GolfGTIforum.co.uk
Model specific boards => Golf mk7 => Topic started by: EB2019 on 30 December 2024, 12:49
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Hi
I've had a detachable tow bar fitted, only for a mountain bike rack, as modern full suspension bikes are getting just too heavy for me to put on the roof these days comfortably without the fear of something going wrong.
Therefore with full fuel, 2 bikes 13+kg each, the tow bar (installed behind the bumper and probably weighs 15kg+), and the bike rack 17kg, I think its sitting very near the bump stops, as the weight is a long way past the rear axle. Thinking that going to Wales or Germany won't be pleasant fully loaded as well.
This kind of rules out any suspension upgrades that go lower as the tow bar bike rack sits low and extends out a reasonable distance. Parking off road sometimes looks perilously close to grounding out.
But was wondering if Golf R rear springs would be an option? 5mm lower but with a higher spring rate they might be more supportive? (likely won't lower due to the lighter GTI which is fine) The Golf R non DCC does run a different spring, bump stop and shock so I could purchase all 3 parts? The TCR non DCC runs the same springs, bump and shocks as the GTI so thats not an option for increasing support over the rear axle.
Other option may be to go for Bilstein B6 dampers, as a more supporting alternative but keep the rest the same, but can't really find anyone saying anything other than they feel harsh.
Any other random thoughts or suggestions welcome.
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The amount of weight you've got on your hitch is nothing like as much as the nose weight a caravan would put on it. Caravan would be somewhere between 80kg and 150kg.
Shouldn't be bogging down your rear suspension at all...
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What do you think? sagged springs? Car has less than 40,000 though.
Its definately sitting like 3 people are in the back when it has the bikes, rack and full tank, which seems to be, or at least feels like it doesn't have much travel, may be i'm just a bit sensitive to the change.
Perhaps I will take a photo next time its loaded up and have a measure.
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Not sure if this helps?
https://www.golfgtiforum.co.uk/index.php?PHPSESSID=3659p40gk5bibn28p696pc7vg2&topic=289011.msg2653782#msg2653782
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Maximum towing weight is to do with largely braking but what I'm on about is nose weight... Which is the amount of force down on the hitch. You try to balance your trailer but there is always a weight on the nose. If you've ever seen a badly hitched caravan with the car all bogged down at the rear then you'll know what I mean...
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Sorry, bit late here, been busy, small child, large dog, too much food, misbehaving prostate in any random order.
Interesting subject.
A few things to consider: the weight of the extra dangly bits (propshaft and rear diff etc) sits under the springs of an R not above it, plus the rear suspension of an R is different to a GTI so the rear spring lower mounts might be a different size.
The slight lowering of R springs will still be in effect as the R hardware sits under them not above. Any extra weight piled on the rear axle from above will lower the car further. This is assuming the rear lower spring mounts are set at the same height, in the same position, bearing in mind the R has a full drive system dangling under its belly not just a set of wheels attached to springs and dampers.
The R’s springs will be rated to carry a little more weight at the back but when matched to GTI springs at the front you might get an imbalance of spring ratings when the car is not heavily rear loaded (ie. Most of the time). This may or may not cause the car to understeer or oversteer in extreme circumstances as the chassis won’t have been developed to run that particular spring set up.
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haven't been out to take and measurements yet due to weather.
I was surprised to find that the top mount and rear arms (support for the springs anti roll bar links and other gubbins) are the same part number GTI, CS, R. The shock is different on the R, and the bump stop, possibly to coincide with the change in spring rate and small drop. Because the platform the spring sits in and the shock top mount are both the same, I think I would be on safe ground to assume all would fit, but like you say, should you do just because you can?
The FWD TCR springs are not a fortune front and rear, stiffer and only a few mm drop like the R. You can buy them for the price of Eibach springs I think, keeping OE+ and the spring rate designed around a specific motion ratio front to rear would be maintained. The TCR has a DSG and not sure how much the DSG weighs over the front axle compared to the manual GTI as everything else is the same??
Doesn't really solve the issue though, that a change of springs would be placed on old pretty cheap Sachs dampers.
Perhaps the next step is just put some Bilstein B6 dampers which would provide a better/supportive platform while also sorting out the old dampers? And go from there if I still want to change springs later on.
Thanks for everyone's help.
