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When I accelerate hard in first gear on my SP23 MT, and if the tires break free on any sand, gravel, or just because I'm gunning it, I get a sickening violent oscillation which I believe is caused by the left and right wheels taking turns biting the road. The car shakes violently left and right. Its about a 4hz shake and lasts for several cycles depending on how fast I take my foot off the gas. I believe this indicates that the left and right tires are taking turns gripping due to the springiness of the driveshaft (you ever look at how thin that driveshaft to the front wheels is? it looks like <3/4" ).

Has anyone else experienced this oscillation, and do you know how to avoid it (without limiting yourself to weak acceleration?) If I get a frame reinforcing bar (connects between shock towers in front, claims to make body more rigid) do you think that will help?
 

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That's pretty normal, as it's wheel slip and torque steer. Stiffer engine mounts would help, but they tend to cause vibration at idle, otherwise you have to limit your acceleration.
 

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This happens to me when turning... usually trying to turn right fast. I just always thought it was the tires losing grip.
 

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sounds like normal wheel hop. We have too much torque in 1st gear for an open-diff FWD car, try to be a little easier on the gas.

IME, I have to launch at less than 2,800 rpm when going straight on dry pavement to avoid the situation, lower RPM may be necessary when the road is sandy. A stiffer shock / softer sidewalled tires may be able to keep the wheels better planted, but it will take some experimentation.
 

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[quote author=ebhcr link=topic=66323.msg1149324#msg1149324 date=1168806164]
This happens to me when turning... usually trying to turn right fast. I just always thought it was the tires losing grip.

[/quote]

I had this happen to me earlier today. I was pulling out from a parking spot and there was a car approaching so I turned the wheel to almost full lock left and gunned the gas pedal.The front end started thumping violently (and loud!), only going away as I eased off the gas pedal. At first I thought it might have been my CV joint(s) or a broken engine mount, but then I only have a bit over 7000km on the odometer and I do not particularly drive my car hard. And I was unable to replicate the symtoms accelerating on a stright line.
 

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It does it more in a turn/steering wheel cocked. I also bet you have an automatic...much harder to cause an auto to lose grip then a manual (so easy to do in my 3i M/T). It is normal on the Mazda 3 and a lot of other cars (though I will admit I haven't seen to many cars where the wheel hop was as bad as on a stock Mazda 3).
-matt
 

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[quote author=azazel1024 link=topic=66323.msg1377932#msg1377932 date=1178029421]
It does it more in a turn/steering wheel cocked. I also bet you have an automatic...much harder to cause an auto to lose grip then a manual (so easy to do in my 3i M/T). It is normal on the Mazda 3 and a lot of other cars (though I will admit I haven't seen to many cars where the wheel hop was as bad as on a stock Mazda 3).
-matt
[/quote]

Actually my car is a manual. It's weird though, when I was still on my winter tires (until 2 weeks ago), I must have done many similar moves like that (on dry pavement), but the front end never once complained. Two weeks ago, I put in a set of Goodyear GS-D3 225/50/16. I know these tires grip much harder than the stock (all season) tires. Could this accentuate the wheel hop problem?
 

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If it's wheel hop, you can get rid of it by dropping your tires to 28 psi.
 

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[quote author=rpn453 link=topic=66323.msg1379010#msg1379010 date=1178051020]
If it's wheel hop, you can get rid of it by dropping your tires to 28 psi.
[/quote]

The Goodyear F1 sidewalls are already quite soft (for a V-rated tire) so I am currently using 36 lbs. I was thinking perhaps the stock
shocks (poor damping) might contribute a bit this this. I am waiting for a set of Koni FSDs to come in. In the meantime, I am going to try experimenting with the tire pressures and see.


Tks
 
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