| Author | Message | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 97 Registered: 4-2009 Posted From: 208.54.14.82  Rating: N/A |
from metric to SAE? I have 255/80 R22.5 tires. since I hear that these are not common, I want to find sizes that are similar/interchangeable. R9 r11,r12, etc... anybody got a conversion table? | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1573 Registered: 12-2000 Posted From: 98.192.173.82  Rating: N/A |
Pete - Have you tried the major tire brand's websites? Most have tables with various sizes based on the tire models. Plug in your current tire size, and check out all the various specs, such as diameter, plies, revs per mile, load range, etc. Then simply look thru the tables for similar sizes with the older 11R, 12R, etc. The truck tire industry's going metric, just like autos did about 10 years or so ago, so do your homework. FWIW & HTH. . .  | ||
| Larry Baird (Airhog)
Registered Member Username: Airhog Post Number: 162 Registered: 1-2001 Posted From: 71.102.18.8  Rating: N/A |
255MM wide / 80% of that is the sidewall, 10" wide / 8" sidewall, 8+8+22.5= 38.5 Dia. I got the first half, anyone want to try the R11? | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 98 Registered: 4-2009 Posted From: 208.54.14.127 Rating: N/A |
RJ, tried searching on the web, I can't find it, otherwise I wouldn't be asking. larry, I thought I measured 40" but that was for the tire cover, I will go measure it agian tomorrow and see if it's closer to 38.5"... | ||
| Paul Lawry (Dreamscape)
Registered Member Username: Dreamscape Post Number: 511 Registered: 5-2007 Posted From: 64.40.215.178  Rating: N/A |
If you going to install tire covers, I bought a set and they advertised, "They will not blow off". Don't believe it, I installed grommets and bought 24" bungee cords, they don't blow off now! | ||
| David Lower (Dave_l)
Registered Member Username: Dave_l Post Number: 159 Registered: 11-2007 Posted From: 67.58.201.132  Rating: N/A |
255/80 R 22.5 is 255mm or 10 inch wide, 80 is the aspect ratio basicly means the side wall height is 80% of the tread width. R means radial tire, 22.5 is the rim size diameter. As Rj said most of the tire manufacturers have all this on there web sites or go by a tire shop and ask. The bus you have is your choise but you should have thought of one that you can get manuals for. Dave L | ||
| Bill 340 (Bill_340)
Registered Member Username: Bill_340 Post Number: 84 Registered: 7-2006 Posted From: 75.200.128.131 Rating: N/A |
That is a standard tire size used on a lot of big motorhomes. try this site to be exact, if half size like 22.5 got to 23 ect. Bill | ||
| Bill 340 (Bill_340)
Registered Member Username: Bill_340 Post Number: 85 Registered: 7-2006 Posted From: 75.200.128.131 Rating: N/A |
Sorry here is the site..http://www.miata.net/garage/tirecalc.html | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1504 Registered: 10-2003 Posted From: 71.58.110.9  Rating: N/A |
Remember to measure from center of wheel to ground as the tread is flat at bottom where it meets the road. If you measure to the top of tire, your calculations will be off some. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 886 Registered: 1-2003 Posted From: 70.58.64.85  Rating: N/A |
Peter, Your 255/80R22.5 tire is more of a European standard than a US one. That said, there are, as has already been mentioned, "RV" tires in this size. Bridgestone, Goodyear, and others consider the 265/75R22.5 to be a "direct replacement" for your size that is more common in the North American market. That tire will give you the closest RPM and load rating match. See: http://www.bridgestonetrucktires.com/us_eng/answers/doctor_specs.asp#5 and http://www.goodyear.com/rv/general/conversionchart.html In "inch" sizing, your tire would be closest to a 10R22.5, but that size really doesn't exist. There is an 11R22.5, but that's a taller tire, with anywhere from 23 to 37 fewer revolutions per mile. While this might give you some higher top end speed at your VR-731's overdrive gear of 0.88, your performance in first and second gears will likely suffer, with resulting additional loads on the engine. I would look for 265/75R22.5 tires to replace your old ones. They are "plug and play." FWIW, and HTH. -Sean http://OurOdyssey.BlogSpot.com (Message edited by Sean on June 09, 2009) | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 887 Registered: 1-2003 Posted From: 70.58.64.85 Rating: N/A |
