richard5933 Report post Posted January 17, 2019 Anyone have any first-hand experience with these tires? We're currently riding on Firestone FS400 tires in 315/80R22.5 size. They are great tires, but since they just hit the 7-year mark I'm looking for replacements. The coach originally came with 12R22.5 tires, and the 315s are a common replacement for them and are easier to find. I assume that's why they were put on by the previous owner. However, on a full turn to either side the corner of the tread makes slight contact with the airbag due to the slightly wider size of the 315s. Usually just a problem during parking, but it's possible to go full turn on the road on tight city streets and such so it can potentially become a problem. In every other way I love the current tires and would replace them with another set of the same, but the potential to rub on the air bags has me worried. So, I'm shopping for the proper 12R22.5 tires. I know that they are harder to find on the road, but since we carry a mounted spare that doesn't bother me quite so much. My big unknowns for the FS561 tires are ride quality/comfort and noise. The current tires are great, so I'm a little concerned that I'll put something on there and be disappointed with a harsher or noisier ride. So, if anyone has run a coach with Firestone FS561 tires I'd love to hear what you thought of them. PS: I have considered the Toyo M170, which is also available in the 12R22.5 size. The problem with them is that they have a loaded radius which is about 0.7" less than our current tires, and since our black tank connection is under the coach I'm afraid that the lower ride height would make it difficult to attach the hose (it's already tight down there.) The Firestone FS561 is the first tire in the correct size I've found with the same loaded radius size as our current tires. Share this post Link to post Share on other sites
kaypsmith Report post Posted January 17, 2019 Does your coach have a trail axel? If it were my choice, I would go with the 12R22.5 on the steer axel and continue with 315's on the drive axel, this arrangement will help retain the radius on the rear which is most likely closer to your tank drain anyway, while avoiding the airbag scrub on the steers. I personally don't like tire scrubbing, but then that's me, not you. Share this post Link to post Share on other sites
richard5933 Report post Posted January 17, 2019 We don't have a bogey or tag axle - just the steer and a single drive axle. The 315s we currently run and the Firestone FS561 would provide the same ride height. So, keeping the 315s on the rear wouldn't really provide any benefit to us. Both the 315 and the FS561 have a 19.8" loaded radius (hub center-to-road) measurement. Downside to mixing the 12r22.5 in the front and 315s in the rear would be that we'd have two different size tires (width, not diameter) on the coach. We could get by still with just spare, but only for short distances if we had to use the spare on the other axle. The only downside to the 12R22.5 is that they are H rated and not L rated. Really doesn't matter though, since even the H rating provides far more weight capacity than we'll ever carry on the coach. There was never a need to put the L rated tires on there. All that said, what you suggested might be a budget-friendly way to do the change. Put the new tires on the front this spring, and leave the 315s on the rear for another 6 months or so and then replace those later on. Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2019 Richard, the FS561 is a good tire. Our coach has the 12R22.5's on it now and I bought these; https://simpletire.com/bfgoodrich-12-r22.5-63223-tires They ride great, no complaints so far and they have 25,000 miles on them and they are just shy of 2 years old. The 12R22.5 should be readily available should you need a replacement, that is a very common over the road truck tire size. Share this post Link to post Share on other sites
richard5933 Report post Posted January 17, 2019 50 minutes ago, jleamont said: Richard, the FS561 is a good tire. Our coach has the 12R22.5's on it now and I bought these; https://simpletire.com/bfgoodrich-12-r22.5-63223-tires They ride great, no complaints so far and they have 25,000 miles on them and they are just shy of 2 years old. The 12R22.5 should be readily available should you need a replacement, that is a very common over the road truck tire size. The ST230 looks to be the BFGoodrich version of the FS561. Did you ever run 315s on your coach? One of my questions in switching from 315s to 12R22.5 tires is about handling & braking. The 12R tires have a narrower tread, which will of course mean less rubber on the road. I can see a potential for the handling & braking to suffer a bit. Of course, running too wide a tire can also affect things negatively, so I really have no idea what will happen since there's also a chance things could be the same or even slightly better. If it weren't for the cost, I'd be more willing to just take a chance and have the new tires installed so I could test them for a while. However, at about $3000 for a full set, this is not something I want to have to do again for a few years. Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2019 We were supposed to have a 295/80R22.5 (factory size), when we bought it it had new tires what were an incorrect load range, those were a 295/75R22.5. Once I saw the error they replaced the steer tires only (only axle that was actually overloaded). I went with the 12R22.5 because of its availability on the road should I need a replacement tire. The 315 was a consideration back then, what turned me off at the time was the weight of the tire was enough to impact MPG's and I was concerned with my wheel offset the tires might "kiss" while in operation. When we put the 12R's on I also replaced the rear inner duals with aluminum wheels to lighten up the rotational mass. Share this post Link to post Share on other sites
manholt Report post Posted January 17, 2019 305's might work better for the scrub. I have 315 front, no scrubbing & 295 drive & tag. Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2019 Richard, check out these two posts; I know you like to read Share this post Link to post Share on other sites
richard5933 Report post Posted January 17, 2019 Interesting read. Thanks. Share this post Link to post Share on other sites
hermanmullins Report post Posted January 17, 2019 Richard, I know you have questions of 12R22.5 or 315/80R225. Just my thinking but you said it came 12R22.5s. Wouldn't they be ok since the manufacturer thought so? Herman Share this post Link to post Share on other sites
manholt Report post Posted January 17, 2019 What happened to my question? If deleted, why? Share this post Link to post Share on other sites
richard5933 Report post Posted January 17, 2019 I think I'm set that the proper size 12r22.5 is the way to go. There are a few options in this size, including the Firestone and the BF Goodrich. Also a Toyo in the running. Related question... Original spec for the coach was tires that spin at 495 revs per mile. Our current tires are running at 490. Many of the tires under consideration run at 487 revs. Am I correct that I will never be able to tell the difference between 495 and 487? Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2019 24 minutes ago, richard5933 said: I think I'm set that the proper size 12r22.5 is the way to go. There are a few options in this size, including the Firestone and the BF Goodrich. Also a Toyo in the running. Related question... Original spec for the coach was tires that spin at 495 revs per mile. Our current tires are running at 490. Many of the tires under consideration run at 487 revs. Am I correct that I will never be able to tell the difference between 495 and 487? Well.....my speedometer is 4 mph off from my actual speed. My coach was built with a tire that was a 499 and now is a 486. Share this post Link to post Share on other sites
hermanmullins Report post Posted January 17, 2019 I have a dash mounted GPS. I set my speed by that because when doing 70 by my GPS my speedometer shows 65 mph. Just as yours does. On the highway I normally set my cruise at 63 mph which is right at 1750 rpm. Seems the best for economy. Herman Share this post Link to post Share on other sites
richard5933 Report post Posted January 17, 2019 25 minutes ago, jleamont said: Well.....my speedometer is 4 mph off from my actual speed. My coach was built with a tire that was a 499 and now is a 486. Speedometer problems I can relate to. But we're already having that problem, far more than from a 5 rev/mi difference. Since we have a manual 4-speed transmission, my concern is more low-end performance. Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2019 Just now, richard5933 said: Since we have a manual 4-speed transmission, my concern is more low-end performance. Yeah, I can understand that. Share this post Link to post Share on other sites
manholt Report post Posted January 18, 2019 One problem is that in 1974, we did not have the tires of today on a coach. Radial and belted tires was on cars, but not RV's. Share this post Link to post Share on other sites
richard5933 Report post Posted January 18, 2019 1 hour ago, manholt said: One problem is that in 1974, we did not have the tires of today on a coach. Radial and belted tires was on cars, but not RV's. True - all the tires listed in the operator's manual were bias ply tires, and the 12.0x22.5 tires ours came with was just one of the many sizes available. I've tried for months to find specs on the actual physical size of a 12.0x22.5 tire, but so far have struck out. The only hard piece of data I've been able to find is that the GM buses were all designed for tires which spun at 495 revolutions per mile. My assumption is that the overall diameter is similar to a 12R22.5 since the RPM for most are pretty close to the 495 number (ranging from 487-490 for the most part.) The car I learned to drive in, a 1974 Grand Safari wagon had first-generation Firestone 500 steel belted radials. Great tires till one exploded on an elevated section of Rt 22 heading into NYC from NJ. Thankfully, radials have gotten better since then. Share this post Link to post Share on other sites
