"Emergency" Starts...
Discussion
Clearly not something that one does regularly, but on the occasion when you need to get away from a standstill in the dry (very) quickly you would expect to see a couple of nice big fat black lines behind you...
However, mine chose instead to send the rear jumping up and down as the car scrabbled for a semblance of grip or traction. Is this normal, or a result of some sort of set-up trait that I'm not aware of (which might in turn have some effect on the on-limit handling... slightly more concerning I would imagine...)???
Answers appreciated as ever.
Jem
However, mine chose instead to send the rear jumping up and down as the car scrabbled for a semblance of grip or traction. Is this normal, or a result of some sort of set-up trait that I'm not aware of (which might in turn have some effect on the on-limit handling... slightly more concerning I would imagine...)???
Answers appreciated as ever.
Jem
No RobF you're not wrong. Ocho, it is a form of axle tramp. If there is a grippy surface and sufficient 'squat' from the 911, then the wheels won't spin, but they will jump around a bit as things wind-up and unwind again. Lot of serious stress involved though; is it really necessary?
john m said:
No RobF you're not wrong. Ocho, it is a form of axle tramp. If there is a grippy surface and sufficient 'squat' from the 911, then the wheels won't spin, but they will jump around a bit as things wind-up and unwind again. Lot of serious stress involved though; is it really necessary?
No, not necessary at all, but you know what it's like. If you own a car like this then you have to let it out every once in a while, and I was just a little surprised at the car's reaction. Nice to know there's nothing wrong with it, and I'll try and be a little more tame in the future!!!
Thanks chaps.
Jem
AFAIK, so long as your Cab isn't several different cars welded together to make one new one or hasn't suffered a serious accident previously then the cause of the the rear bouncing under power are axel tramp and tyre shake.
Unless you're running some twin turbo NO2 monster it's unlikely to be tyre shake.
In truth 911s have a lot of traction
and there is a level between wheel spin and full traction that softly sprung variants can hop a little.
Unless you're running some twin turbo NO2 monster it's unlikely to be tyre shake.
In truth 911s have a lot of traction
and there is a level between wheel spin and full traction that softly sprung variants can hop a little.tony.t said:
In truth 911s have a lot of traction
Tony, thanks for the input. Re what you're saying above, I'm running on oversized rims (19s) with wide (275) rubber at the back - would that make the hopping even more likely?
...i've had this too. Unfortunately it was at le mans, right outside the gathered waterpistol firing mob on the mulsanne straight. They were stopping cars and egging them into standing starts....ok i was young, foolish and easily lead. The thing was i had a passenger in the back at the time which added to the weight in the rear. Dropped the clutch bounced a little (including back passenger's head against roof!) fortunately drifted onto a wet patch of tarmac that the mob had layed, lost traction spun up nicely, lost 5k miles worth of tread on the tarmac and off we went. 100 yards down the road i felt like a complete t**t for having put my pride and joy through the excessive strain. Not big , not cleaver but certainly funny just to see the poor passenger bouncing his pate off the roof!! 
>> Edited by welshnobby on Sunday 9th January 22:24
>> Edited by welshnobby on Sunday 9th January 22:24
Maybe a case of the rear squating under hard accelaration, losing grip momentarily and bouncing up, regaining grip and squating again? I suppose with very low profile tyres on 19" wheels it's going to have more grip but lose it in a more sudden manner than with higher profiles tyres, maybe making it more likely to occur? 
With only very limited experience of " emergancy" standing starts ( but a better understanding of every day standing starts) and having used different suspensions damper/sring rates, different wheel size/weights and diferent tyre types, i would humbly suggest wheel bounce is made worse by;
1) soft spring/damper rate
2) heavier wheels
3) increased tyre grip
and the transistion from spin to grip and vice versa without "bounce" is improved by;
1) stiff springs/dampers
2) light wheels
3) decreased tyre grip
which isn't to say acceleration times or total traction is improved or not.
1) soft spring/damper rate
2) heavier wheels
3) increased tyre grip
and the transistion from spin to grip and vice versa without "bounce" is improved by;
1) stiff springs/dampers
2) light wheels
3) decreased tyre grip
which isn't to say acceleration times or total traction is improved or not.
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