I'm sorry, but I have to say this comment is uncalled-for and has no place in this forum. With very few exceptions, almost every one of us has a coach that is no longer in production and for which certain kinds of information, not to mention parts, might be hard to come by. If you were to post here wondering, for example, where to find the obscure clerestory glass for your MC-7, should we simply tell you that you should have thought to buy a coach where the glass was commonly available? It is decidedly unhelpful to make a remark like this to someone who has already purchased his or her coach and has come here for advice and assistance (as opposed, for example, to suggesting manual availability as a pre-purchase consideration to someone who is still shopping for a bus). Perhaps a helpful suggestion about where to find manuals and technical information would be more appreciated. And I acknowledge here that I am not the world's most tactful person, and I have read people the Riot Act right here on this board for doing something boneheaded, especially when I thought they might be compromising their own safety -- but I consider it mandatory then to at least suggest a concrete path forward. FWIW. -Sean http://OurOdyssey.BlogSpot.com | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 827 Registered: 10-2006 Posted From: 76.195.79.226 Rating: N/A |
"While this might give you some higher top end speed at your VR-731's overdrive gear of 0.88, your performance in first and second gears will likely suffer, with resulting additional loads on the engine." The engine output/road speed in every gear is lower with the final drive ratio of a slush pump. There will be no load difference in any gear , except a loss of speed and tiny increase in torque.Usually the top speed loss is 5 -6 mph. FF | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1575 Registered: 12-2000 Posted From: 98.192.173.82 Rating: N/A |
"The engine output/road speed in every gear is lower with the final drive ratio of a slush pump." Let me qualify Fred's comment just a little. It would have been more accurate if he'd added at the end "compared to the manual V-drive." The bevel gear ratio in a V-drive stick is 0.808:1, whereas the automatic V-730 (and it's variants) have an 0.875:1 bevel ratio. The top speed loss can almost be reclaimed on a GMC coach by going to 11R24.5 tires that turn 470-471 revs per mile, compared to the OEM powertrain's design tire at 495 revs mile. Sean's comment about additional load on the engine is correct, altho, in real world operation, the difference is negligible. Might have to downshift a little earlier, but that's about all. None of the bevel gear discussion applies to a T-drive powertrain, btw. FWIW & HTH. . . | ||
| David Lower (Dave_l)
Registered Member Username: Dave_l Post Number: 162 Registered: 11-2007 Posted From: 67.58.201.132 Rating: N/A |
Peter Michelin lists a tire 255/80R 22.5 XZE there catalog number 94390. It is rated for 75 mph, load range G and has a 38.5 overall diameter. this is an all position tire with a rib tread If you go to a local truck tire shop that sells Michelin they should be able to give you a cost. I priced the same tire here in 11 wide and it was $547 cdn per tire installed. Dave L (The obscure glass someone has mentioned is not so obscure). :-) | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 888 Registered: 1-2003 Posted From: 70.58.64.85 Rating: |
Fred, I was not comparing two different transmissions, I was comparing two different tires. One of those tires has a greater diameter and therefore the top speed will be higher, not lower. RJ, thanks for chiming in. Let me point out, though, that Peter does not have a GMC, and the tire sizes we are discussing are significantly smaller than the 12R22.5 that you suggest could be changed to an 11R24.5. I suspect neither of those sizes will fit on Peter's coach. -Sean http://OurOdyssey.BlogSpot.com | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 100 Registered: 4-2009 Posted From: 204.62.111.51 Rating: N/A |
yep, mine is not a GMC, it also does not have a v731, it has a allison b300... I have noticed that the speedometer is off by quite a significant amount, (when I am going 55 mph my speedo shows 49mph) so I am thinking it's probably designed for a smaller tire... | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 889 Registered: 1-2003 Posted From: 70.58.64.85 Rating: N/A |
Sorry, got your bus confused with someone else's... My statement about top speed vs. insufficient power in lower gears, however, still stands. -Sean http://OurOdyssey.BlogSpot.com | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 841 Registered: 10-2006 Posted From: 76.216.70.120 Rating: N/A |
Dont know if there right , but on the late night truckers show XM 171 about midnight, the clain was the most fuel efficient tire was 11R22 in the low profile version. The reasoning was the lower sidewall flexes and there is less hysterisis loss. Same reasoning the rulers of Kalifornia are demanding wide singles in the rear on trucks . Since these have a small rolling radius , they would cost more speed. The truckers at least can install most any rear to compensate for mandates and keep their speed. The V drives may have to give up some theoretical economy to cruise at traffic speed. FF |