jleamont Report post Posted January 18, 2019 Tires have come a long way!! I love those BFG tires, so far they have proven to be a good choice. Hopefully Tireman will see this and chime in, he would be the right guy to bounce your questions off of. Share this post Link to post Share on other sites
tireman9 Report post Posted January 18, 2019 Found this web page on the FS561 on the right side you can get the info on different size and Load Range. and HERE are the specs on the FS400 You didn't provide your actual "4 corner weights" so I will leave it up to you to confirm how much "Reserve Load" you actually run. I do agree that not having the fronts contact anything should be one of your goals. I seem to recall reading about some adjustment that can be made to limit the max turn of fronts but not sure about your coach. Other than the tire contact, If you are happy with the "Stones" why would you change? Please PM me if you have other questions or you can view/download the complete HD tire databook HERE. Share this post Link to post Share on other sites
richard5933 Report post Posted January 18, 2019 27 minutes ago, tireman9 said: Found this web page on the FS561 on the right side you can get the info on different size and Load Range. and HERE are the specs on the FS400 You didn't provide your actual "4 corner weights" so I will leave it up to you to confirm how much "Reserve Load" you actually run. I do agree that not having the fronts contact anything should be one of your goals. I seem to recall reading about some adjustment that can be made to limit the max turn of fronts but not sure about your coach. Other than the tire contact, If you are happy with the "Stones" why would you change? Please PM me if you have other questions. Thanks for the feedback and comments Roger. I've sent a PM with more specifics, but in general I did look into the adjustment to the front wheel turning limits. What I found was that it is possible, but due to the nature of the power steering system and the importance of getting these settings correct, I've decided that's not the best solution. Better is to get the proper tires on the bus. If the adjustment is made incorrectly, it is possible to blow the power steering system at full turns. Share this post Link to post Share on other sites
wolfe10 Report post Posted January 18, 2019 Yes, if the steering box is a Sheppard M100 (very common in DP's and OTR trucks), all it takes to adjust cut angles is a small standard screwdriver. Screws are external, so not difficult. Screwing them (one on top of steering box/one on the bottom) reduces cut angle. Share this post Link to post Share on other sites
richard5933 Report post Posted January 18, 2019 1 minute ago, wolfe10 said: Yes, if the steering box is a Sheppard M100 (very common in DP's and OTR trucks, all it takes to adjust cut angles is a small standard screwdriver. Screws are external, so not difficult. Screwing them (one on top of steering box/one on the bottom) reduces cut angle. That's what I thought, but apparently it's not that simple in practice. We have a Vickers systems, and according to the manual to do it properly the power steering system must be set to drop pressure with 3/8" clearance still showing between the steering knuckle and the stop screw. Adjusting the stop screw is the easy part - getting the pressure cut off point set properly is apparently more difficult in these things. I thought it was an easy adjustment, but when I chatted with other bus owners they tried to dissuade me from trying this unless there were no other options. Since the steering works perfectly and I have the option of just installing the proper tires, I'm going to go that route. Share this post Link to post Share on other sites
wolfe10 Report post Posted January 18, 2019 Richard, Yes, adjusting the Sheppard box is exactly the same. Set the physical stops to prevent tire contact with body and suspension components. Use the adjustment screws on the steering box to achieve some clearance with the physical stop. The screws are what control pressure drop off. Dianne and I did it on two of our coaches (takes someone turning the steering wheel and someone under the coach). Takes about 20 minutes. Share this post Link to post Share on other sites
richard5933 Report post Posted January 18, 2019 30 minutes ago, wolfe10 said: takes someone turning the steering wheel and someone under the coach There's the rub...no way to get under our coach without a pit or a way to lift the thing up. Only about 7" of clearance on a good day. Since my tires are 7-years old, I'm not sure there's a good reason for me not to just get the correct size tires and be done with this for another few years. I might try this if it was something I could do myself, but to pay a shop to do it is silly. Cost will probably pay for at least a tire or two. Share this post Link to post Share on other sites
