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Loud "pothole impact" sound over bumps normal?

Al_in_Philly

Go Kart Champion
Location
Philadelphia USA
Thanks! And YES that "I just sent my shock through the top hat" feeling is EXACTLY what I thought. I do have 19" wheels (Englishtown/Spielberg) and I figured they wouldn't be doing me any favors in this situation.
I may have figured it out (emphasis on "may"). Maybe those wheels are the source of the loud impact noise. The Engilshtown wheels are quite heavy cast aluminum: 26lbs., almost 50lbs per wheel with tires. That's a lot of unsprung weight*, meaning a lot of inertia for your springs, shocks, and the bumpstops to slow down and stop when the tire goes from quick downward movement to quick upwards movement as it goes over a pothole. Your upwards wheel movement doesn't suddenly stop when it rises up exiting the recess of your pothole; it continues its upwards trajectory until the spring forces (aided by the slowing of the shock dampening) slow the upwards motion and then start the wheel on its downwards return. If there isn't enough resistive force and/or time to reverse the upwards movement of the strut within its normal range of travel, it his the bump stops, sometimes hard enought to transfer the upwards force solidly into the chassis. Voila: "clunk." And since those 235/35/19 tires provide little to no cushioning, this becomes even more critical, as the initial upwards trajectory isn't reduced very much by the elastic cushioning of the tire itself.

I haven't experienced the loud clunking which you are hearing and feeling, and it might be due to the fact that I (like a good many other R owners) switched over to light weight flow-formed wheels, not too long after I bought my R. That loss of around 5 lbs per wheel reduced my overall unsprung weight (and thus the vertical inertial forces which the suspension had to cope with) by a significant amount. The bonus there, aside from aesthetics, was better traction on rough roads, less intense impacts felt in the cabin from potholes and bumps, plus faster acceleration and quicker braking due to the reduced rotational inertia of each wheel.

I can't promise that changing wheels would fix your problem, or that my changing wheels has kept me from experiencing the clunks that you clearly are. But it may be a fix, and there are additional tangible benefits from going to lighter wheels, especially if their construction method doesn't reduce their overall strength. Of course, you do have to pay for them. . .


*unsprung weight is the total amount of weight which moves up and down with each wheel. The further outwards from the suspension pivot points, where the suspension joins the rigid chasis structure, the greater effect this mass has on its vertical movements. So the overall mass of the wheels and tires effect the ride as well as the car's ability to maintain contact with the road.
 
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ATR

Drag Race Newbie
Location
Baltimore
Car(s)
'17 Golf R 6mt
Don't use comfort mode on crap roads. I've noticed that my car will bottom out much harsher in comfort mode then in normal or race modes.
Just in case my post got lost in the shuffle...

I repeat, if your car has DCC don't use comfort mode unless the roads are smooth. As odd as that sounds, think about it for a second...

VW's damper tuning turns the dampers down to super soft in comfort mode (allowing easier full strut travel). This in turn or big dips or harsh potholes will allow the struts to hit the bump stops easier.

As noted before, keep it in at least normal mode or even race mode if you encounter rough roads and want to avoid hitting the bump stops.
 

riceburner

Drag Race Newbie
Location
West Chicagoland
Just in case my post got lost in the shuffle...

I repeat, if your car has DCC don't use comfort mode unless the roads are smooth. As odd as that sounds, think about it for a second...

VW's damper tuning turns the dampers down to super soft in comfort mode (allowing easier full strut travel). This in turn or big dips or harsh potholes will allow the struts to hit the bump stops easier.

As noted before, keep it in at least normal mode or even race mode if you encounter rough roads and want to avoid hitting the bump stops.
i did miss that before - nice tip! i will certainly give that a shot; normal is not a bad mode to stick in anyway. sports not even all too bad.
 

hopelessfish

New member
"17 Skoda Octavia RS with DCC joining in... I too have had this problem from day one. Our country roads in Australia are pretty woeful and any sharp edged impacts (of which there are plenty) result in a huge bang which sounds like the dashboard has been sent into orbit. I find the DCC mode doesn't make much of a difference to the bottoming out problem. Does anyone know if the problem remains with aftermarket coilovers?
 
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