Will get some B6 next month, chuck them on front and rear and leave you all in peace. :whistle: :grin:
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just an update for those looking in the future on the forum.
loaded the car with bike rack, bikes and a full tank, marked the damper body with a marker pen where the dust cover compressed to, then removed the shocks and pushed down on the top mount and checked how much free travel I had before the bump stops.
Turned out the difference between the marked line and pushing further down on the shock till I got resistance from the bumpstop was 5mm. :shocked:
This means that although its not sitting on the bump stop when stationary it will have a massive spring rate change over the slightest bump in the road, and this is what I was feeling. Therefore I fitted new top mounts, B6 dampers and cut the bump stops a little (2cm) to help with free travel, however not so much that when it does hit the bump stop, its becomes edgy.
I decided to cut a little off the top and the bottom. Couldn't find a definitive answer online but both ends are specifically designed. The top is made to sit tight in the mount and I didn't want it lose on the piston shaft, and the bottom is more deformable so I wanted to retain some of that feeling. I guess the plastic ring is so it doesn't spread and split easily during prolonged use and I didn't want to cut that much off one end.
(https://i.postimg.cc/0yh23Wkc/s-l400.jpg) (https://postimages.org/)
(https://i.postimg.cc/Z5PvBVH2/PXL-20250222-125928512.jpg) (https://postimg.cc/MnTpg0hm)
B6 body length compared to standard damper, note the thickness of the bottom bush and surrounding metal. Damper body is actually slimmer, due to mono tube design I guess.
(https://i.postimg.cc/NfD5Q50v/PXL-20250217-140539224.jpg) (https://postimg.cc/kBVncM8T)
(https://i.postimg.cc/jdMdGm8s/PXL-20250217-140603958.jpg) (https://postimg.cc/mtFs9Xfq)
I'll be doing the fronts next month, and will report back in another thread (I started one about what suspension to fit).
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Keep us posted and if you can get picks of the car sagged please fire them up. I’m about to push the button on a detachable tow bar for the exact same reason. My heaviest bike is about 16kg so reading about the sag is pretty concerning.
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Good to read your update Emmett and workaround with the bump stops. Will be interested to see the further updates and results.
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Keep us posted and if you can get picks of the car sagged please fire them up. I’m about to push the button on a detachable tow bar for the exact same reason. My heaviest bike is about 16kg so reading about the sag is pretty concerning.
Sorry didn't take any pics before I installed the rear B6 dampers, should have done so. I would say that 4 adults and boot full luggage is likely the same if not more lowered. Bumpstops are engineered as part of the spring rate by manufacturers these days I read, so its not the end of the world if it sits on them, but I'm just fussy about how it feels :rolleyes:
The brief feedback on the B6 fitted to the rear is that its not noticeable stiffer, its raised the height by 3mm
If you intend to drive to a local trail centre with your bikes I probably wouldn't bother doing anything, but I like taking the bikes to Wales and will be taking them to Germany this year and didn't want that feeling for long journeys, and like you say bikes are getting heavy!
Good to read your update Emmett and workaround with the bump stops. Will be interested to see the further updates and results.
Thanks will let you know when its all done. :wink:
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Great read EB2019! Looking forward to the next update and your overall review of the B6 shock upgrade.
Assume you kept the standard springs and did not change to the TCR or other?
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I still can't believe that a bicycle rack can upset the rear as much as a caravan can and will...
I've driven cars fully loaded with a caravan on the back and it doesn't do what you are describing - honestly!
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Great read EB2019! Looking forward to the next update and your overall review of the B6 shock upgrade.
Assume you kept the standard springs and did not change to the TCR or other?
Correct about the TCR springs, after looking into it, the TCR springs for non DCC are the same on the front as the GTI Performance, so if the front isn't a lower uprated spring I'm assuming the rear springs although different to the rear of the GTI performance, aren't lower or massively uprated. With that in mind I decided to leave the originals for now. DCC and the performance option pack with lower ride height and limiter removed are different, but I think all DCC springs are different to non DCC that i have looked into.
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I still can't believe that a bicycle rack can upset the rear as much as a caravan can and will...
I've driven cars fully loaded with a caravan on the back and it doesn't do what you are describing - honestly!
I understand your reasoning, And i'm not sure why either, but the marker pen marks on the dampers don't lie. For reference my car height is 365 to 370mm at the rear, centre of hub to arch without any load.
