride quality, but I figure there's probably a very large difference between "car low profile" and "truck low profile".

Which tire brand and model?

Yeah, I know, broken record...

Happy coaching!
Buswarrior

Consider the overall cost and the availability of the tires you select. There is only a 4-5% difference between the revs-per-mile of the low-profile 24.5 and the 11.00 X 24.5, and you can use your existing rims. Are your rims steel or aluminum, and are you considering changing them? If you are considering retreads, you must be concerned about cost. The only retread I would recommend is Bandag. They do not list their revs-per-mile, but you could measure them to check that out.

If you have checked past discussions of tires (and there are many), you will find that some brands are preferred over others for dependability, with the Chinese brands coming in on the low end. An indicator of quality is which brands are more likely to be accepted as retreads. Some brands (on trucks, at least), can be recapped several times on the same casing, while the lesser brands are routinely rejected for even one cap.

On our buses usually, time will take it's toll before the tread wears out. So, select a new tire that is durable in the long run, meaning less tendency for the sidewalls to crack, or a retread (on the rears only) that is the first recap (not the second or third). Recaps will have a brand on the sidewall for each capping. In any event, stick with a size that is more readily available should you need a replacement while on the road. Sizes like 12.00 X 22.5 can be hard to find, for example.

Most of us are not getting close to the gvw rating of the bus. For instance, I have 13,000lb front and 23,000lb rear. My loaded weighed is 10,500lb in front 20,500lb in rear. I'm running 11R-24.5 14ply G rated Hankooks. I could go as low as 80psi, but for safety I run 90psi all around.

Yes, bus tires are overkill on many conversions.

Priced a name brand 315/80R22.5 lately?

OUCH!

Happy coaching!
Buswarrior

Michelin recaps should be good also.
Btw, here's an interesting article:

https://www.moderntiredealer.com/tiredealeroftheyear/winner/2010/311773/stay-with-bandag-or-switch-to-michelin

Here's their retread site with tread patterns and tire sizes:

https://www.michelintruck.com/tires-and-retreads/retreads/

Michelin is very picky in choosing casings to re-tread. That's a good thing.

Bandag or Michelin, both good reputations and quality control procedures.

Happy coaching!
Buswarrior

I've got a tire shop about twenty minutes away that does Bandags, that will likely be the route I go - slowly mind you, particularly after tonight's revelations!  Spent about fifteen minutes reaching behind the front tires with my phone until I finally got a picture of the DOT codes (both are stamped on the inner edge of course) so I could figure out the age - only three digits: "118"!  That means my steers were made in '98, so they are legally old enough to drink.  Horrifying.

This weekend I'm going to figure out my axle ratio, but I am currently leaning heavily towards breaking some new ground and putting on 24.5 low-pros.  More to come, in the meantime check out this chasm pictured:

Well gang, I finally got out to the tire shop now that the weather has settled, social distancing and all (I sat out by the road 'working remote' while the guys swapped the tires).  I'd warned them ahead of time that the bus had an air bag suspension, still had to yell at one of the guys to get his head out from under it before they'd blocked it up.  I'd just about convinced myself to stick with the 11r24.5s, but had a last minute change of heart and decided to go for a set of 285/75/r24.5s instead, so I might be breaking new ground on that size here.  Went with a quartet of Double Coin RLB400s (485rpm) on the back and a pair of Firestone FS561s on the front.  Now I can actually drive the thing without worrying about popping a tire off, yay!

They seem pretty close in size to a 12R22.5 tire. Not exact, but close.

Be interested to see what you think of them after you put on a few miles.

11r 22.5

   HI;
       I would suggest checking out the GM club website and ask what most of them are using.
       A lot of useful info there.

                                                  God luck,   Merle.    ;D