Really such a difference between 30 and 35 section tires over bumps? Or is it bumpstops?

yargk

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I have 200 miles on my CTR now; it's a fantastic drivers car.

However, I'm finding that although most bumps are fine, joints on the highway, where there is a change in angle/height across the whole lane or a 1/2ish inch step due to construction or lack of maintenance on a transition on an overpass, it's downright scary with a sharp and very dramatic thud/clunk.

I've inspected my wheels, no bends, and the suspension still seems tight with no damage or noise normally, but this behavior isn't encouraging and I feel like I'm pushing my luck.

My other car has 245/35-20 tires, which I've found to be completely fine. Is there such a large difference between 245/35 and 245/30 that 35 is fine and 30 is awful? Or is it a bump travel problem? Do bumpstops come in too early? Or is the tire hitting the fender liner above? Anyone else having these issues?
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Muggsy

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In my experience there is a significant difference between 30 and 35. I went from the stock tires and 20" rims to Michelin PS4S 255/35/ZR19. I was on edge driving the stock tires and got them off as quickly as I could, because every bump felt like it could lead to a bent rim. I am still careful with the 19s, because the roads I drive to and from work are pretty bad right now, but the extra sidewall gives me less to worry about. I definitely take speed bumps and road depressions slowly, because I've scraped the front lip a few times even with the bigger sidewall.
 
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yargk

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Thanks, I've spent some time watching slow-motion videos of cars going over pot holes and can now completely believe that 30 to 35 section tires is a night and day difference. In the slow mo videos the tire really does deform quite dramatically. With low profile tires, there is no room to deform so much, so the wheel slams into the ground (well, it slams into the tire with no air cushion). In my experience, there's probably ten times as many bumps that are bad for 30 than for 35. It's funny that there are so many bumps that are small enough that 35 section tires have enough room to deform and adsorb, but 30 section tires don't.

(of course, I mean 245/35 vs. 245/30 because since the sideway height = 245 * 0.30 = 73.5 or 245*0.35 = 85.75 mm then 30 section would be okay for very wide tires, 295*0.30 = 88.5 mm)
 

MuffinRacing

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Yeah, half inch bumps in the road wouldn't be enough to hit the bump stops or fenders. It's almost certainly 30 vs 35 and probably also the sidewall stiffness of the tires on the car
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