bobandmaggie Report post Posted April 10, 2022 (edited) I own a 2018 Newmar Ventana model 3407. It has 275 70R 22.5 size times on it now. I would like to increase the tire size to 295 80R 22.5. Is this possible for this size motorhome. My reason for this is that when on the highway and going down hill and on a curve, it feels like the motorhome is going to tip over. Thank you in advance, Bob Edited April 10, 2022 by hermanmullins Personal emails are not good on the Forum Suggest using a PM. Share this post Link to post Share on other sites
richard5933 Report post Posted April 10, 2022 What's your thinking on how increasing the tire size will help you feel more stable? Won't a larger size tire mean that you're actually riding higher, raising your center of gravity? Not sure how long you've had this coach, but it might simply be that you're going too fast for the road & curve. Or, it might be that you're not used to driving a vehicle with an air suspension. They will tend to lean more than a vehicle riding on steel springs under some road conditions. If it's not the speed or just getting used to it, when is the last time that the air suspension was inspected? Are the air bags filling to the proper pressure and at the correct right height? Before even considering the tire size change I'd suggest a call to Newmar. They should be able to confirm whether or not this coach can take a taller/wider tire without having any problems such as clearance issues or tire rubbing issues. You also have to be concerned about proper spacing on the rear dual tires, which Newmar should be able to answer for you. Share this post Link to post Share on other sites
rayin Report post Posted April 10, 2022 (edited) 4 hours ago, richard5933 said: What's your thinking on how increasing the tire size will help you feel more stable? Won't a larger size tire mean that you're actually riding higher, raising your center of gravity? Not sure how long you've had this coach, but it might simply be that you're going too fast for the road & curve. Or, it might be that you're not used to driving a vehicle with an air suspension. They will tend to lean more than a vehicle riding on steel springs under some road conditions. If it's not the speed or just getting used to it, when is the last time that the air suspension was inspected? Are the air bags filling to the proper pressure and at the correct right height? Before even considering the tire size change I'd suggest a call to Newmar. They should be able to confirm whether or not this coach can take a taller/wider tire without having any problems such as clearance issues or tire rubbing issues. You also have to be concerned about proper spacing on the rear dual tires, which Newmar should be able to answer for you. Exactly! Intentionally raising the center of gravity is not a sound idea IMO. We don't know how much air pressure is normally registering on the gauges, that has it's own subset of questions. Edited April 10, 2022 by rayin Share this post Link to post Share on other sites
wildebill308 Report post Posted April 11, 2022 20 hours ago, bobandmaggie said: I own a 2018 Newmar Ventana model 3407. It has 275 70R 22.5 size times on it now. I would like to increase the tire size to 295 80R 22.5. Is this possible for this size motorhome. My reason for this is that when on the highway and going down hill and on a curve, it feels like the motorhome is going to tip over. Thank you in advance, Bob Bob, welcome to the forum. Ok lets start with how much experience do you have driving big RVs? I know it was asked above but. What is your tire preshure? What is your suspension air preshure? Have you changed /upgraded your shocks? Have you checked your rubber bushings in your suspension to see if they are in good shape? On my last coach I replaced the stock ones with pollypropalean ones that were stiffer and it helped. Back to the tire question. I dought it would make enough difference to be noticed. The outher thing is I would check how much clearance you have in the wheel wells. I have always been a proponent of upsizing tires, but on my current camper there is no room. Make shure you check with the air bags dumped. If you want to know the difference in tires look at this app. https://tiresize.com/comparison/ Bill Share this post Link to post Share on other sites
bobandmaggie Report post Posted September 7, 2022 Hi Bill, Long time getting back to you. Try getting an appointment with any RV repair facility soon. (Motor Trucks Inc.). You wait for ever to get a date. I started Rv'ing in 2000. I have owned a Southward, and Alpine Coach and a Monaco Windsor and now a Newmar Ventana. The Alpine and Windsor had the 295 size tires. They both rode great. Nice comfortable rides. The Ventana does not ride as well. I have had the air bags checked -OK. The shocks are only 4 y/o. They seem fine. I called Newmar and they said they do not recommend increasing the tire size. Plus it will increase my fuel amount. ( can't see why) In any case I will do more research to come up with a solution. Thank you for getting back to me, Bob and Maggie Share this post Link to post Share on other sites
rayin Report post Posted September 7, 2022 Larger tires do affect fuel mileage, by increased rolling resistance, increased wind resistance, and together they increase the amount of HP required to turn them. Keep in mind a class A MH with a gas engine is on a medium duty truck chassis with leaf springs, and will ride as such. Some things an owner can do is, travel with a full fresh water tank, keep the tire air pressure at what is listed on the federal tire placard in the vehicle, and drive a bit slower. Share this post Link to post Share on other sites
wildebill308 Report post Posted September 7, 2022 Bob, I don't think bigger tires are the answer to your problem. The first thing I would do is get an all wheel alignment. This would include checking the ride height. Have you driven any outher Newmar Ventana coaches? Bill Share this post Link to post Share on other sites
rayin Report post Posted September 7, 2022 I agree Bill, increasing the unsprung weight will not improve the suspension stiffness. It's a truck chassis after all. IMO Liguid Springs is perhaps the only solution. Share this post Link to post Share on other sites
wildebill308 Report post Posted September 7, 2022 2 hours ago, rayin said: I agree Bill, increasing the unsprung weight will not improve the suspension stiffness. It's a truck chassis after all. IMO Liguid Springs is perhaps the only solution. I am not shure they make liquid spring add ons for diesel suspensions. He should have a tag on that model and I wonder if everything is adjusted correctly. Bill Share this post Link to post Share on other sites
rayin Report post Posted September 7, 2022 1 hour ago, wildebill308 said: I am not shure they make liquid spring add ons for diesel suspensions. He should have a tag on that model and I wonder if everything is adjusted correctly. Bill OK-Duhh; thanks for waking me up. This means he's already riding on air springs, can't get much better ride if as you said, everything is adjusted correctly in the suspension and steering. Share this post Link to post Share on other sites
wildebill308 Report post Posted September 8, 2022 43 minutes ago, rayin said: OK-Duhh; thanks for waking me up. This means he's already riding on air springs, can't get much better ride if as you said, everything is adjusted correctly in the suspension and steering. Yes and that unit should have the Comfort Drive system. I think something is messed up like maybe low air in the tiers or something in the suspension/passive steer or?? Bill Share this post Link to post Share on other sites