The only thing I can think is that a fully loaded car would be on the bump stops too, or close to it at the rear, at least in my car, and yet all the mass would be inside the wheel base and at least more evenly distributed front to rear, what I am using is sitting maybe 4 feet behind the rear axle. Like holding a snooker cue a little at the thin end, it doesn't weigh a great deal but once extended out at one end it is heavy. This would be like your caravan scenario in theory, but a caravan is sitting on its own wheelbase half way along and pivoting around that? Therefore it can slow the vertical movement due to its weight, and working against the rebound force?
Perhaps my theory isn't sound. :wink:
but I still wasn't happy with the 5mm of travel before the bump stops so chopped a little off them.
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Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
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Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
The mass is the same, but the moment (think force used by a lever) increases around the pivot point (the attachment of the bike carrier) the further the weight is away from the car. The resulting force will try and turn the car around the pivot point (so front lifting).Higher rated rear springs will help resist the car moving around the pivot. So, as you point out, the further away the bikes are from the back of the car, the stiffer rear springs you need.
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Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
The mass is the same, but the moment (think force used by a lever) increases around the pivot point (the attachment of the bike carrier) the further the weight is away from the car. The resulting force will try and turn the car around the pivot point (so front lifting).Higher rated rear springs will help resist the car moving around the pivot. So, as you point out, the further away the bikes are from the back of the car, the stiffer rear springs you need.
So springs and not dampers...
But of course this would be optimising it for the loaded scenario and the rest of the time you'd be oversprung and have the rear end bouncing around?
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Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
The mass is the same, but the moment (think force used by a lever) increases around the pivot point (the attachment of the bike carrier) the further the weight is away from the car. The resulting force will try and turn the car around the pivot point (so front lifting).Higher rated rear springs will help resist the car moving around the pivot. So, as you point out, the further away the bikes are from the back of the car, the stiffer rear springs you need.
So springs and not dampers...
But of course this would be optimising it for the loaded scenario and the rest of the time you'd be oversprung and have the rear end bouncing around?
I am a medic rather than a physicist / engineer, but stiffer rear dampers will also resist the tendency to pitch over bumps when driving.
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Have you looked at spring helpers? Used to be a fairly common and they still do them - Google 'Spring helpers for towing'. They just fit in between the coils - though how easy they are to fit/remove I'm not sure!!
My Mk7 GT hatch used to be OK with two bikes on a Thule hitch carrier but you could tell it was on the car when driving. I also used to tow a 1000kg trailer with it and you could hardly notice it, strangely you can on the GT estate I now have, must be to do with the distance the tow bar is from the rear axle.
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Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
As we are just chatting - I think its the return force and how that feels in the car due to hitting bump stops and not so much about a light or heavy weight.
A 100-150kg load on a tow bar will likely feel less harsh on bump stops because the bumpstop when squashed will return at a slower rate than a lighter load for example 50kg. The damper won't control the return speed as the spring rate now is too high, but the change of direction from compression to rebound will be slower as the weight is very high 100 to 150kg and the bumstop struggles to fully stop and extend back up the weight. Using a light hammer vs heavy hammer when direction change is applied (kind of thing). All things being equal the return speed of a heavy object will be slower as the bump stop has to slow, stop, change direction and return a heavier load, this should feel smoother or slower as it changes direction. Drop 1kg on a bump stop it will spring back up very quickly, drop a 15kg on a bump stop and it wil compress more and be slower to return to normal shape.
If you compress a bump stop the same amount, with the same springs and dampers, it will feel more harsh with a faster return (light load) and low damper resistance. I think a heavier load will compress the bumpstop more (your caravan scenario) and return slower, but the return rate of a lighter load would feel more harsh as its a more violent jolt/acceleration back up especially with the weak dampers on the Golf GTI GTD TCR (these are the same dampers from 1.0 Golf to TCR).
I may not have explained this clearly, but in my head it sounds correct. :grin:
Thanks Japes1275 for the tips, I don't think I have that much of an issue but interesting you had different experiences with different cars
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Went to Wales at the Weekend, very impressed, much more supportive. Car feels better with the B6, luggage and bikes than with standard shocks without the added weight. OE was just too little damping control. B6 are nice and tight without feeling wallowy like EO dampers. A slight cut to bump stops, has likely helped too.
Will add to the other thread without an increased payload, just to complete the thread update for future searches.