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Contributor
| Hello- I am new to the group and the FMC world. I recently purchased Coach 737. Of course it has the original 17" split rims and I am looking to upgrade to 19.5" or 22.5" 1 piece rims. I believe I have found a source to build the rims and I wanted to understand the pro's and con's of either size? Question to the group- What Size/width rim and tire size are you running? Look forward to hear from you- Jay #737 |
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Expert
  
Location: Cottage Grove, OR | In my opinion, with a gas engined coach the 19.5 is the only size to consider. The larger wheel rides rougher due to the increase in unsprung weight and will add stress to the be transmission. A larger tire will also reduce the turning radius and costs double what 19.5 tire costs. |
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Extreme Veteran
Location: Ignacio Colorado | Jay, if you have them made, I recommend using the same hub center setup with the 6” center hole and small lug stud holes as the factory 17” rims.
19.5” hub centered so the original lug nuts can be used. This keeps the setup the same as stock with original studs and nuts and will save time and money.
Bill #902+++ |
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Expert
Location: Cottage Grove, OR | Yes, I agree with Bill. |
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Contributor
| Thank you for the replies- I agree with sticking to the 6" Hub centered with the small stud holes (.8125" . Since I do have the stock 440 with 727 trans, the 19.5" rim seems best. The question now is what size tire? 225/70R19.5 is 32.3" diameter which is close to what I have now. Anyone run 245/70R19.5's (33.6" dia)? Also Will slightly wider rims fit in all locations? Stock was 6"- Modern tire sizes I mentioned suggest a 6.75" to 7.5" rim width.
Edited by Jfm7807 2022-07-13 11:27 AM
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Veteran
Location: Soquel, CA. | FYI: I am currently using 225/70R19.5's on my Alcoas. Just one datapoint, but working fine. |
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Expert
Location: Cottage Grove, OR | Frank Borrmann went to a wider tire and he told me not to do it as it affected his steering negatively. We don’t have the weight that a bigger tire is designed to carry. |
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Extreme Veteran
Location: Ignacio Colorado | I run the 8R19.5 tires. They are as close to the 7.50R17 as it gets. The 225’s are shorter.
Bill |
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Elite Veteran
Location: Victoria, BC. Canada | Stephen: I get that you have a negative opinion of the 22.5" wheels and I respect that; regardless, there are many others out there running the larger wheels without issue. What remains unclear to me - especially while I'm trying to sell my disc-brakes with the 22.5" Alcoas - why you would make the statement that 22.5" rubber, "...costs double what 19.5" tire costs."
I have it on good authority that, in the applicable FMC tire sizes between these two wheel sizes, it would actually be a stretch to claim they'd be 30% more dollars... let alone double.
Henceforth, the 10% savings on fuel and wear & tear on your stock 727/440' drive-line running at a lower rpm on the 2-1/2" taller wheels will, down the road, pay significant dividends. No?
No harm, no foul my friend.
Terry #846
Edited by andy1canada 2022-08-08 12:00 PM
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Veteran
Location: Soquel, CA. | I do see what you are saying Terry. But, just to complicate it further, for me, running a stock drivetrain, the RPM I am running seldom has to do with what speed I WANT to be driving, but it is more about keeping the engine and transmission in the best range for the driving conditions (grade, temperature, etc.). It is aimed at keeping things running as cool as possible (or not as hot as possible). Maybe this is because I am seldom running for long on flat terrain, being West Coast based. So, with a stock drivetrain, and purely out of curiosity for discussion, I wonder what larger diameter wheels would do to that calculus. As mentioned above, I have 225/70R19.5's on my Alcoas. |
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Elite Veteran
Location: Victoria, BC. Canada | Hey Greg,
After I finally road tested my coach with my 19.5's and 34" Bridgestones' I realized the Cummins and the 47RH liked the final drive ratio just the way it was. IIRC, Lenny previously eluded to this eventuality some time back during my build. So it was with a heavy heart that I decided to sell the 22.5's and the disk brake pkg. I found this drive-ratio calculator years ago and found it easy to use (https://www.crawlpedia.com/rpm_gear_calculator.htm). On my hunt for new rubber for the 22.5's I settled on these before I decided to ditch the idea in favor of what I had. These wheels (http://aeolustires.com/mrt/HN228.html) I thought were a good tread for the forest service roads we plan to spend considerable time on. They're also apparently good in snow.
In the 255/70 R22.5 (36.6" dia) these babies and a stock driveline will have the 440' spinning under 2800 rpm @ 65 mph. Conversely, with typical 33 1/2" 19.5's your rpm will be over 3000. That equates to about 10% faster rpm and "no" I'm not stupid enough to attempt to state exactly how much fuel savings that would amount to. Maybe someone else could chime in on that. If I recall correctly it was Henry Blair who said years ago that a lot of the Eastern FMC'ers didn't bother with overdrives in their coaches - they just threw on a set of 22.5's and away they went. Many also like the way they look, too.
Does answer your question?
Terry #846
Edited by andy1canada 2022-08-08 3:37 PM
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Veteran
Location: Soquel, CA. | Yep. That was what I figured. My sweet spot for RPM is around 3000 to 3300. Less than that I would be lugging over even a small grade. OK in short spans, but not so great for the transmission temp for longer spans. |
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Wheels and tires- What size rim/tire are you running?
