| Author | Message | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 7 Registered: 1-2009 Posted From: 149.168.204.10  Rating: N/A |
Hi folks, I've got an MC9 that's going to get 6 new tires in a week or two. I'm switching to 11R22.5's because of price and availability. I know the trade-offs and am willing to make the sacrifice in mileage and top speed at this point. My old tires are 12R22.5. Here's my question: Is there any reason not to run two of my old 12R22.5's on the tag axle until I can locate 2 used ones of the other size? All of the other tires will be the new 11R22.5's. I know I'm not supposed to mix tire sizes on the same axle, but my brain says it should be fine. Is my brain right? | ||
| David Guglielmetti (Daveg)
Registered Member Username: Daveg Post Number: 93 Registered: 2-2009 Posted From: 70.135.57.202  Rating: N/A |
Yes, you are right. On the drive axle use tires of the same height/circumference. On the tag you could "run out" your other tires, just know that the tag could be carrying a little more weight, depending on how the height control valve is set up. | ||
| don goldsmith (Bottomacher)
Registered Member Username: Bottomacher Post Number: 255 Registered: 12-2000 Posted From: 98.66.146.121 Rating: N/A |
Make sure to stay within the reduced load capacity of the tires. | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 8 Registered: 1-2009 Posted From: 76.0.172.15 Rating: N/A |
Excellent. Thanks guys. The board comes through again! I thought I had read that it was ok somewhere here in the archives, but could never find it again. The tires load rating (H) is well within limits of my coach, so I'm good there but thanks for the heads-up. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 307 Registered: 1-2009 Posted From: 24.129.232.232  Rating: N/A |
also of lesser noteworthyness: ~maximum legal load rating is based on tread width for the class of road you are traversing (changes with the spring thaw in some areas up here) + this is not to exceed axle weight rating or design or tire factory rating (load range H) so these details must be factored in to your reduced sizes of tire if you don't wish to risk incure heavy overload (huge)fines (yes I know it is rare to see a conversion pulled over for a weight at this time, but murphy's law & revenue generation have a way of changing enforcement procedures (S.O.P.) ~~The other consideration is a change in braking dynamics with a change in outer circumference/width=skid threshold, but this should only be critical if your bus racing or involved in major accident & the insurer is looking for a way out of paying those big bucks or at least play time attrition games. This "brake change" assume no upgraded anti-lock system on your coach, which might compensate or just set a code if it was very modern. ...Cross the eyes & dot the tea... -give Murphy less of a change at running your day- | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 912 Registered: 10-2006 Posted From: 76.192.0.94  Rating: N/A |
For hydro-plaining the most common speed is the sq rt of the inflation pressure times 9. Most bus tires have about the same pressure , hopefully well matched to the weight on the set. FF | ||
| don goldsmith (Bottomacher)
Registered Member Username: Bottomacher Post Number: 256 Registered: 12-2000 Posted From: 98.66.150.252 Rating: N/A |
Hard to imagine many buses that can reach that speed. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 317 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
heard say of one with a marine style Jimmy re-power..... even the cooling system was "rocketed" <actual skidding/ loss of directional control may happen at any speed, it is after all , the point where static friction values undergoes a rapid decrease between the road surface & tire (in bus operator terms), resulting in a whole different set of rules in handling & brakeing or how you don't crash ! ~ perhaps not just of interest for those distant future busnutlings that may be reading on; as they dream of restoring the bus they inherited from us, our legacy if you will ! ... bus on insured... | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 916 Registered: 10-2006 Posted From: 76.192.0.94 Rating: N/A |
"Hard to imagine many buses that can reach that speed." With 100psi in the tire , the Sq Rt of 100 is 10. 10 x 7 is 70mph. I don't know many campers that DON'T go 70! The more worrysome part is a car with 36psi has a sq rt of 6 X 7 is 42 mph. OR 25 psi with a sq rt of 5 x 7 for 40mph Could be a learning experience on a bit of standing water! FF (Message edited by FAST FRED on August 08, 2009) | ||
| L James Jones Jr (Jamo)
Registered Member Username: Jamo Post Number: 83 Registered: 11-2007 Posted From: 74.79.237.9  Rating: N/A |
So, FF, is it 7 or 9 as the multiplier? Not that it matters, my 4104 won't hit 70...had up to 65 once though, with my wife as a chase speedo (don't have once of those speedo things..just a hub-odometer for mileage) Guess if it's 9 I'm even safer, eh? I'd never heard that H/P formula though. Thanks... | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 917 Registered: 10-2006 Posted From: 76.192.0.94 Rating: N/A |
So, FF, is it 7 or 9 as the multiplier? OOOPS it is 9 , so hydroplaning still a concern for most autos , and for bus campers that match the inflation pressures to the actual wheel weight, FF | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 337 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
... don't forget the "leverage factor" gents, you must account for wheelbase and "incline/decline" (variable weight distribution), just like a accident reconstructionalist would do for a insurance company when try to assign liability ! |