Transmission drag...?
Discussion
Here's a thing... Nursy and I have an on-going challenge when driving home. In essence her place is located just off a country(ish) road. When traffic is light it's possible to get up to a certain speed, let's call it 60mph 
then as you pass a certain sign put the gearbox into neutral and see if it's possible to coast all the way to the house... or at least to the driveway. The driveway is a couple of hundred yards long and my record is about 50 yards up it, so we've long since passed the stage of wondering if we can make it to the drive 
Anyway, last weekend I tried it for the first time in the TVR (we're usually in her Rapid or my Connect).
The route goes sign - straight - right-hand bend - straight - left-hand bend - straight - down hill - up hill - sweeping left-hander - sharp left into drive.
To stand a chance of reaching the drive the Rapid and Connect need to be doing at least 40 at the bottom of the dip between the down and uphill, so you're at about 30 at the top of the hill and have to try and swing into the drive as fast as poss. without scrubbing speed off to have a good coast up the drive (I know, sounds daft).
Interestingly I regularly get further in the van than the Skoda before grinding to a halt.
Despite passing the sign doing considerably more than 60 () the TVR dropped speed like a drug dealer caught in a helicopter spotlight and was barely doing 25 at the bottom of the dip so no way was it making the driveway.
I know the brakes aren't dragging so the only thing I can ascribe it to is drag from the diff and gearbox, smacks of shocking power loss if that is the case. Or maybe the aerodynamics are shocking?
Leave aside the legalities of speeding, coasting and hurtling into a near-blind entrance, because I have my hands over my ears and am going laa-laa-laa...
then as you pass a certain sign put the gearbox into neutral and see if it's possible to coast all the way to the house... or at least to the driveway. The driveway is a couple of hundred yards long and my record is about 50 yards up it, so we've long since passed the stage of wondering if we can make it to the drive Anyway, last weekend I tried it for the first time in the TVR (we're usually in her Rapid or my Connect).
The route goes sign - straight - right-hand bend - straight - left-hand bend - straight - down hill - up hill - sweeping left-hander - sharp left into drive.
To stand a chance of reaching the drive the Rapid and Connect need to be doing at least 40 at the bottom of the dip between the down and uphill, so you're at about 30 at the top of the hill and have to try and swing into the drive as fast as poss. without scrubbing speed off to have a good coast up the drive (I know, sounds daft
).Interestingly I regularly get further in the van than the Skoda before grinding to a halt.
Despite passing the sign doing considerably more than 60 (
) the TVR dropped speed like a drug dealer caught in a helicopter spotlight and was barely doing 25 at the bottom of the dip so no way was it making the driveway.I know the brakes aren't dragging so the only thing I can ascribe it to is drag from the diff and gearbox, smacks of shocking power loss if that is the case. Or maybe the aerodynamics are shocking?
Leave aside the legalities of speeding, coasting and hurtling into a near-blind entrance, because I have my hands over my ears and am going laa-laa-laa...
The initial drag from 120mph down to 60 will be aero, below that the tyre drag starts to dominate.
What tyre pressures and widths are you running?
Nice game by the way. For my part I approach my village at 60 and brake down to 30 on the line as hard as possible without locking up. I can do 60-30 in about 5m with warm tyres on a dry road. It also makes sure the brakes are in tip-top condition - keeps them sharp.
What tyre pressures and widths are you running?
Nice game by the way. For my part I approach my village at 60 and brake down to 30 on the line as hard as possible without locking up. I can do 60-30 in about 5m with warm tyres on a dry road. It also makes sure the brakes are in tip-top condition - keeps them sharp.
Well the TVR is 1100Kg-ish and the Connect is 2250 Gross with a 900Kg payload so empty it won't be a kick up the Khyber off the TVR - and the Skoda Rapid isn't exactly fat either.
Tyres are 225/50-15s at 22/24psi I think.
Overall coasting distance is probably the thick end of a mile... but it pales into insignificance alongside the epic coasting we did in the Azores: from the highest point on a road to sea level was 16Km
Tyres are 225/50-15s at 22/24psi I think.
Overall coasting distance is probably the thick end of a mile... but it pales into insignificance alongside the epic coasting we did in the Azores: from the highest point on a road to sea level was 16Km
rev-erend said:
Pump up the TVR tyres to 45psi .. then try the game again
And if that don't work then I'm sure a man of your calibre could make one of these...https://www.google.co.uk/url?sa=t&rct=j&q=...
You could link a tin of "Start ya bastid" to get it going...Although I would recommend it being mounted externally...
Another plus is that you could cook dinner on it when you get home..
A good real-world question! ;-)
To add to the responses above:
Maybe wheel alignment and rolling resistance of tyre choice?
And apart from mass (inertia) and aero, there is also the possible difference between RWD and FWD (diffs, CV, bearings).
But I would check first the brake drag, small as it might seem. If you jack up your cars and give each wheel a spin with your hand (yes CV joints angle not real world like, but still), count how many turns they make. Report back preferably with youtube video and questionable background music ;-)
To add to the responses above:
Maybe wheel alignment and rolling resistance of tyre choice?
And apart from mass (inertia) and aero, there is also the possible difference between RWD and FWD (diffs, CV, bearings).
But I would check first the brake drag, small as it might seem. If you jack up your cars and give each wheel a spin with your hand (yes CV joints angle not real world like, but still), count how many turns they make. Report back preferably with youtube video and questionable background music ;-)
As an addendum, I tried cruising with the clutch in and the car take seven seconds to slow from 35 to 30. It's a technique I use quite often in lower speed limits, so the engine is either on power or idling, to save some petrol for the twisty bits outside the "nutter bars".
Also I just worked out the car travels 102m in that 7 seconds. So you could probably coast about 500m from 30 to zero.
Also I just worked out the car travels 102m in that 7 seconds. So you could probably coast about 500m from 30 to zero.
Edited by adam quantrill on Thursday 27th October 20:44
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