Bigger tires = towing problems?

[3SK]

I towed my boat for the first time after adding bigger tires. Right around 70 mph something is shaking real hard. Hard enough that I wouldn’t drive over 67 mph for a 7 hour drive. The boat is about 4000 lbs. bed was full with a family of 5. Tires went from 275 55 20 to 275 65 20 A/T tires. Zero issues with the boat not attached. I went through death shake with a 3rd gen I had for years. It wasn’t that bad but it didn’t feel far off which is why I didn’t go faster than 67 - I felt safe there. That 3 mph is a world of difference. Not sure I want to deal with it again. Feeling like I just wasted 1200 on rubber. Any ideas/suggestions? Don’t want it to be another nightmare. Thanks

 

[Billy James]

I towed my boat for the first time after adding bigger tires. Right around 70 mph something is shaking real hard. Hard enough that I wouldn’t drive over 67 mph for a 7 hour drive. The boat is about 4000 lbs. bed was full with a family of 5. Tires went from 275 55 20 to 275 65 20 A/T tires. Zero issues with the boat not attached. I went through death shake with a 3rd gen I had for years. It wasn’t that bad but it didn’t feel far off which is why I didn’t go faster than 67 - I felt safe there. That 3 mph is a world of difference. Not sure I want to deal with it again. Feeling like I just wasted 1200 on rubber. Any ideas/suggestions? Don’t want it to be another nightmare. Thanks

Did you try putting more air in the rear tires while towing? Maybe they are a little low and the weight of the boat is affecting them.

 

[3SK]

That would be nice and an easy place to start. I’ll check them. Thanks

 

[Rob5589]

If the only difference is new tires, balance would be the first thing I'd have checked. It is possible to throw a weight and not feel it dry. Adding the gear and tongue weight could make it noticeable. Checking tire pressure while fully loaded is important as well.

 

[Helmetface]

What does the trailer tongue angle look like? Too steep can certainly produce wobbles that would make a Green Beret's butt pucker.

That being said, I've towed for years with 34" tires without a single relatable issue.

Aside from maybe airing being a plausible issue, you've got something else going on - I would not suspect the tire size being the issue.

 

[SColang22]

Not the original poster but I went from stock to 35" tires. Anyone know how much that affects my tow capacity?

 

[Bay Area RAM]

Not the original poster but I went from stock to 35" tires. Anyone know how much that affects my tow capacity?

As long as your new tires are rated for whatever you're towing then weight isn't the issue. I'd be more worried about the spacers.. and the loss of actual power to the ground turning the bigger tires compared to the stock size.

 

[SColang22]

As long as your new tires are rated for whatever you're towing then weight isn't the issue. I'd be more worried about the spacers.. and the loss of actual power to the ground turning the bigger tires compared to the stock size.

Spacers not a worry as the are only 1/4”. Not asking about weight. I ended up pulling 7500lb trailer no issues